OMIM ID:
Cone-Rod Dystrophy with Hearing Loss
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Patients note reduced vision in brightly-lit environments with onset in early adulthood and progressive central vision loss thereafter. Nystagmus, photophobia, and dyschromatopsia may be present. Younger individuals may complain of night blindness. Visual fields show diffuse progressive suppression with relative sparing of selected areas such as the peripapillary region. The ERG documents primary cone dystrophy but less involvement of the rods. EOG testing in 4 patients showed reduced light-dark ratios. Macular degeneration, attenuated vessels, subtle salt-and-pepper pigmentation, and spicular pigmentary deposits in the mid-periphery may be seen.
Systemic Features
The hearing loss is sensorineural in nature and can be progressive from its onset in childhood.
Genetics
Inheritance
This autosomal recessive disorder results from homozygous or compound heterozygous mutations in the CEPL78 (9q21.2) gene.
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.