Rachel Laframboise

Mutations in C5ORF42 Cause Joubert Syndrome in the French Canadian Population

Joubert syndrome (JBTS) is an autosomal-recessive disorder characterized by a distinctive mid-hindbrain malformation, developmental delay with hypotonia, ocular-motor apraxia, and breathing abnormalities. Although JBTS was first described more than 40 years ago in French Canadian siblings, the causal mutations have not yet been identified in this family nor in most French Canadian individuals subsequently described. We ascertained a cluster of 16 JBTS-affected individuals from 11 families living in the Lower St. Lawrence region. SNP genotyping excluded the presence of a common homozygous mutation that would explain the clustering of these individuals. Exome sequencing performed on 15 subjects showed that nine affected individuals from seven families (including the original JBTS family) carried rare compound-heterozygous mutations in C5ORF42. Two missense variants (c.4006C>T [p.Arg1336Trp] and c.4690G>A [p.Ala1564Thr]) and a splicing mutation (c.7400+1G>A), which causes exon skipping, were found in multiple subjects that were not known to be related, whereas three other truncating mutations (c.6407del [p.Pro2136Hisfs*31], c.4804C>T [p.Arg1602*], and c.7477C>T [p.Arg2493*]) were identified in single individuals. None of the unaffected first-degree relatives were compound heterozygous for these mutations. Moreover, none of the six putative mutations were detected among 477 French Canadian controls. Our data suggest that mutations in C5ORF42 explain a large portion of French Canadian individuals with JBTS.

Effect of nitisinone (NTBC) treatment on the clinical course of hepatorenal tyrosinemia in Québec.

BACKGROUND Hepatorenal tyrosinemia (HT1, fumarylacetoacetate hydrolase deficiency, MIM 276700) can cause severe hepatic, renal and peripheral nerve damage. In Québec, HT1 is frequent and neonatal HT1 screening is practiced. Nitisinone (NTBC, Orfadin ®) inhibits tyrosine degradation prior to the formation of toxic metabolites like succinylacetone and has been offered to HT1 patients in Québec since 1994. METHODS We recorded the clinical course of 78 Québec HT1 patients born between 1984 and 2004. There were three groups: those who never received nitisinone (28 patients), those who were first treated after 1 month of age (26 patients) and those treated before 1 month (24 patients). Retrospective chart review was performed for events before 1994, when nitisinone treatment began, and prospective data collection thereafter. FINDINGS No hospitalizations for acute complications of HT1 occurred during 5731 months of nitisinone treatment, versus 184 during 1312 months without treatment (p<0.001). Liver transplantation was performed in 20 non-nitisinone-treated patients (71%) at a median age of 26 months, versus 7 late-treated patients (26%, p<0.001), and no early-treated patient (p<0.001). No early-treated patient has developed detectable liver disease after more than 5 years. Ten deaths occurred in non-nitisinone treated patients versus two in treated patients (p<0.01). Both of the latter deaths were from complications of transplantation unrelated to HT1. One probable nitisinone-related event occurred, transient corneal crystals with photophobia. INTERPRETATION Nitisinone treatment abolishes the acute complications of HT1. Some patients with established liver disease before nitisinone treatment eventually require hepatic transplantation. Patients who receive nitisinone treatment before 1 month had no detectable liver disease after more than 5 years.

Evaluation of BRCA1 and BRCA2 mutation prevalence, risk prediction models and a multistep testing approach in French-Canadian families with high risk of breast and ovarian cancer

Background and objective: In clinical settings with fixed resources allocated to predictive genetic testing for high-risk cancer predisposition genes, optimal strategies for mutation screening programmes are critically important. These depend on the mutation spectrum found in the population under consideration and the frequency of mutations detected as a function of the personal and family history of cancer, which are both affected by the presence of founder mutations and demographic characteristics of the underlying population. The results of multistep genetic testing for mutations in BRCA1 or BRCA2 in a large series of families with breast cancer in the French-Canadian population of Quebec, Canada are reported. Methods: A total of 256 high-risk families were ascertained from regional familial cancer clinics throughout the province of Quebec. Initially, families were tested for a panel of specific mutations known to occur in this population. Families in which no mutation was identified were then comprehensively tested. Three algorithms to predict the presence of mutations were evaluated, including the prevalence tables provided by Myriad Genetics Laboratories, the Manchester Scoring System and a logistic regression approach based on the data from this study. Results: 8 of the 15 distinct mutations found in 62 BRCA1/BRCA2-positive families had never been previously reported in this population, whereas 82% carried 1 of the 4 mutations currently observed in ⩾2 families. In the subset of 191 families in which at least 1 affected individual was tested, 29% carried a mutation. Of these 27 BRCA1-positive and 29 BRCA2-positive families, 48 (86%) were found to harbour a mutation detected by the initial test. Among the remaining 143 inconclusive families, all 8 families found to have a mutation after complete sequencing had Manchester Scores ⩾18. The logistic regression and Manchester Scores provided equal predictive power, and both were significantly better than the Myriad Genetics Laboratories prevalence tables (p<0.001). A threshold of Manchester Score ⩾18 provided an overall sensitivity of 86% and a specificity of 82%, with a positive predictive value of 66% in this population. Conclusion: In this population, a testing strategy with an initial test using a panel of reported recurrent mutations, followed by full sequencing in families with Manchester Scores ⩾18, represents an efficient test in terms of overall cost and sensitivity.

