Huntington's Chorea in the Netherlands. The problem of genetic heterogeneity

For 1100 patients with Huntington's Chorea in 102 families from The Netherlands the average age at death per family is presented. This average ranges from 72 to 38 years. An analysis of variance of the data is strongly indicative of genetic heterogeneity. For the patients with the relatively high age at death little or no difference is observed from the age at death of their non-affected parents and non-affected sibs. Eleven children who presented with the juvenile form of the disease had all inherited the abnormal gene from their father. These 11 children were found only in families with an average age at death below 57 years. Other factors that might possibly influence the variation of average age at death between families are discussed, but cannot explain the observed differences.