Diversity of RET proto-oncogene mutations in familial and sporadic Hirschsprung disease

Hirschsprung disease (HSCR) is a common congenital malformation(1 in 5 000 live births) due to the absence of autonomic gangliain the terminal hindgut, and resulting in intestinal obstructionin neonates. Recently, a dominant gene for familial HSCR hasbeen mapped to chromosome sub-band 10q11.2 and the disease hasbeen ascribed to mutations in a tyrosine kinase receptor genemapping to this region, the RETproto-oncogene. Studying the20 exons of the RET gene by a combination of denaturating gradientgel electrophoresis and single strand conformation polymorphismin a large series of HSCR patients (45 sporadic cases and 35familial forms), we found mutations of the RET gene in 50% offamilial HSCR, regardless of the length of the aganglionic segment.The mean penetrance of the mutant allele in familial HSCR wassignificantly higher in males (72%) than in females (51%). Mostinterestingly, mutations at the RET locus accounted for at least1/3 of sporadic HSCR in our series. These mutations were scatteredalong the length of the gene. Finally, among the mutations identifiedin sporadic cases (16/45), seven proved to be de novo mutationssuggesting that new mutations at the RET locus significantlycontribute to sporadic HSCR. Taken together, the low penetranceof the mutant gene, the lack of genotype-phenotype correlation,the sex-dependent effect of RET mutations and the variable clinicalexpression of the disease support the existence of one or moremodifier genes in familial HSCR.     

Hirschsprung disease in MEN 2A: increased spectrum of RET exon 10 genotypes and strong genotype-phenotype correlation

The RET proto-oncogene encodes a transmembrane receptor with tyrosine kinase activity. Germline mutations in RET are responsible for a number of inherited diseases. These include the dominantly inherited cancer syndromes multiple endocrine neoplasia types 2A and 2B (MEN 2A and MEN 2B) and familial medullary thyroid carcinoma (FMTC), as well as some cases of familial Hirschsprung disease (HSCR1). RET mutations in HSCR1 have been shown to cause a loss of RET function, while the cancer syndromes result in RET oncogenic activation. Occasionally MEN 2A or FMTC occurs in association with HSCR1, albeit with low penetrance. An initial report linked HSCR1 in MEN 2A solely to the C618R and C620R RET mutations. In this study we have analyzed 44 families with MEN 2A. HSCR1 co-segregated with MEN 2A in seven (16%) of the 44 families. The predisposing RET mutation in all seven families had been previously reported in MEN 2A or FMTC and occurred in exon 10 at codons 609, 618 or 620, resulting in C609Y, C618S, C620R or C620W substitution. MEN 2A families with RET exon 10 Cys mutations had a substantially greater risk of developing HSCR1 than those with the more common RET exon 11 Cys634 or exon 14 c804 mutations (P = 0.0005). These findings suggest that expression of HSCR1 in MEN 2A may be peculiar to RET exon 10 Cys mutations . However, HSCR1 in MEN 2A is not exclusive to C618R or C620R RET mutations and can occur with other exon 10 Cys amino acid substitutions. The strong correlation between disease phenotype and position of the MEN 2A RET mutation suggests that oncogenic activation of RET alone is insufficient to account for co-expression of the diseases.      

Low RET mutation frequency and polymorphism analysis of the RET and EDNRB genes in patients with Hirschsprung disease in Taiwan

Hirschsprung disease (HSCR), or congenital intestinal aganglionosis, is a relatively common disorder characterized by the absence of ganglion cells in the nerve plexuses of the lower digestive tract, resulting in intestinal obstruction in neonates. Mutations in genes of the RET receptor tyrosine kinase and endothelin receptor B (EDNRB) signaling pathways have been shown to be associated in HSCR patients. In this study, we collected genomic DNA samples from 55 HSCR patients in central Taiwan and analyzed the coding regions of the RET and EDNRB genes by PCR amplification and DNA sequencing. In the 55 patients, an A to G transition was detected in two (identical twin brothers). The mutation was at the end of RET exon 19 at codon 1062 (Y1062C), a reported critical site for the signaling pathways. Single nucleotide polymorphisms (SNP) in exons 2, 7, 11, 13, and 15 of RET and exon 4 of EDNRB in the HSCR patients or controls were detected. The differences between patients and controls in allele distribution of the five RET polymorphic sites were statistically significant. The most frequent genotype encompassing exons 2 and 13 SNPs (the polymorphic sites with the highest percentage of heterozygotes) was AA/GG in patients, which was different from the AG/GT in the normal controls. Transmission disequilibrium was observed in exons 2, 7, and 13, indicating nonrandom association of the susceptibility alleles with the disease in the patients. This study represents the first comprehensive genetic analysis of HSCR disease in Taiwan.     

