ataxia

Cataracts, Ataxia, Short Stature, and Mental Retardation

Clinical Characteristics
Ocular Features: 

Cataracts are present in both sexes but the opacification is more extensive in males and only partial in females.  The cataracts are congenital in males but apparently develop later in females who complain of blurred vision from early childhood or during teenage years.  The lenses in females have punctate and pulverulent opacities as well as posterior subcapsular sclerosis.  Vision has been estimated as hand motion from early childhood in boys and about 20/40 in females in the first two decades of life.

Systemic Features: 

Males have mild to moderate mental retardation, muscle hypotonia and weakness with postural tremor.  Their standing position is broad-based and they are unable to sit or stand otherwise without some support.  They are usually unable to walk unassisted.  Speech is dysarthric and its development is delayed.  Females are neurologically normal.

Genetics

A locus containing the disease allele at Xpter-q13.1 cosegregates with the cataract phenotype in both sexes.  The gene mutation has not been identified.  This can be called an X-linked recessive disorder with partial expression in heterozygous females.

Pedigree: 
X-linked recessive, carrier mother
X-linked recessive, father affected
Treatment
Treatment Options: 

Cataract surgery may be indicated in young females and may be beneficial in infant boys.

References
Article Title: 

Wolfram Syndrome 2

Clinical Characteristics
Ocular Features: 

As in Wolfram syndrome 1, only insulin dependent diabetes mellitus and optic atrophy are essential to the diagnosis. The optic atrophy is progressive over a period of years and can be the presenting sign.  Its onset, however, is highly variable and may begin in infancy but almost always before the third decade of life.  The majority (77%) of patients are legally blind within a decade of onset.  The visual field may show paracentral scotomas and peripheral constriction.  Both VEPs and ERGs can be abnormal.  Diabetic retinopathy is uncommon and usually mild.

Systemic Features: 

The clinical features of this disorder are many and highly variable.  Sensorineural hearing loss, anemia, seizures, ataxia, and autonomic neuropathy are usually present. Respiratory failure secondary to brain stem atrophy may have fatal consequences by the age of 30 years.  A variety of mental disturbances including mental retardation, dementia, depression, and behavioral disorders have been reported.  The diabetes mellitus is insulin dependent with childhood onset.  Hydroureter is often present.

Diabetes insipidus may be present in patients with Wolfram syndrome 1 (222300) but has not been reported in patients reported with Wolfram syndrome 2.   Upper GI ulceration and bleeding were present in several individuals.

Genetics

This is an autosomal recessive disorder similar to Wolfram syndrome 1 (WFS1; 222300) but caused by mutations in the CISD2 gene (4q22-q24).  The gene codes for a small protein (ERIS) localized to the endoplasmic reticulum. It seems to occur less commonly than WFS1.

Some patients have mutations in mitochondrial DNA as the basis for their disease (598500).  Combined with evidence that point mutations at the 4p16.1 locus predisposes deletions in mtDNA, this suggests that at least some patients with Wolfram syndrome have a recessive disease caused by mutations in both nuclear and mitochondrial genes.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Treatment is supportive for specific organ disease.  Low vision aids may be helpful in selected individuals.

References
Article Title: 

Wolfram Syndrome 1

Clinical Characteristics
Ocular Features: 

Optic atrophy in association with diabetes mellitus is considered necessary to the diagnosis of Wolfram syndrome.  The optic atrophy is progressive over a period of years and can be the presenting symptom.  Its onset, however, is highly variable and may begin in infancy but almost always before the third decade of life.  The majority (77%) of patients are legally blind within a decade of onset.  The visual field may show paracentral scotomas and peripheral constriction.  Both VEPs and ERGs can be abnormal.  Diabetic retinopathy is uncommon and usually mild.

Two sibs with confirmed WFS1 have been reported with microspherophakia, congenital cataracts, and glaucoma in addition to optic atrophy .

