Novel mutations in the sacsin gene in ataxia patients from Maritime Canada.

We ascertained two families in Eastern Canada segregating a form of ataxia consistent with a recessive mode of inheritance. We performed a whole genome scan using dense SNP genotyping, and despite an absence of shared homozygosity in the families we defined linkage to a small region on chromosome 13. Direct DNA resequencing was employed to screen biologically relevant candidate genes in the interval, and two presumptive pathogenic mutations were found in the gene encoding sacsin. One variant is an obligate truncating mutation, the second is a missense variant in a highly conserved residue. Unexpectedly, one family was homozygous for the missense mutation, the other compound heterozygous for the two mutations. Our results expand the genotype phenotype correlation of mutations in the sacsin gene, and highlight the challenge of diagnosing genetically heterogeneous disorders on primarily clinical grounds. We demonstrate that whole genome genotyping on a modest scale can be productive in research, and potentially in a clinical context.

Obesity and lifestyle risk factors for gastroesophageal reflux disease, Barrett esophagus and esophageal adenocarcinoma.

The aim of this study was to examine the association of obesity with esophageal adenocarcinoma, and with the precursor lesions Barrett esophagus and gastroesophageal reflux disease (GERD). This case-control study included cases with GERD (n = 142), Barrett esophagus (n = 130), and esophageal adenocarcinoma (n = 57). Controls comprised 102 asymptomatic individuals. Using logistic regression methods, we compared obesity rates between cases and controls adjusting for differences in age, gender, and lifestyle risk factors. Relative to normal weight, obese individuals were at increased risk for esophageal adenocarcinoma (Odds Ratio [OR] 4.67, 95% Confidence Interval [CI] 1.27-17.9). Diets high in vitamin C were associated with a lower risk for GERD (OR 0.40, 95% CI 0.19-0.87), Barrett esophagus (OR 0.44, 95% CI 0.20-0.98), and esophageal adenocarcinoma (OR 0.21, 95% CI 0.06-0.77). For the more established risk factors, we confirmed that smoking was a significant risk factor for esophageal adenocarcinoma, and that increased liquor consumption was associated with GERD and Barrett esophagus. In light of the current obesity epidemic, esophageal adenocarcinoma incidence rates are expected to continue to increase. Successful promotion of healthy body weight and diets high in vitamin C may substantially reduce the incidence of this disease.

Biomarkers in the molecular pathogenesis of esophageal (Barrett) adenocarcinoma.

Since the early 1970s, a dramatic change has occurred in the epidemiology of esophageal malignancy in both North America and Europe: the incidence of adenocarcinomas of the lower esophagus and esophagogastric junction is increasing. Several lifestyle factors are implicated in this change, including gastroesophageal reflux disease (GERD). Primary esophageal adenocarcinomas are thought to arise from Barrett esophagus, an acquired condition in which the normal esophageal squamous epithelium is replaced by a specialized metaplastic columnar-cell-lined epithelium.Today, gerd is recognized as an important risk factor in Barrett esophagus. Progression of Barrett esophagus to invasive adenocarcinoma is reflected histologically by the metaplasia-dysplasia-carcinoma sequence. Although several molecular alterations associated with progression of Barrett esophagus to invasive adenocarcinoma have been identified, relatively few will ultimately have clinical application. Currently, the histologic finding of high-grade dysplasia remains the most reliable predictor of progression to invasive esophageal adenocarcinoma. However other promising molecular biomarkers include aneuploidy; 17p loss of heterozygosity, which implicates the TP53 tumour suppressor gene; cyclin D1 protein overexpression; and p16 alterations. It is anticipated that models incorporating combinations of objective scores of sociodemographic and lifestyle risk factors (that is, age, sex, body mass index), severity of gerd, endoscopic and histologic findings, and a panel of biomarkers will be developed to better identify patients with Barrett esophagus at increased risk for malignant progression, leading to more rational endoscopic surveillance and screening programs.

Associations between genetic polymorphisms of Phase I and II metabolizing enzymes, p53 and susceptibility to esophageal adenocarcinoma.

