Novel SLC9A6 mutations in two families with Christianson syndrome.

To the Editor : Mutations in SLC9A6 are associated with Christianson syndrome, a syndromic form of X-linked intellectual disability characterized by severe intellectual disability, acquired microcephaly, seizures and ataxia (1, 2). Only nine mutations and two genomic aberrations involving SLC9A6 have been reported to date (1–7). Here, we report on two German families with novel SLC9A6 mutations. The index patient (IV:3, Fig. 1a–c) of family 1 was born with normal birth measurements. He suffered from feeding difficulties in the first weeks of life and had seizures starting from 10 months. At the age of 18 months, he had microcephaly [OFC, occipitofrontal circumference 44 cm (<3rd centile), height 82 cm (25th centile), weight 10 kg (10th centile)] and could neither walk nor talk. His sister (IV:1) had slightly delayed language