OMIM ID:
Hypotonia, Infantile, with Psychomotor Retardation
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Abducens nerve palsy with characteristic strabismus (esotropia) can be present.
Systemic Features
Mothers may note decreased fetal movements. Severe generalized hypotonia can be evident at birth, requiring tube feeding and respiratory assistance. Death may occur before 6 months of age but with intense supportive care children can live for several years. Brain imaging may show enlarged lateral ventricles and thinning of the corpus callosum in some individuals but no abnormalities in others. Muscle biopsies can show severe myopathic changes with increased fibrosis, variation in fiber size, and small atrophic fibers. Cardiac septal defects have been reported. Delayed psychomotor development is a common feature.
Genetics
Inheritance
Homozygous mutations in the CCDC174 gene (3p25.1) are responsible for this condition so far reported in only two families with 6 children affected.
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.