The objectives of this exploratory case-control study were to evaluate whether genetic polymorphisms of selected Phase I and II metabolizing enzymes are associated with the risk of developing primary esophageal adenocarcinoma, and to investigate potential associations between genotypes and p53 tumor suppressor gene alterations. Cases comprised 45 patients with surgically resected esophageal adenocarcinomas, defined according to strict clinico-pathologic criteria. PCR-based assays (RFLP/SSCP) were used to genotype cytochrome P450 (CYP) 1A1 [MspI; Ile:Val], microsomal epoxide hydroxylase (mEH) (fast and slow alleles), and glutathione S-transferase (GST) T1, M1 and P1. Healthy controls (n=45) from the same geographic region were matched for age, gender and smoking history. For GSTP1, the Ile/Val (a/b) and Val/Val (b/b) variants were seen at increased frequency in cases compared to controls (49% versus 27% and 15% versus 9%, respectively), although these differences achieved only borderline statistical significance (P=0.09). For mEH (exon 3), the presence of the Tyr polymorphism (slow allele) was reduced in cases (42%) compared to controls (53%; P=0.05). Predicted high mEH activity was seen more frequently in cases than controls (OR, 2.2; 95% CI, 0.7-7.3). Polymorphism frequencies for GSTT1, GSTM1, and CYP1A1 were not statistically different between cases and controls. Cases with the GSTT1 null genotype had tumors with altered p53 more frequently than did cases with the common form of GSTT1 (25 versus 6%, respectively; P=0.08). We conclude that polymorphisms of GSTP1 and mEH may be implicated in individual susceptibility to esophageal adenocarcinoma, possibly as a result of increased Phase I activation (mEH) and impaired Phase II detoxification (GSTP1). GSTT1 may also play a role in esophageal tumorigenesis through a pathway that involves abnormalities in the p53 tumor suppressor gene.

Exfoliation syndrome: clinical and genetic features.

We have ascertained a large number of individuals and families with exfoliation syndrome in order to clarify the disorder's mode of inheritance. Patients with exfoliation syndrome and their relatives were recruited from the practices of a group of ophthalmologists in Maritime Canada. The degree to which the subjects were affected was graded according to a standardized 1-4-point clinical scheme. Pedigrees were constructed from information supplied by family members and from genealogical sources. A total of 782 patients and relatives participated, of whom 467 were definitely affected. The mean age of affected males and females did not differ significantly, but females appeared to be more severely affected at ascertainment than males. More than half of the affected subjects had definite exfoliation in only one eye. Approximately 30 multiplex families were discovered, including one containing 23 affected members among a total of 137 examined individuals that constitutes the largest exfoliative pedigree thus far described. We observed well-documented paternal transmission of the trait, a finding that has not to our knowledge been previously reported. Clustering of cases in the families provides evidence for the involvement of genetic factors. The possibility of homozygosity is suggested in a few patients by the earlier or more frequent presentation of the disorder in the offspring of two affected parents or consanguineous pairings. Although a multifactorial mode of inheritance cannot be excluded, exfoliation syndrome appears to be inherited as an autosomal dominant trait whose late onset and incomplete penetrance poses a significant but not insuperable obstacle to pedigree construction.

ETn insertion in the mouse Adcy1 gene: transcriptional and phylogenetic analyses.

Early retrotransposons (ETn) are murine transposable elements, bearing some structural similarity to integrated proviruses, and can be insertional mutagens. We have recently identified the causative mutation of the barrelless (Adcy1brl) phenotype as an integration of a 5.7-kb ETn in an intron of the adenylyl cyclase type I (Adcy1) gene. In the present study, Northern blot analysis shows that the ETn insertion results in loss of the normal Adcy1 transcript, a finding consistent with the loss-of-function Adcy1brl mutation, and generation of shorter transcripts. These aberrant transcripts are the products of abnormal RNA splicing and termination owing to the inserted sequence, and transcription initiation within the 3' long terminal repeat (LTR) of the ETn. The DNA sequences of the LTRs were compared in phylogenetic analyses with LTRs from 22 other ETn-related sequences. Three distinct families of ETn sequences can be identified on the basis of their LTRs. The ETn found in Adcy1brl is a member of a family that includes all classified ETn elements known to have recently transposed. Further, of the four known solitary (solo) LTRs, we have identified two that show evidence of recombination between LTRs from different ETn families.

