Periodic hypokalemic paralysis transmitted by an unaffected male with negative family history: a delayed mutation?

A pedigree is described that includes three cases of periodic hypokalemic paralysis. Apparently, the disease has arisen by de novo mutation in a father of two affected daughters, who, however, is not affected himself. This is unexpected, since in males the disorder is generally inherited as a fully dominant trait. Therefore we propose that these findings result from an early somatic or a half-chromatid mutation.