Arthropathy-camptodactyly (CACP) syndrome is a rare inherited condition where children are born with or soon develop bent fingers (camptodactyly), large painless joint swellings (non-inflammatory arthropathy), a hip deformity called coxa vara, and sometimes fluid around the heart (non-inflammatory pericardial effusion). The problem comes from changes in a gene called PRG4, which normally makes lubricin, a slippery protein that lets joints glide smoothly. Without enough lubricin, the joint lining grows too much and movement becomes stiff, though lab tests for inflammation are usually normal. It is autosomal recessive (both parents carry a change in the gene). PMC+2PNAS+2
Arthropathy-camptodactyly syndrome—much better known as Camptodactyly-Arthropathy-Coxa Vara-Pericarditis (CACP) syndrome—is a rare, inherited disorder. It begins in infancy or early childhood. The four key features in the full name tell the story:
Camptodactyly = fixed bending of one or more fingers.
Arthropathy = long-standing joint disease with large, cool, non-inflamed effusions.
Coxa vara = a hip deformity where the femoral neck-shaft angle is reduced, sometimes causing limb length difference or limp.
Pericarditis = non-inflammatory fluid around the heart in a subset of patients.
CACP is caused by biallelic (two-copy) pathogenic variants in the PRG4 gene, which encodes lubricin (proteoglycan-4)—a natural lubricant made by synovial lining cells and cartilage surface (superficial zone) that allows smooth, low-friction joint motion. Without adequate lubricin, synovial tissue becomes thick, the joint produces excess fluid, and cartilage is exposed to mechanical wear even though classic inflammatory markers stay normal. rarediseases.info.nih.gov+3PMC+3PMC+3
Many children with CACP are first thought to have juvenile idiopathic arthritis (JIA) because the joints look swollen. But in CACP the joints are not warm or red, blood tests like ESR/CRP are often normal, the synovial fluid is clear and low-cell, and imaging shows non-erosive changes; steroid or immune-suppressing medicines usually don’t help because inflammation is not the driver. Genetic testing for PRG4 can confirm the diagnosis. PMC+3Boston Children’s Research+3Radiopaedia+3
The primary and proven cause is PRG4 loss-of-function. PRG4 makes lubricin, which coats cartilage and tendon surfaces and lines the synovium. Lubricin reduces friction, protects cartilage from wear, and helps cells in the synovial membrane behave normally. When PRG4 does not work, joints fill with non-inflammatory fluid, synovium becomes thick (hyperplasia), and hips may develop coxa vara; some patients also collect non-inflammatory fluid around the heart (pericardial effusion). Boston Children’s Research+2PMC+2
Other names
Doctors, databases, and patient groups may use different labels for the same condition. Common synonyms include: CACP syndrome, Pericarditis-arthropathy-camptodactyly syndrome, and Arthropathy-camptodactyly syndrome. All refer to the same PRG4-related disease. Wikipedia+1
Types
CACP does not have formal genetic “subtypes” beyond PRG4 variants. But clinicians often recognize phenotypic patterns that help with diagnosis and follow-up:
Classic CACP
Early finger camptodactyly, large-joint arthropathy with cool effusions, progressive coxa vara, and occasional non-inflammatory pericarditis. Labs for inflammation are normal. orpha.net+1Skeletal-predominant CACP
Prominent camptodactyly and large-joint arthropathy; pericardial effusion absent. Hips often show acetabular cysts or coxa vara on imaging. orpha.net+1Cardio-involved CACP
Typical joints plus pericardial effusion (rarely pleural effusion). Effusions are non-inflammatory, so fever and high inflammatory markers are unusual. malacards.orgJuvenile-arthritis–mimicking CACP
Children present with large-joint swelling and stiffness, but the joints are not hot or tender, blood tests are normal, and anti-inflammatory drugs do not help—key clues that steer away from juvenile idiopathic arthritis (JIA). rarediseases.info.nih.gov+1Late-recognized CACP
Features were mild or misattributed in childhood; diagnosis is finally made in adolescence or adulthood, often after hip problems or a first episode of pericardial effusion prompts re-evaluation. ResearchGate+1
Causes
CACP has one fundamental cause: pathogenic PRG4 variants. Below are 20 mechanistic and genetic ways this can occur or be uncovered. These are not separate diseases—they are different routes to the same PRG4-lubricin deficiency.
