Ataxia-pancytopenia syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Ataxia-pancytopenia syndrome is a rare condition that affects the part of the brain that coordinates movement (the cerebellum) and blood-forming cells in the bone marrow. The age when signs and symptoms begin, the severity of the condition, and the rate at which it worsens all vary among affected individuals.

People with ataxia-pancytopenia syndrome have neurological problems associated with a loss of tissue (atrophy) and other changes in the cerebellum. These problems include poor coordination and balance (ataxia), difficulty with movements that involve judging distance or scale (dysmetria), uncontrollable muscle contractions (clonus), and involuntary back-and-forth eye movements (nystagmus). These neurological issues worsen over time, making walking and other movements challenging. Some affected individuals eventually require wheelchair assistance.

Ataxia-pancytopenia syndrome also causes a shortage of one or more types of normal blood cells: red blood cells, white blood cells, and platelets. A shortage of all three of these cell types is known as pancytopenia. Pancytopenia can result in extreme tiredness (fatigue) due to low numbers of red blood cells (anemia), frequent infections due to low numbers of white blood cells (neutropenia), and abnormal bleeding due to low numbers of platelets (thrombocytopenia). Ataxia-pancytopenia syndrome is also associated with an increased risk of certain cancerous conditions of the blood, particularly myelodysplastic syndrome and acute myeloid leukemia.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Ataxia-pancytopenia syndrome is caused by inherited mutations in the SAMD9L gene. The protein produced from this gene is involved in regulating the growth and division (proliferation) and maturation (differentiation) of cells, particularly cells in the bone marrow that give rise to blood cells. Studies suggest that the SAMD9L protein acts as a tumor suppressor, keeping cells from growing and dividing too rapidly or in an uncontrolled way. The SAMD9L protein also appears to play an important role in the brain, particularly the cerebellum, although less is known about the protein's function there.

The mutations that cause ataxia-pancytopenia syndrome are described as "gain-of-function." They increase the SAMD9L protein's ability to block cell growth and division. In the bone marrow, the resulting reduction in cell proliferation leads to a shortage of red blood cells, white blood cells, and platelets. It is unclear how the effects of these mutations are related to ataxia and the other neurological problems associated with ataxia-pancytopenia syndrome.

It seems paradoxical that gain-of-function mutations in the SAMD9L gene, which enhance the protein's tumor suppressor function, could increase the risk of developing cancerous conditions such as myelodysplastic syndrome and acute myeloid leukemia. It appears that certain cells in the bone marrow with an inherited gain-of-function SAMD9L gene mutation can develop additional genetic changes that are associated with milder pancytopenia but an increased cancer risk. These changes include mutations that disable the SAMD9L gene ("loss-of-function" mutations) or a deletion of part of the long (q) arm of chromosome 7 that contains the SAMD9L gene. These additional changes compensate for the effects of the gain-of-function mutation in bone marrow cells. They prevent an overactive SAMD9L protein from excessively restricting cell proliferation, which reduces the severity of pancytopenia in affected individuals. However, a loss of the SAMD9L gene and other genes on the long arm of chromosome 7 may allow cells to grow and divide uncontrollably, leading to cancer. A deletion of the long arm of chromosome 7 is a well-known risk factor for myelodysplastic syndrome and leukemia.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In all reported cases, an affected person has had one parent with the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Ataxia-pancytopenia syndrome appears to be very rare. At least 25 affected individuals from four families have been described in the medical literature.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Ataxia · Very frequent (99-80%)

Ataxia refers to impaired coordination of voluntary muscle movement. Cerebellar ataxia refers to ataxia due to dysfunction of the cerebellum. This causes a variety of elementary neurological deficits including asynergy (lack of coordination between muscles, limbs and joints), dysmetria (lack of ability to judge distances that can lead to under- or overshoot in grasping movements), and dysdiadochokinesia (inability to perform rapid movements requiring antagonizing muscle groups to be switched on and off repeatedly).

Cerebellar atrophy · Very frequent (99-80%)

Cerebellar atrophy is defined as a cerebellum with initially normal structures, in a posterior fossa with normal size, which displays enlarged fissures (interfolial spaces) in comparison to the foliae secondary to loss of tissue. Cerebellar atrophy implies irreversible loss of tissue and result from an ongoing progressive disease until a final stage is reached or a single injury, e.g. an intoxication or infectious event.

Gait disturbance · Very frequent (99-80%)

The term gait disturbance can refer to any disruption of the ability to walk.

Aplasia/Hypoplasia of the cerebellum · Very frequent (99-80%)

Unsteady gait · Very frequent (99-80%)

Abnormal macrophage morphology · Frequent (79-30%)

An abnormality of macrophages.

Abnormality of neutrophils · Frequent (79-30%)

A neutrophil abnormality.

Abnormality of speech or vocalization · Frequent (79-30%)

An abnormality in the sound (volume) or cadence (rate) of speech.

Other findings in the same source

From: Orphanet

Additional reported features include Acute myelomonocytic leukemia (Frequent (79-30%)); Hyperreflexia (Frequent (79-30%)); Hypoplastic anemia (Frequent (79-30%)); Nystagmus (Frequent (79-30%)); Recurrent respiratory infections (Frequent (79-30%)); Splenomegaly (Frequent (79-30%)); Abnormal platelet function (Occasional (29-5%)); Decreased circulating antibody level (Occasional (29-5%)); Microcephaly (Occasional (29-5%)); Pancytopenia (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Ataxia-pancytopenia syndrome is Neurology, with a neurologist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which nervous-system findings help explain the symptoms?
• Would an assessment of walking, communication or daily function be helpful?
• Are rehabilitation or other specialist services relevant?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Ataxia-pancytopenia syndrome. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.