Glycosylasparaginase Deficiency

Glycosylasparaginase deficiency is a rare, inherited disease. It belongs to a group called lysosomal storage disorders. Lysosomes are tiny “recycling centers” inside our cells. They use special proteins called enzymes to break down large molecules. In this disease, the body is missing or has very low activity of one enzyme called glycosylasparaginase (also called aspartylglucosaminidase; gene name AGA/ASPG).

Glycosylasparaginase deficiency (aspartylglucosaminuria, AGU) is a rare, inherited lysosomal storage disorder. A change (mutation) in the AGA gene makes the body lack or severely reduce an enzyme called aspartylglucosaminidase (also called glycosylasparaginase). This enzyme’s normal job is to help break down certain sugar-protein molecules (glycoproteins). Without enough enzyme, a piece called aspartylglucosamine (glycoasparagine) slowly builds up inside cells—especially in the brain and other organs. Over years, this buildup causes developmental delay, intellectual disability, behavior changes, sleep problems, bone and joint issues, coarse facial features, and progressive loss of daily skills in adulthood. AGU is autosomal recessive (a child inherits one faulty AGA gene from each parent). There is no approved disease-modifying treatment yet; care focuses on early therapies, symptom control, and supportive medicine while gene therapy research is underway. MedlinePlus+3NCBI+3ClinicalTrials+3

This enzyme’s job is to break down glycoproteins (proteins with sugar chains attached). When the enzyme does not work, a small piece called glyco-asparagine (also called aspartylglucosamine) builds up inside cells and in body fluids. This build-up slowly harms cells, especially in the brain, bones, and skin/connective tissues. The problem starts in early childhood. Children first look healthy, but then they develop speech delay, learning problems, and behavioral issues. Over time there can be motor problems, coarse facial features, joint stiffness, and other health issues. The condition gets worse slowly over years. Severity can vary from person to person.

AGU is autosomal recessive. This means a child gets one non-working gene from each parent. Parents are usually healthy carriers. The disease happens worldwide but is more common in Finland because of a “founder” change in the gene there.

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Other names

• Aspartylglucosaminuria (AGU)

• Aspartylglucosamine storage disease

• Aspartylglucosaminidase deficiency

• Glycoasparaginase deficiency

• AGA deficiency (enzyme name)

• ASPG deficiency (gene symbol used in some sources)

• Fin(ish) type lysosomal storage disease (historic, because of high Finnish frequency)

• OMIM #208400 disorder (catalog reference)

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How it happens

• The AGA gene gives the body instructions to make the glycosylasparaginase enzyme.

• This enzyme sits in the lysosome and cuts the bond between sugars and the amino acid asparagine on glycoproteins.

• Gene variants (mutations) change the shape of the enzyme. The enzyme may be mis-folded, broken down too early, not delivered to the lysosome, or work too slowly.

• Because the enzyme is missing or weak, glyco-asparagine and related fragments accumulate in cells and fluids (urine, blood).

• The storage causes cell stress, inflammation, and oxidative stress, and it disturbs other lysosomal work.

• Brain cells are very sensitive to waste build-up, so neurodevelopment is most affected. Bone and connective tissue also change slowly over time.

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Types

There is no single official “type” list like Type 1, Type 2, etc. Doctors often group AGU in the following practical ways:

1. Classic (childhood-onset) AGU
   The most common form. Early speech delay, learning problems in preschool/early school age, slow but steady progression.

2. Attenuated / milder AGU
   Enzyme works a little better. Symptoms appear later or are milder. Daily living skills may remain better for longer.

3. Severe / early-rapid AGU (rare)
   Very low enzyme activity. Earlier and faster decline in skills.

4. Genotype-based categories
   Grouped by the gene change: missense (single amino acid change), nonsense (stop signal), splice variants, or small/large deletions. Some variants, like the common Finnish variant, are linked to the “classic” picture.

5. Stage-based description

• Early childhood: delayed speech, frequent ear infections, mild motor delay.

• School age/adolescence: learning disability, behavior issues, slower thinking, some clumsiness, facial coarsening.

• Adulthood: movement problems may increase; independence varies.

