A founding locus within the RET proto-oncogene may account for a large proportion of apparently sporadic Hirschsprung disease and a subset of cases of sporadic medullary thyroid carcinoma

mRNA sequencing provides new insights into the pathogenesis of Hirschsprung's disease in mice

PURPOSE

The aim of this study is to use RNA sequencing and RT-qPCR to identify the main susceptibility genes linked to the occurrence and development of Hirschsprung disease in the colonic tissues of EDNRBm1yzcm and wild mice.

METHODS

RNA was extracted from colon tissues of 3 mutant homozygous mice and 3 wild mice. RNA degradation, contamination concentration, and integrity were then measured. The extracted RNA was then sequenced using the Illumina platform. The obtained sequence data are filtered to ensure data quality and compared to the reference genome for further analysis. DESeq2 was used for gene expression analysis of the raw data. In addition, graphene oxide enrichment analysis and RT-qPCR validation were also performed.

RESULTS

This study identified 8354 differentially expressed genes in EDNRBm1yzcm and wild mouse colon tissues by RNA sequencing, including 4346 upregulated genes and 4005 downregulated genes. Correspondingly, the results of RT-qPCR analysis showed good correlation with the transcriptome data. In addition, GO and KEGG enrichment results suggested that there were 8103 terms and 320 pathways in all DEGs. When P < 0.05, 1081 GO terms and 320 KEGG pathways reached a significant level. Finally, through the existing studies and the enrichment results of differentially expressed genes, it was determined that axon guidance and the focal adhesion pathway may be closely related to the occurrence of HSCR.

CONCLUSIONS

This study analyzed and identified the differential genes in colonic tissues between EDNRBm1yzcm mice and wild mice, which provided new insight for further mining the potential pathogenic genes of Hirschsprung's disease.

Negative Association Between lncRNA HOTTIP rs3807598 C>G and Hirschsprung Disease

Background

Hirschsprung disease (HSCR) is a congenital disease that arises from defective intestinal neural system. LncRNA HOTTIP is a critical gene in various diseases, including HSCR. No epidemiological studies have explored the correlation between lncRNA HOTTIP single nucleotide polymorphisms (SNPs) and HSCR risk. We here lead as a pioneer to explore whether SNPs in lncRNA HOTTIP impact the risk of HSCR and HSCR subtypes in an unrelated Chinese population.

Methods

We used the TaqMan method to genotype rs3807598 C>G of the lncRNA HOTTIP gene using 1470 HSCR cases and 1473 healthy controls. Of them, 1441 cases and 1434 controls were successfully genotyped. We adopted odds ratios (ORs) and 95% confidence intervals (CIs) to quantify the relationship.

Results

We got an unexpected outcome that lncRNA HOTTIP SNP rs3807598 C>G could not modify the risk of HSCR (CG vs. CC: adjusted OR=0.89, 95% CI=0.74–1.07; GG vs. CC: adjusted OR=1.10, 95% CI=0.89–1.37; GG/CG vs CC: adjusted OR=0.95, 95% CI=0.80–1.13; and GG vs. CC/CG: adjusted OR=1.19, 95% CI=0.99–1.43). What’s more, risk effect of lncRNA HOTTIP rs3807598 C>G is still not obvious in stratification analysis by HSCR subtype.

Conclusion

Our studies did not provide statistical evidence of a correlation between lncRNA HOTTIP SNP rs3807598 C>G and susceptibility of HSCR in the Chinese population that is being studied. Further validation study with a larger sample size covering multi-ethnic groups is warranted.

ASSOCIATION OF RS2435357 AND RS1800858 POLYMORPHISMS IN RET PROTO-ONCOGENE WITH HIRSCHSPRUNG DISEASE: SYSTEMATIC REVIEW AND META-ANALYSIS

Introduction:

Many published studies have estimated the association of rs2435357 and rs1800858 polymorphisms in the proto-oncogene rearranged during transfection (RET) gene with Hirschsprung disease (HSCR) risk. However, the results remain inconsistent and controversial.

Aim:

To perform a meta-analysis get a more accurate estimation of the association of rs2435357 and rs1800858 polymorphisms in the RET proto-oncogene with HSCR risk.

Methods:

The eligible literatures were searched by PubMed, Google Scholar, EMBASE, and Chinese National Knowledge Infrastructure (CNKI) up to June 30, 2018. Summary odds ratios (ORs) and 95% confidence intervals (CIs) were used to evaluate the susceptibility to HSCR.

Results:

A total of 20 studies, including ten (1,136 cases 2,420 controls) for rs2435357 and ten (917 cases 1,159 controls) for rs1800858 were included. The overall results indicated that the rs2435357 (allele model: OR=0.230, 95% CI 0.178-0.298, p=0.001; homozygote model: OR=0.079, 95% CI 0.048-0.130, p=0.001; heterozygote model: OR=0.149, 95% CI 0.048-0.130, p=0.001; dominant model: OR=0.132, 95% CI 0.098-0.179, p=0.001; and recessive model: OR=0.239, 95% CI 0.161-0.353, p=0.001) and rs1800858 (allele model: OR=5.594, 95% CI 3.653-8.877, p=0.001; homozygote model: OR=8.453, 95% CI 3.783-18.890, p=0.001; dominant model: OR=3.469, 95% CI 1.881-6.396, p=0.001; and recessive model: OR=6.120, 95% CI 3.608-10.381, p=0.001) polymorphisms were associated with the increased risk of HSCR in overall.

Conclusions:

The results suggest that the rs2435357 and rs1800858 polymorphisms in the RET proto-oncogene might be associated with HSCR risk.

Two Novel SNPs in RET Gene Are Associated with Cattle Body Measurement Traits

The rearrangement of the transfection (RET) gene, which mediates the functions of the ganglion in the gastrointestinal tract, plays an important role in the development of the gastrointestinal nervous system. Therefore, the RET gene is a potential factor influencing animal body measurement. The aim of this study was to reveal the significant genetic variations in the bovine RET gene and investigate the relationship between genotypes and body measurement in two Chinese cattle breeds (Qinchuan and Nanyang cattle). In this study, two SNPs (c.1407A>G and c.1425C>G) were detected in the exon 7 of RET gene by sequencing. For the SNP1 and SNP2, the GG genotype was significantly associated with body height, hip height, and chest circumference in Qinchuan cattle (p < 0.05). Individuals with an AG-CC genotype showed the lowest value of all body measurement in both breeds. Our results demonstrate that the polymorphisms in the bovine RET gene were significantly associated with body measurement, which could be used as DNA marker on the marker-assisted selection (MAS) and improve the performance of beef cattle.

