OMIM ID:
RAB18 Deficiency
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Microphthalmia with microcornea, lens opacities, small and unresponsive pupils, and optic atrophy are the outstanding ocular features of this syndrome. The eyes appear deeply set. Some but not all have ERG evidence of rod and cone dysfunction. The VEP is usually abnormal. Short palpebral fissures have been described.
Systemic Features
Patients with the micro syndrome have many somatic and neurologic abnormalities. Infants usually have feeding problems that is sometimes accompanied by gastroesophageal reflux. Some degree of psychomotor retardation and developmental delays is common. Both spasticity and hypotonia have been described. Some patients have seizures. Facial hypertrichosis, anteverted ears, and a broad nasal bridge are often noted. There may be absence of the corpus callosum while diffuse cortical and subcortical atrophy, microgyria, and pachygyria may be evident on MRI imaging. Hypogenitalism may be a feature in both sexes. Males may also have cryptorchidism and a micropenis while females can have hypoplasia of the labia minora and clitoris and a small introitus. Microcephaly is inconsistently present.
Genetics
Inheritance
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.