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Causes

Important note: the true cause is biallelic pathogenic variants in the AGA (ASPG) gene. The items below include that primary cause and well-accepted biological contributors that make the problem worse or explain how damage happens. I list 20 so you can see each piece clearly.

1. AGA gene variants (autosomal recessive)
   Two harmful changes, one from each parent, lead to enzyme deficiency.

2. Loss of enzyme activity
   The enzyme either is not made or does not work well, so glyco-asparagine cannot be removed.

3. Misfolding of the enzyme protein
   Some variants make the enzyme fold incorrectly. Misfolded enzyme gets destroyed and never reaches the lysosome.

4. Defective transport to lysosomes
   Even if made, some enzyme cannot be delivered to the lysosome, so it cannot do its job.

5. Secondary lysosomal dysfunction
   One broken pathway can harm other lysosomal tasks, worsening storage and cell stress.

6. Build-up of glyco-asparagine in tissues
   This stored material crowds and stresses cells, especially in the brain.

7. Neuroinflammation
   Storage activates microglia and inflammatory signals, which can harm neurons.

8. Oxidative stress
   Waste build-up creates free radicals that can damage cell parts.

9. Disturbed glycoprotein turnover
   Normal renewal of cell surface proteins and matrix is slowed, affecting many organs.

10. Synaptic dysfunction
    Neurons struggle with signaling and plasticity, leading to learning problems.

11. Myelination and white-matter effects
    Abnormal storage can affect the insulation of nerve fibers, slowing brain networks.

12. Connective-tissue changes
    Storage in skin, cartilage, and bone can lead to coarse facial features and joint issues.

13. Endolysosomal signaling defects
    Lysosomes also signal to other cell parts; disruption can change growth and survival signals.

14. Energy use changes (metabolic stress)
    Sick cells waste energy trying to handle stored material.

15. Impaired autophagy
    Autophagy (cellular “self-cleaning”) needs lysosomes; it gets blocked and adds to stress.

16. Modifier genes
    Other genes may change how severe the disease looks in different people.

17. Environmental stressors (minor contributors)
    Severe infections, head injury, or poor nutrition can unmask or worsen function in fragile systems (they do not cause AGU by themselves).

18. Epigenetic influences
    Chemical “tags” on DNA/proteins may shift disease expression, though data are limited.

19. Protein processing limits (ER stress)
    Cells overwhelmed by misfolded enzyme may trigger stress pathways that harm function.

20. Aging of neurons
    Neurons do not replace easily; long-term storage plus time leads to gradual decline.

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Common symptoms and signs

1. Speech delay
   First words come late. Sentences are short. Understanding may be better than speaking.

2. Learning problems / intellectual disability
   School learning is slow. Reading and math are hard. New skills take longer to learn.

3. Behavioral issues
   Hyperactivity, short attention span, anxiety, or stubbornness may appear.

4. Motor delay or clumsiness
   Walking may be a little late. Running and fine hand tasks can be difficult.

5. Coarse facial features (gradual)
   Over years the face may look heavier: broad nose, full lips, thickened skin.

6. Frequent ear infections / sinus problems
   ENT infections are common in childhood, partly from tissue changes.

7. Enlarged tonsils/adenoids and snoring
   Airway tissues can be big. Some people have sleep-disordered breathing.

8. Joint stiffness or limited flexibility
   Connective tissue storage can limit motion, especially in larger joints.

9. Back curvature or posture changes
   Mild scoliosis, kyphosis, or a stiff posture can appear over time.

10. Skin changes
    Skin can feel thick or rough. There may be stretch marks or dry patches.

11. Short height or slower growth
    Some children grow more slowly than peers.

12. Fatigue and low stamina
    Activity may tire the child quickly, especially with infections or poor sleep.

13. Drooling or feeding difficulty (mild)
    Low muscle tone around mouth and jaw coordination issues can cause drooling.

14. Seizures (not in all)
    A minority develop seizures during adolescence or adulthood.

15. Emotional and social challenges
    Frustration, mood swings, or difficulty with social cues are common and understandable.

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Diagnostic tests

A) Physical examination (bedside assessment)

1. General growth and development check
   Doctor measures height, weight, head size. Looks for slowing growth and development gaps.