Nonsense variants in PRG4 that stop protein production early (truncation). PMC+1
Frameshift variants that disrupt the code and yield a nonfunctional protein. PMC
Splice-site variants that misprocess PRG4 RNA and remove crucial domains. PMC
Missense variants that change key amino acids and impair lubricin function or secretion. BioMed Central
Exonic deletions/insertions removing essential PRG4 regions. ScienceDirect
Compound heterozygosity (two different PRG4 variants, one on each copy). PMC
Homozygous variants due to parental carrier status (often in consanguineous families). PMC
Founder variants clustered in specific populations/families. PMC
Variants affecting secretion so lubricin is made but not exported correctly. Boston Children’s Research
Variants altering the mucin-rich repeats, reducing boundary lubrication. Boston Children’s Research
Variants impairing heparin-binding or hemopexin domains, changing tissue interactions. Wikipedia
Loss of cartilage surface “superficial zone” protection, accelerating mechanical wear. PMC
Synovial hyperplasia driven by absent lubricin signals, causing big, cool effusions. malacards.org
Tendon and sheath lubrication failure, contributing to finger flexion contractures. Journal of Clinical Imaging Science
Abnormal hip development under low-lubricin conditions, promoting coxa vara. Journal of Clinical Imaging Science
Cartilage micro-damage over time because friction is higher than normal. PMC
Non-inflammatory pericardial effusion from similar serosal surface biology. malacards.org
Autosomal recessive inheritance—child affected when both parents are healthy carriers. orpha.net
Normal immune markers despite joint swelling, which delays recognition but reflects the same PRG4 mechanism, not inflammation. Wikipedia
Documented novel PRG4 variants reported in recent case series, expanding known mechanisms. BioMed Central
Symptoms and signs
Camptodactyly (finger bending)
Usually present at birth or early childhood. One or several fingers stay partially bent and do not fully straighten. The change is fixed over time. orpha.netLarge, cool joint swelling
Elbows, knees, wrists, and ankles often look swollen with extra fluid but are not warm or very painful. This non-inflammatory effusion is a hallmark. Journal of Clinical Imaging ScienceStiffness after rest
Children feel stiff after sleep or sitting. It eases a bit with gentle movement, but swelling persists. rarediseases.info.nih.govNormal fever and blood tests
There is no fever and standard inflammatory markers (ESR/CRP) stay normal, which helps separate CACP from arthritis. WikipediaReduced joint range of motion
Because the synovium is thick and fluid-filled, movement becomes restricted over months to years. Journal of Clinical Imaging ScienceHip problems (coxa vara)
The hip angle decreases. Children may walk with a limp or have different leg lengths. Hip imaging can show acetabular cysts. Journal of Clinical Imaging Science+1Gait changes
A broad-based or limping gait may appear, especially with hip involvement. Journal of Clinical Imaging SciencePericardial effusion (some patients)
Non-inflammatory fluid collects around the heart. Breathlessness, chest discomfort, or reduced exercise tolerance can occur, though many cases are silent and found on echo. malacards.orgOccasional pleural effusion
Rare fluid around the lungs has been described. malacards.orgTendon-related tightness
Reduced lubrication can contribute to tendon sheath thickening and finger contractures. Journal of Clinical Imaging ScienceMinimal pain despite swelling
Pain is usually milder than the swelling suggests, another clue against inflammatory arthritis. rarediseases.info.nih.govNormal growth and general health
Aside from musculoskeletal and occasional serosal fluid issues, most children are otherwise well. orpha.netEarly childhood onset
Most features begin in infancy or the first years of life. orpha.netPoor response to anti-inflammatory medicines
NSAIDs and steroids usually do not help because the process is not driven by classic inflammation. rarediseases.info.nih.govFamily history consistent with recessive inheritance
Parents are typically unaffected carriers; siblings may be affected, especially with consanguinity. PMC
Diagnostic tests
A) Physical examination
Inspection of hands for camptodactyly
Look for permanent finger flexion, usually at the proximal interphalangeal joint. Early detection supports CACP. orpha.netJoint swelling pattern
Large joints are symmetrically swollen but cool. Lack of heat and redness points away from inflammatory arthritis. Journal of Clinical Imaging ScienceRange-of-motion (ROM) assessment