A novel PAX6 frameshift mutation in a kindred from Atlantic Canada with familial aniridia.

BACKGROUND: Many mutations in PAX6, a member of a family of genes essential for normal development, have been described. We carried out a study to identify the mutation in PAX6 responsible for aniridia, an autosomal dominant disorder, in a kindred from Atlantic Canada. METHODS: Polymerase chain reaction amplification of coding exons, single-strand conformation polymorphism analysis and DNA sequencing. RESULTS: A novel deletion of an adenosine residue at position 1030 (1030delA) was detected. INTERPRETATION: The mutation responsible for aniridia in this kindred is expected to cause a frameshift in the PAX6 coding sequence and truncation of the homeodomain, which is essential for the function of the pax6 protein.

Genotype/phenotype correlations in aniridia.

PURPOSE: To detect and characterize mutations in cases of familial and sporadic aniridia in Maritime Canada, and to look for indications of genotype/phenotype correlation within the cohort. METHODS: Twelve consecutive and unrelated patients (probands) who had total or nearly complete absence of irides, and four affected relatives, were recruited from Maritime Canada. Clinical data were obtained by chart review and electroretinogram testing. Mutations in the PAX6 gene were detected by single-strand conformation polymorphism and characterized by sequence analysis. RESULTS: Eleven different PAX6 mutations, 10 of which are novel, were found. The four patients with congenital cataracts all had mutations in the C-terminal proline-serine-threonine (PST)-rich domain of the PAX6 protein. Electroretinograms of nine of 11 patients displayed depressed scotopic maximum response b-wave amplitudes. The greatest decrease in b-wave amplitudes was seen in patients in whom the paired domain was disrupted by mutation. CONCLUSION: Some aspects of the phenotype of aniridia appear to correlate with the predicted effect of point mutations on the paired and PST domains of the PAX6 protein.

Effects of PAX6 mutations on retinal function: an electroretinographic study.

PURPOSE: To investigate the retinal function in aniridic patients with documented PAX6 mutations to determine the range of electroretinogram abnormalities in aniridic patients and to relate electroretinogram findings with specific PAX6 mutations. METHODS: Eleven patients with typical aniridia and fully characterized PAX6 mutations underwent electroretinography. RESULTS: In all 11 patients, electroretinogram recordings were abnormal, ranging from mild to severe. Rod-related and cone-related activities were equally affected. The amplitude of the oscillatory potentials was the most reduced, followed by the b-wave, then to a milder degree the a-wave. Mutations affecting the paired domain of the PAX6 protein had the biggest impact on the electroretinogram amplitudes. Implicit times were increased in a subgroup with mutations affecting only the homeodomain. CONCLUSION: Patients with aniridia have varying degree of retinal dysfunction, ranging from severely abnormal to almost normal. The paired domain appears to have more impact on retinal function than other regions of the PAX6 protein. It is unclear whether mutations affecting the homeodomain lead to alteration of the photoreceptor function.

Genetic analysis of familial myelodysplastic syndrome: absence of linkage to chromosomes 5q31 and 7q22.

