A type of hearing impairment in one or both ears related to an abnormal functionality of the cochlear nerve.

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).

The disorder described by Hirschsprung (1888) and known as Hirschsprung disease or aganglionic megacolon is characterized by congenital absence of intrinsic ganglion cells in the myenteric (Auerbach) and submucosal (Meissner) plexuses of the gastrointestinal tract. Patients are diagnosed with the short-segment form (S-HSCR, approximately 80% of cases) when the aganglionic segment does not extend beyond the upper sigmoid, and with the long-segment form (L-HSCR) when aganglionosis extends proximal to the sigmoid (Amiel et al., 2008). Total colonic aganglionosis and total intestinal HSCR also occur. Genetic Heterogeneity of Hirschsprung Disease Several additional loci for isolated Hirschsprung disease have been mapped. HSCR2 (600155) is associated with variation in the EDNRB gene (131244) on 13q22; HSCR3 (613711) is associated with variation in the GDNF gene (600837) on 5p13; HSCR4 (613712) is associated with variation in the EDN3 gene (131242) on 20q13; HSCR5 (600156) maps to 9q31; HSCR6 (606874) maps to 3p21; HSCR7 (606875) maps to 19q12; HSCR8 (608462) maps to 16q23; and HSCR9 (611644) maps to 4q31-q32. HSCR also occurs as a feature of several syndromes including the Waardenburg-Shah syndrome (277580), Mowat-Wilson syndrome (235730), Goldberg-Shprintzen syndrome (609460), and congenital central hypoventilation syndrome (CCHS; 209880). Whereas mendelian modes of inheritance have been described for syndromic HSCR, isolated HSCR stands as a model for genetic disorders with complex patterns of inheritance. Isolated HSCR appears to be of complex nonmendelian inheritance with low sex-dependent penetrance and variable expression according to the length of the aganglionic segment, suggestive of the involvement of one or more genes with low penetrance. The development of surgical procedures decreased mortality and morbidity, which allowed the emergence of familial cases. HSCR occurs as an isolated trait in 70% of patients, is associated with chromosomal anomaly in 12% of cases, and occurs with additional congenital anomalies in 18% of cases (summary by Amiel et al., 2008).

Leukodystrophy refers to deterioration of white matter of the brain resulting from degeneration of myelin sheaths in the CNS. Their basic defect is directly related to the synthesis and maintenance of myelin membranes. Symmetric white matter involvement at MRI is a typical finding in patients with leukodystrophies.

Mild or moderate loss of motor function accompanied by spasticity in the lower extremities. This condition is a manifestation of CENTRAL NERVOUS SYSTEM DISEASES that cause injury to the motor cortex or descending motor pathways.

A generalized disorder of peripheral nerves.

A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age.

Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist.

Development of gray hair at a younger than normal age.

A triangular depigmented region of white hairs located in the anterior midline of the scalp.

White color (lack of pigmentation) of the eyelashes.

White color (lack of pigmentation) of the eyebrow.

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

Heterochromia iridis is a difference in the color of the iris in the two eyes.

A markedly blue coloration of the iris.