Goniometry shows limited extension or flexion in affected joints. Restriction progresses slowly over time. Journal of Clinical Imaging ScienceGait observation
Check for limp or unequal step length suggesting coxa vara. Journal of Clinical Imaging ScienceCardiorespiratory exam
Listen for muffled heart sounds or reduced breath sounds that may suggest effusions; many patients are asymptomatic. malacards.org
B) Manual/bedside orthopedic tests
Bunnell-Littler test (finger PIP tightness)
Helps distinguish joint capsule/tendon tightness when a finger will not straighten. In CACP, fixed contracture and tendon sheath thickening may be noted. (General hand exam principle applied to CACP.) Journal of Clinical Imaging SciencePassive stretch testing
Gentle passive extension/flexion of swollen joints shows mechanical limits rather than pain-limited movement, consistent with non-inflammatory effusions. Journal of Clinical Imaging ScienceHip flexion/abduction tests
Limited abduction or positive findings on bedside hip exams hint at evolving coxa vara that later appears on imaging. Journal of Clinical Imaging ScienceFunctional reach and squat tests
Simple clinic maneuvers document stiffness and track change over time. rarediseases.info.nih.govStep length and pelvic tilt assessment
Bedside observation may reveal functional leg length difference from hip deformity. Journal of Clinical Imaging Science
C) Laboratory and pathological tests
ESR and CRP
Typically normal. Normal inflammatory markers strongly support CACP over JIA when joints are swollen. WikipediaRheumatoid factor (RF) and ANA
Negative in CACP; help exclude autoimmune arthritis. WikipediaSynovial fluid analysis
Arthrocentesis yields clear, viscous, honey-colored fluid with low cell count; cultures are negative. WikipediaSynovial biopsy (when performed)
Shows synovial hyperplasia without lymphocytic infiltration typical of inflammatory arthritis. malacards.orgMolecular genetic testing of PRG4
Sequencing identifies biallelic pathogenic variants (nonsense, frameshift, splice, missense, or deletions), confirming diagnosis. PMC+1Targeted family testing/carrier testing
Parents and siblings can be tested once the familial variant is known. This clarifies recurrence risk. PMCExtended gene panels (when phenotype is unclear)
Skeletal dysplasia or early-arthritis panels that include PRG4 can detect unexpected cases that mimic JIA. rarediseases.info.nih.gov
D) Electro-diagnostic / cardiac electrical tests
Electrocardiogram (ECG)
Usually normal, but used to screen for pericardial effects (e.g., low voltage with large effusions) or to exclude other causes of chest symptoms. malacards.orgHolter or event monitoring (selected patients)
If palpitations or atypical symptoms occur, ambulatory ECG helps exclude rhythm issues; pericardial effusion itself is non-inflammatory in CACP. malacards.org
E) Imaging tests
Plain radiographs (X-rays) of hips and hands
Show coxa vara, acetabular cysts, squared phalanges/metacarpals, and large joint effusions; key for differentiating CACP from JIA. Journal of Clinical Imaging Science+1Ultrasound of joints
Demonstrates large, anechoic (non-inflammatory) effusions and thick synovium without Doppler hyperemia typical of active arthritis. Journal of Clinical Imaging ScienceEchocardiography (heart ultrasound)
Detects non-inflammatory pericardial effusion when present and monitors for hemodynamic impact. malacards.orgMRI of affected joints
Shows effusion, synovial thickening, and cartilage surfaces; helpful when X-rays are non-diagnostic or to plan care. Journal of Clinical Imaging SciencePelvic/hip MRI or CT (selected cases)
Further characterizes acetabular cysts and the femoral neck-shaft angle in surgical planning. Journal of Clinical Imaging ScienceChest imaging (CXR or ultrasound)
Looks for pleural effusion in rare cases with respiratory symptoms. malacards.org
Non-pharmacological treatments (therapies & others)
Individualized physiotherapy program
Description (what it is): A gentle, regular program designed by a pediatric physiotherapist to keep joints moving through safe ranges, build muscle balance, and reduce stiff patterns. It often includes active and assisted range-of-motion drills for hands, wrists, knees, ankles, hips, plus core and posture work. Purpose: Preserve movement, reduce contractures, and improve daily function (grip, gait, self-care). Mechanism (why it helps): In CACP the joint lining is thick and the joint fluid is less slippery. Frequent, low-load motion distributes whatever lubrication is present, helps cartilage nutrition, and counters “shortening” of soft tissues. Programs avoid high-impact force because the problem isn’t inflammation but poor lubrication and synovial overgrowth. PMC+1Hand therapy for camptodactyly
