Congenital malformation of the brainstem and agenesis or hypoplasia of the cerebellar vermis leading to an abnormal respiratory pattern, nystagmus, hypotonia, ataxia, and delay in achieving motor milestones. Cognitive abilities are variable, ranging from severe intellectual deficit to normal intelligence. Careful examination of the face shows a characteristic appearance: large head, prominent forehead, high rounded eyebrow. The syndrome is genetically heterogeneous. Seven genes, AHI1 (6q23), NPHP1 (2q13), CEP290 (12q21), TMEM67 (8q22), RPGRIP1L (16q12), ARL13B (3p12.3-q12.3) and CC2D2A (4p15), and two loci on chromosomes 9q34 (JBTS1) and 11p12-q13 (CORS2/JBTS2) have been associated with the disease so far. Transmission is autosomal recessive.