of the cerebellar vermis in stabilizing saccades suggests that the severe vermal hypoplasia must significantly contribute to the complex ocular motility dysfunction seen in this condition.

Santavuori-Haltia Disease

Santavuori-Haltia disease is characterized by a period of normal visual development followed by visual failure, speech and motor deterioration that begins between six months and two years of age.477a This infantile form of ceroid lipofucsinosis differs from acquired forms in that poor vision, nystagmus, retinal lesions, and optic atrophy are present early in the course of the disease. Blindness, ataxia and myoclonic jerks are frequent accompaniments.477a

Infantile Neuroaxonal Dystrophy

Infantile neuroaxonal dystrophy is an autosomal recessive neurodegenerative disorder with onset in the first or second year of life.525 Clinically, affected children show difficulty in walking, psychomotor regression, marked hypotonia, muscular atrophy, pyramidal tract signs, and optic atrophy progressing to blindness.525 MR imaging demonstrates marked cerebellar atrophy, with a striking diffuse hyperintensity of the cerebellar cortex on T2-weighted imaging that is probably secondary to extensive gliosis and shrinkage of the cerebellar cortex.525 The basic metabolic defect is unknown. The diagnosis can be established by skin, nerve, conjunctiva, or muscle biopsy that shows large dystrophic axons (spheroids).583 Children with infantile neuroaxonal dystrophy may have a pendular nystagmus that is clinically indistinguishable from infantile nystagmus.464 The mutation responsible for this disease was recently mapped to the gene encoding phospholipase A2 group VI on chromosome 22q13.1.

Carbohydrate-Deficient Glycoprotein

Syndromes

The carbohydrate-deficient glycoprotein syndromes are a group of lysosomal storage disorders in which there is defective glycosylation of secretory, lysosomal, and mem- brane-bound glycoproteins. The most common form

(type 1a) produces prominent neurologic dysfunction in infancy. Ophthalmologic features are common and include strabismus, nystagmus, and a retinal degeneration with severely diminished scotopic electroretinographic waveform.26,198 Stark et al518 described an infant with carbohy- drate-deficient glycoprotein syndrome type 1a who had diffuse cerebellar hypoplasia with congenital ocular motor apraxia and an ocular flutter that manifested when the child was awakened or startled.

Down Syndrome

Nystagmus is seen in 30% of patients with Down syndrome. While a visual sensory etiology (e.g., congenital cataract, high myopia) is occasionally present, many children with Down syndrome and nystagmus have no visually significant ocular disease.562 Patients with Down syndrome may display a fine rapid horizontal nystagmus. Less commonly, a dissociated pendular nystagmus or a manifest latent nystagmus may be seen. Most children with Down syndrome and nystagmus have associated esotropia.562

Hypothyroidism

About 10% of children with hypothyroidism are reported to have a high-frequency, low-amplitude nystagmus.373,385 Strabismus, most commonly esotropia, is seen in approximately half of hypothyroid children.373 Some children reported to have hypothyroidism and nystagmus actually had bilateral optic nerve hypoplasia with anterior pituitary hormone deficiency.485

Maple Syrup Urine Disease

Maple syrup urine disease is an autosomal recessive disorder of amino acid catabolism in which affected infants present with intermittent lethargy, poor feeding, irregular respirations, and fluctuating muscle tone.601 Biochemical studies show severe metabolic acidosis and ketosis. Older children can present with ataxia or dystonia.531 Various forms of gaze palsies (upgaze paresis, mixed vertical and horizontal paresis, adduction paresis) are frequently seen, as is bilateral ptosis­ .530 Nystagmus is usually confined to the recovery phase (after dietary restrictions are instituted) and consists of