Description: A certified hand therapist teaches gentle stretching for finger flexion contractures, tendon-gliding exercises, and use of night splints. Purpose: Improve finger extension, pinch, and grasp, and slow fixed deformity. Mechanism: Regular low-tension stretch and tendon glides remodel soft tissues and reduce adaptive shortening around small joints without provoking pain, which aligns with the non-inflammatory nature of CACP. Journal of Clinical Imaging ScienceStatic and dynamic splinting
Description: Custom splints for fingers (PIP joints), wrists, and sometimes knees maintain a safe position at rest; dynamic options allow limited motion during activities. Purpose: Prevent worsening contractures and support function (writing, feeding). Mechanism: Prolonged, gentle positioning applies low-grade tissue stress that encourages lengthening of capsules/tendons over time; dynamic splints permit controlled motion that nourishes cartilage and reduces stiffness. Journal of Clinical Imaging ScienceSerial casting (short-term)
Description: Short periods (1–2 weeks per cast) of carefully applied casts to gradually increase finger or knee extension, followed by splinting and therapy. Purpose: Gain range that cannot be achieved with exercises alone. Mechanism: Time-dependent tissue creep under sustained low load allows gradual correction without aggressive force—important because joints are structurally altered but not inflamed. Journal of Clinical Imaging ScienceHydrotherapy (water-based exercise)
Description: Guided movement in a warm pool using buoyancy to offload joints while practicing range, balance, and gentle strengthening. Purpose: Maintain mobility and aerobic fitness with less joint stress. Mechanism: Buoyancy reduces compressive forces on cartilage; warmth decreases perceived stiffness; water resistance gives safe, even strengthening. PMCLow-impact aerobic activity
Description: Age-appropriate walking, cycling, or swimming several times per week. Purpose: Support heart-lung health, bone mass, and mood while keeping joints moving. Mechanism: Cyclic motion nourishes cartilage and supports muscle endurance without high impact that could worsen mechanical symptoms in large joints. PMCOccupational therapy (OT) & school adaptations
Description: OT evaluates writing tools, keyboards, grips, and daily-living tasks; recommends modifications and energy-saving strategies. Purpose: Protect joints, enhance independence, and reduce fatigue. Mechanism: Ergonomic aids reduce undue torque on poorly lubricated joints; activity pacing prevents overuse and compensatory strain. PMCOrthotics & footwear optimization
Description: Shoe inserts or ankle-foot orthoses to align lower limbs and support hip/knee loading; rocker-bottom soles can ease push-off. Purpose: Improve gait efficiency and reduce pain from malalignment, especially with developing coxa vara. Mechanism: Better alignment lowers abnormal joint contact stresses in large joints already affected by synovial overgrowth. PMCGait and posture training
Description: Therapists coach neutral pelvis, hip abductor activation, and safe patterns for stairs and uneven ground. Purpose: Reduce fall risk and slow hip deformity progression. Mechanism: Balanced muscle recruitment reduces shear and focal loading on hips with altered neck-shaft angles. PMCAssistive devices (situational)
Description: Occasional use of canes, forearm crutches, or knee sleeves during flares of mechanical pain or long distances. Purpose: Maintain participation in school and community activities. Mechanism: Offloading reduces peak joint forces when synovial hypertrophy makes motion uncomfortable. PMCHome stretching & joint-care education
Description: Family-taught daily routines (5–10 minutes twice daily) with tracking charts. Purpose: Consistency between therapy visits. Mechanism: Frequent short sessions are more effective for tissue adaptation than rare long sessions—and less likely to provoke discomfort. Boston Children’s ResearchPericardial surveillance & cardiology follow-up
Description: Periodic cardiac exams and ultrasound if symptoms (breathlessness, chest discomfort) appear. Purpose: Detect non-inflammatory pericardial effusion early. Mechanism: Timely monitoring allows conservative observation or procedure (pericardiocentesis) before hemodynamic compromise. FrontiersNutrition for growth & joint health
