Nanophthalmos with Retinitis Pigmentosa
Defective Genes
Clinical Characteristics
Ocular Features
Poor vision is present beginning in childhood and may progress to hand motion or even loss of light perception when retinal detachments occur. Nystagmus has been seen in one patient. Corneal diameters were 11 mm, the angles were open, and axial lengths were shortened to about 17 mm. Alternating areas of hypo- and hyperfluorescence are seen with fluorescein angiography corresponding to areas with pigment clumping seen throughout the fundi. The fundus pigmentation is atypical for retinitis pigmentosa, however, in spite of the title given by the authors. No scotopic or photopic responses are seen on the ERG. Drusen were present in the optic nerves.
Systemic Features
No systemic disease is associated.
Genetics
Inheritance
A single family with affected male and female sibs has been reported and a homozygous nonsense mutation in exon 5 of the CRB1 gene (1q31-32.1) was present in both.
Another recessive form of microphthalmia with retinitis pigmentosa plus has been reported (611040) without nanophthalmos features and having a mutation in the MFRP gene. True nanophthalmos with retinopathy (267760) has some features similar to the disorder described here but with macular cysts. No responsible mutation has been identified in this disorder however.
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.