Prenatal microarray comparative genomic hybridization: Experience from the two first years of activity at the Lyon university-hospital.

OBJECTIVES: This study aims to describe how microarray comparative genomic hybridization (aCGH) has shifted to become a prenatal diagnosis tool at the Lyon university-hospital. MATERIALS AND METHODS: This retrospective study included all patients who were referred in the 3 pluridisciplinary centers for prenatal diagnosis of the Lyon university-hospital and who received a prenatal aCGH between June 2013 and June 2015. aCGH was systematically performed in parallel with a karyotype, using the PréCytoNEM array design. RESULTS: A total of 260 microarrays were performed for the following indications: 249 abnormal ultrasounds (95.8%), 7 characterizations of chromosomal rearrangements (2.7%), and 4 twins with no abnormal ultrasounds (1.5%). With a resolution of 1 mega base, we found 235 normal results (90.4%), 23 abnormal results (8.8%) and 2 non-returns (0.8%). For the chromosomal rearrangements visible on the karyotype, aCGH identified all of the 12 unbalanced rearrangements and did not identify the 2 balanced rearrangements. Among the fetuses with normal karyotypes, 11 showed abnormal microarray results, corresponding to unbalanced cryptic chromosomal rearrangements (4.2%). CONCLUSION: Transferring aCGH to a prenatal diagnosis at the Lyon university-hospital has increased the detection rate of chromosomal abnormalities by 4.2% compared to the single karyotype.

[Autosomal dominant limb-girdle muscular dystrophy associated with conduction defects (LGMD1B): a description of 8 new families with the LMNA gene mutations]. / La dystrophie musculaire des ceintures autosomique dominante associée à des troubles de la conduction cardiaque (LGMD1B). Description de 8 nouvelles familles avec mutations du gène LMNA.

INTRODUCTION: Limb girdle muscular dystrophy type 1b (LGMD1B), due to LMNA gene mutations, is a relatively rare form of LGMD characterized by proximal muscle involvement associated with heart involvement comprising atrio-ventricular conduction blocks and dilated cardiomyopathy. Its clinical and genetic diagnosis is crucial for cardiac management and genetic counselling. Seven LMNA mutations have been previously reported to be responsible for LGMD1B. PATIENTS AND METHODS: We describe the neurological and cardiologic features of 14 patients belonging to 8 families in whom we identified 6 different LMNA mutations, 4 of them having never been reported. Results. Eleven patients had an LGMD1B phenotype with scapulohumeral and pelvic-femoral involvement. Thirteen patients had cardiac disease associating conduction defects (12 patients) or arrhythmias (9 patients). Seven patients needed cardiac device (pacemaker or implantable cardiac defibrillator) and two had heart transplantation. CONCLUSION: This study allowed us to specify the clinical characteristics of this entity and to outline the first phenotype/genotype relations resulting from these observations.

CTG instability in myotonic dystrophy: molecular genetic analysis of families from south-eastern France with characteristics of intergenerational variation in CGT repeat numbers.

We report clinical, genetical and genealogical findings in 149 French families from the Rhône-Alpes area studied over a 5-year period. There was a significant excess of DM females compared to DM males with (CTG) repeat sizes between 1-2 kb. The mean maternal (CTG) repeat size was higher than paternal repeat size. Anticipation phenomenom was significantly higher after maternal than after paternal transmission. A significant correlation between parental (CTG) repeat size and intergenerational variation both in paternal and maternal transmissions was observed. The anticipation phenomenom was more important for sons than daughters particularly after maternal transmission. The mean (CTG) repeat size in mothers of CDM cases was about twice that of mothers of NCDM children. The risk of giving birth to a CDM child increased considerably when the number of maternal (CTG) repeats was over 300 (CTG). A significant excess of DM females was observed. They had on average 24% fewer children than male patients. Paternal transmission (63.6%) of DM occurred more frequently than maternal transmission (52.7%).

Characterisation of 16 polymorphic markers in the NF2 gene: application to hemizygosity detection.

Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder that predisposes to nervous system tumors. Point mutations are evidenced in about 50% of the NF2 patients and large genomic deletions account for approximately 33% of the NF2 gene alterations. To facilitate the deletion screening, 16 polymorphic markers were identified in the NF2 genomic sequence enabling an hemizygosity test in familial studies.

NF2 gene in neurofibromatosis type 2 patients.

Neurofibromatosis type 2 (NF2) is an autosomal dominant disorder that predisposes to nervous system tumors. The schwannomin (also termed merlin) protein encoded by the NF2 gene shows a close relationship to the family of cytoskeleton-to-membrane proteins linkers ERM (ezrin-radixin-moesin proteins). Even though penetrance of the disease is >95% and no genetic heterogeneity has been described, point mutations in the NF2 gene have been observed in only 34-66% of the screened NF2 patients, depending on the series. In order to generate tools that would enable an exhaustive alteration screening for the NF2 gene, we have deduced its entire genomic sequence. This knowledge has provided the delineation of a mutation screening strategy which, when applied to a series of 19 NF2 patients, has revealed a high recurrence of large deletions in the gene and has raised the efficiency of mutation detection in NF2 patients to 84% of the cases in this series. The remaining three patients who express two functional NF2 alleles are all sporadic cases, an observation compatible with the presence of mosaicism for NF2 mutation.