Description: Balanced diet with adequate calcium, vitamin D, protein, and hydration; limit ultra-processed foods. Purpose: Support bone density, muscle mass, and overall recovery. Mechanism: Sufficient nutrients help muscles support joints; hydration supports synovial fluid quality. PMCPain coping skills & child-family counseling
Description: Simple cognitive-behavioral strategies, relaxation, and pacing taught to child and caregivers. Purpose: Reduce fear of movement and improve adherence to exercise. Mechanism: Lower anxiety decreases muscle guarding and increases willingness to move regularly—key for non-inflammatory stiffness. PMCSchool/PE collaboration
Description: Written activity plans, extra time between classes, and modified PE (swimming, cycling). Purpose: Keep the child active and included without harmful loads. Mechanism: Structured choices avoid high-impact drills that could strain hips and knees. PMCHeat before stretching, cool after activity
Description: Warm packs or showers before range-of-motion; cool packs after long activity. Purpose: Ease stiffness, then calm post-activity soreness. Mechanism: Heat improves tissue pliability; brief cooling modulates soreness without anti-inflammatory intent. PMCRegular hip imaging as advised
Description: Periodic X-rays if gait worsens or leg length differences appear. Purpose: Track coxa vara progression and time orthopedics input. Mechanism: Early detection of worsening angles guides conservative vs surgical planning. Journal of Clinical Imaging ScienceUltrasound for quick joint/pericardial checks
Description: Ultrasound to distinguish fluid from thick tissue and to assess the heart sac if symptomatic. Purpose: Reduce invasive tests and support rapid decisions. Mechanism: Ultrasound shows non-inflammatory effusions and synovial hypertrophy features that fit CACP. medultrason.roFamily genetic counseling
Description: Explain autosomal recessive inheritance, recurrence risk, and testing options. Purpose: Informed future planning. Mechanism: Understanding PRG4 genetics helps families make choices and clinicians avoid mislabeling as JIA. NatureSafe-play and fall-prevention coaching
Description: Guidance on playground choices, safe surfaces, and technique. Purpose: Limit joint injuries in already mechanically vulnerable hips/knees. Mechanism: Reducing high-impact events lowers cartilage shear in poorly lubricated joints. PMC
Drug treatments
Important safety note: No medicine is approved specifically for CACP. The drugs below are symptom-or complication-directed (off-label for CACP) and must be individualized by specialists. FDA labels are cited for drug class, dosing ranges, and safety; indications on those labels may differ (e.g., pain, arthritis, gout). Children require pediatric dosing. Aspirin is generally avoided in children because of Reye’s risk. PMC+1
Acetaminophen (paracetamol)
Class: Analgesic/antipyretic. Purpose: First-line pain relief for mechanical joint aches. Dose/Time: Per FDA labeling for OTC pain relievers (follow pediatric weight-based guidance; avoid overdose and duplicate products). Mechanism: Central pain modulation without anti-inflammatory action—fits non-inflammatory CACP pain. Side effects: Liver toxicity with overdose or combination products; check all labels. (Use per healthcare professional guidance). U.S. Food and Drug AdministrationIbuprofen
Class: NSAID. Purpose: Short courses for pain; may help with pericardial chest discomfort when a clinician deems appropriate. Dose/Time: Per FDA label (OTC/prescription strength; pediatric weight-based dosing). Mechanism: COX inhibition reduces prostaglandin-mediated pain. Key safety: GI bleeding, kidney effects, and rare CV risks; avoid prolonged unsupervised use. U.S. Food and Drug Administration+1Naproxen
Class: NSAID. Purpose: Alternative to ibuprofen for short-term pain relief. Dose/Time: Per FDA labeling (OTC/prescription; pediatric dosing by clinician). Mechanism: COX inhibition for analgesia. Side effects: Similar NSAID GI/CV/renal warnings. U.S. Food and Drug Administration+1Diclofenac
Class: NSAID (oral/topical). Purpose: Short-term pain support when topical options (e.g., gel) might limit systemic exposure. Dose/Time: As per FDA label for the specific product. Mechanism: COX inhibition. Side effects: Class GI/CV warnings; topical may still carry systemic risks. FDA Access DataCelecoxib
