OMIM ID:
Harboyan Syndrome
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
The combination of congenital endothelial dystrophy and progressive neural deafness is known as Harboyan syndrome. This disorder must be distinguished from another autosomal recessive disorder, congenital endothelial dystrophy 2 or CHED2 (217700), in which deafness does not occur. While the corneal disease in Harboyan is present at birth, the deafness often does not become obvious until the second and third decades of life although audiometry can detect some hearing loss in the first decade. The cornea is thickened and edematous resulting in various degrees of visual impairment, even to the level of counting fingers. Electrophysiologic studies have been normal.
Systemic Features
No systemic abnormalities have been reported.
Genetics
Inheritance
This is an autosomal recessive disorder caused by a mutation in the SLC4A11 gene located on chromosome 20 (20p13-12). It is allelic to simple, congenital endothelial corneal dystrophy (CHED2) (217700). About half of reported cases occur sporadically and the rest have been reported in offspring of consanguineous matings. Less than 30 cases have been reported worldwide.
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.