OMIM ID:
Retinitis Pigmentosa 2, X-Linked
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
Retinitis pigmentosa consists of a group disorders with great clinical and genetic heterogeneity. The ocular disease is characterized by night blindness, field constriction, and pigmentary changes in the retina. The later is sometimes described as having a ‘bone corpuscle’ appearance with a perivascular distribution. A ring scotoma is sometimes evident. Age of onset and rate of progression is highly variable, even within families.
The X-linked form described here is a pigmentary retinopathy but sometimes labeled chorioretinal degeneration because of the extensive involvement of the choroid. The clinical picture is sometimes referred to by the out-dated term 'choroidal sclerosis'. It is often apparent in males during early childhood and they usually have early deterioration in central vision. Some carrier females experience vision loss and have mild fundus abnormalities but these do no usually appear until middle age and are usually slowly progressive. The ERG shows abnormalities in both sexes but these are highly variable. Older males may have a waxy pallor of the optic nerve. Posterior subcapsular cataracts are common. The vitreous may contain fine, colorless particles even before fundus changes are evident. Prognosis is highly variable but many patients eventually become legally blind by the age of 30 years.
Systemic Features
None.
Genetics
Inheritance
Mutations in more than 100 genes may be responsible for retinitis pigmentosa but sporadic disease occurs as well. Between 5 and 10% of individuals have X-linked disease.
In this form of X-linked retinitis pigmentosa mutations in RP2 (Xp11.3) have been found. The frequent occurrence of mild disease in females can cause diagnostic confusion with autosomal dominant RP but the disease in females in the latter disorder is usually as severe as in males.
This type of X-linked retinitis pigmentosa is far less common than RP3 (300029)caused by mutations in RPGR. The two are clinically similar and genotyping is necessary to distinguish them.
Pedigree
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'.
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.