Mosaic MECP2 variants in males with classical Rett syndrome features, including stereotypical hand movements

Psychological aspects of being a parent of an individual with Rett syndrome: A scoping review

BACKGROUND

Rett syndrome (RTT) causes multiple disabilities with a lifelong need for substantial care, placing a tremendous lifelong responsibility on the parents. Parenting an individual with RTT can therefore be challenging. Research on the psychological aspects of parenting individuals with RTT is limited and unclear. We aimed to identify and map the existing literature on this subject.

METHOD

A scoping review was conducted with systematic searches in PubMed, PsycINFO and CINAHL.

RESULTS

Eighteen studies were included. Negative and positive psychological aspects were described with the majority focusing on the negative. Three factors seemed to especially affect the parents: severity of the diagnosis, time (increasing age of parents or individual with RTT; years of caretaking), work-status of the mother.

CONCLUSIONS

Seemingly, parents are highly affected; however, the literature is scarce and has several gaps. Future research should include older parents, fathers, parents of individuals living in group homes, and positive aspects.

Mosaicism of common pathogenic MECP2 variants identified in two males with a clinical diagnosis of Rett syndrome

Rett (RTT) syndrome, a neurodevelopmental disorder caused by pathogenic variation in the MECP2 gene, is characterized by developmental regression, loss of purposeful hand movements, stereotypic hand movements, abnormal gait, and loss of spoken language. Due to the X-linked inheritance pattern, RTT is typically limited to females. Recent studies revealed somatic mosaicism in MECP2 in male patients with RTT-like phenotypes. While detecting mosaic variation using Sanger sequencing is theoretically possible for mosaicism over ~15%-20%, several variables, including efficiency of PCR, background noise, and/or human error, contribute to a low detection rate using this technology. Mosaic variants in two males were detected by next generation sequencing (NGS; Case 1) and by Sanger re-sequencing (Case 2). Both had targeted digital PCR (dPCR) to confirm the variants. In this report, we present two males with classic RTT syndrome in whom we identified pathogenic variation in the MECP2 gene in the mosaic state (c.730C > T (p.Gln244*) in Patient 1 and c.397C > T (p.Arg133Cys) in Patient 2). In addition, estimates and measures of mosaic variant fraction were surprisingly similar between Sanger sequencing, NGS, and dPCR. The mosaic state of these variants contributed to a lengthy diagnostic odyssey for these patients. While NGS and even Sanger sequencing may be viable methods of detecting mosaic variation in DNA or RNA samples, applying targeted dPCR to supplement these sequencing technologies would provide confirmation of somatic mosaicism and mosaic fraction.

Postzygotic mutations and where to find them - Recent advances and future implications in the field of non-neoplastic somatic mosaicism

The technological progress of massively parallel sequencing (MPS) has triggered a remarkable development in the research on postzygotic mutations. Although the overwhelming majority of studies in the field focus on oncogenesis, non-neoplastic diseases are attracting more and more attention. The aim of this review was to summarize some of the most recent findings in the field of somatic mosaicism in diseases other than neoplastic events. We discuss the abundance and role of postzygotic mutations, with a special emphasis on disorders which occur only in a mosaic form (obligatory mosaic diseases; OMDs). Based on the list of OMDs compiled from the published literature and three databases (OMIM, Orphanet and MosaicBase), we demonstrate the prevalence of cancer-related genes across OMDs and suggest other sources to further explore OMDs and OMD-related genes. Additionally, we comment on some practical aspects related to mosaic diseases, such as approaches to tissue sampling, the MPS coverage required to detect variants at a very low frequency, as well as on bioinformatic and molecular tools dedicated to detect somatic mutations in MPS data.

A rare case of a male child with post-zygotic de novo mosaic variant c.538C > T in MECP2 gene: a case report of Rett syndrome

BACKGROUND

Rett syndrome (RTT) is characterized by a normal perinatal period with a normal head size at birth followed by normal development for the first 6 months of life followed by gradual deceleration of head growth, loss of acquired purposeful hand skills, severe expressive and receptive language impairment, severe intellectual disability and gait and truncal apraxia/ ataxia. It is caused due to mutations in the MECP2 gene and follows an X-linked dominant mode of inheritance. It was observed exclusively in females and was believed to be lethal in males. In contrast to this belief, several males were identified with RTT upon genetic analysis, however, most males expired by the age of 2 years due to neonatal encephalopathy. The ones that survived beyond the age of 2 years, were attributed to the presence of an extra X chromosome (co-occurrence of Klinefelter and RTT) or the ones having mosaic cell lines. Only 11 males with somatic mosaicism are known till date.

