Hereditary Congenital Contralateral Synkinesia

Hereditary congenital contralateral synkinesia is a rare, lifelong movement disorder where an intentional movement on one side of the body is “mirrored” by an involuntary copy on the other side. For example, when a person squeezes the right fist on purpose, the left fist tightens at the same time without trying. The effect is strongest in the hands and fingers, starts in early childhood, and usually stays about the same through life. Thinking and sensation are normal. In most people, there are no other neurological problems. NCBI+1

These mirror movements happen because some of the brain’s motor signals that should cross to the opposite side during development also send signals to the same-side (ipsilateral) pathways. In many affected people, the main motor highway (the corticospinal tract) does not fully cross the midline in the lower brainstem (the pyramidal decussation). This abnormal wiring lets one motor cortex drive movements on both hands at once. Genetic changes in guidance molecules that steer growing nerve fibers—especially the netrin-1/DCC pathway—are a key cause. Nature+2PMC+2

Other names

• Congenital mirror movements (CMM)

• Hereditary congenital mirror movement disorder

• Familial mirror movements

• Hereditary congenital contralateral synkinesis/synkinesia (older or less common phrasing)

• Mirror movements (developmental/isolated type)

These terms usually refer to the same core condition when it is present from birth and runs in families. NCBI

Types

1. Isolated hereditary CMM (autosomal dominant): Mirror movements are the main feature; many families show one affected person in each generation. Variants in DCC, RAD51, or NTN1 are most common here. NCBI+1

2. Recessive CMM: Much rarer; needs two altered copies of a gene, for example DNAL4. alliancegenome.org

3. Gene-defined subtypes:

   • DCC-related CMM

   • RAD51-related CMM

   • NTN1-related CMM

   • ARHGEF7-related CMM (newly implicated)

   • DNAL4-related CMM
     Current research recognizes these five genes as confirmed causes. PubMed+1

4. CMM with brain wiring variants: A subset shows partial or complete absence of corpus callosum or absent/weak crossing of the pyramids on imaging, often in DCC-related cases. PMC+1

5. Sporadic CMM: Appears in a person with no family history, often due to a de novo (new) genetic variant. NCBI

Causes

Below are known causes and plausible mechanisms that together explain hereditary congenital contralateral synkinesia. Items 1–5 are established genes; the rest describe how these genes and related pathways produce the mirror movements.

1. DCC variants (loss-of-function or missense): DCC is the main receptor for netrin-1 that helps motor fibers cross the midline. Faulty DCC disrupts crossing, so one motor cortex sends signals to both hands. PMC

2. RAD51 variants (haploinsufficiency): RAD51 is a DNA repair protein with roles in neural development; reduced function alters motor wiring and leads to CMM. MedlinePlus

3. NTN1 (netrin-1) variants: Netrin-1 is the guidance cue that binds DCC. When netrin-1 is altered, crossing guidance fails, and mirror movements appear. PMC+1

4. ARHGEF7 variants: A signaling partner in the netrin pathway that regulates small GTPases needed for axon guidance; recently implicated in human CMM. Science+1

5. DNAL4 variants (recessive): A dynein light-chain component; biallelic variants are linked to a recessive mirror-movement subtype. alliancegenome.org+1

6. Failed corticospinal tract decussation: The main motor pathway does not cross normally at the pyramids, leaving abnormal same-side projections that co-activate both hands. PMC

7. Persistent ipsilateral corticospinal projections: Even when some fibers cross, extra ipsilateral fibers remain and fire with the voluntary command. PMC

8. Bilateral motor cortex output during “one-hand” tasks: Functional studies show both motor cortices activate when only one hand is supposed to move. PMC

9. Reduced inter-hemispheric inhibition: The normal “brake” one motor cortex gives the other is weak, so the opposite side is not suppressed during one-hand movement. PMC

10. Corpus callosum anomalies (some DCC cases): When the callosum is absent or thin, inter-hemispheric control is altered and mirror movements can be stronger. PMC

11. Developmental timing effects: Early disturbances in the fetal window when axons choose to cross the midline can lock in the abnormal pattern for life. Nature

