Atypical severe muscular dystrophy in a male: genetic implications for female relatives.

Genetic counselling of two younger sisters of a 32-year-old man with a 28-year history of severe progressive muscular dystrophy stimulated efforts to determine his diagnosis and the mode of inheritance. The investigation was complicated by the patient's sudden death during the period of investigation. However, genetic and neurological evaluation, electromyography and nerve conduction studies, serum enzymes and reinterpretation of a muscle biopsy 23 years earlier made it unlikely that inheritance was X-linked, thereby substantially reducing his sisters' risk of bearing affected children. Precise diagnosis, especially of what is not likely in atypically presenting genetic disease, is of paramount importance in managing families at risk for genetic disease in future children. It is an important responsibility of family physicians concerned with preventive genetic medicine.