Male and female differential reproductive rate could explain parental transmission asymmetry of mutation origin in Hirschsprung disease

A systematic review and meta-analysis of GFAP gene variants in Alexander disease

Alexander disease (ALXDRD) is a rare neurodegenerative disorder of astrocytes resulting from pathogenic variants in the GFAP gene. The genotype-phenotype correlation remains elusive due to the variable expressivity of clinical manifestations. In an attempt to clarify the effects of GFAP variants in ALXDRD, numerous studies were collected and analyzed. In particular, we systematically searched for GFAP variants associated with ALXDRD and collected information on the location within the gene and protein, prediction of deleteriousness/pathogenicity, occurrence, sex and country of origin of patients, DNA source, genetic testing, and clinical signs. To identify possible associations, statistical analyses and meta-analyses were applied, thus revealing a higher than expected percentage of adult patients with ALXDRD. Furthermore, substitution of Arginine, the most frequently altered residue among the 550 predominantly missense causative GFAP variants collected, were mostly de novo and more prevalent in early-onset forms of ALXDRD. The effect of defective splicing in modifying the impact of GFAP variants on the age of onset of ALXDRD was also postulated after evaluating the distribution of the corresponding deleterious predictive values. In conclusion, not only previously unrecognized genotype-phenotype correlations were revealed in ALXDRD, but also subtle mechanisms could explain the variable manifestations of the ALXDRD clinical phenotype.

miR-618 rs2682818 C>A polymorphism decreases Hirschsprung disease risk in Chinese children

MicroRNAs (miRNAs) are endogenous non-coding small RNAs that play an important role in the development of many malignant tumors. In addition, recent studies have reported that single nucleotide polymorphisms (SNPs) located in the miRNA functional region was inextricably linked to tumor susceptibility. In the present study, we investigated the susceptibility between miR-618 rs2682818 C>A and Hirschsprung disease (HSCR) in the Southern Chinese population (1470 patients and 1473 controls). Odds ratios (ORs) and 95% confidence intervals (CIs) were used for estimating the strength of interrelation between them. We found that the CA/AA genotypes of miR-618 rs2682818 were associated with a decreased risk of HSCR when compared with the CC genotype (OR = 0.84, 95% CI = 0.72–0.99, P=0.032). Based on the stratified analysis of HSCR subtypes, the rs2682818 CA/AA genotypes were able to significantly lessen the risk of HSCR compared with CC genotype in patients with long-segment HSCR (adjusted OR = 0.70, 95% CI = 0.52–0.93, P=0.013). In conclusion, our results indicated that the miR-618 rs2682818 C>A polymorphism was associated with a reduced risk of HSCR in Chinese children, especially in patients with long-segment HSCR (L-HSCR) subtype.

Copy number variations in candidate genomic regions confirm genetic heterogeneity and parental bias in Hirschsprung disease

Background

Hirschsprung Disease (HSCR) is a congenital defect of the intestinal innervations characterized by complex inheritance. Many susceptibility genes including RET, the major HSCR gene, and several linked regions and associated loci have been shown to contribute to disease pathogenesis. Nonetheless, a proportion of patients still remains unexplained. Copy Number Variations (CNVs) have already been involved in HSCR, and for this reason we performed Comparative Genomic Hybridization (CGH), using a custom array with high density probes.

Results

A total of 20 HSCR candidate regions/genes was tested in 55 sporadic patients and four patients with already known chromosomal aberrations. Among 83 calls, 12 variants were experimentally validated, three of which involving the HSCR crucial genes SEMA3A/3D, NRG1, and PHOX2B. Conversely RET involvement in HSCR does not seem to rely on the presence of CNVs while, interestingly, several gains and losses did co-occur with another RET defect, thus confirming that more than one predisposing event is necessary for HSCR to develop. New loci were also shown to be involved, such as ALDH1A2, already found to play a major role in the enteric nervous system. Finally, all the inherited CNVs were of maternal origin.

Conclusions

Our results confirm a wide genetic heterogeneity in HSCR occurrence and support a role of candidate genes in expression regulation and cell signaling, thus contributing to depict further the molecular complexity of the genomic regions involved in the Enteric Nervous System development. The observed maternal transmission bias for HSCR associated CNVs supports the hypothesis that in females these variants might be more tolerated, requiring additional alterations to develop HSCR disease.