12. Variant type and location within DCC or NTN1: Different changes (e.g., netrin-binding domain vs intracellular domain) can alter severity and the exact wiring error. PMC+1

13. Genotype–phenotype differences (DCC vs RAD51): Families with RAD51 may show more “actual mirroring,” while some DCC carriers show subtler “fractionated” mirroring. PubMed

14. Modifier genes (under study): Additional genes likely tune how strong the mirror output is, which helps explain variability within families. PubMed

15. De novo variants: New mutations in DCC/NTN1/RAD51 can cause CMM without a family history. NCBI

16. Axon guidance signaling imbalance downstream of netrin-1 (e.g., ARHGEF7→Rac1/Cdc42): Mis-signaling can misroute crossing fibers. PMC

17. Abnormal corticospinal conduction patterns shown by TMS: Electrophysiology reveals ipsilateral motor-evoked potentials supporting a wiring cause. jnnp.bmj.com

18. Rare recessive pathways (DNAL4): Dynein complex dysfunction can disturb commissural neuron development and CST crossing. alliancegenome.org

19. Brainstem midline development issues: Subtle anomalies around the pyramidal decussation can be demonstrated with diffusion tractography in some individuals. PMC

20. Non-genetic “look-alikes” (not true hereditary CMM): Mirror-like movements can appear with stroke or Parkinson’s disease, but these are acquired and help underline the role of cortical balance and crossing. Frontiers

Symptoms

1. Obvious mirroring in the hands: When one hand moves on purpose, the other hand makes a smaller, similar movement at the same time. This is the hallmark sign. NCBI

2. Starts in early childhood: Parents often notice it when the child begins using hands for play or writing. It does not suddenly appear in adulthood. NCBI

3. Usually non-progressive: The pattern tends to stay stable over time; it does not steadily worsen. NCBI

4. Hard to do two different hand actions: Tasks like typing, playing piano, gaming with different buttons, or cutting food with knife and fork are difficult. MedlinePlus

5. Fatigue or aching with prolonged hand use: Holding or repeating tasks can cause discomfort because extra muscles are recruited on both sides. MedlinePlus

6. Slower fine motor performance: Pegboard or small-object tasks often take longer due to unhelpful co-contraction. NCBI

7. More mirroring at faster speeds or with effort: The stronger or quicker the intended movement, the clearer the mirror movement. NCBI

8. Hands and fingers are most affected: Arms can also mirror; legs are less commonly involved. MedlinePlus

9. Normal strength and sensation: The problem is in wiring and coordination, not in muscle power or feeling. NCBI

10. No effect on intelligence: School learning is normal; the challenge is handwriting and manual tasks. MedlinePlus

11. Social self-consciousness: People may feel embarrassed when others notice the extra movement. (A common lived experience reported in case series.) Wikipedia

12. May ease with strategy: People often learn tricks (slowing down, stabilizing the other hand) to reduce visible mirroring. NCBI

13. Rarely, associated features: A small subset—especially with DCC—may have partial/complete absence of the corpus callosum, which can subtly affect coordination. PMC

14. Subclinical mirroring: In some family members, mirroring is not obvious to the eye but can be measured with sensors. PubMed

15. Child vs adult patterns: Healthy children under ~10 can show mild iMEPs that normally disappear; in CMM they persist, explaining lifelong mirroring. Frontiers

Diagnostic tests

A) Physical exam at the bedside

1. Observation during simple tasks: The examiner asks for one-hand finger flexion/extension, pinching, or wrist motions and looks for a smaller, simultaneous copy on the other side. This confirms the core sign. NCBI

2. Rapid alternating movements (pronation–supination): Turning one forearm palm-up/palm-down repeatedly brings out clear mirroring in the opposite forearm. NCBI

3. One-hand finger tapping: Fast tapping with one index finger typically triggers smaller taps in the other index finger, useful for grading severity. NCBI

4. Sequential finger-to-thumb opposition: Touching thumb to each fingertip in order with one hand can show rhythmic copies in the other hand. NCBI

5. Task-loading and speed testing: Increasing speed or resistance usually increases mirroring, helping confirm the pattern. NCBI

B) Standardized manual/functional tests

6. Nine-Hole Peg Test: Measures fine motor speed; times are longer because involuntary co-movement interferes. It helps track impact over time. NCBI

