De novo MECP2 duplication in two females with random X-inactivation and moderate mental retardation

Abstract

Xq28 duplications including MECP2 are a well-known cause of severe mental retardation in males with seizures, muscular hypotonia, progressive spasticity, poor speech and recurrent infections that often lead to early death. Female carriers usually show a normal intellectual performance due to skewed X-inactivation (XCI). We report on two female patients with a de novo MECP2 duplication associated with moderate mental retardation. In both patients, the de novo duplication occurred on the paternal allele, and both patients show a random XCI, which can be assumed as the triggering factor for the phenotype. Furthermore, we describe the phenotype that might be restricted to unspecific mild-to -moderate mental retardation with neurological features in early adulthood.

Figure 1

Illustration of the genomic aberration of the MECP2 region with the 6.0 Affymetrix SNP Array and schematic representation of the duplicated region. (a and b) Image of the parents–patient trio analysis, showing the de novo occurrence of the duplication (red arrows) in both cases; (c and d) mapping of the duplicated regions according to UCSC; (e) schematic representation of part of the genomic region Xq28 with the location of the duplication of our two novel patients (blue arrows), the female patients of Reardon et al and Makrythanasis et al (gray arrows) as well as the minimal critical region (MCR) defined by Bartsch et al (red arrow). Gene content of the region is shown from the Ensembl genome browser version 54.36p (NCBI36).

Figure 2

Metaphase and interphase FISH results. (a) Metaphase spread of patient 1 hybridized with the BAC clone RP11-218L14 localized in the duplicated chromosome region Xq28 (red) together with a partial chromosome painting probe for the long arm of the X chromosome (pcpXq, green). Signals are only present on both X chromosomes. (b) Interphase nuclei of the same patient, presenting a normal hybridization signal and a duplicated signal for the Xq28 BAC clone (red). (c) Metaphase spread of patient 2 after hybridization of the Xq28-BAC clone (RP11-218L14, red) together with a chromosome-painting probe for the X chromosome (wcpX, green). Signals are only present on both X chromosomes. (d) Interphase nuclei of patient 2 showing three hybridization signals, a normal signal and a duplicated signal for the Xq28 BAC clone (red). (e) Metaphase spread of the father of patient 2 presenting only one signal on the X chromosome and (f) a normal signal in the interphase nuclei with the Xq28 BAC clone. (g) Metaphase spread of the mother of patient 2 showing a specific hybridization signal on both X chromosomes and (h) two normal signals in the interphase nuclei.

Figure 3

XCI results. Results showing random X inactivation in both patients and proof of complete digestion with methylation-sensitive restriction endonuclease HpaII after PCR amplification of HUMARA (male control and female positive control, respectively). For patient 1 (performed on ABI3100, Genotyper v3.7), trace (a) shows the undigested sample, trace (b) the digested fragments. The lower two traces show the male control (c) undigested and (d) after digestion. The XCI in patient 1 is 39:61. For patient 2 the upper two traces show the patient's sample (a) undigested and (b) digested (CEQ8000, Beckman Coulter), revealing a random XCI of 29:71. The lower traces show a female positive control with complete skewing of X-inactivation in (c) undigested and (d) digested samples.