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Spinocerebellar ataxia, autosomal recessive, with axonal neuropathy 2(SCAN2)

MedGen UID:
340052
Concept ID:
C1853761
Disease or Syndrome
Synonyms: Ataxia with Oculomotor Apraxia; Ataxia with Oculomotor Apraxia 2; Ataxia-ocular apraxia-2; Ataxia-oculomotor apraxia 2; SCAN2
SNOMED CT: AOA2 - ataxia oculomotor apraxia type 2 (725408001); SCAR1 - spinocerebellar ataxia autosomal recessive 1 (725408001); Spinocerebellar ataxia with axonal neuropathy type 2 (725408001); Autosomal recessive cerebellar ataxia with oculomotor apraxia type 2 (725408001)
Modes of inheritance:
Autosomal recessive inheritance
MedGen UID:
141025
Concept ID:
C0441748
Intellectual Product
Source: Orphanet
A mode of inheritance that is observed for traits related to a gene encoded on one of the autosomes (i.e., the human chromosomes 1-22) in which a trait manifests in individuals with two pathogenic alleles, either homozygotes (two copies of the same mutant allele) or compound heterozygotes (whereby each copy of a gene has a distinct mutant allele).
 
Gene (location): SETX (9q34.13)
 
Monarch Initiative: MONDO:0018996
OMIM®: 606002
Orphanet: ORPHA64753

Definition

Ataxia with oculomotor apraxia type 2 (AOA2) is characterized by onset of ataxia between age three and 30 years after initial normal development, axonal sensorimotor neuropathy, oculomotor apraxia, cerebellar atrophy, and elevated serum concentration of alpha-fetoprotein (AFP). [from GeneReviews]

Additional descriptions

From OMIM
Autosomal recessive spinocerebellar ataxia with axonal neuropathy-2 is a neurodegenerative disorder characterized by juvenile onset of progressive cerebellar ataxia, axonal sensorimotor peripheral neuropathy, and increased serum alpha-fetoprotein (AFP; 104150). Oculomotor apraxia is a common but inconsistent finding, found in about 50% of patients; hence this disorder is sometimes referred to as 'ataxia-oculomotor apraxia-2' (AOA2) (Moreira et al., 2004; summary by Ichikawa et al., 2013). Duquette et al. (2005) emphasized that oculomotor apraxia is not a universal finding in this disorder and suggested the name 'spinocerebellar ataxia, autosomal recessive, with axonal neuropathy-2' (SCAN2) to distinguish it from SCAN1 (607250). For a discussion of genetic heterogeneity of ataxia-oculomotor apraxia, see AOA1 (208920). For a discussion of genetic heterogeneity of SCAN, see SCAN1 (607250).  http://www.omim.org/entry/606002
From MedlinePlus Genetics
Ataxia with oculomotor apraxia is a condition characterized by problems with movement that worsen over time. The hallmark of this condition is poor coordination and balance (ataxia), which is often the first symptom. Most affected people also have oculomotor apraxia, which makes it difficult to move their eyes side-to-side. People with oculomotor apraxia have to turn their head to see things in their side (peripheral) vision.

There are several types of ataxia with oculomotor apraxia, the most common of which are types 1, 2, and 4. The types are very similar but are caused by mutations in different genes.

Type 1 begins around age 4. In addition to ataxia and oculomotor apraxia, affected individuals can have involuntary jerking movements (chorea) or muscle twitches (myoclonus); these movement problems tend to disappear over time. Individuals with this type may also develop muscle wasting in their hands and feet, which further impairs movement. As in all forms of ataxia with oculomotor apraxia, nearly all people with type 1 develop nerve abnormalities (neuropathy). Neuropathy impairs reflexes and leads to limb weakness and an inability to sense vibrations. Many individuals with ataxia with oculomotor apraxia require wheelchair assistance, typically 10 to 15 years after the start of movement problems.

People with some types of ataxia with oculomotor apraxia may have characteristic blood abnormalities. Individuals with type 1 tend to have reduced amounts of a protein called albumin, which transports molecules in the blood. The shortage of albumin likely results in elevated levels of cholesterol circulating in the bloodstream. Increased cholesterol levels raise a person's risk of developing heart disease.

Ataxia with oculomotor apraxia type 2 usually begins around age 15. As in type 1, affected individuals may have chorea or myoclonus, although these movement problems persist throughout life in type 2. Neuropathy is also common in this type.