Genetic Background of Hirschsprung Disease: A Bridge Between Basic Science and Clinical Application

Hirschsprung's disease (HSCR) is a congenital disorder, defined by partial or complete loss of the neuronal ganglion cells in the intestinal tract, which is caused by the failure of neural crest cells to migrate completely during intestinal development during fetal life. HSCR has a multifactorial etiology, and genetic factors play a key role in its pathogenesis; these include mutations within several gene loci. These have been identified by screening candidate genes, or by conducting genome wide association (GWAS) studies. However, only a small portion of them have been proposed as major genetic risk factors for the HSCR. In this review, we focus on those genes that have been identified as either low penetrant or high penetrant variants that determine the risk of Hirschsprung's disease. J. Cell. Biochem. 119: 28-33, 2018. © 2017 Wiley Periodicals, Inc.

Effect of 3'UTR RET Variants on RET mRNA Secondary Structure and Disease Presentation in Medullary Thyroid Carcinoma

Background

The RET S836S variant has been associated with early onset and increased risk for metastatic disease in medullary thyroid carcinoma (MTC). However, the mechanism by which this variant modulates MTC pathogenesis is still open to discuss. Of interest, strong linkage disequilibrium (LD) between RET S836S and 3'UTR variants has been reported in Hirschsprung's disease patients.

Objective

To evaluate the frequency of the RET 3’UTR variants (rs76759170 and rs3026785) in MTC patients and to determine whether these variants are in LD with S836S polymorphism.

Methods

Our sample comprised 152 patients with sporadic MTC. The RET S836S and 3’UTR (rs76759170 and rs3026785) variants were genotyped using Custom TaqMan Genotyping Assays. Haplotypes were inferred using the phase 2.1 program. RET mRNA structure was assessed by Vienna Package.

Results

The mean age of MTC diagnosis was 48.5±15.5 years and 57.9% were women. The minor allele frequencies of RET polymorphisms were as follows: S836S, 5.6%; rs76759170, 5.6%; rs3026785, 6.2%. We observed a strong LD among S836S and 3’UTR variants (|D’| = -1, r² = 1 and |D’| = -1, r² = 0,967). Patients harboring the S836S/3’UTR variants presented a higher percentage of lymph node and distant metastasis (P = 0.013 and P<0.001, respectively). Accordingly, RNA folding analyses demonstrated different RNA secondary structure predictions for WT(TCCGT), S836S(TTCGT) or 3’UTR(GTCAC) haplotypes. The S836S/3’UTR haplotype presented a greater number of double helices sections and lower levels of minimal free energy when compared to the wild-type haplotype, suggesting that these variants provides the most thermodynamically stable mRNA structure, which may have functional consequences on the rate of mRNA degradation.

Conclusion

The RET S836S polymorphism is in LD with 3’UTR variants. In silico analysis indicate that the 3’UTR variants may affect the secondary structure of RET mRNA, suggesting that these variants might play a role in posttranscriptional control of the RET transcripts.

Exome sequencing reveals a high genetic heterogeneity on familial Hirschsprung disease

Hirschsprung disease (HSCR; OMIM 142623) is a developmental disorder characterized by aganglionosis along variable lengths of the distal gastrointestinal tract, which results in intestinal obstruction. Interactions among known HSCR genes and/or unknown disease susceptibility loci lead to variable severity of phenotype. Neither linkage nor genome-wide association studies have efficiently contributed to completely dissect the genetic pathways underlying this complex genetic disorder. We have performed whole exome sequencing of 16 HSCR patients from 8 unrelated families with SOLID platform. Variants shared by affected relatives were validated by Sanger sequencing. We searched for genes recurrently mutated across families. Only variations in the FAT3 gene were significantly enriched in five families. Within-family analysis identified compound heterozygotes for AHNAK and several genes (N = 23) with heterozygous variants that co-segregated with the phenotype. Network and pathway analyses facilitated the discovery of polygenic inheritance involving FAT3, HSCR known genes and their gene partners. Altogether, our approach has facilitated the detection of more than one damaging variant in biologically plausible genes that could jointly contribute to the phenotype. Our data may contribute to the understanding of the complex interactions that occur during enteric nervous system development and the etiopathology of familial HSCR.

Next-generation-based targeted sequencing as an efficient tool for the study of the genetic background in Hirschsprung patients

BACKGROUND

The development of next-generation sequencing (NGS) technologies has a great impact in the human variation detection given their high-throughput. These techniques are particularly helpful for the evaluation of the genetic background in disorders of complex genetic etiology such as Hirschsprung disease (HSCR). The purpose of this study was the design of a panel of HSCR associated genes as a rapid and efficient tool to perform genetic screening in a series of patients.

METHODS

We have performed NGS-based targeted sequencing (454-GS Junior) using a panel containing 26 associated or candidate genes for HSCR in a group of 11 selected HSCR patients.

RESULTS

The average percentage of covered bases was of 97%, the 91.4% of the targeted bases were covered with depth above 20X and the mean coverage was 422X. In addition, we have found a total of 13 new coding variants and 11 new variants within regulatory regions among our patients. These outcomes allowed us to re-evaluate the genetic component associated to HSCR in these patients.

CONCLUSIONS

Our validated NGS panel constitutes an optimum method for the identification of new variants in our patients. This approach could be used for a fast, reliable and more thorough genetic screening in future series of patients.

KIT Mutation and Loss of 14q May Be Sufficient for the Development of Clinically Symptomatic Very Low-Risk GIST

The aim of this study was to determine the minimal set of genetic alterations required for the development of a very low risk clinically symptomatic gastro-intestinal stromal tumour within the stomach wall. We studied the genome of a very low-risk gastric gastro-intestinal stromal tumour by whole-genome sequencing, comparative genomic hybridisation and methylation profiling. The studied tumour harboured two typical genomic lesions: loss of the long arm of chromosome 14 and an activating mutation in exon 11 of KIT. Besides these genetic lesions, only two point mutations that may affect tumour progression were identified: A frame-shift deletion in RNF146 and a missense mutation in a zinc finger of ZNF407. Whilst the frameshift deletion in RNF146 seemed to be restricted to this particular tumour, a similar yet germline mutation in ZNF407 was found in a panel of 52 gastro-intestinal stromal tumours from different anatomical sites and different categories. Germline polymorphisms in the mitotic checkpoint proteins Aurora kinase A and BUB1 kinase B may have furthered tumour growth. The epigenetic profile of the tumour matches that of other KIT-mutant tumours. We have identified mutations in three genes and loss of the long arm of chromosome 14 as the so far minimal set of genetic abnormalities sufficient for the development of a very low risk clinically symptomatic gastric stromal tumour.

