Clinical Characteristics
Ocular Features
Congenital nuclear cataracts are the only ocular abnormalities in these conditions. There may be some cortical opacifications as well. The nuclear opacifications may not be sufficiently dense in some patients to require cataract surgery. Nothing is known of their natural history, however.
Systemic Features
No systemic disease is associated with these congenital cataracts.
Genetics
Inheritance
All three of these nuclear cataracts are inherited in autosomal recessive patterns. They have been reported in rare families in which the parents were consanguineous.
CATCN1 was reported in a 4-generation Pakistani family having an unknown mutation localized to 19q13.
Another congenital nuclear cataract (CATCN2) results from mutations in the CRYBB3 (22q11.23) gene reported in 2 consanguineous Pakistani families.
CATCN3 results from mutations in CRYBB1 (22q12.1) as reported in two consanguineous Israeli Bedouin families with 14 affected individuals.
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.