Familial hypokalemic periodic paralysis. 50-year follow-up of a large family.

A large family with hypokalemic periodic paralysis was reexamined after 50 years. Two new cases were found in the third generation and 12 in the fourth generation. This family now includes 28 affected patients in four generations. The reexamination ascertained the presence of permanent muscle weakness (PMW) in all investigated affected sibs. This fact, and the fact that indications of the presence of PMW without paralytic attacks were found in only one subject, is strong evidence that both are manifestations of the same more or less fully penetrant dominant gene. A linkage study in this family could not localize the gene on the human genome, but close linkage with 25 genetic marker systems could be excluded.