Retinal Dystrophy Associated With RLBP1 Retinitis Pigmentosa: A Five-Year Prospective Natural History Study.

Purpose: To assess the progression in functional and structural measures over a five-year period in patients with retinal dystrophy caused by RLBP1 gene mutation. Methods: This prospective, noninterventional study included patients with biallelic RLBP1 mutations from two clinical sites in Sweden and Canada. Key assessments included ocular examinations, visual functional measures (best-corrected visual acuity [BCVA], contrast sensitivity [CS], dark-adaptation [DA] kinetics up to six hours for two wavelengths [450 and 632 nm], Humphrey visual fields [HVF], full-field flicker electroretinograms), and structural ocular assessments. Results: Of the 45 patients enrolled, 38 completed the full five years of follow-up. At baseline, patients had BCVA ranging from -0.2 to 1.3 logMAR, poor CS, HVF defects, and prominent thinning in central foveal thickness. All patients had extremely prolonged DA rod recovery of approximately six hours at both wavelengths. The test-retest repeatability was high across all anatomic and functional endpoints. Cross-sectionally, poorer VA was associated with older age (right eye, correlation coefficient [CC]: 0.606; left eye, CC: -0.578; P < 0.001) and HVF MD values decreased with age (right eye, CC: -0.672, left eye, CC: -0.654; P < 0.001). However, no major changes in functional or structural measures were noted longitudinally over the five-year period. Conclusions: This natural history study, which is the first study to monitor patients with RLBP1 RD for five years, showed that severely delayed DA sensitivity recovery, a characteristic feature of this disease, was observed in all patients across all age groups (17-69 years), making it a potentially suitable efficacy assessment for gene therapy treatment in this patient population.

A novel pathogenic missense ADAMTS17 variant that impairs secretion causes Weill-Marchesani Syndrome with variably dysmorphic hand features.

Weill-Marchesani syndrome (WMS) is a rare disorder displaying short stature, brachydactyly and joint stiffness, and ocular features including microspherophakia and ectopia lentis. Brachydactyly and joint stiffness appear less commonly in patients with WMS4 caused by pathogenic ADAMTS17 variants. Here, we investigated a large family with WMS from Newfoundland, Canada. These patients displayed core WMS features, but with proportionate hands that were clinically equivocal for brachydactyly. Whole exome sequencing and autozygosity mapping unveiled a novel pathogenic missense ADAMTS17 variant (c.3068 G > A, p.C1023Y). Sanger sequencing demonstrated variant co-segregation with WMS, and absence in 150 population matched controls. Given ADAMTS17 involvement, we performed deep phenotyping of the patients' hands. Anthropometrics applied to hand roentgenograms showed that metacarpophalangeal measurements of affected patients were smaller than expected for their age and sex, and when compared to their unaffected sibling. Furthermore, we found a possible sub-clinical phenotype involving markedly shortened metacarpophalangeal bones with intrafamilial variability. Transfection of the variant ADAMTS17 into HEK293T cells revealed significantly reduced secretion into the extracellular medium compared to wild-type. This work expands understanding of the molecular pathogenesis of ADAMTS17, clarifies the variable hand phenotype, and underscores a role for anthropometrics in characterizing sub-clinical brachydactyly in these patients.

The genetic architecture of Stargardt macular dystrophy (STGD1): a longitudinal 40-year study in a genetic isolate.