Waardenburg syndrome type 4: report of two new cases caused by SOX10 mutations in Spain

Shah-Waardenburg syndrome or Waardenburg syndrome type 4 (WS4) is a neurocristopathy characterized by the association of deafness, depigmentation and Hirschsprung disease. Three disease-causing genes have been identified so far for WS4: EDNRB, EDN3, and SOX10. SOX10 mutations, found in 45-55% of WS4 patients, are inherited in autosomal dominant way. In addition, mutations in SOX10 are also responsible for an extended syndrome involving peripheral and central neurological phenotypes, referred to as PCWH (peripheral demyelinating neuropathy, central dysmyelinating leucodystrophy, Waardenburg syndrome, Hirschsprung disease). Such mutations are mostly private, and a high intra- and inter-familial variability exists. In this report, we present a patient with WS4 and a second with PCWH due to SOX10 mutations supporting again the genetic and phenotypic heterogeneity of these syndromes. Interestingly, the WS4 family carries an insertion of 19 nucleotides in exon 5 of SOX10, which results in distinct phenotypes along three different generations: hypopigmentation in the maternal grandmother, hearing loss in the mother, and WS4 in the proband. Since mosaicism cannot explain the three different related-WS features observed in this family, we propose as the most plausible explanation the existence of additional molecular events, acting in an additive or multiplicative fashion, in genes or regulatory regions unidentified so far. On the other hand, the PCWH case was due to a de novo deletion in exon 5 of the gene. Efforts should be devoted to unravel the mechanisms underlying the intrafamilial phenotypic variability observed in the families affected, and to identify new genes responsible for the still unsolved WS4 cases.

Pathways systematically associated to Hirschsprung's disease

Despite it has been reported that several loci are involved in Hirschsprung's disease, the molecular basis of the disease remains yet essentially unknown. The study of collective properties of modules of functionally-related genes provides an efficient and sensitive statistical framework that can overcome sample size limitations in the study of rare diseases. Here, we present the extension of a previous study of a Spanish series of HSCR trios to an international cohort of 162 HSCR trios to validate the generality of the underlying functional basis of the Hirschsprung's disease mechanisms previously found. The Pathway-Based Analysis (PBA) confirms a strong association of gene ontology (GO) modules related to signal transduction and its regulation, enteric nervous system (ENS) formation and other processes related to the disease. In addition, network analysis recovers sub-networks significantly associated to the disease, which contain genes related to the same functionalities, thus providing an independent validation of these findings. The functional profiles of association obtained for patients populations from different countries were compared to each other. While gene associations were different at each series, the main functional associations were identical in all the five populations. These observations would also explain the reported low reproducibility of associations of individual disease genes across populations.

Contribution of rare and common variants determine complex diseases-Hirschsprung disease as a model

Finding genes for complex diseases has been the goal of many genetic studies. Most of these studies have been successful by searching for genes and mutations in rare familial cases, by screening candidate genes and by performing genome wide association studies. However, only a small fraction of the total genetic risk for these complex genetic diseases can be explained by the identified mutations and associated genetic loci. In this review we focus on Hirschsprung disease (HSCR) as an example of a complex genetic disorder. We describe the genes identified in this congenital malformation and postulate that both common 'low penetrant' variants in combination with rare or private 'high penetrant' variants determine the risk on HSCR, and likely, on other complex diseases. We also discuss how new technological advances can be used to gain further insights in the genetic background of complex diseases. Finally, we outline a few steps to develop functional assays in order to determine the involvement of these variants in disease development.

Allele-specific expression at the RET locus in blood and gut tissue of individuals carrying risk alleles for Hirschsprung disease

RET common variants are associated with Hirschsprung disease (HSCR; colon aganglionosis), a congenital defect of the enteric nervous system. We analyzed a well-known HSCR-associated RET haplotype that encompasses linked alleles in coding and noncoding/regulatory sequences. This risk haplotype correlates with reduced level of RET expression when compared with the wild-type counterpart. As allele-specific expression (ASE) contributes to phenotypic variability in health and disease, we investigated whether RET ASE could contribute to the overall reduction of RET mRNA detected in carriers. We tested heterozygous neuroblastoma cell lines, ganglionic gut tissues (18 HSCR and 14 non-HSCR individuals) and peripheral blood mononuclear cells (PBMCs; 16 HSCR and 14 non-HSCR individuals). Analysis of the data generated by SNaPshot and Pyrosequencing revealed that the RET risk haplotype is significantly more expressed in gut than in PBMCs (P = 0.0045). No ASE difference was detected between patients and controls, irrespective of the sample type. Comparison of total RET expression levels between gut samples with and without ASE, correlated reduced RET expression with preferential transcription from the RET risk haplotype. Nonrandom RET ASE occurs in ganglionic gut regardless of the disease status. RET ASE should not be excluded as a disease mechanism acting during development.

Mutational spectrum of semaphorin 3A and semaphorin 3D genes in Spanish Hirschsprung patients

Hirschsprung disease (HSCR, OMIM 142623) is a developmental disorder characterized by the absence of ganglion cells along variable lengths of the distal gastrointestinal tract, which results in tonic contraction of the aganglionic colon segment and functional intestinal obstruction. The RET proto-oncogene is the major gene associated to HSCR with differential contributions of its rare and common, coding and noncoding mutations to the multifactorial nature of this pathology. In addition, many other genes have been described to be associated with this pathology, including the semaphorins class III genes SEMA3A (7p12.1) and SEMA3D (7q21.11) through SNP array analyses and by next-generation sequencing technologies. Semaphorins are guidance cues for developing neurons implicated in the axonal projections and in the determination of the migratory pathway for neural-crest derived neural precursors during enteric nervous system development. In addition, it has been described that increased SEMA3A expression may be a risk factor for HSCR through the upregulation of the gene in the aganglionic smooth muscle layer of the colon in HSCR patients. Here we present the results of a comprehensive analysis of SEMA3A and SEMA3D in a series of 200 Spanish HSCR patients by the mutational screening of its coding sequence, which has led to find a number of potentially deleterious variants. RET mutations have been also detected in some of those patients carrying SEMAs variants. We have evaluated the A131T-SEMA3A, S598G-SEMA3A and E198K-SEMA3D mutations using colon tissue sections of these patients by immunohistochemistry. All mutants presented increased protein expression in smooth muscle layer of ganglionic segments. Moreover, A131T-SEMA3A also maintained higher protein levels in the aganglionic muscle layers. These findings strongly suggest that these mutants have a pathogenic effect on the disease. Furthermore, because of their coexistence with RET mutations, our data substantiate the additive genetic model proposed for this rare disorder and further support the association of SEMAs genes with HSCR.

