X-linked syndrome: mental retardation, hip luxation, and G6PD variant [Gd(+) Butantan]

X-linked variations inSHROOM4are implicated in congenital anomalies of the urinary tract and the anorectal, cardiovascular and central nervous systems

Background

SHROOM4is thought to play an important role in cytoskeletal modification and development of the early nervous system. Previously, single-nucleotide variants (SNVs) or copy number variations (CNVs) inSHROOM4have been associated with the neurodevelopmental disorder Stocco dos Santos syndrome, but not with congenital anomalies of the urinary tract and the visceral or the cardiovascular system.

Methods

Here, exome sequencing and CNV analyses besides expression studies in zebrafish and mouse andknockdown(KD) experiments using a splice blocking morpholino in zebrafish were performed to study the role ofSHROOM4during embryonic development.

Results

In this study, we identified putative disease-causing SNVs and CNVs inSHROOM4in six individuals from four families with congenital anomalies of the urinary tract and the anorectal, cardiovascular and central nervous systems (CNS). Embryonic mouse and zebrafish expression studies showedShroom4expression in the upper and lower urinary tract, the developing cloaca, the heart and the cerebral CNS. KD studies in zebrafish larvae revealed pronephric cysts, anomalies of the cloaca and the heart, decreased eye-to-head ratio and higher mortality compared with controls. These phenotypes could be rescued by co-injection of human wild-typeSHROOM4mRNA and morpholino.

Conclusion

The identified SNVs and CNVs in affected individuals with congenital anomalies of the urinary tract, the anorectal, the cardiovascular and the central nervous systems, and subsequent embryonic mouse and zebrafish studies suggestSHROOM4as a developmental gene for different organ systems.

PRMT6-mediated H3R2me2a guides Aurora B to chromosome arms for proper chromosome segregation

The kinase Aurora B forms the chromosomal passenger complex (CPC) together with Borealin, INCENP, and Survivin to mediate chromosome condensation, the correction of erroneous spindle-kinetochore attachments, and cytokinesis. Phosphorylation of histone H3 Thr3 by Haspin kinase and of histone H2A Thr120 by Bub1 concentrates the CPC at the centromere. However, how the CPC is recruited to chromosome arms upon mitotic entry is unknown. Here, we show that asymmetric dimethylation at Arg2 on histone H3 (H3R2me2a) by protein arginine methyltransferase 6 (PRMT6) recruits the CPC to chromosome arms and facilitates histone H3S10 phosphorylation by Aurora B for chromosome condensation. Furthermore, in vitro assays show that Aurora B preferentially binds to the H3 peptide containing H3R2me2a and phosphorylates H3S10. Our findings indicate that the long-awaited key histone mark for CPC recruitment onto mitotic chromosomes is H3R2me2a, which is indispensable for maintaining appropriate CPC levels in dynamic translocation throughout mitosis.

The proteins of the chromosomal passenger complex help chromosomes condense before cell division, but how this complex arrives at chromosomes was not known. Here the authors show that PRMT6 methylates histone H3 to recruit the chromosomal passenger complex.

[New X linked mental retardation syndrome]

INTRODUCTION

Researching inherited mental retardation, from a diagnostic and aetiological point of view, is a great challenge. A particular type of mental retardation is the one linked to the X chromosome which is classified under syndromic and non-syndromic types, according to the presence or absence of a specific physical, neurological or metabolic pattern associated with mental retardation.

PATIENTS AND METHOD

Five generations of a family have been studied with eight males suffering from mental retardation. Six of these males were clinically tested using anthropometric indicators and genetic tests: high resolution karyotypes, fragile X research, linkage and MID1 and PQBP1 gene studies.

RESULTS

Along with mental retardation, the clinical study showed a pattern of microcephaly, micrognathia, osteoarticular and genital anomalies, short stature and other less frequent malformations. The linkage study mapped the possible causal gene of this mental retardation syndrome and multiple congenital abnormalities in the Xp11.23-q21.32 segment, with a LOD score of 2. As far as we know, a medical profile, similar to the one these patients have, linked to this X segment has not been described.

CONCLUSIONS

We suspect that this family has a "new syndrome" of mental retardation and multiple congenital anomalies linked to the X chromosome.

XLMR genes: update 2000

This is the sixth edition of the catalogue of XLMR genes, ie X-linked genes whose malfunctioning causes mental retardation. The cloning era is not yet concluded, actually much remains to be done to account for the 202 XLMR conditions listed in this update. Many of these may eventually prove to be due to mutations in the same gene but the present number of 33 cloned genes falls surely short of the actual total count. It is now clear that even small families or individual patients with cytogenetic rearrangements can be instrumental in pinning down the remaining genes. DNA chip technology will hopefully allow (re)screening large numbers of patients for mutations in candidate genes or testing the expression levels of many candidate genes in informative families. Slowly, our knowledge of the structure and functioning of the proteins encoded by these genes is beginning to cast some light on the biological pathways required for the normal development of intelligence. Correlations between the molecular defects and the phenotypic manifestations are also being established. In order to facilitate the exchange of existing information and to allow its timely update, we prepared the first edition of the XLMR database (available at http://homepages.go.com/~xlmr/home.htm) and invite all colleagues, expert in the field, to contribute with their experience.

XLMR genes: update 1996

A current list of all known forms of X-linked mental retardation (XLMR) and a slightly revised classification are presented. The number of known disorders has not increased because 6 disorders have been combined based on new molecular data or on clinical grounds and only 6 newly described XLMR disorders have been reported. Of the current 105 XLMR disorders, 34 have been mapped, and 18 disorders and 1 nonspecific XLMR (FRAXE) have been cloned. The number of families with nonspecific XLMR with a LOD score of > or = 2.0 has more than doubled, with 42 (including FRAXE) now being known. a summary of the localization of presumed nonspecific mental retardation (MR) genes from well-studied X-chromosomal translocations and deletions is also included. Only 10-12 nonoverlapping loci are required to explain all localizations of nonspecific MR from both approaches. These new trends mark the beginning of a significantly improved understanding of the role of genes on the X chromosome in producing MR. Continued close collaboration between clinical and molecular investigators will be required to complete the process.

XLMR genes: update 1994

We provide a comprehensive list of all known forms of X-linked mental retardation. It comprises 127 entries, subdivided into 5 categories (syndromes, dominant disorders, metabolic disorders, neuromuscular disorders, and nonspecific mental retardation). Map location of 69 putative loci demonstrates several overlaps, which will only be resolved by more refined mapping or cloning of the respective genes. The ultimate goal of identifying all the genes on the X chromosome whose mutations cause mental retardation will require a concerted effort between clinical and molecular investigators.

XLMR genes: update 1992

Up to now, we have identified 77 X-linked conditions in which mental retardation is the primary or a major component manifestation. These conditions were subdivided into 2 categories, designated respectively "X-linked mental retardation syndromes" and "Non-specific X-linked mental retardation". Forty genes have been regionally mapped onto the X chromosome. However, in several instances the data were derived from a single family and most lod scores were less than 3.0.