Myelodysplastic syndrome (MDS) is a hematological disorder that occurs primarily in the elderly as an acquired, sporadic disease. Familial cases of MDS are rare. We have identified a kindred with three affected individuals, with early age of onset, suggesting a possible inherited predisposition to this disease. Using a molecular genetic approach, we examined whether bands 5q31 or 7q22 or both, the chromosomal regions most frequently associated with sporadic MDS, are involved in familial expression of MDS in this pedigree. Linkage analysis using polymorphic microsatellite DNA markers demonstrated that neither 5q31 nor 7q22 cosegregated with MDS in this family. There was no history of common environmental or occupational exposure among family members with MDS. In addition, analysis of polymorphisms at two loci [glutathione S-transferase T1 and M1 (GSTT1 and GSTM1)] involved in carcinogen detoxification and associated with cancer susceptibility, including increased risk for MDS, showed no evidence for enhanced sensitivity to environmental carcinogens in affected family members. Taken together, our findings suggest that (1) there is an inherited predisposition to MDS in this kindred; and (2) genes at 5q31 and 7q22, the regions most commonly associated with sporadic MDS, are excluded from a causal role in this family's disease.

Loss of adenylyl cyclase I activity disrupts patterning of mouse somatosensory cortex.

The somatosensory (SI) cortex of mice displays a patterned, nonuniform distribution of neurons in layer IV called the 'barrelfield' (ref. 1). Thalamocortical afferents (TCAs) that terminate in layer IV are segregated such that each barrel, a readily visible cylindrical array of neurons surrounding a cell-sparse center, represents a distinct receptive field. TCA arbors are confined to the barrel hollow and synapse on barrel-wall neurons whose dendrites are oriented toward the center of the barrel. Mice homozygous for the barrelless (brl) mutation, which occurred spontaneously in ICR stock at Université de Lausanne (Switzerland), fail to develop this patterned distribution of neurons, but still display normal topological organization of the SI cortex. Despite the absence of barrels and the overlapping zones of TCA arborization, the size of individual whisker representations, as judged by 2-deoxyglucose uptake, is similar to that of wild-type mice. We identified adenylyl cyclase type I (Adcy1) as the gene disrupted in brl mutant mice by fine mapping of proximal chromosome 11, enzyme assay, mutation analysis and examination of mice homozygous for a targeted disruption of Adcy1. These results provide the first evidence for involvement of cAMP signalling pathways in pattern formation of the brain.

Polymerase chain reaction-based risk assessment for Wilms tumor in sporadic aniridia.

PURPOSE: Sporadic cases of aniridia have a 30% risk for the development of Wilms tumor. Current guidelines for sporadic aniridia recommend screening by renal ultrasonography for the presence of tumors every 6 months until age 5 years. Deletions of chromosome 11p13 that affect both PAX6 (aniridia) and WT1 (Wilms tumor) loci are the basis for the association of these two uncommon disorders. We sought to develop a rapid polymerase chain reaction-based test that could rule out a chromosome 11p13 deletion covering the PAX6-WT1 region in sporadic aniridia. METHODS: Five patients with sporadic aniridia were recruited. Polymerase chain reaction-based genotyping was carried out for six highly informative marker loci across the PAX6-WT1 region to determine whether these patients had one or two haplotypes. The results were compared with those obtained from two cell lines with known deletions in the PAX6-WT1 region. RESULTS: All five patients were heterozygous at least at one of the four marker loci in the PAX6-WT1 region, indicating that there were no cases of gross chromosomal deletion. The cell lines showed hemizygosity in the four marker loci within the PAX6-WT1 region and in one of the two flanking marker loci. CONCLUSIONS: We have developed a rapid DNA test with an estimated sensitivity of 94.0% to 99.2%, using standard DNA diagnostic techniques and equipment, to rule out chromosomal deletion in sporadic aniridia. Patients in whom a chromosome 11p13 deletion has been ruled out do not require repeated renal imaging to screen for Wilms tumor.

Lattice corneal dystrophy type 1 in a Canadian kindred is associated with the Arg124 --> Cys mutation in the kerato-epithelin gene. sgupta@ogh.on.ca.

PURPOSE: To identify the mutation responsible for lattice corneal dystrophy type 1 in an extended Canadian kindred. METHODS: A search for a mutation in the candidate gene, kerato-epithelin, was carried out by single-strand conformation polymorphism and sequencing analyses. RESULTS: AC --> T mutation at position 417 was detected in exon 4 of the kerato-epithelin gene, which is expected to cause an Arg124 --> Cys change. This is the same nucleotide change described previously in two Swiss families with lattice corneal dystrophy type 1. CONCLUSION: Although the possibility that the three families (two previously described Swiss families and this Canadian kindred) are related has not been excluded, it appears that the unique phenotype of lattice corneal dystrophy type 1 is caused by this particular amino acid change.