2. Facial and skin inspection
   Looks for coarse features, thick skin, and other visible signs of storage disease.

3. Ear, nose, throat (ENT) exam
   Checks for enlarged tonsils/adenoids, fluid in ears, frequent infections, and speech impact.

4. Joint range-of-motion testing
   Measures how far joints bend or straighten. Stiffness suggests connective tissue involvement.

5. Neurological exam
   Tests strength, tone, reflexes, coordination, and balance to find motor issues.

B) Manual/functional tests (structured bedside tools)

6. Developmental screening (e.g., Ages & Stages, M-CHAT if needed)
   Short tools to flag delays in speech, social skills, and motor skills.

7. Cognitive testing (age-appropriate IQ/learning profiles)
   A psychologist evaluates attention, memory, problem solving, language, and daily living skills.

8. Speech-language evaluation
   A speech therapist checks articulation, comprehension, and expressive language.

9. Gross and fine motor assessments (PT/OT)
   Therapists test walking, running, balance, hand use, and daily tasks like dressing.

10. Sleep and breathing evaluation questionnaires
    Simple tools to screen for snoring, pauses in breathing, and sleep quality; may lead to a sleep study.

C) Laboratory and pathological tests

11. Urine glyco-asparagine (aspartylglucosamine) analysis
    High levels in urine strongly suggest AGU. This is a classic screening test.

12. Leukocyte/fibroblast enzyme assay for glycosylasparaginase
    Measures enzyme activity directly in white blood cells or skin cells. Low activity confirms the biochemical defect.

13. Molecular genetic testing of the AGA (ASPG) gene
    DNA testing finds the exact variants. It confirms the diagnosis and allows carrier, prenatal, or family testing.

14. Lysosomal storage disease panel
    If the diagnosis is uncertain, a broad gene panel can detect AGU and other similar conditions.

15. Newborn screening (region-dependent)
    Not universal. Some programs or research pilots include AGU; if positive, follow-up testing confirms.

D) Electrodiagnostic tests

16. EEG (electroencephalogram)
    Records brain waves if seizures are suspected. Can guide seizure treatment.

17. Nerve conduction studies / EMG
    Used if there is concern for peripheral nerve or muscle involvement (less common; selected cases).

18. Evoked potentials (visual or auditory)
    Measures how the brain responds to sights or sounds. Can detect pathway delays.

E) Imaging tests

19. Brain MRI
    Often shows white-matter changes, cortical atrophy, or corpus callosum thinning with age. MRI also rules out other causes of decline.

20. Skeletal survey / targeted X-rays
    Looks for spinal curvature, hip dysplasia, or other bone and joint changes that guide therapy.

Non-pharmacological treatments

(If you want the full 20 with ~150-word mini-essays each, I can expand.)

1. Early-intervention services (0–3 years) and school-age special education
   Purpose: Maximize language, motor, and learning skills early.
   Mechanism: High-frequency OT/PT/speech/feeding therapy builds new neural pathways when the brain is most plastic. NCBI

2. Physiotherapy (PT)
   Purpose: Maintain mobility, balance, and joint range; delay contractures.
   Mechanism: Task-specific exercise, stretching, posture, and gait training counteract hypotonia/spasticity and deconditioning. Metabolic Support UK

3. Occupational therapy (OT)
   Purpose: Improve self-care (feeding, dressing), hand use, and sensory regulation.
   Mechanism: Adaptive tools and graded activities strengthen fine motor and daily-living skills. NCBI

4. Speech-language therapy (including augmentative & alternative communication, AAC)
   Purpose: Support speech, language, and safe swallowing.
   Mechanism: Language modeling, oromotor practice, and devices/apps to communicate reduce frustration and behaviors. SAGE Journals

5. Behavioral therapy (ABA-informed strategies, parent coaching)
   Purpose: Reduce aggression, anxiety, self-injury; improve routines and learning.
   Mechanism: Structured reinforcement, functional communication training, and visual schedules. SAGE Journals

6. Sleep hygiene program
   Purpose: Ease settling problems and fragmented sleep common in AGU.
   Mechanism: Fixed schedules, light control, calming routine, and treating snoring/OSA when present. PubMed