7. Purdue Pegboard Test: Assesses dexterity and bimanual coordination; scores reflect the difficulty of doing different tasks with each hand. NCBI

8. Box-and-Blocks Test: Larger-object transfer still shows mirroring and gives a broader functional picture. NCBI

9. Handwriting sample and timed writing: Reveals overflow into the “resting” hand and explains school/work challenges. Wikipedia

10. Functional bimanual tasks (buttons, tying laces): Real-life tasks demonstrate the disability in a way patients and families easily recognize. MedlinePlus

C) Laboratory / pathological (genetic) tests

11. Targeted sequencing of DCC: First-line in many families; identifies pathogenic variants in a significant subset. NCBI

12. Multi-gene panel for CMM: Panels covering DCC, RAD51, NTN1, ARHGEF7, DNAL4 increase the diagnostic yield and are now available in clinical labs. fulgentgenetics.com+1

13. Exome or genome sequencing: Used if a panel is negative; helpful in sporadic cases or when the family pattern is unclear. PubMed

14. Family segregation testing: Testing relatives clarifies inheritance, penetrance, and recurrence risks. NCBI

D) Electrodiagnostic / neurophysiology

15. Surface EMG (electromyography): Records synchronous activity in matching muscles of both hands during a one-hand task, objectively showing mirroring. PMC

16. Transcranial Magnetic Stimulation (TMS): Evokes ipsilateral motor-evoked potentials (iMEPs) in hand muscles—evidence of same-side corticospinal projections that should not be there. jnnp.bmj.com

17. Cutaneomuscular reflex / evoked responses: Can show bilateral reflex patterns tied to the same abnormal wiring. PMC

E) Imaging tests

18. Brain MRI: Often normal, but checks for associated findings like agenesis of corpus callosum in some DCC cases and rules out other causes. PMC

19. Diffusion tensor imaging (DTI) tractography: May reveal reduced or absent pyramidal decussation and unusual corticospinal routes supporting the diagnosis in research/advanced centers. PMC

20. Functional MRI (fMRI): Shows bilateral motor cortex activation during one-hand tasks; supportive evidence for the bilateral drive mechanism. PMC

Non-Pharmacological Treatments (therapy/other)

Note: These are practical, low-risk strategies used to reduce strain, improve function, and protect comfort. None “erase” the mirror wiring; they help you live well with it.

1. Occupational therapy (OT) program—12-week block
   Purpose: Build efficient ways to write, type, cook, dress, and do crafts without pain.
   Mechanism: Task-specific practice teaches the brain and muscles to reduce overflow by using slower tempo, chunking motions, and stable postures; OT also sets up tools and routines to lower the demand on the “mirroring” hand. NCBI

2. School/work accommodations (extra time, reduced handwriting, keyboard use)
   Purpose: Keep grades/productivity up while preventing fatigue.
   Mechanism: Longer time and alternative input (typing, speech-to-text) cut repetitive fine-motor load that drives discomfort and overflow. NCBI

3. Bimanual coordination training (graded tasks)
   Purpose: Improve independence of the two hands in everyday tasks.
   Mechanism: Progressive exercises (e.g., asymmetric drumming patterns) strengthen inhibitory control across hemispheres and encourage cleaner task separation. NCBI

4. Ergonomic writing kit (pen grip, sloped board, forearm support)
   Purpose: Reduce cramping and involuntary copy-grips while writing.
   Mechanism: Larger grips and forearm support reduce finger-level effort; sloped surfaces align the wrist and reduce the trigger for mirror activity. NCBI

5. Task pacing & breaks (Pomodoro-style)
   Purpose: Prevent pain flares during typing/writing sessions.
   Mechanism: Short cycles limit motor overflow and give muscles recovery time, lowering cumulative strain. NCBI

6. Alternate input methods (speech-to-text, predictive typing)
   Purpose: Finish written work with less finger activity.
   Mechanism: Offloading keystrokes lowers bilateral co-activation and fatigue. NCBI

7. Instrument/sport selection & modification
   Purpose: Keep music and sport participation enjoyable.
   Mechanism: Choose activities with symmetric or slower bimanual patterns (e.g., percussion with simplified sticking), and use adaptive grips or rules to reduce asymmetric fine demands. NCBI