A novel mutation in Exon 4 of the low density lipoprotein receptor gene resulting in heterozygous familial hypercholesterolemia associated with decreased ligand binding.

Familial hypercholesterolemia (FH) is an autosomal dominant disorder caused by mutations in the low density lipoprotein (LDL) receptor gene. Currently, diagnosis of heterozygous FH relies on clinical phenotype; however, the use of clinical criteria for the diagnosis of heterozygous FH does not always permit unequivocable diagnosis of the disease. Molecular diagnosis of FH is clinically valuable especially in regions where founder mutations exist or where polygenic hypercholesterolemia is prevalent. In this paper we report the identification of a novel mutation, a cytosine to guanine substitution, at codon 152 in exon 4 of the LDL receptor gene in a Nova Scotian family clinically diagnosed with heterozygous FH. The mutation creates a recognition sequence for the restriction endonuclease BsrI, and can be readily detected by BsrI restriction analysis of a 160 bp amplicon spanning the mutation. This analysis was used to show that the mutation segregated with the disease in this family and is the probable cause of FH in this kindred.

Establishment and characterization of a renal cell carcinoma line from a patient with von Hippel-Lindau syndrome.

It is not known how the von Hippel-Lindau (VHL) gene and the, as yet unidentified, renal cell carcinoma (RCC) gene(s) interact to result in RCC; nor is it known if mutations in both, or all genes are necessary for this progression. The availability of a RCC cell line from a VHL patient would be useful in studies comparing sporadic RCC with RCC resulting from VHL syndrome; and for determining the relationship or interaction of the RCC gene with the VHL gene to produce a common tumor type. This paper describes the isolation and characterization of a renal cell carcinoma cell line derived from a patient with von Hippel-Lindau disease. The line is epithelial in origin and the genome contains a familial mutation in the VHL gene. Tissue culture studies indicate that this cell line, although immortalized, is not fully transformed. Chromosomal analysis performed on cells derived from disseminated primary tumor cells revealed no detectable chromosomal abnormalities. However, analysis performed on cells at passages 9, 19, 41, and 79 showed both numerical and structural chromosomal changes. The cytogenetic profile of this cell line demonstrated a number of abnormalities known to be associated with RCC from patients with and without VHL syndrome.

Altered sensory processing in the somatosensory cortex of the mouse mutant barrelless.

Mice homozygous for the barrelless (brl) mutation, mapped here to chromosome 11, lack barrel-shaped arrays of cell clusters termed "barrels" in the primary somatosensory cortex. Deoxyglucose uptake demonstrated that the topology of the cortical whisker representation is nevertheless preserved. Anterograde tracers revealed a lack of spatial segregation of thalamic afferents into individual barrel territories, and single-cell recordings demonstrated a lack of temporal discrimination of center from surround information. Thus, structural segregation of thalamic inputs is not essential to generate topological order in the somatosensory cortex, but it is required for discrete spatiotemporal relay of sensory information to the cortex.

Passage of X-ray-induced immortal, non-transformed phenotype by DNA-mediated transfection.

To better understand the molecular basis of X-ray-induced carcinogenesis, the immortalization step of this multistep process was examined. Primary rat embryo cells were X-irradiated in vitro and six clones were isolated. Three of these, one designated X-REF-23, were immortal and non-transformed. Transfection of high molecular weight DNA from rat X-REF-23 cells into primary mouse cells yielded two immortal and non-transformed mouse clones, 1K and 2I. Using a 2.3 kb rat-specific repetitive sequence as probe, 1K and 2I were demonstrated to contain rat DNA. This transfected DNA was not any of the known immortalization-associated proto-oncogenes. DNA from 1K was then transfected into primary mouse cells, with or without co-transfection of pSV2 neo DNA. Six immortal mouse clones were isolated and confirmed to contain rat sequences. In conclusion, the immortal phenotype can be transferred by DNA transfection.