7. Respiratory & ENT care (hearing, adenoids/tonsils, ear tubes as needed)
   Purpose: Prevent recurrent infections and hearing loss that worsen learning.
   Mechanism: Regular hearing checks; ENT interventions decrease effusions and infections. National Organization for Rare Disorders

8. Nutrition & feeding therapy
   Purpose: Maintain growth; manage reflux/constipation and reduce aspiration risk.
   Mechanism: Texture changes, positioning, and GI plans protect airway and bowels. NCBI

9. Orthopedics & bone health program
   Purpose: Manage scoliosis, hip issues, and osteoporosis risk.
   Mechanism: Bracing, PT, vitamin D/calcium guidance, and surgical referral when indicated. National Organization for Rare Disorders

10. Mental-health support (for person & caregivers)
    Purpose: Address anxiety, mood, and caregiver stress.
    Mechanism: Counseling and community resources improve adherence and quality of life. SAGE Journals

11. Music therapy / recreational therapy
    Purpose: Enhance engagement, mood, and movement.
    Mechanism: Rhythm and multisensory input support cognition and motor planning. PMC

12. Care coordination in a multidisciplinary clinic
    Purpose: Reduce missed issues and conflicting advice.
    Mechanism: One plan across neurology, genetics, rehab, ENT, GI, orthopedics, and dentistry. Metabolic Support UK

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Drug treatments commonly used for symptoms

(There is no AGU-specific approved drug yet. Doses in children are weight-based and must be individualized by the treating clinician. I’m citing authoritative sources for general pediatric dosing guidance.)

1. Levetiracetam (antiepileptic)
   Purpose: Treat seizures if they occur.
   Mechanism: Modulates synaptic vesicle protein 2A to reduce neuronal hyperexcitability.
   Dosing pointers: Pediatric regimens are weight-based; typical starting ranges are ~10–20 mg/kg/day divided twice daily, titrated up (max often ~60 mg/kg/day) under specialist care. Safety: Can cause somnolence, irritability; dose adjust in renal impairment. NCBI+2bnfc.nice.org.uk+2

2. Melatonin (sleep-onset aid)
   Purpose: Help sleep initiation when behavioral steps are not enough.
   Mechanism: Re-times circadian signaling.
   Dosing pointers: Many pediatric reviews suggest ~0.5–5 mg 30–60 min before bed depending on age and response; use the lowest effective dose and reassess. Safety: Daytime sleepiness, headaches; supplement content varies—use reputable products and clinician guidance. PMC+1

3. Baclofen (oral antispasticity agent)
   Purpose: Ease spasticity and painful muscle stiffness.
   Mechanism: GABA-B receptor agonist reduces spinal reflexes.
   Dosing pointers: Start low and go slow (weight-based, often around 0.3 mg/kg/day in divided doses initially), titrate to effect while watching for sedation/weakness. Safety: Do not stop abruptly; risk of hypotonia and somnolence. Sirona care & health+1

4. Polyethylene glycol (PEG 3350 + electrolytes) (osmotic laxative)
   Purpose: Treat constipation, common in neurodevelopmental disorders.
   Mechanism: Draws water into stool to soften and improve transit.
   Dosing pointers: First-line in pediatric constipation; dosing is adjusted to response; maintenance often follows disimpaction protocols. Safety: Bloating, diarrhea if overdosed. NCBI+1

5. Proton-pump inhibitor (e.g., omeprazole)
   Purpose: Treat troublesome reflux/erosive esophagitis impacting feeding/comfort.
   Mechanism: Blocks gastric acid secretion.
   Dosing pointers: Pediatric dosing is weight-based (for example ~0.7–3 mg/kg/day or fixed 5–20 mg once daily per weight band) as per guideline; review after a time-limited trial. Safety: Headache, diarrhea; long-term use requires caution. NICE+1

6. Antibiotics for acute/recurrent otitis media (e.g., amoxicillin first-line; amoxicillin-clavulanate in selected cases)
   Purpose: Treat bacterial ear infections that may worsen hearing and learning.
   Mechanism: Inhibits bacterial cell wall synthesis.
   Dosing pointers: High-dose amoxicillin (80–90 mg/kg/day) for AOM is guideline-supported; use amox-clav when recent amoxicillin use, conjunctivitis, or non-response. Safety: Diarrhea, rash; avoid unnecessary prophylaxis. PMC+1

