Genetic Counseling 1n Retinitis Pigmentosa

During his lifetime the practicing ophthalmologist will see more than a few retinitis pigmentosa cases. It is his responsibility not only to diagnose and prognosticate this eye disease, but also to set aside a little time in which to advise the patient and his family on its genetic aspects. Retinitis pigmentosa has been established as a definite hereditary disorder. Therefore, the most important factor to consider for accurate counseling is the family history. Unfortunately, for one reason or another, this is not always available, and the investigator may need to rely on the nature and severity of the disease, examination of other members of the family; and the presence of other disorders. Pseudoretinitis pigmentosa caused by inflammation or drugs should be ruled out. Family pedigrees of typical retinitis pigmentosa exist for nearly every known mode of genetic transmission. Over 90% of these pedigrees are concerned with an autosomal recessive gene, while 3 % to 6% are related to an autosomal dominant gene. X-linked genes constitute 1 % to 3% and may be recessive, intermediate, or dominant. It is important to recognize the mode of transmission in individual cases. Unless this is done, no reliable eugenic advice can be forthcoming. The autosomal recessive mode of inheritance is characterized by an unrevealing family history, although a history of consanguinity may be' discovered (opinions vary, but this could be as high as 40%). This form of the disease is serious, with complete blindness by age fifty to sixty usually the rule. Parents of affected individuals are phenotypically normal. Also characteristic of the recessive gene is the frequent association with other disorders. Such coexisting anomalies may offer a clue to the recessive nature of this gene when family history is lacking. The relationship of retinitis pigmentosa to any congenital anomaly is too great to be explained by mere coincidence. Most notable are afflictions of