CASE PRESENTATION

This case reports an ultra-rare case of a male affected with RTT surviving beyond the age of 2 years due to post-zygotic de novo somatic mosaicism. He was identified with a known pathogenic variant c.538C > T (p.R180*), which to the best of our knowledge is exclusively seen in females and has never been reported in a male before.

CONCLUSION

The present case is the first report of a mosaic male affected with RTT from India. The present report also carried out genotype-phenotype correlations across surviving mosaic males with RTT. We also postulate the effect of variant type, position along the gene and the variant allele fraction in different tissue types to be correlated with disease severity.

MECP2-Related Disorders in Males

Methyl CpG binding protein 2 (MECP2) is located at Xq28 and is a multifunctional gene with ubiquitous expression. Loss-of-function mutations in MECP2 are associated with Rett syndrome (RTT), which is a well-characterized disorder that affects mainly females. In boys, however, mutations in MECP2 can generate a wide spectrum of clinical presentations that range from mild intellectual impairment to severe neonatal encephalopathy and premature death. Thus, males can be more difficult to classify and diagnose than classical RTT females. In addition, there are some variants of unknown significance in MECP2, which further complicate the diagnosis of these children. Conversely, the entire duplication of the MECP2 gene is related to MECP2 duplication syndrome (MDS). Unlike in RTT, in MDS, males are predominantly affected. Usually, the duplication is inherited from an apparently asymptomatic carrier mother. Both syndromes share some characteristics, but also differ in some aspects regarding the clinical picture and evolution. In the following review, we present a thorough description of the different types of MECP2 variants and alterations that can be found in males, and explore several genotype-phenotype correlations, although there is still a lot to understand.

MECP2 mutation spectrum and its clinical characteristics in a Chinese cohort

The dysfunction of methyl-CpG-binding protein 2 (MeCP2) is associated with several neurological disorders, of which Rett syndrome (RTT) is the most prominent. This study focused on a Chinese patient cohort with MECP2 mutations, and analyzed the characteristics of these mutations and their clinical manifestations. In total, 666 patients were identified with 126 different MECP2 mutations, including 22 novel mutations. Over 80% of patients carried an MECP2 mutation on exon 4. Nonsense and missense mutations were the most commonly reported types. Missense mutations were mainly located on methyl-CpG-binding domain (MBD), and nonsense mutations predominantly occurred on transcription repression domain (TRD) and inter domain. The predilection site of large deletion was exon 3 and/or exon 4. Patients with p.R133C, p.R294*, p.R306C, and C-terminal domain (CTD) deletions were less severely affected. Significant differences were found in ambulation ability, hand function, and language among different mutation groups. Three female patients with MECP2 mutations (1 with p.R306P and 2 with p.R309W) only presented with intellectual disability/developmental delay (ID/DD), and no obvious RTT symptoms were reported. Eight male individuals with MECP2 mutations were also identified in this study, including 2 diagnosed with typical RTT, 3 with atypical RTT and 3 with ID/DD.

MeCP2_e2 partially compensates for lack of MeCP2_e1: A male case of Rett syndrome

Background

Rett syndrome (RTT) is a neurodevelopmental disorder that predominantly affects girls. Its causative gene is the X‐linked MECP2 encoding the methyl‐CpG‐binding protein 2 (MeCP2). The gene comprises four exons and generates two isoforms, namely MECP2_e1 and MECP2_e2. However, it remains unclear whether both MeCP2 isoforms have similar function in the brain.

Methods

We report a case of a boy with typical RTT. Male cases with MECP2 variants have been considered inviable, but somatic mosaicism of the variants can cause RTT in males. Whole‐exome sequencing was performed to search for the genetic background.

Results

A novel nonsense and mosaic variant was identified in exon 1 of MECP2, and the variant allele fraction (VAF) was 28%. Our patient had the same level of VAF as that in reported male cases with mosaic variants in MECP2 exon 3 or 4, but manifested RTT symptoms that were milder in severity compared to those in these patients.

Conclusion

This is probably because the variants in MECP2 exon 3 or 4 disrupt both isoforms of MeCP2, whereas the variant in exon 1, as presented in this study, disrupts only MeCP2_e1 but not MeCP2_e2. Therefore, our findings indicate that MeCP2_e2 may partially compensate for a deficiency in MeCP2_e1.