A genome-wide association study identifies potential susceptibility loci for Hirschsprung disease

Hirschsprung disease (HSCR) is a congenital and heterogeneous disorder characterized by the absence of intramural nervous plexuses along variable lengths of the hindgut. Although RET is a well-established risk factor, a recent genome-wide association study (GWAS) of HSCR has identified NRG1 as an additional susceptibility locus. To discover additional risk loci, we performed a GWAS of 123 sporadic HSCR patients and 432 unaffected controls using a large-scale platform with coverage of over 1 million polymorphic markers. The result was that our study replicated the findings of RET-CSGALNACT2-RASGEF1A genomic region (_rawP = 5.69×10⁻¹⁹ before a Bonferroni correction; _corrP = 4.31×10⁻¹³ after a Bonferroni correction) and NRG1 as susceptibility loci. In addition, this study identified SLC6A20 (_adjP = 2.71×10⁻⁶), RORA (_adjP = 1.26×10⁻⁵), and ABCC9 (_adjP = 1.86×10⁻⁵) as new potential susceptibility loci under adjusting the already known loci on the RET-CSGALNACT2-RASGEF1A and NRG1 regions, although none of the SNPs in these genes passed the Bonferroni correction. In further subgroup analysis, the RET-CSGALNACT2-RASGEF1A genomic region was observed to have different significance levels among subgroups: short-segment (S-HSCR, _corrP = 1.71×10⁻⁵), long-segment (L-HSCR, _corrP = 6.66×10⁻⁴), and total colonic aganglionosis (TCA, _corrP>0.05). This differential pattern in the significance level suggests that other genomic loci or mechanisms may affect the length of aganglionosis in HSCR subgroups during enteric nervous system (ENS) development. Although functional evaluations are needed, our findings might facilitate improved understanding of the mechanisms of HSCR pathogenesis.

Genetic effects on DNA methylation and its potential relevance for obesity in Mexican Americans

Several studies have identified effects of genetic variation on DNA methylation patterns and associated heritability, with research primarily focused on Caucasian individuals. In this paper, we examine the evidence for genetic effects on DNA methylation in a Mexican American cohort, a population burdened by a high prevalence of obesity. Using an Illumina-based platform and following stringent quality control procedures, we assessed a total of 395 CpG sites in peripheral blood samples obtained from 183 Mexican American individuals for evidence of heritability, proximal genetic regulation and association with age, sex and obesity measures (i.e. waist circumference and body mass index). We identified 16 CpG sites (∼4%) that were significantly heritable after Bonferroni correction for multiple testing and 27 CpG sites (∼6.9%) that showed evidence of genetic effects. Six CpG sites (∼2%) were associated with age, primarily exhibiting positive relationships, including CpG sites in two genes that have been implicated in previous genome-wide methylation studies of age (FZD9 and MYOD1). In addition, we identified significant associations between three CpG sites (∼1%) and sex, including DNA methylation in CASP6, a gene that may respond to estradiol treatment, and in HSD17B12, which encodes a sex steroid hormone. Although we did not identify any significant associations between DNA methylation and the obesity measures, several nominally significant results were observed in genes related to adipogenesis, obesity, energy homeostasis and glucose homeostasis (ARHGAP9, CDKN2A, FRZB, HOXA5, JAK3, MEST, NPY, PEG3 and SMARCB1). In conclusion, we were able to replicate several findings from previous studies in our Mexican American cohort, supporting an important role for genetic effects on DNA methylation. In addition, we found a significant influence of age and sex on DNA methylation, and report on trend-level, novel associations between DNA methylation and measures of obesity.

Chromosomal and related Mendelian syndromes associated with Hirschsprung's disease

Hirschsprung's disease (HSCR) is a fairly frequent cause of intestinal obstruction in children. It is characterized as a sex-linked heterogonous disorder with variable severity and incomplete penetrance giving rise to a variable pattern of inheritance. Although Hirschsprung's disease occurs as an isolated phenotype in at least 70% of cases, it is not infrequently associated with a number of congenital abnormalities and associated syndromes, demonstrating a spectrum of congenital anomalies. Certain of these syndromic phenotypes have been linked to distinct genetic sites, indicating underlying genetic associations of the disease and probable gene-gene interaction, in its pathogenesis. These associations with HSCR include Down's syndrome and other chromosomal anomalies, Waardenburg syndrome and other Dominant sensorineural deafness, the Congenital Central Hypoventilation and Mowat-Wilson and other brain-related syndromes, as well as the MEN2 and other tumour associations. A number of other autosomal recessive syndromes include the Shah-Waardenburg, the Bardet-Biedl and Cartilage-hair hypoplasia, Goldberg-Shprintzen syndromes and other syndromes related to cholesterol and fat metabolism among others. The genetics of Hirschsprung's disease are highly complex with the majority of known genetic sites relating to the main susceptibility pathways (RET an EDNRB). Non-syndromic non-familial, short-segment HSCR appears to represent a non-Mendelian condition with variable expression and sex-dependent penetrance. Syndromic and familial forms, on the other hand, have complex patterns of inheritance and being reported as autosomal dominant, recessive and polygenic patterns of inheritance. The phenotypic variability and incomplete penetrance observed in Hirschsprung's disease could also be explained by the involvement of modifier genes, especially in its syndromic forms. In this review, we look at the chromosomal and Mendelian associations and their underlying signalling pathways, to obtain a better understanding of the pathogenetic mechanisms involved in developing aganglionosis of the distal bowel.