Mutations of the RET proto-oncogene in the multiple endocrine neoplasia type 2 syndromes,related sporadic tumours,and Hirschsprung disease

The RET proto-oncogene codes for a receptor tyrosine kinase thought to play a role in the development of neural crest and its derivatives. Mutations in the RET proto-oncogene have been found in patients with the multiple endocrine neoplasia type 2 syndromes (MEN 2), the related sporadic tumours medullary thyroid carcinoma and pheochromocytoma, and familial and sporadic Hirschsprung disease, a syndrome of congenital absence of enteric innervation. Germline mutations in one of eight codons within RET cause the three subtypes of MEN 2, namely, MEN 2A, MEN 2B, and familial medullary thyroid carcinoma. Somatic mutation in an overlapping group of nine codons have been found in a proportion of sporadic medullary thyroid carcinoma and pheochromocytoma. In contrast to MEN 2, approximately 25% of patients with Hirschsprung disease have germline mutations scattered throughout the length of RET. Hum Mutat 9:97–109, 1997. © 1997 Wiley-Liss, Inc.     

RET基因调控区遗传变异与先天性巨结肠患病风险研究

目的先天性巨结肠（HSCR）是一种复杂的先天性疾病,RET是其主要的易感性基因。本研究对RET非编码区单核甘酸多态性（SNP）-5G〉A（rs10900296）,-1A〉C（rs10900297）和intron1 C〉T（rs2435357）进行分型分析,评估RET基因调控区SNPs及单倍型与先天性巨结肠之间的相关性。方法选取115名病例组病人和139名对照组正常人群,应用聚合酶链反应（PCR）技术和直接测序的方法进行基因分型。回归模型中使用OR值和95%置信区间（CI）作为基因型危险性的评价指标。结果 -5G〉A,-1A〉C,intron1C〉T各基因型频率在病例和对照人群的分布具有显著差异。-5 AA（OR=6.26,95%CI=3.62-10.83）,-1 CC（OR=7.54,95%CI=2.06-27.66）和intron1 TT（OR=19.22,95% CI=7.54-48.99）基因型均能显著增加HSCR发病的风险。单倍型A-C-T（OR=6.28,95% CI=3.77-10.46）和双体型A-C-T/A-C-T（OR=13.62,95% CI=3.48-53.30）分析同样表明与HSCR发病风险存在较强的相关性,并呈现出一定的累积效应。结论 RET基因调控区的基因多态性可能与HSCR的发病易感性有关,支持RET通路的常见变异在HSCR的发展过程中起着重要的作用的假设。     

RET haplotype, not linked to the C620R activating mutation, associated with Hirschsprung disease in a novel MEN2 family

Hirschsprung disease is a congenital form of aganglionic megacolon that results from cristopathy. Hirschsprung disease usually occurs as a sporadic disease, although it may be associated with several inherited conditions, such as multiple endocrine neoplasia type 2. The rearranged during transfection (RET) proto-oncogene is the major susceptibility gene for Hirschsprung disease, and germline mutations in RET have been reported in up to 50% of the inherited forms of Hirschsprung disease and in 15-20% of sporadic cases of Hirschsprung disease. The prevalence of Hirschsprung disease in multiple endocrine neoplasia type 2 cases was recently determined to be 7.5% and the cooccurrence of Hirschsprung disease and multiple endocrine neoplasia type 2 has been reported in at least 22 families so far. It was initially thought that Hirschsprung disease could be due to disturbances in apoptosis or due to a tendency of the mutated RET receptor to be retained in the Golgi apparatus. Presently, there is strong evidence favoring the hypothesis that specific inactivating haplotypes play a key role in the fetal development of congenital megacolon/Hirschsprung disease. In the present study, we report the genetic findings in a novel family with multiple endocrine neoplasia type 2: a specific RET haplotype was documented in patients with Hirschsprung disease associated with medullary thyroid carcinoma, but it was absent in patients with only medullary thyroid carcinoma. Despite the limited number of cases, the present data favor the hypothesis that specific haplotypes not linked to RET germline mutations are the genetic causes of Hirschsprung disease.     