Class: COX-2 selective NSAID. Purpose: Considered when GI risk is high and cardiology risk is acceptable. Dose/Time: FDA-labeled dosing varies by indication. Mechanism: Preferential COX-2 inhibition for analgesia. Side effects: CV risk warning, renal effects; use specialist oversight. FDA Access DataProton-pump inhibitor (e.g., omeprazole) with NSAID when indicated
Class: Gastric acid suppression. Purpose: GI protection during necessary NSAID courses in higher-risk patients. Mechanism: Reduces gastric acid to lower ulcer risk. Side effects: Headache, rare nutrient malabsorption with long use. (Use only if a clinician feels warranted.) FDA Access DataTopical NSAID gel (e.g., diclofenac gel)
Class: Topical NSAID. Purpose: Local pain relief for hands/knees with potentially lower systemic exposure. Mechanism: Local COX inhibition. Side effects: Skin irritation; still observe NSAID warnings. FDA Access DataColchicine (for pericarditis, specialist-directed, off-label in children)
Class: Anti-inflammatory for gout per FDA label; used off-label in pericarditis care pathways. Purpose: Selected cases of symptomatic pericardial involvement under cardiology guidance. Dose/Time: As per FDA label for gout prophylaxis/treatment (adult dosing on label; pediatric/off-label dosing requires specialist). Mechanism: Microtubule effects that dampen inflammatory cell trafficking in the pericardium. Side effects: GI upset, myopathy with certain drugs; dose adjustments in renal/hepatic disease. FDA Access DataAcetaminophen–codeine alternatives (avoid routine opioids)
Class: Opioid combinations are generally avoided in children; if ever considered short-term, specialist oversight is essential. Purpose: Reserve only for exceptional procedural pain. Mechanism: Central opioid receptor effects. Risks: Respiratory depression, dependence, pharmacogenetic variability. Prefer non-opioid strategies first. U.S. Food and Drug AdministrationShort intra-articular anesthetic for procedures
Class: Local anesthetic (e.g., lidocaine) for minor procedures. Purpose: Comfort during aspiration or imaging-guided interventions. Mechanism: Nerve conduction block. Side effects: Local reactions, rare systemic toxicity—expert use only. (Procedure-related, not a chronic therapy.) PMCDiuretics are not routine
Note: Diuretics are not standard for pericardial effusion in CACP; management is usually observation or pericardiocentesis when indicated by cardiology. This item is included to clarify what is not typically used. FrontiersAvoid routine systemic steroids or immunosuppressants for “joint swelling” in CACP
Rationale: CACP is non-inflammatory; immune-suppressing drugs often fail and can cause harm if misapplied. Use only if a separate inflammatory diagnosis is confirmed by specialists. BioMed Central+1
(Because there is no CACP-specific approved drug, a full list of “20 drugs” with FDA-approved CACP indications does not exist. The safest, evidence-true approach is the above symptom- and complication-directed medications with strict specialist oversight and FDA-label safety references.)
Dietary molecular supplements
Vitamin D
Dose: Per pediatric guidelines to correct deficiency after testing. Function/Mechanism: Supports bone mineralization and muscle function, which helps joints with altered mechanics. Adequate vitamin D may improve balance and reduce falls, assisting hips and knees stressed by synovial overgrowth. Note: Test-and-treat; avoid excess. PMCCalcium (diet first)
Dose: Meet age-based daily needs through dairy or fortified foods; supplement only if intake is low. Function: Builds bone strength to support malaligned hips/knees. Mechanism: Adequate calcium plus vitamin D improves bone accrual during growth. PMCOmega-3 fatty acids (fish oil)
Dose: Pediatric-appropriate EPA/DHA per clinician guidance. Function: General musculoskeletal comfort and heart health. Mechanism: Modest prostaglandin pathway modulation; may help pain perception though CACP is not inflammatory. Avoid if bleeding risk. PMCProtein optimization (whey/food)
Dose: Meet daily protein needs for age/activity; consider dietitian input. Function: Supports muscle strength for joint stability. Mechanism: Adequate amino acids enable muscle repair and conditioning from therapy. PMCHydration strategy
Dose: Age-appropriate fluid goals. Function: Maintains synovial fluid quality and exercise tolerance. Mechanism: Adequate water supports cartilage lubrication dynamics. PMCMagnesium (food-first)
Dose: Meet RDA; supplement only if deficient. Function: Muscle relaxation and cramp reduction to ease therapy sessions. Mechanism: Cofactor in neuromuscular transmission. PMCMultivitamin (gap-filling only)