A key feature of ataxia with oculomotor apraxia type 2 is high amounts of a protein called alpha-fetoprotein (AFP) in the blood. (Raised levels of this protein are normally seen in the bloodstream of pregnant women.) Individuals with type 2 may also have high amounts of a protein called creatine phosphokinase (CPK) in their blood. This protein is normally found primarily in muscle tissue. The effect of abnormally high levels of AFP or CPK in people with ataxia with oculomotor apraxia type 2 is unknown. Although individuals with type 2 usually have normal albumin levels, cholesterol may be elevated.

Ataxia with oculomotor apraxia type 4 begins around age 4. In addition to ataxia and oculomotor apraxia, individuals with this type typically develop dystonia, which is involuntary, sustained muscle tensing that causes unusual positioning of body parts. Dystonia can be the first feature of the condition, and it tends to disappear gradually over time. Muscle wasting in the hands and feet and neuropathy are also common in individuals with type 4.

In ataxia with oculomotor apraxia type 4, albumin levels can be low, and cholesterol or AFP can be elevated. However, the amounts of these molecules are normal in many affected individuals.

Intelligence is usually not affected by ataxia with oculomotor apraxia, but some people with the condition have intellectual disability.  https://medlineplus.gov/genetics/condition/ataxia-with-oculomotor-apraxia