8. Stabilization strategies (light “parking” of the mirroring hand)
   Purpose: Reduce unwanted movements during precision tasks.
   Mechanism: Resting the non-task hand on the table or lightly holding an object adds proprioceptive feedback that dampens overflow. NCBI

9. Energy conservation in exams/work
   Purpose: Maintain quality while minimizing hand pain.
   Mechanism: Rearranging tasks (type first, sign later), using templates, and rotating roles avoids long continuous fine work. NCBI

10. Stress-reduction skills (breathing, brief mindfulness)
    Purpose: Lower performance anxiety that can worsen overflow.
    Mechanism: Reducing sympathetic arousal lessens co-contraction and mirroring during timed tasks. NCBI

11. Home exercise set (5–10 minutes daily)
    Purpose: Maintain comfortable range and strength without provoking mirroring.
    Mechanism: Slow, symmetrical mobility and light resistance patterns condition muscles and decrease cramp risk. NCBI

12. Keyboard adaptations (split keyboard, key remaps)
    Purpose: Make typing more comfortable and accurate.
    Mechanism: Split boards reduce cross-hand interference; remaps reduce awkward combinations that trigger overflow. NCBI

13. Note-taking alternatives (record lectures, outlines)
    Purpose: Reduce heavy handwriting loads.
    Mechanism: Audio capture and structured notes minimize continuous fine motor demand. NCBI

14. OT-guided handwriting retraining
    Purpose: Cleaner script with less pain.
    Mechanism: Larger letters, slower cadence, and wrist-neutral positions reduce mirror triggers. NCBI

15. Graded independence games (metronome-paced)
    Purpose: Practice different actions in each hand.
    Mechanism: Metronome and visual cues support hemispheric timing separation. NCBI

16. Parent/teacher coaching
    Purpose: Protect opportunities and reduce stigma.
    Mechanism: Understanding that intelligence is normal and the condition is lifelong prevents unfair grading and social labeling. NCBI

17. Career counseling
    Purpose: Choose jobs that fit well with hand-use profile.
    Mechanism: Avoid highly repetitive, complex bimanual roles; seek roles with flexible input methods. NCBI

18. Protective splinting for long tasks (select cases)
    Purpose: Decrease finger overuse.
    Mechanism: Light resting splints during prolonged tasks can limit extremes that provoke mirroring; use under therapist guidance. NCBI

19. Assistive tech in exams (approved devices)
    Purpose: Fair testing conditions.
    Mechanism: Laptops or scribe services replace high-strain handwriting under exam rules. NCBI

20. Research/tertiary referrals (TMS/fMRI protocols)
    Purpose: Clarify physiology and explore experimental strategies where available.
    Mechanism: Centers studying CMM can assess ipsilateral excitability and track outcomes. ClinicalTrials

---

Drug Treatments

There is no FDA-approved medication for CMM, and evidence for medicines changing mirror movements is limited to small reports (e.g., isolated botulinum toxin use). Drug use, if tried, is purely off-label and symptomatic (e.g., to reduce painful overactivity). Below I list examples clinicians sometimes consider to address spasticity/overflow or discomfort, together with official FDA label facts on class, dosing ranges, and safety—not endorsements for CMM. Always individualize with a specialist.

Muscle overactivity / spasticity agents (label facts for safety):

• Baclofen (oral; various brands such as OZOBAX/LYVISPAH/FLEQSUVY)—GABAB_BB​ agonist for spasticity; typical total daily dose titrated (e.g., 5 mg TID upward); common adverse effects include drowsiness and dizziness; caution in renal impairment. These are label facts, not CMM indications. FDA Access Data+2FDA Access Data+2

• Tizanidine (ZANAFLEX)—central α2-agonist for spasticity; short-acting; individualized dosing with liver and hypotension cautions. Again, label facts only. FDA Access Data+1

• Benzodiazepines (e.g., clonazepam; diazepam/Valium or diazepam nasal spray VALTOCO)—GABAA_AA​ modulators; may reduce co-contraction but carry sedation, dependence, and dangerous opioid interaction risks per boxed warnings. Off-label symptomatic consideration only. FDA Access Data+2FDA Access Data+2