Stargardt disease (STGD1) is a form of inherited retinal dystrophy attributed to variants affecting function of the large ABCA4 gene and is arguably the most complex monogenic disease. Therapeutic trials in patients depend on identifying causal ABCA4 variants in trans, which is complicated by extreme allelic and clinical heterogeneity. We report the genetic architecture of STGD1 in the young genetically isolated population of Newfoundland, Canada. Population-based clinical recruitment over several decades yielded 29 STGD1 and STGD1-like families (15 multiplex, 14 singleton). Family interviews and public archival records reveal the vast majority of pedigree founders to be of English extraction. Full gene sequencing and haplotype analysis yielded a high solve rate (38/41 cases; 92.7%) for STGD1 and identified 16 causative STGD1 alleles, including a novel deletion (NM_000350.3: ABCA4 c.67-1delG). Several STGD1 alleles of European origin (including NM_000350.3: ABCA4 c.5714 + 5G>A and NM_000350.3: ABCA4 c.5461-10T>C) have drifted to a relatively high population frequency due to founder effect. We report on retinal disease progression in homozygous patients, providing valuable allele-specific insights. The least involved retinal disease is seen in patients homozygous for c.5714 + 5G>A variant, a so-called "mild" variant which is sufficient to precipitate a STGD1 phenotype in the absence of other pathogenic variants in the coding region and intron/exon boundaries of ABCA4. The most severe retinal disease is observed in cases with ABCA4 c.[5461-10T>C;5603A>T] complex allele. We discuss the advantages of determining genetic architecture in genetic isolates in order to begin to meet the grand challenge of human genetics.

Impact of colonoscopic screening in Familial Colorectal Cancer Type X.

BACKGROUND: Hereditary Non-Polyposis Colorectal cancer is caused by Lynch Syndrome (LS; an autosomal dominant condition) or by Familial Colorectal Cancer Type-X (FCCTX; a condition of high family risk that fulfills Amsterdam criteria). The lifetime risk of developing colorectal cancer (CRC) in FCCTX family members is high and CRC occurs later than in LS. METHODS: To determine the impact of primary prevention colonoscopic screening in asymptomatic first-degree relatives of incident CRC cases in 20 families with FCCTX, we compared cancer incidence and survival in 79 males and 83 females, assumed to be at 50% risk of inheriting a genetic CRC susceptibility factor, who entered screening to an unscreened control group from the families, matched for age at entry into screening and for sex. RESULTS: In males, median age at entry into screening was 44.8 years, median follow-up 12.4 years, 12% developed CRC, and 46% died after 30 years of follow-up. Compared to the unscreened group, relative risk of CRC was 0.27 (95% confidence intervals (CI) 0.10-0.71). In screened females, comparable results were 44.5 years at entry, 11.2 years of follow-up, 7.1% developed CRC, and 7.2% died after 30 years of follow-up. The relative risk of CRC compared to the unscreened group was 0.19 (95% CI 0.07-0.48). CONCLUSION: Primary prevention screening colonoscopy in asymptomatic family members significantly decreased the risk of CRC in FCCTX.

Evidence for GALNT12 as a moderate penetrance gene for colorectal cancer.

Characterizing moderate penetrance susceptibility genes is an emerging frontier in colorectal cancer (CRC) research. GALNT12 is a strong candidate CRC-susceptibility gene given previous linkage and association studies, and inactivating somatic and germline alleles in CRC patients. Previously, we found rare segregating germline GALNT12 variants in a clinic-based cohort (N = 118) with predisposition for CRC. Here, we screened a new population-based cohort of incident CRC cases (N = 479) for rare (MAF ≤1%) deleterious germline GALNT12 variants. GALNT12 screening revealed eight rare variants. Two variants were previously described (p.Asp303Asn, p.Arg297Trp), and additionally, we found six other rare variants: five missense (p.His101Gln, p.Ile142Thr, p.Glu239Gln, p.Thr286Met, p.Val290Phe) and one putative splice-altering variant (c.732-8 G>T). Sequencing of population-matched controls (N = 400) revealed higher burden of these variants in CRC cases compared with healthy controls (P = 0.0381). We then functionally characterized the impact of substitutions on GALNT12 enzyme activity using in vitro-derived peptide substrates. Three of the newly identified GALNT12 missense variants (p.His101Gln, p.Ile142Thr, p.Val290Phe) demonstrated a marked loss (>2-fold reduction) of enzymatic activity compared with wild-type (P ≤ 0.05), whereas p.Glu239Gln exhibited a ∼2-fold reduction in activity (P = 0.077). These findings provide strong, independent evidence for the association of GALNT12 defects with CRC-susceptibility; underscoring implications for glycosylation pathway defects in CRC.

Screening of BMPR1a for pathogenic mutations in familial colorectal cancer type X families from Newfoundland.