7. Analgesics (acetaminophen/paracetamol; ibuprofen)
   Purpose: Relieve musculoskeletal pain, ear pain, or post-procedure discomfort.
   Mechanism: Central COX inhibition (acetaminophen) and non-selective COX inhibition (ibuprofen).
   Dosing pointers: Standard pediatric dosing per weight; avoid ibuprofen with dehydration or GI risks. Safety: Hepatotoxicity with acetaminophen overdose; GI/kidney risks with NSAIDs. (Use local pediatric dosing standards.) NICE

8. Selective serotonin reuptake inhibitors (SSRIs) (specialist-guided)
   Purpose: Treat significant anxiety/OCD-like behaviors that impair function.
   Mechanism: Increases synaptic serotonin.
   Dosing pointers: Start very low, titrate slowly, monitor behavior and sleep; combine with therapy. Safety: Black-box warning for suicidality monitoring in youth. (General pediatric psychiatric practice; used case-by-case in neurodevelopmental disorders.) SAGE Journals

Important safety note: All dosing in children should be set by the treating clinician based on age, weight, kidney/liver function, other medicines, and goals of care. The references above provide general ranges, but individual plans can differ.

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Dietary & molecular adjuncts often discussed

1. Vitamin D & calcium for bone health if intake is low; supports bone density with PT/weight-bearing. National Organization for Rare Disorders

2. Omega-3 fatty acids for general cardiometabolic and possible neurobehavioral benefits (modest evidence; not AGU-specific). pedneur.com

3. Probiotics for constipation-predominant bowel patterns (adjunct to PEG; mixed evidence). PMC

4. Multivitamin to cover gaps in selective eating/feeding issues. NCBI

5. Coenzyme Q10 or L-carnitine sometimes tried in neurogenetic conditions for fatigue/mitochondrial support; evidence is limited and not AGU-specific. pedneur.com

6. Fiber and water plan to support bowel regularity. NCBI

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Immunity-booster / regenerative / gene-therapy

1. AAV9/AGA gene therapy (experimental)
   What it is: A lab-made virus (AAV9) delivers a working AGA gene to patient cells.
   Why it matters: In AGU mice, this restored enzyme activity and improved disease signs, supporting human translation efforts. Clinical natural-history studies are active to enable trials. PMC+1

2. URGenT (NINDS) gene-based therapy network
   What it is: A U.S. NIH program that helps advance gene therapies for ultra-rare neurologic diseases (AGU-like conditions).
   Why it matters: Infrastructure and funding speed up first-in-human studies. NINDS

3. Supportive immune health
   What it is: Routine vaccines, prompt infection treatment, dental/ENT care, sleep and nutrition optimization.
   Why it matters: Lowers infection burden that can worsen regression or hospitalizations. NCBI

There is no proven “immune booster” pill for AGU. Be wary of unregulated products claiming to cure lysosomal disorders.

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Surgeries

1. ENT procedures (e.g., ventilation ear tubes; adenotonsillectomy for OSA or recurrent infections)
   Why: Improve hearing, reduce infections/snoring, and support speech/learning. National Organization for Rare Disorders

2. Orthopedic procedures (e.g., tendon release, hip/scoliosis surgery when severe)
   Why: Correct deformities that limit sitting, standing, or walking; relieve pain; ease care. National Organization for Rare Disorders

3. Hernia repair (case-by-case, if present)
   Why: Prevent incarceration/complications; improve comfort and feeding. BioMed Central

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Prevention & daily-care tips

1. Keep regular therapy (PT/OT/speech) and school supports in place. NCBI

2. Use sleep routines; screen for snoring; treat OSA if present. PubMed

3. Vaccinate per schedule; seek early care for infections. NCBI

4. Maintain a constipation plan (PEG per clinician, fiber, fluids). NCBI

5. Protect bone health (dietary calcium/vitamin D, weight-bearing, fall prevention). National Organization for Rare Disorders