NADH-coenzyme Q reductase (complex I) deficiency : heterogeneity in phenotype and biochemical findings

SummaryTwelve patient cell lines with biochemically proven complex I deficiency were compared for clinical presentation and outcome, together with their sensitivity to galactose and menadione toxicity. Each patient had elevated lactate to pyruvate ratios demonstrable in fibroblast cultures. Each patient also had decreased rotenone-sensitive NADH-cytochromec reductase (complexes I and III) with normal succinate cytochromec reductase (complexes II and III) and cytochrome oxidase (complex IV) activity in cultured skin fibroblasts, indicating a deficient NADH-coenzyme Q reductase (complex I) activity. The patients fell into five categories: severe neonatal lactic acidosis; Leigh disease; cardiomyopathy and cataracts; hepatopathy and tubulopathy; and mild symptoms with lactic acidaemia. Cell lines from 4 out of the 12 patients were susceptible to both galactose and menadione toxicity and 3 of these also displayed low levels of ATP synthesis in digitonin-permeabilized skin fibroblasts from a number of substrates. This study highlights the heterogeneity of complex I deficiency at the clinical and biochemical level.

Outcome of individuals with low-moderate methylmalonic aciduria detected through a neonatal screening program

BACKGROUND The clinical spectrum of methylmalonic aciduria (MMAuria) ranges from severe, neonatal acidosis to benign asymptomatic organic aciduria. In 1975, screening for MMAuria was established in the province of Quebec. Although newborn screening programs facilitate presymptomatic detection and treatment and also detect asymptomatic variants, uncertainties about potential long-term hazards of mild to moderate elevations of MMA create concern. The objective of this study was to examine the outcome of individuals excreting low to intermediate quantities of MMA, ascertained by a newborn screening program. RESULTS AND STUDY DESIGN One hundred and thirty-six individuals with elevations of urinary MMA were initially identified by the screening program; 122 individuals were noted to have excretion of urinary MMA <1400 micromol/mmol creatinine. At follow-up assessment at 1 year of age, in 65 of these 122 individuals, the MMA excretion had resolved. Of the remaining individuals, 9 were lost to follow-up, 13 had symptoms, and the remaining 35 were free of symptoms. Among the 35 individuals with asymptomatic persistent MMAuria, MMA excretion has resolved in 13 over 1 year; 22 individuals exhibit persistent low-moderate MMAuria (range, 210 to 1133 micromol/mmol creatinine). CONCLUSION Follow-up examination of individuals in the latter asymptomatic cohort with persistent low-moderate MMAuria indicates normal somatic and cognitive outcomes.

Molecular and genealogical characterization of the R1443X BRCA1 mutation in high-risk French-Canadian breast/ovarian cancer families

The Quebec population contains about six-million French Canadians, descended from the French settlers who colonized “Nouvelle-France” between 1608 and 1765. Although the relative genetic contribution of each of these founders is highly variable, altogether they account for the major part of the contemporary French-Canadian gene pool. This study was designed to analyze the role of this founder effect in the introduction and diffusion of the BRCA1 recurrent R1443X mutant allele. A highly conserved haplotype, observed in 18 French-Canadian families and generated using 17 microsatellite markers surrounding the BRCA1 locus, supports the fact that the R1443X mutation is a founder mutation in the Quebec population. We also performed haplotyping analysis of R1443X carriers on 19 other families from seven different nationalities; although the same alleles are shared for three markers surrounding the BRCA1 gene, distinct haplotypes were obtained in four families, suggesting multiple origins for the R1443X mutation. Ascending genealogies of the 18 French Canadian families and of controls were reconstructed on an average depth of 10 generations. We identified the founder couple with the highest probability of having introduced the mutation in the population. Based on the descending genealogy of this couple, we detected the presence of geographical concentration in the diffusion pattern of the mutation. This study demonstrates how molecular genetics and demogenetic analyses can complement each other to provide findings that could have an impact on public health. Moreover, this approach is certainly not unique to breast cancer genetics and could be used to understand other complex traits.

