Translocation and trisomic Down's syndrome in a family with a familial D-G translocation.

The reports on familial Down's syndrome (mongolism) date in the medical literature from the 20th years of this century. Familial Down's syndrome is now well-described event but relatively rare. Penrose states that pairs of affected sibs appear about once for every 100 single cases of mongolism collected at random (quoted by Soltan et al. 1964). About two-thirds of the mongoloids are close relations and one third of the cases is of more distant relationship. Owing to the high incidence of Down's syndrome in the general population, it is possible to speak about random coincidence in some cases in the latter group (Zellweger 1964). For a short time the prevailing opinion was that translocation Down's syndrome is the most common cause of familial