The "extreme phenotype approach" applied to male breast cancer allows the identification of rare variants of ATR as potential breast cancer susceptibility alleles.

In oncogenetics, some patients could be considered as "extreme phenotypes", such as those with very early onset presentation or multiple primary malignancies, unusually high numbers of cancers of the same spectrum or rare cancer types in the same parental branch. For these cases, a genetic predisposition is very likely, but classical candidate gene panel analyses often and frustratingly remains negative. In the framework of the EX2TRICAN project, exploring unresolved extreme cancer phenotypes, we applied exome sequencing on rare familial cases with male breast cancer, identifying a novel pathogenic variant of ATR (p.Leu1808*). ATR has already been suspected as being a predisposing gene to breast cancer in women. We next identified 3 additional ATR variants in a cohort of both male and female with early onset and familial breast cancers (c.7762-2A>C; c.2078+1G>A; c.1A>G). Further molecular and cellular investigations showed impacts on transcripts for variants affecting splicing sites and reduction of ATR expression and phosphorylation of the ATR substrate CHEK1. This work further demonstrates the interest of an extended genetic analysis such as exome sequencing to identify very rare variants that can play a role in cancer predisposition in extreme phenotype cancer cases unexplained by classical cancer gene panels testing.

First description of a double heterozygosity for BRCA1 and BRCA2 pathogenic variants in a French metastatic breast cancer patient: A case report.

Hereditary breast and ovarian cancer syndrome is an autosomal dominant disease caused primarily by germline mutations in the BRCA1 or BRCA2 gene. Rare cases of double heterozygosity for BRCA1 and BRCA2 mutations have been reported quite exceptionally in non-Ashkenazi individuals. We describe the case of a woman who developed a bilateral breast cancer, discovered concomitantly, at 46 years old. Biopsies confirmed the presence of two breast cancers with distinct histology. BRCA analysis was tested due to a positive family history of breast cancer, and two pathogenic monoallelic mutations were detected, one in the BRCA1 gene and one in the BRCA2 gene. There is no known Ashkenazi Jewish ancestry. We report the first description of a never described double heterozygosity for BRCA1 and BRCA2 pathogenic variants in a French metastatic breast cancer patient, with two distinct histology, and two distinct mutations.

A Variant of GJD2, Encoding for Connexin 36, Alters the Function of Insulin Producing ß-Cells.

Signalling through gap junctions contributes to control insulin secretion and, thus, blood glucose levels. Gap junctions of the insulin-producing ß-cells are made of connexin 36 (Cx36), which is encoded by the GJD2 gene. Cx36-null mice feature alterations mimicking those observed in type 2 diabetes (T2D). GJD2 is also expressed in neurons, which share a number of common features with pancreatic ß-cells. Given that a synonymous exonic single nucleotide polymorphism of human Cx36 (SNP rs3743123) associates with altered function of central neurons in a subset of epileptic patients, we investigated whether this SNP also caused alterations of ß-cell function. Transfection of rs3743123 cDNA in connexin-lacking HeLa cells resulted in altered formation of gap junction plaques and cell coupling, as compared to those induced by wild type (WT) GJD2 cDNA. Transgenic mice expressing the very same cDNAs under an insulin promoter revealed that SNP rs3743123 expression consistently lead to a post-natal reduction of islet Cx36 levels and ß-cell survival, resulting in hyperglycemia in selected lines. These changes were not observed in sex- and age-matched controls expressing WT hCx36. The variant GJD2 only marginally associated to heterogeneous populations of diabetic patients. The data document that a silent polymorphism of GJD2 is associated with altered ß-cell function, presumably contributing to T2D pathogenesis.

Connexin36 and pancreatic beta-cell functions.

Most cell types are functionally coupled by connexin (Cx) channels, i.e. exchange cytoplasmic ions and small metabolites through gap junction domains of their membrane. This form of direct cell-to-cell communication occurs in all existing animals, whatever their position in the phylogenetic scale, and up to humans. Pancreatic beta-cells are no exception, and normally cross-talk with their neighbors via channels made of Cx36. These exchanges importantly contribute to coordinate and synchronize the function of individual cells within pancreatic islets, particularly in the context of glucose-induced insulin secretion. Compelling evidence now indicates that Cx36-mediated coupling, and/or the Cx36 protein per se, play significant regulatory roles in various beta-cell functions, ranging from the biosynthesis, storage and release of insulin. Recent preliminary data further suggest that the protein may also be implicated in the balance of beta-cell growth versus necrosis and apoptosis, and in the regulated expression of specific genes. Here, we review this evidence, discuss the possible involvement of Cx36 in the pathophysiology of diabetes, and evaluate the relevance of this connexin in the therapeutic approaches to the disease.