Four new loci associations discovered by pathway-based and network analyses of the genome-wide variability profile of Hirschsprung's disease

Finding gene associations in rare diseases is frequently hampered by the reduced numbers of patients accessible. Conventional gene-based association tests rely on the availability of large cohorts, which constitutes a serious limitation for its application in this scenario. To overcome this problem we have used here a combined strategy in which a pathway-based analysis (PBA) has been initially conducted to prioritize candidate genes in a Spanish cohort of 53 trios of short-segment Hirschsprung’s disease. Candidate genes have been further validated in an independent population of 106 trios. The study revealed a strong association of 11 gene ontology (GO) modules related to signal transduction and its regulation, enteric nervous system (ENS) formation and other HSCR-related processes. Among the preselected candidates, a total of 4 loci, RASGEF1A, IQGAP2, DLC1 and CHRNA7, related to signal transduction and migration processes, were found to be significantly associated to HSCR. Network analysis also confirms their involvement in the network of already known disease genes. This approach, based on the study of functionally-related gene sets, requires of lower sample sizes and opens new opportunities for the study of rare diseases.

RET 3'UTR polymorphisms and its protective role in Hirschsprung disease in southeastern Chinese

BACKGROUND

Hirschsprung disease (HSCR) is a complex congenital disorder characterized by intestinal obstructions owing to the absence of the intestinal ganglion cells of the nerve plexuses in variable lengths of the digestive tract. Several RET polymorphisms and haplotypes have been described as underrepresented in HSCR patients with respect to controls. We thus sought to investigate whether polymorphisms in RET 3'UTR are associated with isolated HSCR in the Chinese population.

METHODS

Polymerase chain reaction amplification and direct sequencing were used to screen polymorphisms in RET 3'UTR in patients with sporadic HSCR and ethnically matched controls in Han Chinese populations. Association tests of RET 3'UTR variants and haplotypes with HSCR were performed.

RESULTS

We examined a total of 107 Chinese sporadic HSCR patients and 89 ethnically matched controls by sequencing the 3'UTR of the RET gene. Five single nucleotide polymorphisms (SNPs) and 2 monomorphic SNPs were identified. The genotype distributions and the allele frequencies of the 5 SNPs were significantly different between HSCR cases and controls and occurred more frequently in the control population. Haplotype analysis has shown a higher frequency of haplotypes comprising variant alleles in controls as compared with cases.

CONCLUSIONS

The significant deviations of the genotype distributions and the allele frequencies of these SNPs in the HSCR population compared with the control population demonstrate that these SNPs have a strong negative association with HSCR and could act as protective alleles.

Advances in molecular genetics of Hirschsprung's disease

Hirschsprung's disease (HSCR) is a developmental disorder of the enteric nervous system, which occurs due to the failure of neural crest cells to fully colonize the gut during embryonic development. It is characterized by the absence of the enteric ganglia in a variable length of the intestine. Substantial progress has been made in understanding the genetic basis of HSCR with the help of advanced genetic analysis techniques and animal models. More than 11 genes have been found to be involved in the pathogenesis of HSCR. The RET gene is the most important susceptibility gene involved in HSCR with both coding and non- coding sequence mutations. Due to phenotypic diversity and genetic complexity observed in HSCR, mutational analysis has limited practical value in genetic counseling and clinical practice. In this review, we discuss the progress that has been made in understanding the molecular genetics of HSCR and summarize the currently identified genes as well as interactions between pathways and gene-modifying loci in HSCR.

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.

Molecular basis of medullary thyroid carcinoma: the role of RET polymorphisms

Medullary thyroid carcinoma is a rare malignant tumor originating in parafollicular C cells. It accounts for 5 to 8% of all thyroid cancers. MTC develops in either sporadic (75%) or hereditary form (25%). Genetic and molecular studies have demonstrated the involvement of the RET proto-oncogene in hereditary MTC and, less often, in its sporadic form. Although a strong genotype-phenotype correlation has been described, wide clinical heterogeneity is observed among families with the same RET mutation or even in carriers of the same kindred. In recent years, several single nucleotide polymorphisms of the RET gene have been described in the general population as well as in patients with MTC. Some studies have reported associations between the presence of polymorphisms and development or progression of MTC. Nonetheless, other studies failed to demonstrate any effect of the RET variants. Differences in the genetic background of distinct populations or methodological approaches have been suggested as potential reasons for the conflicting results. Here, we review current knowledge concerning the molecular pathogenesis of sporadic and hereditary MTC. In particular, we analyze the role of RET polymorphisms in the clinical presentation and prognosis of MTC based on the current literature.

Risk profiles and penetrance estimations in multiple endocrine neoplasia type 2A caused by germline RET mutations located in exon 10

Multiple endocrine neoplasia type 2 is characterized by germline mutations in RET. For exon 10, comprehensive molecular and corresponding phenotypic data are scarce. The International RET Exon 10 Consortium, comprising 27 centers from 15 countries, analyzed patients with RET exon 10 mutations for clinical-risk profiles. Presentation, age-dependent penetrance, and stage at presentation of medullary thyroid carcinoma (MTC), pheochromocytoma, and hyperparathyroidism were studied. A total of 340 subjects from 103 families, age 4-86, were registered. There were 21 distinct single nucleotide germline mutations located in codons 609 (45 subjects), 611 (50), 618 (94), and 620 (151). MTC was present in 263 registrants, pheochromocytoma in 54, and hyperparathyroidism in 8 subjects. Of the patients with MTC, 53% were detected when asymptomatic, and among those with pheochromocytoma, 54%. Penetrance for MTC was 4% by age 10, 25% by 25, and 80% by 50. Codon-associated penetrance by age 50 ranged from 60% (codon 611) to 86% (620). More advanced stage and increasing risk of metastases correlated with mutation in codon position (609→620) near the juxtamembrane domain. Our data provide rigorous bases for timing of premorbid diagnosis and personalized treatment/prophylactic procedure decisions depending on specific RET exon 10 codons affected.

Comprehensive analysis of RET common and rare variants in a series of Spanish Hirschsprung patients confirms a synergistic effect of both kinds of events

Background

RET is the major gene associated to Hirschsprung disease (HSCR) with differential contributions of its rare and common, coding and noncoding mutations to the multifactorial nature of this pathology. In the present study, we have performed a comprehensive study of our HSCR series evaluating the involvement of both RET rare variants (RVs) and common variants (CVs) in the context of the disease.

Methods

RET mutational screening was performed by dHPLC and direct sequencing for the identification of RVs. In addition Taqman technology was applied for the genotyping of 3 RET CVs previously associated to HSCR, including a variant lying in an enhancer domain within RET intron 1 (rs2435357). Statistical analyses were performed using the SPSS v.17.0 to analyze the distribution of the variants.

Results

Our results confirm the strongest association to HSCR for the "enhancer" variant, and demonstrate a significantly higher impact of it in male versus female patients. Integration of the RET RVs and CVs analysis showed that in 91.66% of cases with both kinds of mutational events, the enhancer allele is in trans with the allele bearing the RET RV.

Conclusions

A gender effect exists on both the transmission and distribution of rare coding and common HSCR causing mutations. In addition, these RET CVs and RVs seem to act in a synergistic way leading to HSCR phenotype.