Intrinsic susceptibility to misfolding of a hot-spot for Hirschsprung disease mutations in the ectodomain of RET

Loss-of-function mutations in RET cause abnormal development of the enteric nervous system, a congenital condition known as Hirschsprung disease. Hirschsprung mutations in the extracellular domain of RET (RETECD) affect processing in the endoplasmic reticulum (ER) and prevent RET expression at the cell surface. We have investigated the processing and function of a series of Hirschsprung disease mutations affecting different biochemical properties of the RETECD. All mutations examined prevented the maturation of RETECD in the ER and abolished its ability to interact with the GDNF/GFRalpha1 ligand complex, indicating defects in protein folding. Immature forms of RETECD accumulating intracellularly associated with the ER chaperone Grp78/BiP and showed different degrees of protein ubiquitination. Maturation of RETECD mutants, including those deficient in Ca2+ binding and disulfide bridge formation, could be rescued by allowing protein expression to proceed at 30 degrees C, a condition known to facilitate protein folding. Several of the mutants produced at 30 degrees C regained their ability to bind to the GDNF/GFRalpha1 complex comparable to wild-type, demonstrating that the mutations affected RETECD folding but not function. Analysis of autonomous folding subunits in the RETECD indicated an intrinsic propensity to misfolding in three N-terminal cadherin-like domains, CLD1-3, which also concentrate the majority of Hirschsprung mutations affecting the RETECD. In agreement with this, expression and maturation of these subdomains was specifically improved at 30 degrees C, identifying them as temperature-sensitive determinants in RETECD. Intriguingly, while production of human and mouse RETECD was suboptimal at 37 degrees C compared with 30 degrees C, expression of Xenopus RETECD was higher at 37 degrees C, a non-physiological temperature for amphibians. The intrinsic susceptibility to misfolding of mammalian RETECD may be the result of a trade-off that helps to avoid an increased incidence of tumors, at the expense of a greater vulnerability to Hirschsprung disease.     

De novo mutation of GDNF, ligand for the RET/GDNFR-alpha receptor complex, in Hirschsprung disease

Hirschsprung disease (HSCR) is a common congenital abnormality characterized by absence of the enteric ganglia in the hind gut. In 10- 40% of HSCR cases, mutations of the RET receptor tyrosine kinase have been found. The recent identification of a multimeric RET ligand/receptor complex suggested that mutations of genes encoding other components of this complex might also occur in HSCR. To investigate this role, we examined the gene for glial cell line-derived neurotrophic factor (GDNF), the circulating ligand of the RET receptor complex, for mutations in a panel of sporadic and familial HSCR. We identified GDNF sequence variants in 2/36 HSCR patients. The first of these was a conservative change which did not affect the GDNF protein sequence. The second variant was a de novo missense mutation in a family with no history of HSCR and without mutation of the RET gene. Thus, our data are consistent with a causative role for GDNF mutations in some HSCR cases.      

SIP1基因编码区点突变及多态性在先天性巨结肠症中的检测与分析

目的 检测先天性巨结肠症(Hirschsprung disease,HSCR)患者SIP1(Smad-interacting protein 1)基因编码区点突变及单核苷酸多态性特点,探讨SIP1基因与HSCR的关系.方法 应用聚合酶链反应.单链构像多态性(polymerase chain reaction-single strand conformation polymorphism,PCR-SSCP)和DNA直接测序技术,对50例HSCR、30名正常对照外周血SIP1基因编码区的10个外显子,进行点突变与单核苷酸多态性的检测与分析.结果 HSCR与正常对照突变图谱比较,有1例病例在第7外显子出现杂合性缺失,密码子157位点GTG→GTA置换,引起亮氨酸的同义突变,属于单核苷酸多态性,突变率为2%(1/50).有4例患者在第8外显子出现突变,突变率为8%(4/50).PCR-SSCP银染分析,第2外显子2例出现相同类型泳动变位;第7外显子3例出现相同类型泳动变位;第8外显子7例出现相同类型泳动变位.结论 HSCR有SIP1基因突变,提示SIPI基因与HSCR的发病存在一定程度的关联.     