Detection of familial defective apolipoprotein B-100 among patients clinically diagnosed with heterozygous familial hypercholesterolemia in maritime Canada.

Familial defective apolipoprotein B-100 (FDB) is a genetic disorder resulting from a mutation in the apolipoprotein B-100 (apo B-100) gene, most frequently at position 3500, in which arginine is substituted for glutamine in the mature protein. This mutation drastically decreases the affinity of the mutant apo B-100 particle for the low-density lipoprotein (LDL) receptor, and hence decreases the clearance of cholesterol from the circulation. Familial hypercholesterolemia (FH), also a disorder of lipid metabolism, results from mutations in the gene for the LDL receptor. Both FDB and heterozygous FH occur at approximately the same frequency (1 in 500) among Caucasians and both produce clinical symptoms and signs that can be indistinguishable. Polymerase chain reaction (PCR) amplification and subsequent restriction analysis have been used to detect the substitution at codon 3500 in the apo B-100 gene using mutagenic PCR primers. At least one proband from 10 unrelated families with a history of hypercholesterolemia was screened by mutagenic PCR for FDB. Only one of 10 patients demonstrated the mutation for FDB. The mutant apo B-100 allele was shown to segregate with other clinically affected family members. These results demonstrate that molecular analysis is essential to distinguish between FDB and heterozygous FH in hypercholesterolemic families.

Regulation of low density lipoprotein receptor and 3-hydroxy-3-methyl-glutaryl-CoA reductase activities are differentially affected in Niemann-Pick type C and type D fibroblasts.

Defective regulation of intracellular cholesterol metabolism has been investigated in cultured fibroblasts from two subtypes of Niemann-Pick type II disease: the panethnic Niemann-Pick type C (NPC) and the Nova Scotia type D (NPD). Cell extracts from NPC and NPD fibroblasts cultured in lipoprotein-deficient medium exhibited activities of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase that were two-fold greater than in normal cells. Addition of serum resulted in only a 15% decrease in HMG-CoA reductase activity within 6 h in these cells, compared with a decrease of 80% in normal fibroblasts. The initial rate of return to maximal values for the first 6 h after removal of serum was similar in all three cell types; thereafter, the rate was faster in the mutant fibroblasts. Binding and internalization of 125I-labeled low density lipoprotein (LDL) was not decreased within 12 h of incubation of NPC fibroblasts with serum, while a decrease of 50% was observed for both NPD and normal fibroblasts over this time period. Northern blot analysis also indicated a slower decrease in steady-state LDL receptor mRNA in NPC relative to normal and NPD cells. In all three cell types, inhibition of HMG-CoA reductase with mevinolin had no effect on serum-stimulated cholesterol esterification, while inhibition of acyl-CoA:cholesterol acyltransferase with Sandoz 58-035 did not influence HMG-CoA reductase activity, indicating that defects in these regulatory mechanisms are independent.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevation of the thyroid hormone receptor erb A-alpha 2 mRNA in transformed rodent cells is due to increased message stability.

Previously, the authors reported an elevation of erb A-alpha 2 mRNAs in transformed rodent cells when compared with their non-transformed counterparts (Cancer Res., 52(1992) 2186-2190). To investigate this phenomenon further the rates of gene transcription and the effects of translation/transcription inhibition on erb A-alpha 2 mRNA expression were examined. The present study found no difference between non-transformed and transformed cells in erb A-alpha 2 gene transcription rate, nor an effect of cycloheximide on erb A-alpha 2 mRNA expression. However, a significant difference was obtained with actinomycin D. With this inhibitor, the half-life of erb A-alpha 2 mRNAs in nontransformed rodent cells was determined to be approximately 8 h. In contrast, the alpha 2 transcripts in their transformed counterparts showed no decay during this period, suggesting that the elevation of erb A-alpha 2 mRNAs in transformed rodent cells was due to increased transcript stability.