MYH biallelic mutation can inactivate the two genetic pathways of colorectal cancer by APC or MLH1 transversions

MYH associated polyposis is a hereditary syndrome responsible for early colorectal cancer with a distinct genetic pathway from the Familial Adenomatous Polyposis or the Hereditary Non Polyposis Colorectal Cancer syndrome. We have studied a family with three members bearing a biallelic mutation in MYH at c.1185_1186dup. One patient who developed colon cancer had loss of expression of MLH1 on tumoral tissue and microsatellite instability (MSI) phenotype. Analysis of MLH1 based on his blood sample revealed no germline mutation or large genomic deletion. No methylation of the promoter was identified in tumoral DNA. No transversion mutations were identified in APC or KRAS in tumor DNA of this patient. Loss of expression of MLH1 was due to a transversion in intron 7 at position +5 (c.588 + 5G > T) leading to a complete deletion of exon 7 at the RNA level. This observation demonstrates that MLH1 can be a target of MYH transversions leading to MSI phenotype.

Variants in RET associated with Hirschsprung's disease affect binding of transcription factors and gene expression

BACKGROUND & AIMS

Two noncoding variations in RET-the T allele of the single nucleotide polymorphism (SNP) rs2435357 (Enh1:C>T) and the A allele of the SNP rs2506004 (Enh2:C>A)-are associated with Hirschsprung's disease. These SNPs are in strong linkage disequilibrium and located in an enhancer element in intron 1 of the RET gene. The T allele of the Enh1 variant results in reduced expression of RET, compared with the C allele, because the T allele disrupts binding to the transcription factor SOX10. We studied whether the A allele of Enh2 (Enh2-A) also affects RET gene expression.

METHODS

We evaluated the function of Enh1 and Enh2 using luciferase reporter assays with constructs that contained each allele, separately or in combination. We performed in silico analysis to identify transcription activators or repressors that bind to Enh2-C.

RESULTS

The Enh1-T and the Enh2-A alleles reduced expression of the luciferase reporter gene. In silico analysis identified the sequence of Enh2-C and its surrounding sequence (ACGTG) as a potential binding site for the NXF-ARNT2 and SIM2-ARNT2 transcription factor heterodimers. The affinity of NXF-ARNT2 for Enh2-C was confirmed by electrophoresis mobility shift and supershift assays. Transfection of neuroblastoma cell lines with NXF-ARNT2 or SIM2-ARNT2 increased and decreased expression of RET, respectively.

CONCLUSIONS

More than one SNP on an associated haplotype can influence gene expression and ultimately disease phenotype. Binding of the transcription factors NXF, ARNT2, and SIM2 to RET depend on the RET polymorphism of Enh2 and affect RET expression and the development of Hirschsprung's disease.

Association studies in thyroid cancer susceptibility: are we on the right track?

It is widely accepted that thyroid cancer is strongly determined by the individual genetic background. In this regard, it is expected that sporadic thyroid cancer is the result of multiple low- to moderate-penetrance genes interacting with each other and with the environment, thus modulating individual susceptibility. In the last years, an important number of association studies on thyroid cancer have been published, trying to determine this genetic contribution. The aim of this review is to provide a comprehensive and critical evaluation of the associations reported so far in thyroid cancer susceptibility in case-control studies performed in both non-medullary (papillary and follicular) and medullary thyroid cancers, including their potential strengths and pitfalls. We summarize the genetic variants reported to date, and stress the importance of validating the results in independent series and assessing the functional role of the associated loci.

Novel association of severe neonatal encephalopathy and Hirschsprung disease in a male with a duplication at the Xq28 region

Background

Hirschsprung disease (HSCR) is a neurocristopathy characterized by the absence of parasympathetic intrinsic ganglion cells in the submucosal and myenteric plexuses along a variable portion of the intestinal tract. In approximately 18% of the cases HSCR also presents with multiple congenital anomalies including recognized syndromes.

Methods

A combination of MLPA and microarray data analysis have been undertaken to refine a duplication at the Xq28 region.

Results

In this study we present a new clinical association of severe neonatal encephalopathy (Lubs syndrome) and HSCR, in a male patient carrying a duplication at the Xq28 region which encompasses the MECP2 and L1CAM genes.

Conclusions

While the encephalopathy has been traditionally attributed to the MECP2 gene duplication in patients with Lubs syndrome, here we propose that the enteric phenotype in our patient might be due to the dosage variation of the L1CAM protein, together with additional molecular events not identified yet. This would be in agreement with the hypothesis previously forwarded that mutations in L1CAM may be involved in HSCR development in association with a predisposing genetic background.

Hirschsprung's disease

Hirschsprung's disease (HSCR) is characterized by absence of the enteric nervous system in a variable portion of the distal gut. Affected infants usually present in the days after birth with bowel obstruction. Despite surgical advances, long-term outcomes remain variable. In the last 2 decades, great advances have been made in understanding the genes and molecular biological mechanisms that underlie the disease. In addition, our understanding of normal enteric nervous system development and how motility develops in the developing fetus and infant has also increased. This review aims to draw these strands together to explain the developmental and biological basis of HSCR, and how this knowledge may be used in the future to aid children with HSCR.

Novel MLPA procedure using self-designed probes allows comprehensive analysis for CNVs of the genes involved in Hirschsprung disease

BACKGROUND

Hirschsprung disease is characterized by the absence of intramural ganglion cells in the enteric plexuses, due to a fail during enteric nervous system formation. Hirschsprung has a complex genetic aetiology and mutations in several genes have been related to the disease. There is a clear predominance of missense/nonsense mutations in these genes whereas copy number variations (CNVs) have been seldom described, probably due to the limitations of conventional techniques usually employed for mutational analysis. In this study, we have looked for CNVs in some of the genes related to Hirschsprung (EDNRB, GFRA1, NRTN and PHOX2B) using the Multiple Ligation-dependent Probe Amplification (MLPA) approach.

METHODS

CNVs screening was performed in 208 HSCR patients using a self-designed set of MLPA probes, covering the coding region of those genes.

RESULTS

A deletion comprising the first 4 exons in GFRA1 gene was detected in 2 sporadic HSCR patients and in silico approaches have shown that the critical translation initiation signal in the mutant gene was abolished. In this study, we have been able to validate the reliability of this technique for CNVs screening in HSCR.

CONCLUSIONS

The implemented MLPA based technique presented here allows CNV analysis of genes involved in HSCR that have not been not previously evaluated. Our results indicate that CNVs could be implicated in the pathogenesis of HSCR, although they seem to be an uncommon molecular cause of HSCR.

New roles of EDNRB and EDN3 in the pathogenesis of Hirschsprung disease

PURPOSE

Hirschsprung disease is characterized by the absence of intramural ganglion cells in the myenteric and submucosal plexuses within distal intestine, because of a fail in the enteric nervous system formations process. Endothelin-3-endothelin receptor B signaling pathway is known to play an essential role in this process. The aim of this study was to evaluate the implication of the EDN3 and EDNRB genes in a series of patients with Hirschsprung disease from Spain and determinate their mutational spectrum.