Interaction between a chromosome 10 RET enhancer and chromosome 21 in the Down syndrome–Hirschsprung disease association

Individuals with Down syndrome (DS) display a 40‐fold greater risk of Hirschsprung disease (HSCR) than the general population of newborns implicating chromosome 21 in HSCR etiology. Here we demonstrate that the RET enhancer polymorphism RET+9.7 (rs2435357:C>T) at chromosome 10q11.2 is associated with HSCR in DS individuals both by transmission disequilibrium (P=0.0015) and case–control (P=0.0115) analysis of matched cases. Interestingly, the RET+9.7 T allele frequency is significantly different between individuals with DS alone (0.26±0.04), HSCR alone (0.61±0.04), and those with HSCR and DS (0.41±0.04), demonstrating an association and interaction between RET and chromosome 21 gene dosage. This is the first report of a genetic interaction between a common functional variant (rs2435357) and a not infrequent copy number error (chromosome 21 dosage) in two human developmental disorders. Hum Mutat 30:1–5, 2009. © 2009 Wiley‐Liss, Inc.     

RET基因启动子区遗传变异与先天性巨结肠合并小肠结肠炎风险

目的先天性巨结肠（Hirschsprung＇s disease，HSCR）是一种肠神经系统发育异常导致的先天性消化道畸形，巨结肠合并小肠结肠炎是最常见的严重并发症之一。RET基因是HSCR的主要致病基因，本研究探讨RET启动子区的两个功能性单核苷酸多态-5G／A和-1A／C与先天性巨结肠合并小肠结肠炎风险的关系。方法以聚合酶链反应（PCR）和直接测序（direct-squencing）分析方法，检测了52例先天性巨结肠患者，其中合并小肠结肠炎者18例和120例正常对照者RET-5G／A和-1A／C的基因型，比较不同基因型与疾病风险的相关性。结果RET-5AA和-1CC基因型频率在先天性巨结肠患者和正常对照中的分布有显著性差异，其中以-5AA较显著（P值〈0．001）。此外，与正常对照组相比，携带RET-5AA基因型者罹患先天性巨结肠合并小肠结肠炎的风险亦增加（P值=0．004），但与单纯HSCR患者组相比，RET-5AA基因型者并无增加合并小肠结肠炎的风险（P值=0．461）。结论RET基因启动子区遗传变异-5G／A和-1A／C与先天性巨结肠合并小肠结肠炎风险增加相关，但并不增加原有HSCR患者合并小肠结肠炎的风险。     

Novel point mutation in exon 10 of the RET proto-oncogene in a family with medullary thyroid carcinoma

Medullary thyroid carcinoma (MTC) may occur sporadically or as part of the autosomal dominant multiple endocrine neoplasia type 2 (MEN 2). Three hereditary forms of MEN 2 have been identified: MEN 2A, MEN 2B, and familial MTC (FMTC). Missense germ-line mutations in the RET proto-oncogene have been identified as cause of these endocrine diseases. Mutations are found in exons 10 and 11 in MEN 2A and FMTC families and in a small number of families in exons 13, 14, and 15. Although a strong correlation between codon mutations and phenotypes has been described, not all the expected cystein codon mutations have been found. Therefore, the more mutations are found, the better it is possible to establish phenotype-genotype correlations. We report on a novel RET mutation at codon 611 in a family with MTC without other clinical manifestations and of rather benign course. Am. J. Med. Genet. 78:271–273, 1998. © 1998 Wiley-Liss, Inc.     

Alu element insertion in the MLH1 exon 6 coding sequence as a mutation predisposing to Lynch syndrome

Lynch syndrome (LS) is the most frequent cause of hereditary colorectal cancer. A subset of patients with a history of LS shows no causal germline pathogenic alteration and are identified as having Lynch‐like syndrome (LLS). Alu retrotransposons are the most abundant mobile DNA sequences in the human genome and have been associated with numerous human cancers by either disrupting coding regions or altering epigenetic modifications or splicing signals. We report a family first classified as having LLS by Sanger sequencing analysis. Next‐generation sequencing (NGS) analysis identified an AluY5a insertion in MLH1 exon 6 that led to exon skipping. This splicing alteration inducing a pathogenic frameshift was found in patients who developed colorectal adenocarcinomas. Retroelement insertion might thus be an important but underestimated mechanism of cancer genetics that could be systematically tested in patients with a phenotype suggesting LS to accurately assess family risk and surveillance approaches.