The Canadian province of Newfoundland and Labrador (NL) reports one of the highest incidence rates of familial colorectal cancer (CRC) worldwide. The NL population is an invaluable resource for studying genetic disorders because of a unique ancestry, and a willingness to participate in research studies. Familial colorectal cancer type X (FCCTX) describes a cluster of families with strong predisposition for CRC, of unknown etiology. A putative link between FCCTX and BMPR1a mutations has been identified in the Finnish population; however these findings have not been independently replicated. To investigate a potential connection between BMPR1a and FCCTX, we screened a cohort of 22 probands from unrelated NL FCCTX families using Sanger sequencing. This analysis did not independently replicate findings seen in Finland; as no candidate pathogenic BMPR1a mutations were uncovered. Our findings highlight that BMPR1a mutations are not a major contributor of FCCTX incidence in NL. Further investigation of additional FCCTX populations may assist in delineating a role for BMPR1a, if any, in FCCTX globally.

Novel 25 kb Deletion of MERTK Causes Retinitis Pigmentosa With Severe Progression.

Purpose: Retinitis pigmentosa (RP) describes a complex group of inherited retinal dystrophies with almost 300 reported genes and loci. We investigated the genetic etiology of autosomal recessive RP (arRP) in a large kindred with 5 affected family members, who reside on the island of Newfoundland, Canada. Methods: Genetic linkage analysis was performed on 12 family members (Infinium HumanOmni2.5-8 BeadChip). Whole exome sequencing analysis (Illumina HiSeq) was performed on one affected individual. A custom pipeline was applied to call, annotate, and filter variants. FishingCNV was used to scan the exome for rare copy number variants (CNVs). Candidate CNVs subsequently were visualized from microarray data (CNVPartition v.3.1.6.). MERTK breakpoints were mapped and familial cosegregation was tested using Sanger Sequencing. Results: We found strong evidence of linkage to a locus on chromosome 2 (logarithm of the odds [LOD] 4.89 [θ = 0]), at an interval encompassing the MERTK gene. Whole exome sequencing did not uncover candidate point mutations in MERTK, or other known RP genes. Subsequently, CNV analysis of the exome data and breakpoint mapping revealed a 25,218 bp deletion of MERTK, encompassing exons 6 to 8, with breakpoints in introns 5 (chr2:112,725,292) and 8 (chr2:112,750,421). A 48 bp insertion sequence was buried within the breakpoint; 18 bps shared homology to MIR4435-2HG and LINC00152, and 30 bp mapped to MERTK. The deletion cosegregated with arRP in the family. Conclusions: This study describes the molecular and clinical characterization of an arRP family segregating a novel 25 kb deletion of MERTK. These findings may assist clinicians in providing a diagnosis for other unsolved RP cases.

Genetic structure of the Newfoundland and Labrador population: founder effects modulate variability.

The population of the province of Newfoundland and Labrador (NL) has been a resource for genetic studies because of its historical isolation and increased prevalence of several monogenic disorders. Controversy remains regarding the genetic substructure and the extent of genetic homogeneity, which have implications for disease gene mapping. Population substructure has been reported from other isolated populations such as Iceland, Finland and Sardinia. We undertook this study to further our understanding of the genetic architecture of the NL population. We enrolled 494 individuals randomly selected from NL. Genome-wide SNP data were analyzed together with that from 14 other populations including HapMap3, Ireland, Britain and Native American samples from the Human Genome Diversity Project. Using multidimensional scaling and admixture analysis, we observed that the genetic structure of the NL population resembles that of the British population but can be divided into three clusters that correspond to religious/ethnic origins: Protestant English, Roman Catholic Irish and North American aboriginals. We observed reduced heterozygosity and an increased inbreeding coefficient (mean=0.005), which corresponds to that expected in the offspring of third-cousin marriages. We also found that the NL population has a significantly higher number of runs of homozygosity (ROH) and longer lengths of ROH segments. These results are consistent with our understanding of the population history and indicate that the NL population may be ideal for identifying recessive variants for complex diseases that affect populations of European origin.

Adult siblings with homozygous G6PC3 mutations expand our understanding of the severe congenital neutropenia type 4 (SCN4) phenotype.

