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).

Mild intellectual disability is defined as an intelligence quotient (IQ) in the range of 50-69.

Excessive sensitivity to light with the sensation of discomfort or pain in the eyes due to exposure to bright light.

A myoclonic seizure is a type of motor seizure characterized by sudden, brief (<100 ms) involuntary single or multiple contraction of muscles or muscle groups of variable topography (axial, proximal limb, distal). Myoclonus is less regularly repetitive and less sustained than is clonus.

Rhythmic, involuntary oscillations of one or both eyes related to abnormality in fixation, conjugate gaze, or vestibular mechanisms.

An area of depressed vision located at the point of fixation and that interferes with central vision.

An anomaly in the ability to discriminate between or recognize colors.

Diminished clarity of vision.

Cerulean cataract, first described by Vogt (1922), is an autosomal dominant, early-onset, bilateral cataract with complete penetrance. Newborns appear asymptomatic until the age of 18 to 24 months, at which time they can be clinically diagnosed by slit-lamp examination through the appearance of tiny blue or white opacities that form first in the superficial layers of the fetal lens nucleus. The opacities progress throughout the adult lens nucleus and the cortex, forming concentric layers, with central lesions oriented radially. Histologically the lesions appear to be tapered cavities between lens fibers. Progression of the cataract is slow, such that patients may have lens extractions between the ages of 16 and 35 years (Armitage et al., 1995). The preferred title/symbol of this entry was formerly 'Cataract, Congenital, Cerulean Type, 1; CCA1.'

A pale yellow discoloration of the optic disc (the area of the optic nerve head in the retina). The optic disc normally has a pinkish hue with a central yellowish depression.