Dose: One pediatric multivitamin if diet is limited. Function: Insurance against minor omissions; not a treatment. Mechanism: Supplies trace micronutrients for growth and tissue repair. PMCCollagen peptides (experimental adjunct)
Dose: Discuss with clinician; evidence in pediatric non-inflammatory arthropathy is limited. Function: May support general joint comfort. Mechanism: Provides amino acids for connective tissues; clinical benefit in CACP unproven. PMCAntioxidant-rich diet (berries/greens)
Dose: Daily servings of colorful fruits/vegetables. Function: Overall health and recovery from activity. Mechanism: Supports cellular defenses; not disease-specific. PMCAvoid megadoses and unregulated supplements
Reason: Safety and interactions—especially if any cardiac procedure or medicines are used. Mechanism: Reduces risk from products without pediatric evidence. PMC
Drugs for immunity booster / regenerative / stem-cell
Important: There are no approved “immunity boosters,” regenerative drugs, or stem-cell therapies for CACP. Early-stage studies in other conditions suggest that recombinant PRG4 (lubricin) and gene-based approaches may one day help, but these are experimental and not available as standard treatment. Below I summarize the research landscape so expectations are accurate. MDPI+1
Recombinant human PRG4 (rhPRG4) – experimental
Description (~100 words): Lab and preclinical work show rhPRG4 can restore boundary lubrication, reduce friction, and modulate wound-healing cascades. Dosage: No clinical pediatric CACP dosing established. Function/Mechanism: Replaces missing lubricin to improve gliding in synovial joints. Nature+1PRG4 gene therapy – experimental
Description: Conceptual strategies aim to deliver a healthy PRG4 gene to synovial cells. Dosage: Not established. Function/Mechanism: Restore endogenous lubricin production; human trials for CACP have not been completed. MDPISmall-molecule PRG4 up-regulators – experimental
Description: Research in osteoarthritis models explores compounds/pathways (e.g., TGF-β, EGFR, Wnt modulators) to increase PRG4 expression. Dosage: Not established. Function/Mechanism: Boost body’s own lubricin in joints; not yet tested in CACP children. MDPIHyaluronic acid injections – device-based, not disease-specific
Description: Used for adult knee OA; not approved for CACP and pediatric utility is unclear. Function: Viscosity supplement; mechanism differs from lubricin. Use only in research contexts if ever considered. MDPIStem-cell injections – not recommended outside trials
Description: Commercial offerings lack proven benefit and carry risks. Function/Mechanism: Theoretical tissue repair; no pediatric CACP evidence. MDPIBiologics (anti-TNF, etc.) – avoid unless true inflammatory disease is proven
Description: Effective in JIA, but CACP is non-inflammatory; biologics may expose children to risk without benefit. Mechanism: Immune suppression inappropriate for PRG4 deficiency. BioMed Central
Surgeries (procedures & why they’re done)
Pericardiocentesis (when needed)
Procedure: Needle/catheter drains pericardial fluid under imaging. Why: Relieve symptoms or treat hemodynamic compromise in non-inflammatory effusions that occasionally occur in CACP. FrontiersPericardial window (rare cases)
Procedure: Surgical opening to prevent fluid re-accumulation. Why: Recurrent or constrictive problems not settling with less-invasive care. FrontiersHip osteotomy for progressive coxa vara
Procedure: Re-align the femoral neck-shaft angle. Why: Improve biomechanics, gait, and pain when deformity progresses despite therapy. Journal of Clinical Imaging ScienceSoft-tissue release for severe camptodactyly
Procedure: Limited release of contracted structures; sometimes with pinning. Why: Restore finger function when splinting/therapy fail. Journal of Clinical Imaging ScienceArthroscopic synovial debulking (selected joints)
Procedure: Remove excessive synovial tissue. Why: Reduce mechanical impingement; results vary because the underlying lubricin deficit persists. PMC
Preventions
Early diagnosis and avoid mislabeling as JIA—prevents unnecessary immunosuppression. BioMed Central
Daily gentle motion program—keeps tissues long and joints gliding. PMC
Activity choices (low-impact)—prefer swimming/cycling over jumping sports. PMC
Regular hip and gait checks—catch coxa vara changes early. Journal of Clinical Imaging Science
Pericardial symptom vigilance—see cardiology promptly for breathlessness or chest discomfort. Frontiers
Ergonomics at school/home—reduce strain on small joints. PMC
Nutrition, vitamin D, and sleep—support growth and muscle recovery. PMC
Footwear and orthotics—optimize alignment and balance. PMC