BACKGROUND: Severe congenital neutropenia type 4 (SCN4) is an autosomal recessive disorder caused by mutations in the third subunit of the enzyme glucose-6-phosphatase (G6PC3). Its core features are congenital neutropenia and a prominent venous skin pattern, and affected individuals have variable birth defects. Oculocutaneous albinism type 4 (OCA4) is caused by autosomal recessive mutations in SLC45A2. METHODS: We report a sister and brother from Newfoundland, Canada with complex phenotypes. The sister was previously reported by Cullinane et al., 2011. We performed homozygosity mapping, next generation sequencing and conventional Sanger sequencing to identify mutations that cause the phenotype in this family. We have also summarized clinical data from 49 previously reported SCN4 cases with overlapping phenotypes and interpret the medical histories of these siblings in the context of the literature. RESULTS: The siblings' phenotype is due in part to a homozygous mutation in G6PC3, [c.829C > T, p.Gln277X]. Their ages are 38 and 37 years respectively and they are the oldest SCN4 patients published to date. Both presented with congenital neutropenia and later developed Crohn disease. We suggest that the latter is a previously unrecognized SCN4 manifestation and that not all affected individuals have an intellectual disability. The sister also has a homozygous mutation in SLC45A2, which explains her severe oculocutaneous hypopigmentation. Her brother carried one SLC45A2 mutation and was diagnosed with "partial OCA" in childhood. CONCLUSIONS: This family highlights that apparently novel syndromes can in fact be caused by two known autosomal recessive disorders.

Colorectal cancer linkage on chromosomes 4q21, 8q13, 12q24, and 15q22.

A substantial proportion of familial colorectal cancer (CRC) is not a consequence of known susceptibility loci, such as mismatch repair (MMR) genes, supporting the existence of additional loci. To identify novel CRC loci, we conducted a genome-wide linkage scan in 356 white families with no evidence of defective MMR (i.e., no loss of tumor expression of MMR proteins, no microsatellite instability (MSI)-high tumors, or no evidence of linkage to MMR genes). Families were ascertained via the Colon Cancer Family Registry multi-site NCI-supported consortium (Colon CFR), the City of Hope Comprehensive Cancer Center, and Memorial University of Newfoundland. A total of 1,612 individuals (average 5.0 per family including 2.2 affected) were genotyped using genome-wide single nucleotide polymorphism linkage arrays; parametric and non-parametric linkage analysis used MERLIN in a priori-defined family groups. Five lod scores greater than 3.0 were observed assuming heterogeneity. The greatest were among families with mean age of diagnosis less than 50 years at 4q21.1 (dominant HLOD = 4.51, α = 0.84, 145.40 cM, rs10518142) and among all families at 12q24.32 (dominant HLOD = 3.60, α = 0.48, 285.15 cM, rs952093). Among families with four or more affected individuals and among clinic-based families, a common peak was observed at 15q22.31 (101.40 cM, rs1477798; dominant HLOD = 3.07, α = 0.29; dominant HLOD = 3.03, α = 0.32, respectively). Analysis of families with only two affected individuals yielded a peak at 8q13.2 (recessive HLOD = 3.02, α = 0.51, 132.52 cM, rs1319036). These previously unreported linkage peaks demonstrate the continued utility of family-based data in complex traits and suggest that new CRC risk alleles remain to be elucidated.

Cancer risks for relatives of patients with serrated polyposis.