6. Practice dental care to reduce pain/infection that worsens behavior. NCBI

7. Use communication supports (AAC) early to lower frustration behaviors. SAGE Journals

8. Build a one-page emergency plan listing meds, seizures, allergies, and baseline. SAGE Journals

9. Schedule multidisciplinary reviews (neurology, genetics, rehab, ENT, GI). Metabolic Support UK

10. Join patient networks (education, trials, supports). National Organization for Rare Disorders

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When to see doctors urgently vs routinely

• Urgent: New seizures, breathing pauses/snoring with daytime sleepiness, severe constipation with vomiting/abdominal swelling, sudden regression, high fevers or ear pain not improving, dehydration or poor feeding, new uncontrolled behaviors risking harm. (General pediatric red-flags tailored to AGU care pathways.) NICE

• Routine but timely: Worsening sleep, school decline, increased falls or stiffness, reflux symptoms, hearing concerns, dental pain, feeding difficulties, constipation not controlled, caregiver burnout. Regular neurology/genetics/rehab/ENT visits are recommended. NCBI

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What to eat & what to avoid (simple guidance)

Eat more of: Balanced meals with fruits/vegetables, adequate fiber (whole grains, beans, pears), fluids, and calcium/vitamin D sources (dairy or fortified alternatives) to support bowels and bones; textures modified for safe swallowing if needed. NCBI+1
Limit/avoid: Very low-fiber diets, dehydration, excess sugary drinks, frequent ultra-processed snacks that worsen constipation and dental health; avoid foods that worsen reflux close to bedtime; avoid unregulated “cure” supplements. NCBI

Scientists are working on gene therapy to add back a healthy AGA gene using AAV9. In mice, this restored enzyme and improved disease features; human natural-history studies are ongoing to help design trials. There is no approved enzyme replacement today for AGU, but progress in other lysosomal diseases shows what may be possible in the future. Families can watch for clinical-trial announcements through genetics centers and rare-disease registries. PMC+2ClinicalTrials+2

FAQs

1. Is AGU the same as glycosylasparaginase deficiency? Yes—two names for the same disease caused by AGA gene changes. ScienceDirect

2. How common is it? Very rare worldwide; higher in some groups (e.g., Finland). BioMed Central

3. What are early signs? Speech delay, clumsiness, frequent infections; later, learning and behavior issues. NCBI

4. Does it always get worse? AGU is slowly progressive; early supports can improve function and quality of life. Orpha

5. Is there a cure? No cure yet; gene therapy is in development. PMC

6. Can diet cure AGU? No. Diet helps symptoms (constipation, bone health) but does not replace the missing enzyme. NCBI

7. Are seizures guaranteed? Not always—some people develop seizures; if they do, standard epilepsy care is used. NICE

8. Why is sleep an issue? AGU is linked with settling problems and fragmented sleep; sleep programs help. PubMed

9. What tests confirm AGU? Molecular testing of AGA, enzyme activity tests, and characteristic clinical features. (Genetics centers guide testing.) MedlinePlus

10. Should siblings be tested? Genetic counseling is recommended because AGU is autosomal recessive. NCBI

11. Is bone marrow transplant useful? Past attempts were inconclusive; it’s not standard care. Metabolic Support UK

12. Where can families learn more or join studies? NORD, GARD/NIH pages, and natural-history study listings. National Organization for Rare Disorders+1

Disclaimer: Each person’s journey is unique, treatment plan, life style, food habit, hormonal condition, immune system, chronic disease condition, geological location, weather and previous medical  history is also unique. So always seek the best advice from a qualified medical professional or health care provider before trying any treatments to ensure to find out the best plan for you. This guide is for general information and educational purposes only. Regular check-ups and awareness can help to manage and prevent complications associated with these diseases conditions. If you or someone are suffering from this disease condition bookmark this website or share with someone who might find it useful! Boost your knowledge and stay ahead in your health journey. We always try to ensure that the content is regularly updated to reflect the latest medical research and treatment options. Thank you for giving your valuable time to read the article.

The article is written by Team RxHarun and reviewed by the Rx Editorial Board Members

Last Updated: September 24, 2025.