Variable phenotypic expression of a MECP2 mutation in a family

Abstract

We report a three generation family in which five members, three females and two males, demonstrate a 44 bp deletion (1164-1207del44) in the MECP2 gene associated with Rett syndrome, leading to a truncation of the C-terminus of the protein. Two of the three females and both males do not meet RTT criteria whereas the youngest female has classic RTT. Both males demonstrated a clear pattern of progressive involvement including dystonia. The transmitting females do not demonstrate features of RTT as a result of unbalanced X chromosome inactivation (XCI) and were only identified as carriers following the evaluation of the affected males and the girl with classic RTT. As such, accurate assessment of the precise frequency of MECP2 mutations in carrier females with mild cognitive impairment or borderline cognitive function will be under-represented unless an affected offspring is recognized. Strategies for accurate diagnosis in such instances should be considered carefully.

Keywords: Dystonia; MECP2; Male; Mutation; Phenotype-genotype; Rett syndrome; X chromosome inactivation.

Fig. 1

The family pedigree: The five individuals with MECP2 mutations are depicted in this three generation pedigree. The female in generation I represented by the bulls-eye has cognitive delay and lacks the clinical features of RTT; the female in generation II represented by the checkerboard pattern has cognitive delay and aberrant behavior and lacks the clinical features of RTT; the female in generation III represented by the vertical stripes has typical features of RTT; and both males have cognitive delay and a pattern of progressive motor impairments that do not reflect the clinical features of RTT