OBJECTIVES: Serrated polyposis (hyperplastic polyposis) is characterized by multiple polyps with serrated architecture in the colorectum. Although patients with serrated polyposis are known to be at increased risk of colorectal cancer (CRC) and possibly extracolonic cancers, cancer risk for their relatives has not been widely explored. The aim of this study was to estimate the risks of CRC and extracolonic cancers for relatives of patients with serrated polyposis. METHODS: A cohort of the 1,639 first- and second-degree relatives of 100 index patients with serrated polyposis recruited regardless of a family history of polyps or cancer from genetic clinics in Australia, New Zealand, Canada, and the USA, were retrospectively analyzed to estimate the country-, age-, and sex-specific standardized incidence ratios (SIRs) for relatives compared with the general population. RESULTS: A total of 102 CRCs were observed in first- and second-relatives (SIR 2.25, 95% confidence interval (CI) 1.75-2.93; P<0.001), with 54 in first-degree relatives (SIR 5.16, 95% CI 3.70-7.30; P<0.001) and 48 in second-degree relatives (SIR 1.38, 95% CI 1.01-1.91; P=0.04). Six pancreatic cancers were observed in first-degree relatives (SIR 3.64, 95% CI 1.70-9.21; P=0.003). There was no statistical evidence of increased risk for cancer of the stomach, brain, breast, or prostate. CONCLUSIONS: Our finding that relatives of serrated polyposis patients are at significantly increased risk of colorectal and pancreatic cancer adds to the accumulating evidence that serrated polyposis has an inherited component.

Inherited deleterious variants in GALNT12 are associated with CRC susceptibility.

A recent report detailed the occurrence of both somatic and constitutional variants in the GALNT12 gene, located at 9q22.33, in some colorectal cancer (CRC) patients. In this study, we investigate the occurrence of inherited deleterious variants in GALNT12 in 118 families referred to a cancer genetics clinic. We discovered two deleterious variants (c.907G>A (p.Asp303Asn); c.1187A>G (p.Tyr396Cys)) in 4/118 probands. The variants, which were not found in 149 control individuals (P = 0.0376), cosegregate with CRC and/or adenomatous polyps in other family members. The probability by chance that cosegregation of c.907G>A with CRC and/or adenomatous polyps occurred, in the two pedigrees combined, was 1.56%. Although this study does not provide irrefutable evidence that GALNT12 variants are highly penetrant alleles that predispose to CRC in the majority of unexplained hereditary CRC families, it does provide additional evidence to support an important role of these variants in a proportion of this considerable high-risk group.

Lynch syndrome: barriers to and facilitators of screening and disease management.

BACKGROUND: Lynch syndrome is a hereditary cancer with confirmed carriers at high risk for colorectal (CRC) and extracolonic cancers. The purpose of the current study was to develop a greater understanding of the factors influencing decisions about disease management post-genetic testing. METHODS: The study used a grounded theory approach to data collection and analysis as part of a multiphase project examining the psychosocial and behavioral impact of predictive DNA testing for Lynch syndrome. Individual and small group interviews were conducted with individuals from 10 families with the MSH2 intron 5 splice site mutation or exon 8 deletion. The data from confirmed carriers (n = 23) were subjected to re-analysis to identify key barriers to and/or facilitators of screening and disease management. RESULTS: Thematic analysis identified personal, health care provider and health care system factors as dominant barriers to and/or facilitators of managing Lynch syndrome. Person-centered factors reflect risk perceptions and decision-making, and enduring screening/disease management. The perceived knowledge and clinical management skills of health care providers also influenced participation in recommended protocols. The health care system barriers/facilitators are defined in terms of continuity of care and coordination of services among providers. CONCLUSIONS: Individuals with Lynch syndrome often encounter multiple barriers to and facilitators of disease management that go beyond the individual to the provider and health care system levels. The current organization and implementation of health care services are inadequate. A coordinated system of local services capable of providing integrated, efficient health care and follow-up, populated by providers with knowledge of hereditary cancer, is necessary to maintain optimal health.

Increased cancer predisposition in family members of colorectal cancer patients harboring the p.V600E BRAF mutation: a population-based study.