Involvement of gap junctional communication in secretion.

Glands were the first type of tissues in which the permissive role of gap junctions in the cell-to-cell transfer of membrane-impermeant molecules was shown. During the 40 years that have followed this seminal finding, gap junctions have been documented in all types of multicellular secretory systems, whether of the exocrine, endocrine or pheromonal nature. Also, compelling evidence now indicates that gap junction-mediated coupling, and/or the connexin proteins per se, play significant regulatory roles in various aspects of gland functions, ranging from the biosynthesis, storage and release of a variety of secretory products, to the control of the growth and differentiation of secretory cells, and to the regulation of gland morphogenesis. This review summarizes this evidence in the light of recent reports.

Conversely to its sibling Drosophila melanogaster, D. simulans overcomes the immunosuppressive effects of the parasitoid Asobara citri.

The endoparasitoid Asobara citri avoids Drosophila melanogaster immune defenses, thanks to immune suppressive effects. We investigated whether this parasitoid could also circumvent the immune reaction of D. simulans, a sibling species of D. melanogaster. The rates of infestation, successful parasitism, total encapsulation and mortality were measured after complete development of both D. melanogaster and D. simulans larvae parasitized by A. citri. Results showed that the parasitoids were almost never encapsulated in D. melanogaster larvae, while 45% were encapsulated in D. simulans. A. citri induced a targeted disruption of the hematopoietic organs and a decrease of the hemocytes load in host larvae of both species. Despite such disruptive immune effects most D. simulans larvae succeeded in encapsulating A. citri eggs, probably thanks to their ability to immediately mount a capsule after infestation. This work brings some insight into the diversity of the immune potentials evolved by Drosophila species towards parasitoids.

Kir6.2 mutations are a common cause of permanent neonatal diabetes in a large cohort of French patients.

Permanent neonatal diabetes (PND), requiring insulin within the first months of life, is unexplained at the molecular level in most cases. It has very recently been shown that heterozygous activating mutations in the KCNJ11 gene, encoding the Kir6.2 subunit of the pancreatic ATP-sensitive K(+) channel involved in the regulation of insulin secretion, cause PND. In the present study, we screened the KCNJ11 gene for mutations in French patients with PND. Patients were recruited through the French network for the study of neonatal diabetes. Seventeen at-term babies with a median age at diagnosis of diabetes of 64 days (range 1-260) were included. We identified in nine patients seven heterozygous nonsynonymous mutations: three of them (V59M, R201C, and R201H) were already described, and the four novel mutations resulted in an amino acid change of Kir6.2 at positions F35L, G53N, E322K, and Y330C. More patients with a Kir6.2 mutation (six of nine) were reported to have a smaller birth weight than those without mutation (two of eight). Although Kir6.2 mutation carriers do not represent a phenotypically specific form of PND, an impaired function of Kir6.2 is associated with in utero insulin secretory insufficiency and growth retardation. In conclusion, we confirmed that Kir6.2 mutations are a common cause (53%) of PND in Caucasians.

Genome-wide search for type 2 diabetes in Japanese affected sib-pairs confirms susceptibility genes on 3q, 15q, and 20q and identifies two new candidate Loci on 7p and 11p.

The genetic background that predisposes the Japanese population to type 2 diabetes is largely unknown. Therefore, we conducted a 10-cM genome-wide scan for type 2 diabetes traits in the 359 affected individuals from 159 families, yielding 224 affected sib-pairs of Japanese origin. Nonparametric multipoint linkage analyses performed in the whole population showed one suggestive linked region on 11p13-p12 (maximum logarithm of odds score [MLS] 3.08, near Pax6) and seven potentially linked regions (MLS >1.17) at 1p36-p32, 2q34, 3q26-q28, 6p23, 7p22-p21, 15q13-q21, and 20q12-q13 (near the gene for hepatocyte nuclear factor-4alpha [HNF-4alpha]). Subset analyses according to maximal BMI and early age at diagnosis added suggestive evidence of linkage with type 2 diabetes at 7p22-p21 (MLS 3.51), 15q13-q21 (MLS 3.91), and 20q12-q13 (MLS 2.32). These results support previous indication for linkage found on chromosome 3q, 15q, and 20q in other populations and identifies two new potential loci on 7p and 11p that may confer genetic risk for type 2 diabetes in the Japanese population.