OMIM ID:
Retinitis Pigmentosa 78
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Onset of visual complaints is in the third or fourth decades with night blindness and visual field defects. These symptoms are progressive with the oldest of three reported patients having 20/1250 vision at 51 years of age. Classic signs of retinitis pigmentosa are usually present including disc pallor, pigment clumping, peripheral field constriction, and attenuated retinal vessels. Intraretinal cysts may be detected with optical coherence tomography. The full-field ERG shows general photoreceptor dysfunction with the rods most severely involved while pattern ERGs shows variable macular involvement.
Systemic Features
No systemic disease has been detected in the three reported individuals.
Genetics
Inheritance
Three unrelated individuals have been reported with homozygous or compound heterozygous mutations in the ARHGEF18 gene (19p13.2). Five different mutant alleles were found among these patients.
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.