BACKGROUND: The serrated pathway represents a distinct molecular pathway of colorectal carcinogenesis and is associated with the p.V600E BRAF mutation. The objective of this study is to characterize the cancer family history and clinicopathologic features of colorectal cancer (CRC) patients according to the microsatellite instability (MSI) and BRAF mutation status of their tumors. METHODS: The tumors from 558 population-based CRC patients underwent pathologic examination and molecular analysis for MSI, BRAF, and germline mutations in mismatch repair genes MUTYH and APC. The cancer history in first-degree relatives (FDR) of index patients was ascertained. RESULTS: The risk of CRC in FDRs of index patients with MSI-H BRAF mutation [hazard ratio (HR) = 2.49; 95% confidence interval (95% CI), 1.57- 3.93] and microsatellite-stable BRAF mutation tumors (HR = 1.64; 95% CI, 1.01-2.66) was significantly elevated compared with FDRs of index patients with microsatellite-stable BRAF wild-type tumors. The incidence of nonmelanoma skin cancer was also significantly elevated in FDRs of patients with BRAF mutation CRC (HR = 2.52; 95% CI, 1.31-4.86). Furthermore, BRAF mutation CRC was associated with a distinct clinical, molecular, and pathologic phenotype. CONCLUSIONS: The increased incidence of cancer in FDRs of index CRC patients with the p.V600E BRAF mutation may be explained by a genetic predisposition to develop cancer through the serrated pathway of colorectal carcinogenesis. IMPACT: Family members of BRAF CRC patients have an increased predisposition to develop cancer. Future work should aim to identify the causative genetic factors.

Autosomal recessive Bardet-Biedl syndrome: first-degree relatives have no predisposition to metabolic and renal disorders.

Bardet-Biedl Syndrome (BBS) is an autosomal recessive, multisystem, genetically heterogeneous, ciliopathic condition caused by mutations in multiple genes. Here we sought to determine if inheritance of a single BBS mutation increased the risks of frequent disorders of this syndrome such as obesity, hypertension, and diabetes. Various metabolic and renal diseases in a cohort of 46 patients with BBS, prospectively followed for up to 28 years, were compared to recent assessments of these factors in 96 relatives with a heterozygote mutation (carriers) and 37 relatives without a contributing mutation (non-carriers). Ten mutations in 6 genes causing this syndrome were identified in 21 families from whom DNA was obtained. The body mass index or the incidences of hypertension, diabetes, or stage 3 chronic kidney diseases were found to be similar between carriers and non-carriers but were all significantly less than those of family members with BBS. Similarly, the median age of onset of hypertension or diagnosis of stage 3 kidney disease, or the diagnosis of diabetes by age 70 were all significantly lower in those with BBS than in gene carriers or non-carriers. While our study shows that metabolic and renal events occurred frequently and at an early age in BBS, the heterozygous inheritance of any of the 10 described BBS mutations did not predispose family members to obesity, diabetes, hypertension, or renal impairment.

Profound, prelingual nonsyndromic deafness maps to chromosome 10q21 and is caused by a novel missense mutation in the Usher syndrome type IF gene PCDH15.

We studied a consanguineous family (Family A) from the island of Newfoundland with an autosomal recessive form of prelingual, profound, nonsyndromic sensorineural hearing loss. A genome-wide scan mapped the deafness trait to 10q21-22 (max LOD score of 4.0; D10S196) and fine mapping revealed a 16 Mb ancestral haplotype in deaf relatives. The PCDH15 gene was mapped within the critical region and was an interesting candidate because truncating mutations cause Usher syndrome type IF (USH1F) and two missense mutations have been previously associated with isolated deafness (DFNB23). Sequencing of the PCDH15 gene revealed 33 sequencing variants. Three of these variants were homozygous exclusively in deaf siblings but only one of them was not seen in ethnically matched controls. This novel c.1583 T>A transversion predicts an amino-acid substitution of a valine with an aspartic acid at codon 528 (V528D). Like the two DFNB23 mutations, the V528D mutation in Family A occurs in a highly conserved extracellular cadherin (EC) domain of PCDH15 and is predicted to be more deleterious than the previously identified DFNB23 missense mutations (R134G and G262D). Physical assessment, vestibular and visual function testing in deaf adults ruled out syndromic deafness because of Usher syndrome. This study validates the DFNB23 designation and supports the hypothesis that missense mutations in conserved motifs of PCDH15 cause nonsyndromic hearing loss. This emerging genotype-phenotype correlation in USH1F is similar to that in several other USH1 genes and cautions against a prognosis of a dual sensory loss in deaf children found to be homozygous for hypomorphic mutations at the USH1F locus.

The phenotypic expression of three MSH2 mutations in large Newfoundland families with Lynch syndrome.

