Diversity of ARSACS mutations in French-Canadians.

BACKGROUND: The growing number of spastic ataxia of Charlevoix-Saguenay (SACS) gene mutations reported worldwide has broadened the clinical phenotype of autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS). The identification of Quebec ARSACS cases without two known SACS mutation led to the development of a multi-modal genomic strategy to uncover mutations in this large gene and explore phenotype variability. METHODS: Search for SACS mutations by combining various methods on 20 cases with a classical French-Canadian ARSACS phenotype without two mutations and a group of 104 sporadic or recessive spastic ataxia cases of unknown cause. Western blot on lymphoblast protein from cases with different genotypes was probed to establish if they still expressed sacsin. RESULTS: A total of 12 mutations, including 7 novels, were uncovered in Quebec ARSACS cases. The screening of 104 spastic ataxia cases of unknown cause for 98 SACS mutations did not uncover carriers of two mutations. Compounds heterozygotes for one missense SACS mutation were found to minimally express sacsin. CONCLUSIONS: The large number of SACS mutations present even in Quebec suggests that the size of the gene alone may explain the great genotypic diversity. This study does not support an expanding ARSACS phenotype in the French-Canadian population. Most mutations lead to loss of function, though phenotypic variability in other populations may reflect partial loss of function with preservation of some sacsin expression. Our results also highlight the challenge of SACS mutation screening and the necessity to develop new generation sequencing methods to ensure low cost complete gene sequencing.

A novel founder SCN4A mutation causes painful cold-induced myotonia in French-Canadians.

BACKGROUND: Myotonia is observed in classic congenital myotonia caused by CLCN1 mutations and in sodium-channel myotonia (SCM) due to SCN4A mutations. METHODS: We assessed 66 electrically proven cases of myotonia belonging to 17 French-Canadian families living in the Saguenay Lac St-Jean area of Quebec, a region well known for its genetic founder effects. The CLCN1 gene was sequenced in one affected member of each family. SCN4A exons with known SCM mutations were subsequently sequenced in families where no CLCN1 mutations were found. RESULTS: Six families, 33% of cases (22/66), presenting classic congenital myotonia phenotypes were found to carry two previously identified CLCN1 mutations. In the other 11 families comprising 66% of cases (44/66), a new dominant SCN4A mutation in exon 24 (M1476I) was uncovered and segregated with a variable SCM phenotype. Although all carriers of this novel mutation had electrical myotonia, some were asymptomatic (25%) and age at onset was variable in the others (5 to 67, mean 21). Cold aggravated myotonia was observed in 41% of cases and painful myotonia in 18%. Additional features observed include aggravation of symptoms with pregnancies (7%), localized muscle swelling (2%), myotonic reactions to anesthesia (2%), and food-induced paralysis (2%). CONCLUSIONS: This cohort is the largest described with a variable sodium-channel myotonia phenotype caused by a single SCN4A mutation. The clinical variability observed in this cohort underlines the phenotypic heterogeneity of SCN4A mutations and suggests that variants in other genes likely modulate clinical expression.

Two mutations in the HSN2 gene explain the high prevalence of HSAN2 in French Canadians.

BACKGROUND: Hereditary sensory and autonomic neuropathy type 2 (HSAN2; MIM 201300) is a rare recessive neuropathy typically diagnosed in the first decade. The 1973 study of a French Canadian family led to the definition of HSAN2. OBJECTIVES: To demonstrate that the apparent higher prevalence of HSAN2 in Quebec is due to the presence of two HSN2 mutations and that carriers of different mutations appear to have a similar phenotype. METHODS: Through attending physicians, the authors recruited French Canadian patients with HSAN2. Exclusion of linkage to the known HSAN loci and linkage to the HSAN2 was performed using standard methods. Sequencing of the HSN2 gene was used to uncover the causal mutations. RESULTS: A large cluster of HSAN2 patients comprising 16 affected individuals belonging to 13 families was identified. The mode of inheritance is clearly autosomal recessive. All patients originated from southern Quebec, and 75% are from the Lanaudière region. Whereas linkage to the HSAN1, 3, and 4 loci was excluded, linkage to the 12p13.33 HSAN2 locus was confirmed. Sequencing of the HSN2 gene uncovered two French Canadian mutations and a novel nonsense mutation in a patient of Lebanese origin, all predicted to lead to truncations of the HSN2 protein. The comparison of clinical variables between patients with different genotypes does not suggest any difference in phenotype. CONCLUSIONS: Two founder mutations are responsible for the apparently higher prevalence of HSAN2 in French Canadians. Genotype-phenotype correlation does not suggest any significant clinical variability.

Monoclonal 3C6F9 distribution in human breast carcinomas: image cytometry of immunocytochemical assays.

MoAbF9 immunoreactivity was investigated in frozen sections of 123 breast carcinomas using an avidin or streptavidin biotin peroxidase kit. A standardized computer image analysis system was used to evaluate immunostaining. The percent of cell surface staining and mean optical densities were correlated with morphological criteria of prognosis such as tumor size histological grade, blood and lymph invasion and axillary lymph node involvement, with immunoreactivity to other MoAb, i.e. Ki67, anti-RE and anti-RP, anti-p.HER-2/neu and with tumor aneuploidy and AgNORs content in tumor cell nuclei. Despite some heterogeneity, MoAbF9 was reactive with all breast carcinomas tested. The percent of F9 immunostained cell surface and mean optical density increased with Ki67 immunoreactivity, tumor aneuploidy and AgNORs nucleus surface but were independent of p.HER-2/neu oncoprotein distribution and tumor receptor content. These findings suggest that F9 could not only allow detection axillary lymph node micrometastases but also be used as plasmatic marker for tumor recurrence and metastases.