METHODS

We performed the mutational screening of both genes in 196 patients with Hirschsprung disease using denaturing high-performance liquid chromatography technology. A case-control study using TaqMan Technology was also carried out to evaluate some common polymorphisms and haplotypes as susceptibility factors for Hirschsprung disease.

RESULTS

Besides several novel mutations in both genes, we found a truncating mutation in an alternative isoform of EDNRB. Interestingly, we obtained an overrepresentation of a specific EDN3 haplotype in cases versus controls.

CONCLUSIONS

Our results suggest that the isoform EDNRB Delta 3 might be playing an essential role in the formation of enteric nervous system. In addition, based on the haplotype distribution, EDN3 might be considered as a common susceptibility gene for sporadic Hirschsprung disease in a low-penetrance fashion.

Practical pathology and genetics of Hirschsprung's disease

Diagnosis and management of Hirschsprung's disease (HSCR) requires understanding of the malformation's anatomic features and multigenic nature. Rectal biopsies, intraoperative frozen sections, and resection specimens provide invaluable information. Extraction of these data requires thoughtful biopsy technique, adequate histologic sections, histochemistry, and collaboration of surgeon and pathologist. Critical consideration of transition zone anatomy and published studies of "transition zone pull through" indicate that more research is needed to determine how much ganglionic bowel should be resected from HSCR patients. Many HSCR-susceptibility genes have been identified, but mutational analysis has limited practical value unless family history or clinical findings suggest syndromic HSCR.

Genetic basis of Hirschsprung's disease

Hirschsprung's disease (HSCR) is a developmental disorder characterized by the absence of ganglion cells in the lower digestive tract. Aganglionosis is attributed to a disorder of the enteric nervous system (ENS) whereby ganglion cells fail to innervate the lower gastrointestinal tract during embryonic development. HSCR is a complex disease that results from the interaction of several genes and manifests with low, sex-dependent penetrance and variability in the length of the aganglionic segment. The genetic complexity observed in HSCR can be conceptually understood in light of the molecular and cellular events that take place during the ENS development. DNA alterations in any of the genes involved in the ENS development may interfere with the colonization process, and represent a primary etiology for HSCR. This review will focus on the genes known to be involved in HSCR pathology, how they interact, and on how technology advances are being employed to uncover the pathological processes underlying this disease.

Evaluation of RET polymorphisms in a six-generation family with G533C RET mutation: specific RET variants may modulate age at onset and clinical presentation

CONTEXT

We previously described a six-generation family with G533C RET mutation and medullary thyroid carcinoma, in the largest family reported do date. Of particular interest, phenotype variability regarding the age of onset and clinical presentation of the disease, was observed.

OBJECTIVE

We evaluate whether single SNPs within RET oncogene or haplotype comprising the RET variants (defined by Haploview) could predispose to early development of MTC in this family and influence the clinical manifestation.

DESIGN

Eight SNPs were selected based on their previous association with the clinical course of hereditary or sporadic MTC, in particular promoting an early onset of disease. The variants were initially tested in 77 G533C-carriers and 100 controls using either PCR-direct sequencing or PCR-RFLP. Association between a SNP or haplotype and age at diagnosis or presence of lymph node metastasis was tested in 34 G533C-carries with MTC. Different bioinformatic tools were used to evaluate the potential effects on RNA splicing.

RESULTS

An association was found between IVS1-126G > T and age at diagnosis. The variant [IVS8 +82A > G; 85-86 insC] was associated with the presence of lymph node metastases at diagnosis. In silico analysis suggested that this variant may induce abnormal splicing. This in silico analysis predicted that the [IVS8 +82A > G; 85-86 insC] could alter the splicing by disrupting and/or creating exonic splicing enhancer motifs.

CONCLUSIONS

We here identified two RET variants that were associated with phenotype variability in G533C-carriers, which highlights the fact that the modifier effect of a variant might depend on the type of mutation.

Medullary thyroid cancer: management guidelines of the American Thyroid Association

BACKGROUND

Inherited and sporadic medullary thyroid cancer (MTC) is an uncommon and challenging malignancy. The American Thyroid association (ATA) chose to create specific MTC Clinical Guidelines that would bring together and update the diverse MTC literature and combine it with evidence-based medicine and the knowledge and experience of a panel of expert clinicians.

METHODS

Relevant articles were identified using a systematic PubMed search and supplemented with additional published materials. Evidence-based recommendations were created and then categorized using criteria adapted from the United States Preventive Services Task Force, Agency for Healthcare Research and Quality.

RESULTS

Clinical topics addressed in this scholarly dialog included: initial diagnosis and therapy of preclinical disease (including RET oncogene testing and the timing of prophylactic thyroidectomy), initial diagnosis and therapy of clinically apparent disease (including preoperative testing and imaging, extent of surgery, and handling of devascularized parathyroid glands), initial evaluation and treatment of postoperative patients (including the role of completion thyroidectomy), management of persistent or recurrent MTC (including the role of tumor marker doubling times, and treatment of patients with distant metastases and hormonally active metastases), long-term follow-up and management (including the frequency of follow-up and imaging), and directions for future research.

CONCLUSIONS

One hundred twenty-two evidence-based recommendations were created to assist in the clinical care of MTC patients and to share what we believe is current, rational, and optimal medical practice.

The influence of gender, age, and RET polymorphisms on C-cell hyperplasia and medullary thyroid carcinoma

BACKGROUND

RET germline mutations predispose to the development of hereditary medullary thyroid carcinoma (hMTC). Several single nucleotide polymorphisms (SNPs) are described associated with sporadic MTC (sMTC). However, the findings regarding their influence on the clinical course and biological behavior of this disorder are discordant. To clarify the contradictory findings, we studied the association of certain SNPs considering age, gender, and histopathology in a large Austrian cohort with C-cell hyperplasia (CCH) and MTC.

METHODS

Genotyping of SNPs located in RET codons 691, 769, 836, and 904 from 199 patients with MTC and CCH (basal calcitonin > 10 pg/mL, pentagastrin stimulated > 100 pg/mL) was performed, and the results were analyzed considering gender, age at diagnosis, and histopathology.

RESULTS

No significant difference of SNP frequencies was found in the study patients versus normal controls. In sMTC and sporadic CCH (sCCH) no significant association of SNP frequency with the age at diagnosis was found. In patients with sporadic C-cell disease (sCCH and sMTC), 3.7 times more males than females suffered synchronously from papillary or follicular thyroid cancer (20/97 [20.6%] males; 3/54 [5.6%] females; p = 0.02). sCCH was revealed more frequently in males (89/97, 91.7%) than in females (27/54, 50%; p = 10(-8)). In contrast to males, the ratio of CCH to total C-cell disease was significantly higher in females with hereditary (26/32, 81%) compared to those with sporadic disease (27/54, 50%; p = 0.006).