Systemic Features: 

The clinical features of this disorder are many and highly variable.  Sensorineural hearing loss, diabetes insipidus, anemia, seizures, vasopressin deficiency, ataxia, and autonomic neuropathy are usually present. Respiratory failure secondary to brain stem atrophy may have fatal consequences by the age of 30 years.  A variety of mental disturbances including mental retardation, dementia, depression, and behavioral disorders have been reported.  The diabetes mellitus is insulin dependent with childhood onset.  Dilated ureters and neurogenic bladder are frequently seen, especially in older patients..

Genetics

Wolfram syndrome 1 is an autosomal recessive disorder that can be caused by mutations in the WFS1 gene (4p16.1) encoding wolframin, a small protein important to maintenance of the endoplasmic reticulum.  However, a minority of individuals also have deletion mutations in mitochondrial DNA (598500).  Some evidence suggests that point mutations at 4p16.1 predispose deletions in mtDNA, and, if so, this recessive disorder may owe its appearance to combined mutations in both nuclear and mitochondrial DNA.  In addition, rare families with the Wolfram syndrome phenotype and mutations in the WFS1 gene show transmission patterns consistent with autosomal dominant inheritance.

Wolfram syndrome 2 (WFS2) (604928) results from mutations in CISD2 at 4q22-q24.

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No treatment is available for Wolfram syndrome but the administration of thiamin can correct the anemia.  Low vision aids may be helpful in early stages of disease.

References
Article Title: 

Neuraminidase Deficiency

Clinical Characteristics
Ocular Features: 

A cherry red spot is may be seen in late childhood or early adolescence.  It occurs in nearly 100% of patients with type I while only 75% of type II patients have this feature possibly because their early death from the more severe systemic disease prevents full ascertainment.  Visual acuity is reduced, sometimes severely.  Some but not all individuals have corneal and lens opacities.  A subtle corneal haze has also been seen.  Nystagmus has been reported. 

Systemic Features: 

This is a neurodegenerative disorder with progressive deterioration of muscle and central nervous system functions.  Myoclonus, mental deterioration, hepatosplenomegaly, muscle weakness and atrophy are common.  The defect in neuraminidase activity leads to abnormal amounts of sialyl-oligosaccharides in the urine.  Spinal deformities such as kyphosis are common.  Deep tendon reflexes are exaggerated.  Ataxia and hearing loss may be present.  Coarse facies, a barrel chest, and short stature are characteristic.  Hepatic cells contain numerous vacuoles and numerous inclusions.

Sialidosis types I and II are both caused by mutations in the neuroaminidase gene.  Type I is associated with milder disease than type II which has an earlier age of onset and may present in infancy or even begin in utero.  Early death within two years of age is common in the congenital or infantile forms.  There is, however, significant variability in age of onset and the course of disease among types. 

Genetics

The sialidoses are autosomal recessive lysosomal storage disorders resulting from mutations in the NEU1 gene (6p21.3) which lead to an intracellular accumulation of glycoproteins containing sialic acid residues.  Both types I and II are caused by mutations in the same gene. 

Treatment
Treatment Options: 

Treatment is focused on symptom management. 

References
Article Title: 

Sandhoff Disease

Clinical Characteristics
Ocular Features: 

Retinal ganglion cells are rendered dysfunctional from the toxic accumulation of intra-lysosomal GM2 ganglioside molecules causing early visual symptoms.  These cells in high density around the fovea centralis create a grayish-white appearance.  Since ganglion cells are absent in the foveolar region, this area retains the normal reddish appearance, producing the cherry-red spot.  Axonal decay and loss of the ganglion cells leads to optic atrophy and blindness. 

