Classic congenital or infantile nystagmus presents as conjugate, horizontal oscillations of the eyes, in primary or eccentric gaze, often with a preferred head turn or tilt. Other associated features may include mildly decreased visual acuity, strabismus, astigmatism, and occasionally head nodding. Eye movement recordings reveal that infantile nystagmus is predominantly a horizontal jerk waveform, with a diagnostic accelerating velocity slow phase. However, pendular and triangular waveforms may also be present. The nystagmus may rarely be vertical. As these patients often have normal visual acuity, it is presumed that the nystagmus represents a primary defect in the parts of the brain responsible for ocular motor control; thus the disorder has sometimes been termed 'congenital motor nystagmus' (Tarpey et al., 2006; Shiels et al., 2007). For a discussion of genetic heterogeneity of congenital nystagmus, see NYS1 (310700).

Ataxia-telangiectasia-like disorder-1 is an autosomal recessive disorder characterized clinically by progressive cerebellar degeneration resulting in ataxia and oculomotor apraxia. Laboratory studies of patient cells showed increased susceptibility to radiation, consistent with a defect in DNA repair. The disorder shares some phenotypic features of ataxia-telangiectasia (AT; 208900), but telangiectases and immune deficiency are not present in ATLD1 (summary by Hernandez et al., 1993 and Stewart et al., 1999). Genetic Heterogeneity of Ataxia-Telangiectasia-Like Disorder See also ATLD2 (615919), caused by mutation in the PCNA gene (176740) on chromosome 20p12.