CONCLUSIONS

In this study RET SNPs had no clinical impact on the development of sporadic C-cell disease when the age of diagnosis or gender is considered. C-cell disease seems to predispose males to the development of papillary and follicular thyroid cancer. In addition, at least in females with CCH RET germline mutation, screening is recommended even if the family history is negative for MTC.

Polymorphisms in the genes encoding the 4 RET ligands, GDNF, NTN, ARTN, PSPN, and susceptibility to Hirschsprung disease

PURPOSE

Hirschsprung disease (HSCR) is a developmental disorder caused by a failure of neural crest cells to migrate, proliferate, and/or differentiate during the enteric nervous system development. It presents a multifactorial, nonmendelian pattern of inheritance, with several genes playing some role in its pathogenesis. Its major susceptibility gene is the RET protooncogene, which encodes a receptor tyrosine kinase activating several key signaling pathways in the enteric nervous system development. Given the pivotal role of RET in HSCR, the genes encoding their ligands (GDNF, NRTN, ARTN, and PSPN) are also good candidates for the disease.

METHODS

We have performed a case-control study using Taqman technology to evaluate 10 polymorphisms within these genes, as well as haplotypes comprising them, as susceptibility factors for HSCR.

RESULTS

No differences were found in the allelic frequencies of the variants or in the haplotype distribution between patients and controls. In addition, no particular association was detected of the variants/haplotypes to any demographic/clinical parameters within the group of patients.

CONCLUSION

These data would be consistent with the lack of association between these polymorphisms and HSCR, although they do not permit to completely discard a possible role of other variants within these genes in the disease. Moreover, because the gene-by-gene approach does not take into account the polygenic nature of HSCR disease, it would be interesting to investigate sets of variants in many other different susceptibility loci described for HSCR, which may permit to consider possible interactions among susceptibility genes.

RET polymorphisms and the risk of Hirschsprung's disease in a Chinese population

Hirschsprung's disease (HSCR) is a congenital disorder characterized by intestinal obstructions due to the absence of enteric ganglia along variable lengths of the intestinal tract. RET coding mutations have been found in approximately 50% of familial cases, but they only explain a minority of sporadic cases. Here, we report our investigation of a possible role of RET non-coding mutations in sporadic HSCR patients. The haplotypes of seven single nucleotide polymorphisms (SNPs), all located in a region 4 kb upstream of the gene through to 23 kb of intron 1, and one SNP in exon 2 were constructed in 125 Han Chinese patients with sporadic HSCR and in 148 Han Chinese controls. Our results indicated that eight SNPs were significantly associated with HSCR (P < 0.0001). The C allele of rs2505535 would appear to represent a protecting allele for the Chinese population. One single haplotype composed of these eight markers was present in 59.6% of patients, versus 18.1% of controls. Based on our results, we conclude that non-coding mutations in RET have important roles in the development of HSCR. The unknown functional disease variant(s), with a dosage-dependent effect in HSCR, is likely to be located in the 5'-region of the RET gene.

Familial medullary carcinoma prevention, risk evaluation, and RET in children of families with MEN2

The ability to predict the risk of MEN2 and medullary thyroid carcinoma (MTC) by genetic RET proto-oncogene analysis has provided an essential tool in identifying patients in whom thyroid cancer can be prevented by prophylactic thyroidectomy but emphasizes the need for clear policy guidelines. Children of families with RET cysteine mutations (exons 10, 11, 13, and 16) may develop early metastatic tumours and require prophylactic thyroidectomy. The 918 mutation associated with MEN2B is associated with early aggressive behaviour and distant metastatic spread. This has led to active screening of affected families underlining the need for specific intervention strategies.

AIM

To evaluate the risk to children of families with MEN2 and to assess the risk and determine the treatment.

METHODS

Twenty-five patients from 10 families with MEN2 phenotypes were screened for RET mutations. Polymerase chain reaction amplification was performed on all 21 exons of the RET proto-oncogene, followed by heteroduplex single-strand conformation polymorphism (HEX-SSCP) analysis. Polymerase chain reaction products demonstrating variation in the HEX-SSCP gels were subjected to automated DNA sequencing analysis.

RESULTS

Eleven significant RET mutations were detected in affected families. Eight index cases received initial thyroidectomy for established MTC (plus 2 advised). In the family members screened, 3 prophylactic thyroidectomies (2 with early MTC) were performed and a further 2 recommended. An exon 10 C620W missense mutation (the "Janus" gene) was detected in a patient with Hirschsprung's disease plus 1 family member.

CONCLUSION

RET analysis of MEN has revolutionized the management of children of families with MEN2 and allowed surgical prediction and prophylaxis to take place. The presence of an exon 10 C620W mutation in association with Hirschsprung's disease was difficult to assess. We suggest possible guidelines for management of families with MTC and the role of genetic testing in their evaluation.

A complex additive model of inheritance for Hirschsprung disease is supported by both RET mutations and predisposing RET haplotypes

PURPOSE

The RET proto-oncogene is considered to be the major susceptibility gene involved in Hirschsprung disease. Traditional RET germline mutations account for a small subset of Hirschsprung disease patients, but several studies have shown that there is a specific haplotype of RET associated with the sporadic forms of Hirschsprung disease. We have investigated for RET germline mutations and analyzed the RET haplotypic distribution in carriers versus noncarriers of RET germline mutations.

METHODS

We have screened the coding region of RET in 106 Spanish Hirschsprung disease patients using dHPLC technology. Statistical comparisons of the distribution of RET haplotypes between sporadic patients with and without a RET germline mutation were performed.

RESULTS

Nine novel germline mutations and one previously described were identified. A significant over-transmission of the "Hirschsprung disease haplotype" was detected when comparing transmitted versus nontransmitted alleles in the group of Hirschsprung disease triads without mutation. However, no distortion of the transmission of alleles was found in the group of mutated families.

CONCLUSIONS

These results would be concordant with a complex additive model of inheritance. The whole findings seem to suggest that low-penetrance mutations would be necessary but not sufficient and the additional presence of the "Hirschsprung disease haplotype" could contribute to the manifestation of the disease.