New mutations in the X-linked form of Charcot-Marie-Tooth disease.

Mutations in the gene for connexin 32 are associated with a chromosome X-linked form of Charcot-Marie-Tooth disease. The prevalence of this form is probably underestimated. We screened 12 candidate families and found 7 missense mutations of which 4 are new. These mutations are located in intra- and extramembraneous parts of the protein. Some mutations are probably present with a higher frequency. This study further confirms variation of connexin 32 mutations with scarcity in the second transmembrane domain and, so far, absence in the fourth transmembrane domain and in the carboxy-terminal region.

Mutations in the X-linked form of Charcot-Marie-Tooth disease in the French population.

The present study reports eight additional mutations in the connexin32 gene associated with the X-linked form of Charcot-Marie-Tooth disease. One of these mutations was found twice in two apparently unrelated families. This form of the disease is demyelinating and dominant. However, patient selection for mutational screening should not be limited to these criteria since presentation can either be familial or sporadic, and some patients may be incorrectly classified as suffering from an 'axonal' form. These new mutations complete our previously published work on 12 other mutations and enable meaningful observation in a representative sample of the French population. Mutations are found in all regions of the gene. The most frequently observed mutations were those affecting arginines and mainly involved CpG sequences. Compared with other sources, some of the mutations were present at a higher frequency in the French population.

X-linked dominant Charcot-Marie-Tooth neuropathy (CMTX): new mutations in the connexin32 gene.

X-linked dominant Charcot-Marie-Tooth (CMTX) neuropathy has been mapped to the Xq13 region. Subsequently, several mutations that could account for CMTX have been detected in the coding part of the connexin32 (Cx32) gene, which is located within this region. In order to develop more specific diagnostic tools, we have begun a systematic screening of families with dominant CMTX for mutations in the coding region of the Cx32 gene. This report describes a study of ten families and different mutations segregating with the disease were detected in five of them. In addition to the previously reported Arg22stop and Arg215Trp substitutions, three novel mutations are described, including two different missense mutations at codon Arg22 (Arg22Pro and Arg22Gly), and a nonsense mutation at codon Trp133. The identification of new CMTX-causing mutations is a critical step for carrier detection and presymptomatic diagnosis, and should provide essential information on the structure-function relationship of Cx32 in vitro as well as in vivo.

Molecular diagnosis of Charcot-Marie-Tooth 1A disease and hereditary neuropathy with liability to pressure palsies by quantifying CMT1A-REP sequences: consequences of recombinations at variant sites on chromosomes 17p11.2-12.

The most frequent form of Charcot-Marie-Tooth disease (CMT1A; OMIM118.220) is the result of a duplication on chromosome 17 in pll.2-p12. This region contains PMP22, a gene expressed in peripheral myelin. The mutation results from an unequal crossing-over involving repeated sequences, CMT1A-REP, located on both sides of the duplicated region. The reciprocal product of this recombination is a deletion of the same region, which is associated with hereditary neuropathy with liability to pressure palsies (HNPP; OMIM162.500). Proximal and distal CMT1A-REP sequences can be distinguished by the presence of a variant EcoRI site. We quantified the number of these repeat sequences in 36 CMT1A and 40 HNPP patients. CMT1A-REP sequences are involved in almost all of the mutations. The majority of recombination breakpoints occur distally from the variant EcoRI site. However, a few have a breakpoint proximal to this site, which creates the risk of misinterpretation with respect to a duplicated/deleted status.

Mutations in the myelin protein zero gene associated with Charcot-Marie-Tooth disease type 1B.

Charcot-Marie-Tooth type 1 (CMT1) disease is an autosomal dominant neuropathy of the peripheral nerve. The majority of CMT 1 cases are due to a duplication of an 1.5-Mb DNA fragment on chromosome 17p11.2 (CMT 1a). Micromutations were found in the gene for peripheral myelin protein 22 (PMP22) located in the duplicated region of CMT 1a, and in the peripheral myelin protein zero (PO) located on chromosome 1q21-q23 (CMT 1b). We have characterized two new mutations in the PO gene in two french families presenting CMT disease. Both mutations occur in the extracellular domain of the PO protein. One mutation is a de novo mutation and is from paternal origin.

[Renal hypoplasia, polydactyly, cardiopathy: a new syndrome?]. / Hypoplasie rénale, polydactylie, cardiopathie: un nouveau syndrome?

The occurrence of a polymalformation pattern associated with a polydactyly indicates a mendelian inheritance. We report a case with renal hypoplasia, polydactyly, congenital heart defects. A large literature review makes the differential diagnosis and brings this case nearer to an anterior observation of the literature. We discuss an eventual new syndrome with autosomal recessive inheritance.

[Female pseudohermaphroditism associated with cloacal dysgenesis]. / Pseudo-hermaphrodisme féminin associé à une dysgénésie cloacale.

Pregnancy terminated for a severe oligoamnios and renal dysplasia. Chromosomal, gonadal, internal genitalia sexes are female. There is a cloacal dysgenesis, with caudal appendice and hypoplastic external genitalia of male type. Single umbilical artery and congenital cardiac malformation (complete atrio ventricular communication) are associated. Embryopathologic explanation for this female pseudo-hermaphroditism is proposed.