Systemic Features: 

Sandhoff disease may be clinically indistinguishable from Tay-Sachs disease even though the same enzyme is defective (albeit in separate subunits A and B that together comprise the functional enzymes).  The presence of hepatosplenomegaly in Sandoff disease may be distinguishing. The infantile form of this lysosomal storage disease seems to be the most severe.  Infants appear to be normal until about 3-6 months of age when neurological development slows and muscles become weak.  Seizures, loss of interest, and progressive paralysis begin after this together with loss of vision and hearing.  An exaggerated startle response is considered an early and helpful sign in the diagnosis.  Among infants with early onset disease, death usually occurs by 3 or 4 years of age.   

Ataxia with spinocerebellar degeneration, motor neuron disease, dementia, and progressive dystonia are more common in individuals with later onset of neurodegeneration.  The juvenile and adult-onset forms of the disease also progress more slowly.  

Genetics

Sandhoff disease results from mutations in the beta subunit of the hexosaminidase A and B enzymes.  It is an autosomal recessive disorder caused by mutations in HEXB (5q13). 

Tay-Sachs disease (272800) can be clinically indistinguishable from Sandoff disease and they are allelic disorders.  However, the mutation in Tay-Sachs (272800) is in HEXA resulting in dysfunction of the alpha subunit of hexosaminidase A enzyme. 

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

No specific treatment is available beyond general support with proper nutrition and maintainence of airways.  Anticonvulsants may be helpful in some stages.  Gene therapy in fibroblast cultures has achieved some restoration of  hexosaminidase A activity in Tay-Sachs disease and may have potential in Sandhoff disease as well. 

References
Article Title: 

Neuropathy, Ataxia, and Retinitis Pigmentosa

Clinical Characteristics
Ocular Features: 

Night blindness and visual field restriction are early symptoms usually in the second decade of life.  The retina may first show a salt-and-pepper pigmentary pattern which later resembles the classic bone-spicule pattern of retinitis pigmentosa with vascular attenuation.  The optic nerve becomes pale and eventually marked optic atrophy develops.  Severe vision loss is evident in young adults and some patients become blind. 

Systemic Features: 

The onset of systemic symptoms such as unsteadiness occurs some time in the second decade of life.  Irritability, delayed development, and psychomotor retardation may be evident in children whereas older individuals can have frank dementia.  The MRI may reveal cerebral and cerebellar atrophy.  Seizures may have their onset by the third decade.  Numbness, tingling and pain in the extremities are common.  EMG and nerve conduction studies can demonstrate a peripheral neuropathy.  Neurogenic muscle weakness can be marked and muscle biopsy may show partial denervation. Some patients have hearing loss.  A few patients have cardiac conduction defects. 

Genetics

This is a mitochondrial disorder with pedigrees showing maternal transmission.  Mutations (8993T-G) have been found in subunits of mitochondrial H(+)-ATPase or MTATP6.  The amount of heteroplasmy is variable and likely responsible for the clinical heterogeneity in this disorder.  Individuals with more than 90% mutated chromosomes are considered to have a subtype of Leigh syndrome (MILS) with earlier onset (3-12 months of age).  NARP patients usually have 70-80% or less of mutated mitochondria.  The amount of heteroplasmy may vary among tissues. 

Treatment
Treatment Options: 

No treatment is available for this disease but low vision aids can be helpful in early stages of disease.  Recently it has been demonstrated that alpha-ketoglutarate/aspartate application to fibroblast cell cultures can provide some protection from cell death in NARP suggesting a potential therapeutic option. 

References
Article Title: 

Retinopathy of NARP syndrome

Kerrison JB, Biousse V, Newman NJ. Retinopathy of NARP syndrome. Arch Ophthalmol. 2000 Feb;118(2):298-9.

PubMed ID: 
10676807

Neuronal Ceroid Lipofuscinoses

Clinical Characteristics
Ocular Features: 

At least 13 genotypically distinct forms of neuronal ceroid lipofuscinosis have been described.  The ocular features are highly similar in all forms with blindness the end result in all types (although not all cases with an adult onset suffer vision loss).  The onset of visual signs and symptoms is highly variable.  Optic atrophy is the most common finding which may occur as early as two years of age in the infantile form.  Night blindness is a symptom in those with a later onset but panretinal degeneration with unrecordable ERGs eventually occurs.  Pigmentary changes throughout the retina are often seen and sometimes occur in a bull’s-eye pattern.  Retinal blood vessels may be attenuated and lens opacities of various types are common. 

