Cataracts, Congenital, X-Linked
Patient Information
Characteristics
Background and History
Cataracts (opacities in the lens of the eye) are caused by many mechanisms. Those present at birth are called congenital and a significant proportion of these are inherited. Those caused by mutations on the X chromosome are known as X-linked.
Clinical Correlations
X-linked congenital cataracts are present at birth and are most dense in males. However, carrier females, such as the mothers of such boys, may have small, dot-like opacities. Males may also have facial and dental malformations in which case the disorder is called Nance-Horan syndrome. At this time it is uncertain if individuals without such additional characteristics have the same disorder as those with the facial features. Some individuals with congenital cataracts also have small corneas (the windshield of the eye) and even small eyeballs.
Genetics
Inheritance
These cataracts are caused by mutations carried on the X chromosome. Males do not have affected male children but their daughters all inherit the mutant X chromosome and are called carriers (heterozygotes). Such females can expect that half their sons will inherit the mutation causing this type of cataract.
Pedigree
X-linked recessive, father affected
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the father, he has the disease since his only X chromosome is mutant and he has no normal X to blunt the effects of the abnormal gene. His sons only receive his Y chromosome and thus are all normal. However, all his daughters receive his one and only X chromosome and will be healthy 'carriers'. Thus such males will have no affected children but half their grandsons from those daughters will have the same disease as he does.
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the father, he has the disease since his only X chromosome is mutant and he has no normal X to blunt the effects of the abnormal gene. His sons only receive his Y chromosome and thus are all normal. However, all his daughters receive his one and only X chromosome and will be healthy 'carriers'. Thus such males will have no affected children but half their grandsons from those daughters will have the same disease as he does.
X-linked recessive, carrier mother
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the mother, she usually does not have the disease since the normal X chromosome without the mutation neutralizes the mutation in the abnormal X chromosome. However, half her sons will inherit the mutation-containing X chromosome and therefore have the X-linked disease. Half the daughters will inherit the mutation-bearing X chromosome and are usuallly healthy 'carriers'.
X-linked disorders are caused by a mutation on the X chromosome and both sexes can pass this to their children. If the mutation is in a recessive gene and carried by the mother, she usually does not have the disease since the normal X chromosome without the mutation neutralizes the mutation in the abnormal X chromosome. However, half her sons will inherit the mutation-containing X chromosome and therefore have the X-linked disease. Half the daughters will inherit the mutation-bearing X chromosome and are usuallly healthy 'carriers'.
Diagnosis and Prognosis
To allow the visual system to mature properly, the dense cataracts in males must be removed soon after birth. Life expectancy is normal
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