• Anticholinergic for dystonia-like overflow (trihexyphenidyl/Artane)—can reduce abnormal tone in some movement disorders; anticholinergic side effects limit use. Label details provided for safety only. FDA Access Data+1

• Gabapentinoids (gabapentin immediate-release/GRALISE/HORIZANT; pregabalin/LYRICA, LYRICA CR)—neuromodulators for neuropathic pain; sometimes tried when discomfort dominates; monitor CNS depression and renal dosing; not CMM-specific. FDA Access Data+3FDA Access Data+3FDA Access Data+3

Focal chemodenervation:

• OnabotulinumtoxinA (BOTOX)—neuromuscular blocker approved for several movement/spasticity indications; rare case-level consideration for focal painful overflow; carries boxed warning about distant spread of toxin effect. Not approved for CMM. FDA Access Data+1

Bottom line: if medication is considered, it is for pain/overactivity relief, not to “fix” the wiring. Shared decision-making and careful monitoring are essential. NCBI

---

Dietary Molecular Supplements

Supplements do not cure CMM. These options are sometimes used to support general neuromuscular health or reduce fatigue/pain. Use only with clinician approval and within evidence-based safety limits.

1. Omega-3 fatty acids (EPA/DHA)—commonly 1–2 g/day combined EPA+DHA from diet/supplement for general health; check anticoagulant use. NIH ODS provides dosing and safety ranges. Office of Dietary Supplements

2. Vitamin D—correct deficiency per labs (e.g., 800–2000 IU/day, individualized); supports muscle function and bone health. Office of Dietary Supplements

3. Vitamin B12—treat deficiency (oral or IM per clinician); supports nerve health and myelin. Office of Dietary Supplements

4. Magnesium—meet RDA via diet/supplement; excessive doses can cause diarrhea; adjust for kidney disease. Office of Dietary Supplements

5. Acetyl-L-carnitine—studied for mitochondrial/nerve support; evidence mixed; discuss dose (e.g., 500–1500 mg/day) with clinician. Office of Dietary Supplements

6. Coenzyme Q10—antioxidant involved in cellular energy; generally well-tolerated; dosing varies (e.g., 100–200 mg/day). Evidence is general, not CMM-specific. Cancer.gov+1

7. Alpha-lipoic acid—antioxidant with data in neuropathy; typical 300–600 mg/day in studies; monitor glucose meds. NCBI+1

8. Thiamin (B1)—ensure adequacy for nerve function; dose per RDA or deficiency plan. Office of Dietary Supplements

9. Riboflavin (B2)—mitochondrial cofactor; ensure adequate intake. Office of Dietary Supplements

10. Balanced multivitamin only if dietary gaps exist—avoid megadoses; use evidence-based RDA guidance. Office of Dietary Supplements

---

Immunity-booster / Regenerative / Stem-cell drugs

There are no approved immune-boosting, regenerative, or stem-cell drugs for CMM. No stem-cell, gene, or biologic therapy has proven benefit for mirror movements in clinical trials. If you see such claims, treat them with extreme caution and seek specialist advice or clinical-trial enrollment information. NCBI+1

---

Surgeries

There is no established surgery to correct the corticospinal miswiring that causes CMM. Procedures used for other movement disorders (e.g., selective peripheral denervation, deep brain stimulation) are not indicated for isolated CMM and lack evidence here. Surgery would be considered only for features of a separate syndrome (for example, spinal surgery for severe scoliosis in ROBO3-related HGPPS)—not for mirror movements themselves. NCBI+1

---

Preventions

Because CMM is developmental and genetic, we cannot “prevent” it, but we can prevent strain and secondary pain:

1. Use extra time and typed answers for long writing. NCBI

2. Break up repetitive hand work into short blocks. NCBI

3. Choose keyboards/pens that reduce finger effort. NCBI

4. Practice slow, clean technique before speed. NCBI

5. Warm-up hands before heavy tasks. NCBI

6. Stabilize the non-task hand during precision work. NCBI

7. Prefer jobs/hobbies with flexible input methods. NCBI

8. Treat vitamin deficiencies that can worsen fatigue/pain. Office of Dietary Supplements+1

9. Manage stress and sleep to limit overflow. NCBI

10. See OT/physiatry early to set up long-term supports. NCBI

---

When to See a Doctor

• At first recognition of persistent mirror movements after age ~7, for diagnosis and reassurance.

