OMIM ID:
Cerebellar Atrophy, Visual Impairment, and Psychomotor Retardation
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Patients usually have deep-set eyes. Cortical visual impairment has been described in one patient but optic atrophy has been seen in another. The VEP and ERG are described as ‘abnormal’. Strabismus, hyperopia, and myopia are sometimes seen.
Systemic Features
Progressive microcephaly is often noted. Truncal hypotonia and scoliosis may be present while muscle tone is increased in the extremities in the presence of diminished deep tendon reflexes in other patients. Dystonic posturing occurs in some families. Gingival hyperplasia is a common feature and retrognathia is often present.
Brain imaging reveals progressive cerebellar atrophy and a foreshortened corpus callosum in all families. Various degrees of cerebral atrophy have been identified while intellectual disability may be marked. Speech delay is common.
Genetics
Inheritance
This is an autosomal recessive condition associated with homozygous mutations in the EMC1 gene (1p36.13).
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.