| A form of familial primary hypomagnesemia characterized by low serum magnesium values but normal urinary magnesium values. The typical clinical features are recurrent muscle cramps, episodes of tetany, tremor, and muscle weakness, especially in distal limbs. The disease is potentially fatal. The disease has only been described in one large Brazilian kindred with 46 family members, of whom 21 were affected. Caused by a N255D mutation in the KCNA1 gene (12p13), which encodes the voltage-gated potassium channel Kv1.1. Mutations in KCNA1 result in a nonfunctional channel protein, with a dominant negative effect on wild-type Kv1.1 channel function, which is involved in the maintenance of membrane voltage and optimal function of the TRPM6 channel. Transmission is autosomal dominant. |