• If pain, cramps, or fatigue limit school/work/sport.

• If there are additional findings (learning concerns, eye movement issues, scoliosis, smell loss) that could indicate a syndrome needing separate care.

• For genetic counseling/testing if there’s a family pattern or for family planning. NCBI

---

What to Eat / What to Avoid

1. Build a balanced, protein-adequate diet to support muscle recovery; hydrate well on heavy hand-use days. (General health guidance.) Office of Dietary Supplements

2. Include omega-3-rich foods (fish, walnuts) weekly; consider supplements if intake is low and your clinician agrees. Office of Dietary Supplements

3. Ensure vitamin D and B12 sufficiency, especially if vegetarian/vegan or limited sun exposure. Office of Dietary Supplements+1

4. Get magnesium from foods (nuts, legumes); supplement only if needed. Office of Dietary Supplements

5. Avoid megadose supplements without medical advice; more is not better. Office of Dietary Supplements

6. Limit excess caffeine before fine-motor tasks if it worsens tremulousness. (Practical performance tip.) NCBI

7. Maintain steady blood sugar with regular meals to avoid fatigue dips during exams. (General performance nutrition.) Office of Dietary Supplements

8. If using omega-3 supplements, discuss anticoagulants/bleeding risks with your clinician. Office of Dietary Supplements

9. If supplementing B12, follow evidence-based dosing (oral vs IM) guided by labs. Office of Dietary Supplements

10. Keep a personal trigger diary (foods, timing, stress) to see what worsens overflow or cramps. NCBI

---

Frequently Asked Questions

1. Is this a brain disease?
   It’s a wiring variant that begins before birth: some motor fibers don’t cross the midline normally, so each command can reach both sides. It’s stable, not degenerative. NCBI

2. Will it get worse?
   Usually no—it tends to remain similar across life. Planning and accommodations make a big difference. NCBI

3. Is intelligence affected?
   No—intelligence is typically normal. Some DCC carriers with corpus callosum changes may need standard learning supports. NCBI

4. Is it rare?
   Yes; estimates are <1 in a million, and many mild cases go undiagnosed. MedlinePlus

5. Which genes are most important?
   DCC, NTN1, and RAD51 are the best-validated; more genes are under study. NCBI+2PMC+2

6. Can physical therapy cure it?
   Therapy can improve function and comfort, but it does not remove the wiring difference. NCBI

7. Are there medicines that help?
   No medicine is approved or proven to stop mirror movements. Some are tried off-label to reduce painful overactivity; risks and benefits must be weighed carefully. NCBI

8. Is botulinum toxin a cure?
   No. Rare, carefully chosen cases may try focal injections for painful overflow in specific muscles, but this is off-label and limited by side effects and function trade-offs. FDA Access Data

9. Is surgery an option?
   No standard surgery corrects CMM. Surgery addresses other issues only in syndromic conditions (e.g., scoliosis in HGPPS). PMC

10. Can training separate my hands better?
    Yes—bimanual training and task pacing can improve independence and reduce strain over time. NCBI

11. Do stress or fatigue make it worse?
    Often yes; using breaks, breathing techniques, and good sleep helps. NCBI

12. Should my child get genetic testing?
    Testing confirms the cause, informs family risk, and supports accommodations; discuss with genetics professionals. NCBI

13. What about clinical trials?
    CMM is actively studied for its physiology; trials are rare but registries and research studies exist. ClinicalTrials

14. Can supplements help?
    Supplements don’t fix CMM, but correcting low D, B12, or magnesium and general omega-3 intake can support overall function; always use evidence-based doses. Office of Dietary Supplements+2Office of Dietary Supplements+2

15. How do I advocate at school/work?
    Share a brief letter explaining CMM, request extra time, typed work, and reduced handwriting, and involve OT to set tools and routines. NCBI

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: October 25, 2025.

PDF Documents For This Disease Condition References