Mental Retardation, AD 34
Patient Information
Characteristics
Background and History
Individuals with various forms of developmental delay may be difficult to diagnose. Among those with no history of birthing difficulties or postpartum infections, etc., many have a gene change that is responsible. Some of these have been identified as in the disorder reported here but among nearly half no cause can be identified.
This condition was found by a large screening program of developmentally delayed individuals in England in which 3 male persons with somewhat similar clinical features were found to have the same presumably causative gene change (mutation).
Clinical Correlations
Global (physical and mental) developmental delay is a common feature. The head does not grow to normal size after birth and mental retardation to some degree is present. Facial expression appears bland and the muscles lack normal tone. One individual had coarse and curly hair, a broad-based gait, drooling, and drooping of the eyelids (ptosis). The eyelid fissures generally slant upward. There may be fusion of the second and third toes, and wide spaces between the teeth. Seizures are of the generalized tonic-clonic variety.
Genetics
Inheritance
All 3 of the reported individuals were from different families but all had a mutation in the same gene on chromosome 5. On this basis, the pattern of inheritance is likely to be autosomal dominant and the risk of recurrence in such families would be 50%. No family data to corroborate this has been reported however.
Pedigree
Autosomal dominant
Autosomal dominant disorders require only one mutation for the disease to be expressed. Since an affected parent has two chromosomes, only one of which has the mutant gene, parents can expect that half (50%) of their children will receive that one and inherit the disease. It is common for individuals that inherit the mutation, however, to not have evidence of the disease (nonpenetrance).
Autosomal dominant inheritance leads to a vertical pattern of transmission
Diagnosis and Prognosis
This condition would be difficult to diagnose at birth because of the nonspecific nature of the physical malformations. The neurologic manifestations such as mental retardation likely will be manifest later. However, there is no longitudinal data on progression of this disorder available. Prognosis is unknown.
Supportive care is required but no prognostic or treatment information is available on these three isolated individuals.
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