The inheritance of primary lymphoedema.

A family study is reported on 312 index patients who had primary lymphoedema with onset before 36 years. All had been investigated at St Thomas's Hospital, London, between 1965 and 1980. Most of the information was obtained by questionnaire, but 70 patients were also interviewed to check the reliability of the answers to the questionnaire. The frequency at birth of those who will develop primary lymphoedema is estimated to be about 1 in 6000, with a sex ratio of about one male to three females. Approximately 10% of children of index patients and 10% of sibs were affected when these relatives were at least five years older than the age of onset in the index patient. The proportion of female relatives affected was between two and four times that of males affected. The proportion of parents affected was about 10%. The proportion of grandparents, aunts, and uncles was about 2.5%. Where the index patient had an affected parent, the proportion affected of sibs and children was about 20%. The risk to relatives of male index patients was about 50% higher than for female index patients.