To compare the phenotypic expression of three different MSH2 mutations causing Lynch syndrome, 290 family members at 50% risk of inheriting a mutation were studied. Two truncating mutations of the MSH2 gene have been identified in Newfoundland: an exon 8 deletion in five families (N=74 carriers) and an exon 4-16 deletion in one family (N=65 carriers). The third mutation was an intron 5 splice site mutation resulting in deletion of exon 5 in RNA and occurred in 12 families (N=151 carriers). Age to onset of first cancer, first colorectal cancer (CRC), first extracolonic cancers and death were compared. By age 60, 89% of family members with the intron 5 mutation, 81% with the exon 8 deletion, and 85% with the exon 4-16 deletion had developed cancer. For all three mutations males had a higher age-related risk of CRC and death compared to females. In the intron 5 splice site mutation carriers, the number of transitional cell cancers of the urinary tract was significantly lower and time to first ovarian cancer was significantly higher than in the carriers of the genomic deletions. The incidence of CRC in MSH2 mutation carriers, exposed to the same environment, is not modified by the specific mutation, although there is a suggestion that type of mutation may influence development of some extracolonic cancers.

High frequency of hereditary colorectal cancer in Newfoundland likely involves novel susceptibility genes.

PURPOSE: Newfoundland has one of the highest rates of colorectal cancer in North America. The most common hereditary form of colorectal cancer is hereditary nonpolyposis colorectal cancer caused by mutations in genes involved in mismatch repair. Our purpose was to determine the proportion of hereditary colorectal cancer and to determine the genetic basis of disease in both population and clinically referred cohorts from Newfoundland. EXPERIMENTAL DESIGN: Seventy-eight colorectal cancer patients were accrued over a 2-year period from the Avalon Peninsula of Newfoundland. We also examined 31 hereditary nonpolyposis colorectal cancer-like families, which had been referred to the Provincial Medical Genetics Program. Tumors from probands were tested by immunohistochemistry for deficiencies in MLH1, MSH2, and MSH6 proteins and tested for DNA microsatellite instability. Mutation analyses of MLH1, MSH2, and MSH6 were undertaken by direct sequencing and an assay to detect deletions, amplifications, and rearrangements in MSH2 and MLH1. RESULTS: We identified eight population-based families that fulfill the Amsterdam I or II criteria, 4 (50%) of which seem to have hereditary cancer not attributable to the most commonly mutated mismatch repair genes. In addition, in 16 of 21 (76%) referred families fulfilling Amsterdam I or II criteria, no mutations were found in the three most commonly altered mismatch repair genes, and tumor analyses corroborated these findings. CONCLUSIONS: It seems that strong and novel genetic causes of hereditary colorectal cancer are responsible for a high proportion of colorectal cancer in this population. Conditions are suitable for the identification of these genes by linkage studies of large Newfoundland cancer families.

Clinical and genetic epidemiology of Bardet-Biedl syndrome in Newfoundland: a 22-year prospective, population-based, cohort study.

Bardet-Biedl syndrome (BBS) and Laurence-Moon syndrome (LMS) have a similar phenotype, which includes retinal dystrophy, obesity, and hypogenitalism. They are differentiated by the presence of spasticity and the absence of polydactyly in LMS. The aims of this study were to describe the epidemiology of BBS and LMS, further define the phenotype, and examine genotype-phenotype correlation. The study involved 46 patients (26 males, 20 females) from 26 families, with a median age of 44 years (range 1-68 years). Assessments were performed in 1986, 1993, and 2001 and included neurological assessments, anthropometric measurements, and clinical photographs to assess dysmorphic features. The phenotype was highly variable within and between families. Impaired co-ordination and ataxia occurred in 86% (18/21). Thirty percent (14/46) met criteria for psychiatric illness; other medical problems included cholecystectomy in 37% (17/46) and asthma in 28% (13/46). Dysmorphic features included brachycephaly, large ears, and short, narrow palpebral fissures. There was no apparent correlation of clinical or dysmorphic features with genotype. Two patients were diagnosed clinically as LMS but both had mutations in a BBS gene. The features in this population do not support the notion that BBS and LMS are distinct. The lack of a genotype-phenotype correlation implies that BBS proteins interact and are necessary for the development of many organs.