Recurrent copy number variations as risk factors for autism spectrum disorders: analysis of the clinical implications

Chromosomal microarray analysis (CMA) is currently considered a first-tier diagnostic assay for the investigation of autism spectrum disorders (ASD), developmental delay and intellectual disability of unknown etiology. High-resolution arrays were utilized for the identification of copy number variations (CNVs) in 195 ASD patients of Greek origin (126 males, 69 females). CMA resulted in the detection of 65 CNVs, excluding the known polymorphic copy number polymorphisms also found in the Database of Genomic Variants, for 51/195 patients (26.1%). Parental DNA testing in 20/51 patients revealed that 17 CNVs were de novo, 6 paternal and 3 of maternal origin. The majority of the 65 CNVs were deletions (66.1%), of which 5 on the X-chromosome while the duplications, of which 7 on the X-chromosome, were rarer (22/65, 33.8%). Fifty-one CNVs from a total of 65, reported for our cohort of ASD patients, were of diagnostic significance and well described in the literature while 14 CNVs (8 losses, 6 gains) were characterized as variants of unknown significance and need further investigation. Among the 51 patients, 39 carried one CNV, 10 carried two CNVs and 2 carried three CNVs. The use of CMA, its clinical validity and utility was assessed.

Complex rearrangements of chromosome 15 in two patients with mild/atypical Prader Willi syndrome

Multiple mechanisms are responsible for the development of Prader Willi syndrome (PWS), the most common genetic cause of obesity in childhood. Molecular findings are usually deletions and uniparental disomy (UPD) of the 15q11-13 region. Rarely, structural rearrangements of the pericentromeric region of chromosome 15 are also detected. Two cases with mild PWS phenotype and complex maternal UPD identified by microsatellite analysis are described: the first patient had uniparental iso and heterodisomy and the second displayed biallelic inheritance and uniparental isodisomy.

Association of repeat polymorphisms in the estrogen receptors alpha, beta (ESR1, ESR2) and androgen receptor (AR) genes with the occurrence of breast cancer

Genetic variation in genes involved in estrogen biosynthesis, metabolism and signal transduction have been suggested to play a role in breast cancer. To determine the possible contribution of genetic variation in the ESR1 (ER-alpha), ESR2 (ER-beta) and AR genes in breast cancer risk the -1174(TA)(7-27), c. 1092+3607(CA)(10-26) and c. 172(CAG)(6-40) repeat variants were studied in a case-control study of 79 women with sporadic breast cancer and 155 controls. No significant difference was observed in the frequency distribution of -1174(TA)(7-27) in the ESR1 gene between patients and controls, while a significant difference was observed for repeat polymorphisms c. 1092+3607(CA)(10-26) in the ESR2 gene and c. 172(CAG)(6-40) in the AR gene (p0.0001). A significantly decreased odds ratio (OR) for breast cancer risk was observed in individuals having the LL and the SL genotypes for both the ESR2 (OR=0.010, 95% CI 0.003-0.036, p<0.001; OR=0.013, 95% CI 0.004-0.040, p<0.0001, respectively) and the AR gene (OR=0.040, 95% CI 0.011-0.138, p<0.0001; OR=0.189, 95% CI 0.10-0.359, p<0.0001, respectively), compared to SS genotype. The protective effect of these genotypes remained evident even after adjustment for various risk factors (BMI, age, age at menarche and menopause, family history). In conclusion, an association for breast cancer risk between short (SS) alleles for the repeat variants of the ESR2 and AR genes was found in women of Greek descent.

Audiological profile of the prevalent genetic form of childhood sensorineural hearing loss due to GJB2 mutations in northern Greece

The present study describes the audiological profile of genetic hearing loss resulting from GJB2 mutations in northern Greece, as this represents the most frequent single cause of childhood sensorineural hearing loss. The 35delG mutation in homozygosity was detected in 27 of 107 patients (25.2%). The audiological profile is that of a profound or severe sensorineural hearing loss, with a sloping or flat configuration of the audiogram, mostly symmetrical, non-progressive and affecting more the higher frequencies. This profile underlines the importance of early identification and genetic family counseling leading to the future possibility of prevention of deafness.

Prelingual nonsyndromic hearing loss in Greece. Molecular and clinical findings

Mutations in the gene encoding the gap-junction protein connexin 26 (GJB2) on chromosome 13q11 have been shown as a major contributor to prelingual, sensorineural, nonsyndromic deafness. One specific mutation, 35delG, has accounted for the majority of the mutations detected in the GJB2 gene in Caucasian populations and is one of the most frequent disease mutations identified so far with highest carrier frequency of 3,5% in the Greek population. In a collaboration with the major referral centers for childhood deafness in Greece, patients were examined by an extensive questionnaire to exclude syndromic forms and environmental causes of deafness and by allele-specific PCR for the detection of the 35delG mutation. The 35delG mutation was found in 32.1% of the alleles in 173 unrelated cases of prelingual deafness: 50 homozygotes and 11 heterozygotes. Individuals heterozygous for the 35delG mutation were further analyzed by direct genomic sequencing of the coding region of the GJB2 gene, which revealed R184P and 486insT mutations in single alleles. We conclude that the 35delG GJB2 mutation is responsible for one third of prelingual, sensorineural deafness in Greece, which is higher than the usually quoted 20% for Caucasian populations.

Prenatal diagnosis of prelingual deafness: carrier testing and prenatal diagnosis of the common GJB2 35delG mutation

Mutations in the gene encoding the gap-junction protein connexin 26 (GJB2) on chromosome 13q11 (DFNB1 locus) have been shown as a major contributor to prelingual, non-syndromic, autosomal recessive deafness in Caucasian populations. One specific mutation, 35delG, has accounted for the majority of the mutations detected in the GJB2 gene and is one of the most frequent disease mutations identified to date. We have previously reported a carrier frequency of 35delG of 3.5% in the Greek population, and the 35delG mutation has been detected in one-third of the alleles in Greek patients with sensorineural, prelingual, non-syndromic deafness. The description of this common mutation has opened the way to prenatal diagnosis of prelingual deafness, and we here describe our experience with 29 couples requesting counseling, carrier testing and prenatal diagnosis of DFNB1 deafness.

Mutation analysis of the GJB2 (connexin 26) gene by DGGE in Greek patients with sensorineural deafness

The GJB2 (connexin 26) gene, one of the major genes responsible for autosomal recessive deafness, has been investigated previously by a variety of techniques, including PCR-SSCP and sequencing of the entire gene for screening of unknown mutations, and allele-specific PCR, ASO, and PCR-mediated site-directed mutagenesis for the detection of the common mutation 35delG. Here, we present the development of a DGGE method for the characterization of the full spectrum of mutations in the GJB2 gene. The GJB2 cDNA and flanking sequences were amplified in three overlapping segments. We screened 26 Greek patients with prelingual, sensorineural deafness, where syndromic forms and environmental causes of deafness had been excluded. The 35delG mutation was detected in 28 chromosomes (53.8%), while another three sequence variations accounted for 7.6% of the alleles. The sequence variation R127H, previously described in a few Spanish and Balkan patients, was detected in two patients as the sole mutation. A novel sequence variation, K224Q, was identified as the sole mutation in one patient. Use of this approach may contribute to the full description of mutations in this important deafness gene.