Retinitis Pigmentosa and Mental Retardation
Patient Information
Characteristics
Background and History
Retinitis pigmentosa (RP) is a type of progressive retinal degeneration in which vision gradually deteriorates. A deficiency of night vision and loss of side vision is characteristic but has not been reported in this disorder. RP may occur by itself but in many cases is associated with neurological problems as in this rare condition.
Clinical Correlations
Newborns are floppy at birth but may seem normal otherwise. Developmental milestones such as sitting, walking, and speaking are usually delayed and in some patients never develop. Physical growth is slow and the head remains small. Mental retardation is common and may be severe. The spine is abnormally curved while the fingers and toes appear abnormally long and thin.
Vision problems become apparent in childhood and the typical changes in the retina may be apparent at that age. Extreme nearsightedness is common. Eventually vision is limited to light perception.
Genetics
Inheritance
Only a few families have been reported but the family pattern suggests an autosomal recessive form of inheritance. No specific gene mutation has been identified but it is likely that parents are carriers of a gene change that, if present in both parents, would transmit a risk of 25% to each child of inheriting this condition.
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.
Diagnosis and Prognosis
The diagnosis is most likely to be made by a neurologist with confirmation by an ophthalmologist. No treatment is known and the progressive nature of this disorder leads to immobility in many patients. Nothing is known about longevity.
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