Delineation of large deletions of the MECP2 gene in Rett syndrome patients, including a familial case with a male proband

Abstract

Comprehensive genetic screening programs have led to the identification of pathogenic methyl-CpGbinding protein 2 (MECP2) mutations in up to 95% of classical Rett syndrome (RTT) patients. This high rate of mutation detection can partly be attributed to specialised techniques that have enabled the detection of large deletions in a substantial fraction of otherwise mutation-negative patients. These cases would normally be missed by the routine PCR-based screening strategies. Here, we have identified large multi-exonic deletions in 12/149 apparently mutation-negative RTT patients using multiplex ligationdependent probe amplification (MLPA). These deletions were subsequently characterised using real-time quantitative PCR (qPCR) and long-range PCR with the ultimate aim of defining the exact nucleotide positions of the breakpoints and rearrangements. We detected an apparent deletion in one further patient using MLPA; however, this finding was contradicted by subsequent qPCR and long-range PCR results. The patient group includes an affected brother and sister with a large MECP2 deletion also present in their carrier mother. The X chromosome inactivation pattern of all female patients in this study was determined, which, coupled with detailed clinical information, allowed meaningful genotype -phenotype correlations to be drawn. This study reaffirms the view that large MECP2 deletions are an important cause of both classical and atypical RTT syndrome, and cautions that apparent deletions detected using high-throughput diagnostic techniques require further characterisation.

Exon-level array CGH in a large clinical cohort demonstrates increased sensitivity of diagnostic testing for Mendelian disorders

“…A variety of other studies have also reported a higher proportion of deletions among copy number mutations within single genes. 19,20 Several explanations may account for this observation. For example, carrying a complete extra copy of a gene is often not pathogenic.…”

Inherited human IRAK-1 deficiency selectively impairs TLR signaling in fibroblasts

“…To our knowledge, a deletion encompassing both MECP2 and IRAK1 has never before been reported in a male patient. Such deletions have been reported only in heterozygous female patients (94)(95)(96)(97)(98)(99)(100)(101)(102). Neither IRAK1 mRNA (evaluated by quantitative PCR) nor IRAK-1 protein (evaluated by Western blotting) was detected in the patient's SV40-immortalized fibroblasts (SV40-fibroblasts).…”

The phenotype associated with a large deletion on MECP2

“…Both classic and atypical presentations have been reported in those with large deletions, [6][7][8] but these studies have had relatively few cases (n¼12-22) or have not included a comparison group of individuals with other types of mutations. Larger studies have confirmed that a large deletion is associated with a severe phenotype, for example, in comparison with the phenotype of cases with the p.R133C 9 or a C-terminal deletion, 10 which are both considered to be generally mild.…”