Systemic Features: 

The neuronal ceroid lipofuscinosis are a group of inherited neurodegenerative lysosomal-storage disorders characterized by the intracellular accumulation of autofluorescent lipopigment causing damage predominantly in the central nervous system.  The result is a progressive encephalopathy with cognitive and motor decline, eventual blindness, and seizures with early death.  While early descriptions distinguished several types based primarily on age of onset, genotyping has now identified responsible mutations in at least 10 genes and time of onset is no longer considered a reliable indicator of the NCL type. 

Genetics

The NCLs are usually inherited in autosomal recessive patterns with the exception of some adult onset cases in which an autosomal dominant pattern is sometimes seen.

The various forms of NCL are often divided according to ages of onset but overlap is common.  Thus the congenital form (CLN10; 610127), caused by a mutation in the CTSD gene at 11p15.5, can have an onset of symptoms at or around birth but also is responsible for an adult form (Vida infra).  The CLN1 infantile form (256730), caused by a mutation in the PPT1 gene at 1p32, has an onset between 6 and 24 months  There are several mutations causing late infantile disease (CLN2, 204500) involving the TPP1 gene (11p15.5) leading to symptoms between 2-4 years, the CLN5 gene (256731) at 13q21.1-q32 with onset between 4 and 7 years, the CLN6 gene (601780) at 15q21-q23 showing symptoms between 18 months and 8 years, and the CLN8 gene (610003) at 8p23 with symptoms beginning between 3 and 7 years.  Another early juvenile form (CLN7; 610951) is caused by mutations in MFSD8 (4q228.1-q28.2).

A juvenile form (sometimes called Batten disease or Spielmeyer-Vogt with onset between 4 and 10 years results from mutations in CLN3 (204200) as well as in TPP1, PPT1, and CLN9 (609055).  An adult form known as ANCL or Kuf’s disease results from mutations in CTSD, PPT, CLN3, CLN5, and CLN4 (204300) and has its onset generally between the ages of 15 and 50 years. 

Homozygous mutations in the ATP13A2 gene (1p36.13), known to cause Kufor-Rakeb type parkinsonism (606693), have also been found in NCL.

Pedigree: 
Autosomal dominant
Autosomal recessive
Treatment
Treatment Options: 

Treatment is primarily symptomatic for sleep disorders, seizures, psychoses, malnutrition, dystonia and spasticity.  However, there is recent progress in the application of enzyme-replacement therapies in the soluble lysosomal forms of CNL.  Gene therapies and the use of stem cells also hold promise. 

References
Article Title: 

Niemann-Pick Disease, Type C2

Clinical Characteristics
Ocular Features: 

The primary ocular feature of type C2 Niemann-Pick disease is supranuclear gaze palsy.  A cherry red spot is rarely seen. 

Systemic Features: 

Neurodegeneration is the outstanding clinical manifestation and often the cause of death.  The onset usually occurs in infancy and the course is rapid with death often in the first year of life.  The clinical disease is similar to that of the more common type C1 (257220) although there is considerable clinical heterogeneity in all types of NPC.  Pulmonary involvement can be a prominent feature of C2 disease.  Other neurologic symptoms include ataxia, facial dyskinesis, bradykinesia, expressive aphasia, dysarthria and cognitive decline.  Visceromegaly seems to be less common than in type C1 (257220).  Cholesterol esterification is impaired with accumulation in intracellular organelles. 

Genetics

Like other types of NPC disease, this disorder follows an autosomal recessive pattern of inheritance.  It results from mutations in the NPC2 gene (14q24.3).  These mutations are far less common than those in the NPC1 (257220)gene.  