Clinical features

From HPO
Pes cavus
MedGen UID:
675590
Concept ID:
C0728829
Congenital Abnormality
An increase in height of the medial longitudinal arch of the foot that does not flatten on weight bearing (i.e., a distinctly hollow form of the sole of the foot when it is bearing weight).
Dysphagia
MedGen UID:
41440
Concept ID:
C0011168
Disease or Syndrome
Difficulty in swallowing.
Chorea
MedGen UID:
3420
Concept ID:
C0008489
Disease or Syndrome
Chorea (Greek for 'dance') refers to widespread arrhythmic involuntary movements of a forcible, jerky and restless fashion. It is a random-appearing sequence of one or more discrete involuntary movements or movement fragments. Movements appear random because of variability in timing, duration or location. Each movement may have a distinct start and end. However, movements may be strung together and thus may appear to flow randomly from one muscle group to another. Chorea can involve the trunk, neck, face, tongue, and extremities.
Dysarthria
MedGen UID:
8510
Concept ID:
C0013362
Mental or Behavioral Dysfunction
Dysarthric speech is a general description referring to a neurological speech disorder characterized by poor articulation. Depending on the involved neurological structures, dysarthria may be further classified as spastic, flaccid, ataxic, hyperkinetic and hypokinetic, or mixed.
Dystonic disorder
MedGen UID:
3940
Concept ID:
C0013421
Sign or Symptom
An abnormally increased muscular tone that causes fixed abnormal postures. There is a slow, intermittent twisting motion that leads to exaggerated turning and posture of the extremities and trunk.
Tremor
MedGen UID:
21635
Concept ID:
C0040822
Sign or Symptom
An unintentional, oscillating to-and-fro muscle movement about a joint axis.
Polyneuropathy
MedGen UID:
57502
Concept ID:
C0152025
Disease or Syndrome
A generalized disorder of peripheral nerves.
Abnormal pyramidal sign
MedGen UID:
68582
Concept ID:
C0234132
Sign or Symptom
Functional neurological abnormalities related to dysfunction of the pyramidal tract.
Areflexia
MedGen UID:
115943
Concept ID:
C0234146
Finding
Absence of neurologic reflexes such as the knee-jerk reaction.
Head tremor
MedGen UID:
68690
Concept ID:
C0239882
Finding
An unintentional, oscillating to-and-fro muscle movement affecting head movement.
Hyporeflexia
MedGen UID:
195967
Concept ID:
C0700078
Finding
Reduction of neurologic reflexes such as the knee-jerk reaction.
Cerebellar atrophy
MedGen UID:
196624
Concept ID:
C0740279
Disease or Syndrome
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.
Limb ataxia
MedGen UID:
196692
Concept ID:
C0750937
Finding
A kind of ataxia that affects movements of the extremities.
Gait ataxia
MedGen UID:
155642
Concept ID:
C0751837
Sign or Symptom
A type of ataxia characterized by the impairment of the ability to coordinate the movements required for normal walking. Gait ataxia is characteirzed by a wide-based staggering gait with a tendency to fall.
Peripheral axonal neuropathy
MedGen UID:
266071
Concept ID:
C1263857
Disease or Syndrome
An abnormality characterized by disruption of the normal functioning of peripheral axons.
Progressive gait ataxia
MedGen UID:
375309
Concept ID:
C1843885
Finding
A type of gait ataxia displaying progression of clinical severity.
Pontocerebellar atrophy
MedGen UID:
381261
Concept ID:
C1853766
Disease or Syndrome
Atrophy affecting the pons and the cerebellum.
Impaired distal vibration sensation
MedGen UID:
381262
Concept ID:
C1853767
Finding
A decrease in the ability to perceive vibration in the distal portions of the limbs.
Impaired proprioception
MedGen UID:
346424
Concept ID:
C1856691
Finding
A loss or impairment of the sensation of the relative position of parts of the body and joint position.
Decreased motor nerve conduction velocity
MedGen UID:
388130
Concept ID:
C1858729
Finding
A type of decreased nerve conduction velocity that affects the motor neuron.
Reduced tendon reflexes
MedGen UID:
356648
Concept ID:
C1866934
Finding
Diminution of tendon reflexes, which is an invariable sign of peripheral nerve disease.
Oculomotor apraxia
MedGen UID:
483686
Concept ID:
C3489733
Disease or Syndrome
Ocular motor apraxia is a deficiency in voluntary, horizontal, lateral, fast eye movements (saccades) with retention of slow pursuit movements. The inability to follow objects visually is often compensated by head movements. There may be decreased smooth pursuit, and cancellation of the vestibulo-ocular reflex.
Chronic axonal neuropathy
MedGen UID:
867220
Concept ID:
C4021578
Disease or Syndrome
An abnormality characterized by chronic impairment of the normal functioning of the axons.
Impaired distal tactile sensation
MedGen UID:
867225
Concept ID:
C4021583
Finding
A reduced sense of touch (tactile sensation) on the skin of the distal limbs. This is usually tested with a wisp of cotton or a fine camel's hair brush, by asking patients to say 'now' each time they feel the stimulus.
Scoliosis
MedGen UID:
11348
Concept ID:
C0036439
Disease or Syndrome
The presence of an abnormal lateral curvature of the spine.
Distal muscle weakness
MedGen UID:
140883
Concept ID:
C0427065
Finding
Reduced strength of the musculature of the distal extremities.
Distal amyotrophy
MedGen UID:
338530
Concept ID:
C1848736
Disease or Syndrome
Muscular atrophy affecting muscles in the distal portions of the extremities.
Increased circulating antibody level
MedGen UID:
1713383
Concept ID:
C5397581
Finding
An increased level of gamma globulin (immunoglobulin) in the blood.
Elevated circulating alpha-fetoprotein concentration
MedGen UID:
65916
Concept ID:
C0235971
Finding
Concentration of alpha-fetoprotein in the blood circulation above the upper limit of normal.
Elevated circulating creatine kinase concentration
MedGen UID:
69128
Concept ID:
C0241005
Finding
An elevation of the level of the enzyme creatine kinase (also known as creatine phosphokinase (CK; EC 2.7.3.2) in the blood. CK levels can be elevated in a number of clinical disorders such as myocardial infarction, rhabdomyolysis, and muscular dystrophy.
Conjunctival telangiectasia
MedGen UID:
66780
Concept ID:
C0239105
Disease or Syndrome
The presence of small (ca. 0.5-1.0 mm) dilated blood vessels near the surface of the mucous membranes of the conjunctiva.
Nystagmus
MedGen UID:
45166
Concept ID:
C0028738
Disease or Syndrome
Rhythmic, involuntary oscillations of one or both eyes related to abnormality in fixation, conjugate gaze, or vestibular mechanisms.
Strabismus
MedGen UID:
21337
Concept ID:
C0038379
Disease or Syndrome
A misalignment of the eyes so that the visual axes deviate from bifoveal fixation. The classification of strabismus may be based on a number of features including the relative position of the eyes, whether the deviation is latent or manifest, intermittent or constant, concomitant or otherwise and according to the age of onset and the relevance of any associated refractive error.
Saccadic smooth pursuit
MedGen UID:
373096
Concept ID:
C1836479
Finding
An abnormality of tracking eye movements in which smooth pursuit is interrupted by an abnormally high number of saccadic movements.
Gaze-evoked nystagmus
MedGen UID:
1808161
Concept ID:
C5574666
Disease or Syndrome
Nystagmus made apparent by looking to the right or to the left.

Term Hierarchy

CClinical test,  RResearch test,  OOMIM,  GGeneReviews,  VClinVar  
  • CROGVSpinocerebellar ataxia, autosomal recessive, with axonal neuropathy 2

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