GJC2 and Milroy disease: First, mutations in human GJC2, coding for gap junction protein gamma-2 (OMIM 608803), are the cause of hypomyelinating leukodystrophy 2 (OMIM 608804), lymphatic malformation 3 (OMIM 613480), and autosomal recessive spastic paraplegia 44 (OMIM 613206).