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We have identified a deletion of 3 base pairs in the dystrophin gene (DMD), c.9711_9713del, in a family with nonspecific X-linked intellectual disability (ID) by sequencing of the exons of 86 known X-linked ID genes. This in-frame deletion results in the deletion of a single-amino-acid residue, Leu3238, in the brain-specific isoform Dp71 of dystrophin. Linkage analysis supported causality as the mutation was present in the 7.6 cM linkage interval on Xp22.11-Xp21.1 with a maximum positive LOD score of 2.41 (MRX85 locus). Molecular modeling predicts that the p.(Leu3238del) deletion results in the destabilization of the C-terminal domain of dystrophin and hence reduces the ability to interact with β-dystroglycan. Correspondingly, Dp71 protein levels in lymphoblastoid cells from the index patient are 6.7-fold lower than those in control cell lines (P=0.08). Subsequent determination of the creatine kinase levels in blood of the index patient showed a mild but significant elevation in serum creatine kinase, which is in line with impaired dystrophin function. In conclusion, we have identified the first DMD mutation in Dp71 that results in ID without muscular dystrophy. [ABSTRACT FROM AUTHOR]

Duplications in Xq28 involving MECP2 have been described in patients with severe mental retardation, infantile hypotonia, progressive spasticity, and recurrent infections. However, it is not yet clear to what extent these and accompanying symptoms may vary. In addition, the frequency of Xq28 duplications including MECP2 has yet to be determined in patients with unexplained X-linked mental retardation and (fe)males with severe encephalopathy. In this study, we used multiplex ligation-dependent probe amplification to screen Xq28 including MECP2 for deletions and duplications in these patient cohorts. In the group of 283 patients with X-linked mental retardation, we identified three Xq28 duplications including MECP2, which suggests that approximately 1% of unexplained X-linked mental retardation may be caused by MECP2 duplications. In addition, we found three additional MECP2 duplications in 134 male patients with mental retardation and severe, mostly progressive, neurological symptoms, indicating that the mutation frequency could be as high as 2% in this group of patients. In 329 female patients, no Xq28 duplications were detected. In total, we assessed 13 male patients with a MECP2 duplication from six unrelated families. Moderate to severe mental retardation and childhood hypotonia was noted in all patients. The majority of the patients also presented with absent speech, seizures, and progressive spasticity as well as ataxia or an ataxic gait and cerebral atrophy, two previously unreported symptoms. We propose to implement DNA copy number testing for MECP2 in the current diagnostic testing in all males with moderate to severe mental retardation accompanied by (progressive) neurological symptoms.European Journal of Human Genetics (2009) 17, 444–453; doi:10.1038/ejhg.2008.208; published online 5 November 2008 [ABSTRACT FROM AUTHOR]

Rett syndrome (RTT) is one of the most common neurodevelopmental disorders in females. The disease is caused by mutations in the methyl-CpG-binding protein 2 gene (MECP2), and various mutations have been reported. The phenotypic spectrum in both female and male patients is diverse, ranging from very mild to congenital encephalopathy and prenatal lethality. In this study, the question was addressed as to whether implementation of systematic screening of MECP2 in patients with an unexplained mental retardation in DNA diagnostics would be reasonable, and the spectrum of phenotypes resulting from mutations in this gene was further explored. Mutational analysis of MECP2 was performed in mentally retarded female patients who were negative for FMR1 CGG repeat expansion, in male and female patients with clinical features suggestive of either Angelman or Prader-Willi syndrome without methylation defects on chromosome 15q11-q13. In the cohort of females negative for the molecular Fragile-X studies (N=92), one nonsense mutation (p.Q406X) was found. In the cohort of Angelman-negative patients (N=63), two missense mutations (p.R133C in a female patient and a mosaic p.T158M in a male patient) were found, which have been reported many times in patients with classical RTT syndrome. In the Prader-Willi-negative group (N=98), no pathogenic mutations were found.The results support testing of patients with features suggestive of Angelman syndrome, but without methylation defects on chromosome 15q11-q13 for mutations in MECP2. In the remaining patients with unexplained mental retardation, additional clinical features should determine whether analysis of MECP2 is indicated.European Journal of Human Genetics (2004) 12, 24-28. doi:10.1038/sj.ejhg.5201080 Published online 15 October 2003 [ABSTRACT FROM AUTHOR]

Kleefstra syndrome (KS) is a neurodevelopmental disorder caused by mutations in the histone methyltransferase EHMT1. To study the impact of decreased EHMT1 function in human cells, we generated excitatory cortical neurons from induced pluripotent stem (iPS) cells derived from KS patients. Neuronal networks of patient-derived cells exhibit network bursting with a reduced rate, longer duration, and increased temporal irregularity compared to control networks. We show that these changes are mediated by upregulation of NMDA receptor (NMDAR) subunit 1 correlating with reduced deposition of the repressive H3K9me2 mark, the catalytic product of EHMT1, at the GRIN1 promoter. In mice EHMT1 deficiency leads to similar neuronal network impairments with increased NMDAR function. Finally, we rescue the KS patient-derived neuronal network phenotypes by pharmacological inhibition of NMDARs. Summarized, we demonstrate a direct link between EHMT1 deficiency and NMDAR hyperfunction in human neurons, providing a potential basis for more targeted therapeutic approaches for KS. Kleefstra syndrome is a neurodevelopmental disorder associated with hapoinsufficiency of the histone methyltransferase EHMT1. Here the authors show using induced pluripotent cells-derived neurons from patients that network dysfunction occurs and is due to dysfunction of the NMDA receptor. [ABSTRACT FROM AUTHOR]