Haplotypes of the human RET proto-oncogene associated with Hirschsprung disease in the Italian population derive from a single ancestral combination of alleles

The RET proto-oncogene is the major gene involved in the complex genetics of Hirschsprung disease (HSCR), or aganglionic megacolon, showing causative loss-of-function mutations in 15-30% of the sporadic cases. Several RET polymorphisms and haplotypes have been described in association with the disease, suggesting a role for this gene in HSCR predisposition, also in the absence of mutations in the coding region. Finally, the presence of a functional variant in intron 1 has repeatedly been proposed to explain such findings. Here we report a case-control study conducted on 97 Italian HSCR sporadic patients and 85 population matched controls, using 13 RET polymorphisms distributed throughout the gene, from the basal promoter to the 3'UTR. Linkage disequilibrium and haplotype analyses have shown increased recombination between the 5' and 3' portions of the gene and an over-representation, in the cases studied, of two haplotypes sharing a common allelic combination that extends from the promoter up to intron 5. We propose that these two disease-associated haplotypes derive from a single founding locus, extending up to intron 19 and successively rearranged in correspondence with a high recombination rate region located between the proximal and distal portions of the gene. Our results suggests the possibility that a common HSCR predisposing variant, in linkage disequilibrium with such haplotypes, is located further downstream than the previously suggested interval encompassing intron 1.

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.

RET as a diagnostic and therapeutic target in sporadic and hereditary endocrine tumors

The RET gene encodes a receptor tyrosine kinase that is expressed in neural crest-derived cell lineages. The RET receptor plays a crucial role in regulating cell proliferation, migration, differentiation, and survival through embryogenesis. Activating mutations in RET lead to the development of several inherited and noninherited diseases. Germline point mutations are found in the cancer syndromes multiple endocrine neoplasia (MEN) type 2, including MEN 2A and 2B, and familial medullary thyroid carcinoma. These syndromes are autosomal dominantly inherited. The identification of mutations associated with these syndromes has led to genetic testing to identify patients at risk for MEN 2 and familial medullary thyroid carcinoma and subsequent implementation of prophylactic thyroidectomy in mutation carriers. In addition, more than 10 somatic rearrangements of RET have been identified from papillary thyroid carcinomas. These mutations, as those found in MEN 2, induce oncogenic activation of the RET tyrosine kinase domain via different mechanisms, making RET an excellent candidate for the design of molecular targeted therapy. Recently, various kinds of therapeutic approaches, such as tyrosine kinase inhibition, gene therapy with dominant negative RET mutants, monoclonal antibodies against oncogene products, and nuclease-resistant aptamers that recognize and inhibit RET have been developed. The use of these strategies in preclinical models has provided evidence that RET is indeed a potential target for selective cancer therapy. However, a clinically useful therapeutic option for treating patients with RET-associated cancer is still not available.

Mutations in the DNA mismatch repair gene MLH1 associated with early-onset colon cancer

Hereditary nonpolyposis colon cancer (HNPCC) is an autosomal dominant disorder characterized by the predisposition to develop a number of cancers, especially colorectal cancer (CRC). We present a HNPCC family with CRC at age 12 years. Our observations suggest that the germline mutation of the both copies of the MLH1 gene may play a role in the early onset of CRC.

Analysis of RET polymorphisms and haplotypes in the context of sporadic medullary thyroid carcinoma

CONTEXT

Little is known about the etiology of sporadic medullary thyroid carcinoma (sMTC). While germline gain-of-function mutations in the RET proto-oncogene cause hereditary MTC, the molecular mechanisms leading to the sporadic forms remain obscure. Our group had evidence about the existence of a low-penetrance susceptibility locus for sMTC in linkage disequilibrium with RET variants S836S/IVS1-126G>T, and probably in 5' with respect to both variants. In this study we sought to identify such locus. On the other hand, because an overrepresentation of G691S/S904S variants in patients with sMTC had been previously reported, we sought to determine if such association was present in our series.

DESIGN

We performed a case-control study analysing a wide spectrum of RET variants in the 5' region of the gene, as well as the variants G691S/S904S. Haplotype distribution were also analyzed. A total of 58 patients with sMTC were included in the study. In addition, 100 unselected, unrelated race-, age-, and gender-matched normal controls were also evaluated.

MAIN OUTCOME

Although the overrepresentation of IVS1-126G>T remains present in our current sMTC series, thus supporting our previous hypothesis, no differences were obtained among cases and controls in the distribution of the variants tested upstream this position. On the other hand, the frequency and distribution of G691S/S904S variants were similar in both groups of study, leading to exclude their role in sMTC in our series.

CONCLUSIONS

These findings would suggest that the major genetic events contributing to the appearance of sMTC may reside in several different RET loci. In this way, we could hypothesize about the existence of at least two sMTC loci, linked to S836S-IVS1-126G>T, or to G691S-S904S, respectively.

A common haplotype at the 5' end of the RET proto-oncogene, overrepresented in Hirschsprung patients, is associated with reduced gene expression

Hirschsprung disease (HSCR) is a complex genetic defect of intestinal innervation mainly ascribed to loss of function mutations of the RET gene. Although RETcoding mutations account for only 15% of HSCR sporadic cases, several linkage and association studies still indicate RET as a major HSCR gene, suggesting the existence of noncoding RET variants or common polymorphisms which can act in HSCR pathogenesis. We previously described a predisposing RET haplotype (A-C-A) composed of alleles at three SNPs (-1 bp and -5 bp from the RET transcription start site, NT_033985.6:g.975824G>A and NT_033985.6:g.975820C>A, respectively, and silent polymorphism c.135G>A), which was present in 62% of chromosomes from HSCR patients but only in 22% of control chromosomes. Here we address the question of how this 5' ACA haplotype may functionally act as a predisposing factor in HSCR pathogenesis by performing functional analysis of the same three SNPs. We demonstrate that neither the two promoter variants nor the exon 2 SNP interfere with reporter gene transcription or RET mRNA splicing, respectively. However, real-time RT-PCR, performed in RNA obtained from lymphoblasts of selected individuals, has shown that homozygosity for the whole ACA haplotype is associated with reduced RET gene expression. We propose that a yet unidentified variant in linkage disequilibrium with the ACA haplotype, rather than the single characterizing SNPs, acts as a HSCR susceptibility allele by affecting the normal amount of RET receptor on the cell surface.

Molecular mechanisms of RET-induced Hirschsprung pathogenesis

The RET proto-oncogene is the major gene involved in the pathogenesis of Hirschsprung (HSCR), a complex genetic disease characterized by lack of ganglia along variable lengths of the gut. Here we present a survey of the different molecular mechanisms through which RET mutations lead to the disease development. Among these, loss of function, gain of function, apoptosis, aberrant splicing and decreased gene expression are exemplified and considered with respect to their pathogenetic impact. In particular, RET transcription regulation represents a new insight into the outline of HSCR susceptibility, and having reached important progress in the last few years, deserves to be reviewed. Notably, gene expression impairment seems to be at the basis of the association of HSCR disease with several RET polymorphisms, allowing us to define a predisposing haplotype spanning from the promoter to exon 2. Putative functional variants, in the promoter and in intron 1, and proposed as low penetrant predisposing alleles, are presented and discussed. Finally, based on the RET mutation effects thus summarized, we attempt to derive conclusions which may be useful for HSCR risk prediction and genetic counselling.