Fine mapping of the 9q31 Hirschsprung's disease locus.

Hirschsprung's disease (HSCR) is a congenital disorder characterised by the absence of ganglia along variable lengths of the intestine. The RET gene is the major HSCR gene. Reduced penetrance of RET mutations and phenotypic variability suggest the involvement of additional modifying genes in the disease. A RET-dependent modifier locus was mapped to 9q31 in families bearing no coding sequence (CDS) RET mutations. Yet, the 9q31 causative locus is to be identified. To fine-map the 9q31 region, we genotyped 301 tag-SNPs spanning 7 Mb on 137 HSCR Dutch trios. This revealed two HSCR-associated regions that were further investigated in 173 Chinese HSCR patients and 436 controls using the genotype data obtained from a genome-wide association study recently conducted. Within one of the two identified regions SVEP1 SNPs were found associated with Dutch HSCR patients in the absence of RET mutations. This ratifies the reported linkage to the 9q31 region in HSCR families with no RET CDS mutations. However, this finding could not be replicated. In Chinese, HSCR was found associated with IKBKAP. In contrast, this association was stronger in patients carrying RET CDS mutations with p = 5.10 x 10(-6) [OR = 3.32 (1.99, 5.59)] after replication. The HSCR-association found for IKBKAP in Chinese suggests population specificity and implies that RET mutation carriers may have an additional risk. Our finding is supported by the role of IKBKAP in the development of the nervous system.

Genetic model system studies of the development of the enteric nervous system, gut motility and Hirschsprung's disease.

The enteric nervous system (ENS) is the largest and most complicated subdivision of the peripheral nervous system. Its action is necessary to regulate many of the functions of the gastrointestinal tract including its motility. Whilst the ENS has been studied extensively by developmental biologists, neuroscientists and physiologists for several decades it has only been since the early 1990s that the molecular and genetic basis of ENS development has begun to emerge. Central to this understanding has been the use of genetic model organisms. In this article, we will discuss recent advances that have been achieved using both mouse and zebrafish model genetic systems that have led to new insights into ENS development and the genetic basis of Hirschsprung's disease.

Hirschsprung disease, associated syndromes and genetics: a review.

Hirschsprung disease (HSCR, aganglionic megacolon) represents the main genetic cause of functional intestinal obstruction with an incidence of 1/5000 live births. This developmental disorder is a neurocristopathy and is characterised by the absence of the enteric ganglia along a variable length of the intestine. In the last decades, the development of surgical approaches has importantly decreased mortality and morbidity which allowed the emergence of familial cases. Isolated HSCR appears to be a non-Mendelian malformation with low, sex-dependent penetrance, and variable expression according to the length of the aganglionic segment. While all Mendelian modes of inheritance have been described in syndromic HSCR, isolated HSCR stands as a model for genetic disorders with complex patterns of inheritance. The tyrosine kinase receptor RET is the major gene with both rare coding sequence mutations and/or a frequent variant located in an enhancer element predisposing to the disease. Hitherto, 10 genes and five loci have been found to be involved in HSCR development.

A novel susceptibility locus for Hirschsprung's disease maps to 4q31.3-q32.3.

We report on a multigenerational family with isolated Hirschsprung's disease (HSCR). Five patients were affected by either short segment or long segment HSCR. The family consists of two main branches: one with four patients (three siblings and one maternal uncle) and one with one patient. Analysis of the RET gene, the major gene involved in HSCR susceptibility, revealed neither linkage nor mutations. A genome wide linkage analysis was performed, revealing suggestive linkage to a region on 4q31-q32 with a maximum parametric multipoint LOD score of 2.7. Furthermore, non-parametric linkage (NPL) analysis of the genome wide scan data revealed a NPL score of 2.54 (p = 0.003) for the same region on chromosome 4q (D4S413-D4S3351). The minimum linkage interval spans a region of 11.7 cM (12.2 Mb). No genes within this chromosomal interval have previously been implicated in HSCR. Considering the low penetrance of disease in this family, the 4q locus may be necessary but not sufficient to cause HSCR in the absence of modifying loci elsewhere in the genome. Our results suggest the existence of a new susceptibility locus for HSCR at 4q31.3-q32.3.