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

Treatment is available for symptoms such as seizures and dystonia.  Good pulmonary hygiene is important and precautions should be taken to prevent aspiration. 

References
Article Title: 

Gillespie Syndrome

Clinical Characteristics
Ocular Features: 

Bilateral aniridia, partial or complete, is the ocular characteristic of Gillespie syndrome.  The iris may be relatively intact but immobile leading to the description in some patients of "dilated and fixed pupils", or congenital mydriasis.  The pupillary margin may be scalloped with iris strands to the lens.  The pupillary sphincter is sometimes absent and the mesodermal surface missing.  The fovea sometimes appears hypoplastic and some patients have decreased visual acuity.  Strabismus and ptosis are often present.  There may also be retinal hypopigmentation.  Cataract, glaucoma, and corneal opacities are not present. 

Systemic Features: 

Most patients have some degree of developmental delay ranging from difficulties with fine motor tasks to frank mental retardation.  Many have a hand tremor, some degree of hypotonia, and learning difficulties.  MRI imaging often shows cerebellar and sometimes cerebral hypoplasia. 

Genetics

This is an autosomal dominant disorder usually due to a heterozygous mutation in the PAX6 gene (11p13).  However, some patients with typical features do not have a mutation in this gene suggesting that there is genetic heterogeneity.  Some patients without point mutations nevertheless have defects in adjacent DNA suggesting a positional effect.  The possibility of autosomal recessive inheritance in some families with parental consanguinity cannot be ruled out.  The PAX6 gene plays an important role in iris development as it is also mutant in simple aniridia (106210) and in Peters anomaly (604229).

Mutations in the ITPR1 gene have also been identified in Gillespie syndrome.

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

No treatment is available.

References
Article Title: 

Spinocerebellar Ataxia 7

Clinical Characteristics
Ocular Features: 

Pigmentary changes in the retina are somewhat variable but often begin with a granular appearance in the macula and spread into the periphery.  The macula often becomes atrophic and dyschromatopsia is common.   Retinal thinning is evident, especially in the macula.  Decreased visual acuity and loss of color vision are early symptoms and the ERG shows abnormalities of both rod and cone function.  External ophthalmoplegia without ptosis is a frequent sign.  Most adults and some children eventually are blind. 

Systemic Features: 

Symptoms of developmental delay and failure to thrive may appear in the first year of life followed by loss of motor milestones.  Dysarthria and ataxia are nearly universal features while pyramidal and extrapyramidal signs are more variable.  This can be a rapidly progressive disease and children who develop symptoms by 14 months are often deceased before two years of age.  However, adults with mild disease can survive into the 5th and 6th decades.  Peripheral neuropathy with sensory loss and motor deficits are usually present to some degree but the range of clinical disease is wide.  Cognitive decline and some degree of dementia occur sometimes. 

Genetics

Spinocerebellar ataxia 7 is caused by expanded trinucleotide repeats (CAG) in the ATXN7 gene (3p21.1-p12) and inherited in an autosomal dominant pattern.  The number of repeats is variable and correlated with severity of disease.  Most patients with 36 or more repeats have significant disease. This disorder is sometimes classified as a progressive cone-rod dystrophy.  It is sometimes referred to as olivopontocerebellar atrophy type III or OPCA3.

This disorder exhibits genetic anticipation especially with paternal transmission as succeeding generations often have earlier onset with more severe and more rapidly progressive disease. This is explained by the fact that younger generations tend to have a larger number of repeats and sometimes the diagnosis is made in children before the disease appears in parents or grandparents.

Spinocerebellar ataxia 1 (164400) is a similar autosomal dominant disorder with many of the same clinical and genetic features.  It is caused by excess CAG repeats on the ATXN1 gene on chromosome 6. 

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

No effective treatment is known for the disease.  Low vision aids and mobility training may be useful in early stages. 

References
Article Title: 

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