No Evidence of False Reassurance among Women with an Inconclusive BRCA1/2 Genetic Test Result

Background: Little is known about how women who receive an inconclusive result from BRCA1/2 testing interpret their result. Clinical observations suggest that some of them may be falsely reassured and, consequently, may not adhere to recommended surveillance. The purpose of this study is to evaluate whether women with inconclusive BRCA1/2 test results are falsely reassured. Methods: Participants were adult women with a family history suggestive of a germ-line mutation in either the BRCA1 or the BRCA2 gene who underwent genetic testing in the context of the interdisciplinary research program INHERIT BRCAs. Data were collected using selfadministered questionnaires at genetic counseling and 1 month after result disclosure. Reassurance was assessed through indicators of cancer risk perception, cancer worry, relief following result disclosure, painfulness of the test result, and its effect on quality of life. Results: Five-hundred women (105 carriers, 140 noncarriers, and 255 inconclusive) were included in this analysis. Compared to noncarriers, women with inconclusive results had higher cancer risk perception, were more worried about cancer, were less relieved by their test result, and perceived their quality of life as being more adversely affected by it. Conclusion: The differences observed between noncarriers and women who received an inconclusive result run counter to the hypothesis that the latter are falsely reassured following BRCA1/2 testing. For clinicians, our findings show the value of taking precautions to fully explain to women that inconclusive results do not rule out the possibility that they still may face a higher risk of developing breast and/or ovarian cancer. (Cancer Epidemiol Biomarkers Prev 2005;14(12):2862–7)

LRPPRC mutations cause a phenotypically distinct form of Leigh syndrome with cytochrome c oxidase deficiency

Background The natural history of all known patients with French-Canadian Leigh disease (Saguenay-Lac-St-Jean cytochrome c oxidase deficiency, MIM220111, SLSJ-COX), the largest known cohort of patients with a genetically homogeneous, nuclear encoded congenital lactic acidosis, was studied. Results 55 of 56 patients were homozygous for the A354V mutation in LRPPRC. One was a genetic compound (A354V/C1277Xdel8). Clinical features included developmental delay, failure to thrive, characteristic facial appearance and, in 90% of patients, acute crises that have not previously been detailed, either metabolic (fulminant lactic acidosis) and/or neurological (Leigh syndrome and/or stroke-like episodes). Survival ranged from 5 days to >30 years. 46/56 patients (82%) died, at a median age of 1.6 years. Of 73 crises, 38 (52%) were fatal. The immediate causes of death were multiple organ failure and/or Leigh disease. Major predictors of mortality during crises (p<0.005) were hyperglycaemia, hepatic cytolysis, and altered consciousness at admission. Compared to a group of SURF1-deficient Leigh syndrome patients assembled from the literature, SLSJ-COX is distinct by the occurrence of metabolic crises, leading to earlier and higher mortality (p=0.001). Conclusion SLSJ-COX is clinically distinct, with acute fatal acidotic crises on a backdrop of chronic moderate developmental delay and hyperlactataemia. Leigh syndrome is common. Stroke-like episodes can occur. The Leigh syndrome of SLSJ-COX differs from that of SURF1-related COX deficiency. SLSJ-COX has a different spectrum of associated abnormalities, acidotic crises being particularly suggestive of LRPPRC related Leigh syndrome. Even among A354V homozygotes, pronounced differences in survival and severity occur, showing that other genetic and/or environmental factors can influence outcome.

CHD2 haploinsufficiency is associated with developmental delay, intellectual disability, epilepsy and neurobehavioural problems

BackgroundThe chromodomain helicase DNA binding domain (CHD) proteins modulate gene expression via their ability to remodel chromatin structure and influence histone acetylation. Recent studies have shown that CHD2 protein plays a critical role in embryonic development, tumor suppression and survival. Like other genes encoding members of the CHD family, pathogenic mutations in the CHD2 gene are expected to be implicated in human disease. In fact, there is emerging evidence suggesting that CHD2 might contribute to a broad spectrum of neurodevelopmental disorders. Despite growing evidence, a description of the full phenotypic spectrum of this condition is lacking.MethodsWe conducted a multicentre study to identify and characterise the clinical features associated with haploinsufficiency of CHD2. Patients with deletions of this gene were identified from among broadly ascertained clinical cohorts undergoing genomic microarray analysis for developmental delay, congenital anomalies and/or autism spectrum disorder.ResultsDetailed clinical assessments by clinical geneticists showed recurrent clinical symptoms, including developmental delay, intellectual disability, epilepsy, behavioural problems and autism-like features without characteristic facial gestalt or brain malformations observed on magnetic resonance imaging scans. Parental analysis showed that the deletions affecting CHD2 were de novo in all four patients, and analysis of high-resolution microarray data derived from 26,826 unaffected controls showed no deletions of this gene.ConclusionsThe results of this study, in addition to our review of the literature, support a causative role of CHD2 haploinsufficiency in developmental delay, intellectual disability, epilepsy and behavioural problems, with phenotypic variability between individuals.

Identification of 34 novel and 56 known FOXL2 mutations in patients with blepharophimosis syndrome

Blepharophimosis syndrome (BPES) is caused by loss‐of‐function mutations in the single‐exon forkhead transcription factor gene FOXL2 and by genomic rearrangements of the FOXL2 locus. Here, we focus on 92 new intragenic FOXL2 mutations, 34 of which are novel. Specifically, we found 10 nonsense mutations (11%), 13 missense mutations (14%), 40 deletions or insertions leading to a frameshift (43%), and 29 in‐frame changes (32%), of which 28 (30%) lead to a polyalanine expansion. This study confirms the existence of two previously described mutational hotspots. Moreover, we gained novel insights in genotype‐phenotype correlations, emphasizing the need to interpret genotype‐phenotype correlations individually and always in the context of further clinical observations.