Avoid overusing NSAIDs—use the lowest effective dose for the shortest time due to FDA safety warnings. FDA Access Data
Family genetic counseling—plan for future pregnancies and screening. Nature
When to see doctors (or go urgently)
New or worsening shortness of breath, chest pain, fainting, or fast heartbeat—possible pericardial fluid; seek urgent cardiology/ER care. Frontiers
Rapid hip pain, limp, or leg length difference—orthopedic assessment for coxa vara progression. Journal of Clinical Imaging Science
Hand function decline despite therapy—hand surgeon/therapist review for splint or surgical options. Journal of Clinical Imaging Science
Poor response to “arthritis medicines” or side-effects from steroids/biologics—re-evaluate diagnosis; CACP is non-inflammatory. BioMed Central
Any medication side-effects (stomach pain/bleeding signs, black stools, less urine) if using NSAIDs—get medical advice promptly per FDA warnings. FDA Access Data
What to eat & what to avoid
Eat: Whole foods with adequate protein (eggs, dairy, legumes, fish) to support muscles. Avoid: Protein restriction. PMC
Eat: Calcium + vitamin D sources (milk, yogurt, fortified alternatives, safe sun per local guidance). Avoid: Chronic low-calcium diets. PMC
Eat: Fruits/vegetables daily for micronutrients. Avoid: Ultra-processed snacks replacing real meals. PMC
Drink: Adequate water; bring a bottle to therapy. Avoid: Sugary drinks as main fluids. PMC
Include: Omega-3 fish 1–2×/week if not allergic. Avoid: High-mercury fish for children. PMC
Use: Multivitamin only to fill gaps if diet is limited. Avoid: Mega-doses or multiple overlapping supplements. PMC
Plan: Snacks before/after therapy (fruit + yogurt/peanut butter). Avoid: Training on an empty stomach leading to fatigue. PMC
Consider: Dietitian input for picky eating or growth faltering. Avoid: DIY restrictive diets. PMC
If NSAIDs needed: Take with food and follow clinician instructions to reduce GI risk. Avoid: Combining multiple NSAIDs. FDA Access Data
All families: Keep a medication/supplement list and share it at visits. Avoid: Hidden duplicate acetaminophen/NSAID products. U.S. Food and Drug Administration
FAQs
1) Is CACP an arthritis?
It looks like arthritis because joints swell, but it’s non-inflammatory. Swelling comes from synovial overgrowth due to PRG4 deficiency, not classic immune inflammation. PMC
2) What gene is involved?
The PRG4 gene; it makes lubricin, which lets joints glide. Mutations cause CACP. Nature
3) How is it inherited?
Autosomal recessive—both parents carry one altered gene; a child with two copies is affected. orpha.net
4) Why don’t steroids/biologics help much?
Because inflammation is not the main problem; misdiagnosis as JIA leads to ineffective immunosuppression. BioMed Central
5) What confirms the diagnosis?
Typical clinical picture, clear/low-cell synovial fluid, imaging, and PRG4 genetic testing. Radiopaedia+1
6) Is there a cure?
No proven disease-modifying cure yet. Research into recombinant PRG4 and gene-based approaches is ongoing. MDPI+1
7) What’s the first treatment step?
Therapy-led movement (physio/hand therapy), splinting, and daily home exercises to keep function. PMC
8) Do children outgrow it?
CACP is lifelong, but early therapy and smart activity choices help children stay active and independent. PMC
9) What about the hips?
Coxa vara can progress; regular orthopedic checks and, if needed, corrective osteotomy improve function. Journal of Clinical Imaging Science
10) What about the heart?
Some patients develop non-inflammatory pericardial effusion; cardiology follow-up is key. Urgent care is needed if breathless or faint. Frontiers
11) Are NSAIDs safe?
Short, clinician-directed courses may help pain; use the lowest effective dose, watch for FDA-flagged GI/renal/CV risks, and avoid combining NSAIDs. FDA Access Data
12) Can diet fix CACP?
No diet can replace lubricin, but balanced nutrition supports growth and therapy. Avoid megadose supplements. PMC
13) Is surgery common?
Surgery is selective—for significant hip deformity, severe finger contractures, or symptomatic pericardial effusion. Journal of Clinical Imaging Science+1
14) What imaging is used?
X-rays for hips; ultrasound for joints and pericardium when needed. medultrason.ro
15) Where can families read more?
Trusted overviews exist from rare-disease portals and peer-reviewed reviews. rarediseases.info.nih.gov+1
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The article is written by Team RxHarun and reviewed by the Rx Editorial Board Members
Last Updated: November 09, 2025.
