Jerzy Bal

GJB2 Mutations and Degree of Hearing Loss: A Multicenter Study

Hearing impairment (HI) affects 1 in 650 newborns, which makes it the most common congenital sensory impairment. Despite extraordinary genetic heterogeneity, mutations in one gene, GJB2, which encodes the connexin 26 protein and is involved in inner ear homeostasis, are found in up to 50% of patients with autosomal recessive nonsyndromic hearing loss. Because of the high frequency of GJB2 mutations, mutation analysis of this gene is widely available as a diagnostic test. In this study, we assessed the association between genotype and degree of hearing loss in persons with HI and biallelic GJB2 mutations. We performed cross-sectional analyses of GJB2 genotype and audiometric data from 1,531 persons, from 16 different countries, with autosomal recessive, mild-to-profound nonsyndromic HI. The median age of all participants was 8 years; 90% of persons were within the age range of 0-26 years. Of the 83 different mutations identified, 47 were classified as nontruncating, and 36 as truncating. A total of 153 different genotypes were found, of which 56 were homozygous truncating (T/T), 30 were homozygous nontruncating (NT/NT), and 67 were compound heterozygous truncating/nontruncating (T/NT). The degree of HI associated with biallelic truncating mutations was significantly more severe than the HI associated with biallelic nontruncating mutations (P<.0001). The HI of 48 different genotypes was less severe than that of 35delG homozygotes. Several common mutations (M34T, V37I, and L90P) were associated with mild-to-moderate HI (median 25-40 dB). Two genotypes--35delG/R143W (median 105 dB) and 35delG/dela(GJB6-D13S1830) (median 108 dB)--had significantly more-severe HI than that of 35delG homozygotes.

Variation in a Repeat Sequence Determines Whether a Common Variant of the Cystic Fibrosis Transmembrane Conductance Regulator Gene Is Pathogenic or Benign

An abbreviated tract of five thymidines (5T) in intron 8 of the cystic fibrosis transmembrane conductance regulator (CFTR) gene is found in approximately 10% of individuals in the general population. When found in trans with a severe CFTR mutation, 5T can result in male infertility, nonclassic cystic fibrosis, or a normal phenotype. To test whether the number of TG repeats adjacent to 5T influences disease penetrance, we determined TG repeat number in 98 patients with male infertility due to congenital absence of the vas deferens, 9 patients with nonclassic CF, and 27 unaffected individuals (fertile men). Each of the individuals in this study had a severe CFTR mutation on one CFTR gene and 5T on the other. Of the unaffected individuals, 78% (21 of 27) had 5T adjacent to 11 TG repeats, compared with 9% (10 of 107) of affected individuals. Conversely, 91% (97 of 107) of affected individuals had 12 or 13 TG repeats, versus only 22% (6 of 27) of unaffected individuals (P<.00001). Those individuals with 5T adjacent to either 12 or 13 TG repeats were substantially more likely to exhibit an abnormal phenotype than those with 5T adjacent to 11 TG repeats (odds ratio 34.0, 95% CI 11.1-103.7, P<.00001). Thus, determination of TG repeat number will allow for more accurate prediction of benign versus pathogenic 5T alleles.

Detection of a cystic fibrosis modifier locus for meconium ileus on human chromosome 19q13

Detection of a cystic fibrosis modifier locus for meconium ileus on human chromosome 19q13

Analysis of cftr , spink1 , prss1 and aat Mutations in Children With Acute or Chronic Pancreatitis

Objectives: Defects of PRSS1, SPINK1, CFTR and AAT are considered causative or predisposing to pancreatitis. The aim of this study was to evaluate the impact of these defects into molecular pathology of chronic pancreatitis (CP) and acute recurrent pancreatitis (ARP). Methods: Ninety-two children with CP or ARP, 55 family members and 50 controls were investigated. The subjects were screened for PRSS1 mutations: R122H, R122C, A16V, N29I; SPINK1 N34S variant; panel of 14 CFTR defects: INNOLiPA CFTR12, CFTRdele2,3 and IVS8-T variant or panel of 3 CFTR defects-F508del, CFTRdele2,3 and IVS8-T; AAT mutations: E264V, E342K. Results: We identified 1 mutated allele in at least 1 of 4 genes in 31 of 92 patients and 12 of 50 controls (P = 0.157). Mutations in SPINK1 and PRSS1 were most frequent. PRSS1 mutations were identified mainly in CP patients (9.6% of CP vs 2.5% of ARP alleles, P = 0.094), whereas N34S SPINK1 mutation was present with comparable frequency in CP and ARP patients (7.7% vs 10.0%, P = 0.768). The frequency of mutations in CFTR alleles was similar to controls (4.9% vs 5%, P = 0.587). Overall frequency of AAT mutations was lower than in the controls. Family studies showed that defects in the examined genes did not always segregate with disease. Conclusions: PRSS1 defects seem to be causative for pancreatitis, whereas defects in SPINK1 are suggested to be associated with the disease. No association between CFTR mutations and pancreatitis was observed. The importance of AAT variants remains speculative.

4-nitroquinoline-1-oxide: A good mutagen for Aspergillus nidulans

Abstract Conditions for using 4-nitroquinoline-1-oxide as a mutagen for Aspergillus nidulans were established. High frequencies of mutations (about 0.5%) and a broad spectrum of mutants were obtained. The stability of NQO in solutions and safety precautions are described.

Phenotypic variability of patients homozygous for the GJB2 mutation 35delG cannot be explained by the influence of one major modifier gene

Hereditary hearing loss (HL) is a very heterogeneous trait, with 46 gene identifications for non-syndromic HL. Mutations in GJB2 cause up to half of all cases of severe-to-profound congenital autosomal recessive non-syndromic HL, with 35delG being the most frequent mutation in Caucasians. Although a genotype–phenotype correlation has been established for most GJB2 genotypes, the HL of 35delG homozygous patients is mild to profound. We hypothesise that this phenotypic variability is at least partly caused by the influence of modifier genes. By performing a whole-genome association (WGA) study on 35delG homozygotes, we sought to identify modifier genes. The association study was performed by comparing the genotypes of mild/moderate cases and profound cases. The first analysis included a pooling-based WGA study of a first set of 255 samples by using both the Illumina 550K and Affymetrix 500K chips. This analysis resulted in a ranking of all analysed single-nucleotide polymorphisms (SNPs) according to their P-values. The top 250 most significantly associated SNPs were genotyped individually in the same sample set. All 192 SNPs that still had significant P-values were genotyped in a second independent set of 297 samples for replication. The significant P-values were replicated in nine SNPs, with combined P-values between 3 × 10−3 and 1 × 10−4. This study suggests that the phenotypic variability in 35delG homozygous patients cannot be explained by the effect of one major modifier gene. Significantly associated SNPs may reflect a small modifying effect on the phenotype. Increasing the power of the study will be of greatest importance to confirm these results.

Novel mutation of IL1RAPL1 gene in a nonspecific X-linked mental retardation (MRX) family.

Mental retardation (MR) affects approximately 2% of the population. About 10% of all MR cases result from defects of X‐linked genes. Mutations in most of more than 20 known genes causing nonspecific form of X‐linked MR (MRX) are very rare and may account for less than 0.5–1% of MR. Linkage studies in extended pedigrees followed by mutational analysis of known MRX genes in the linked interval are often the only way to identify a genetic cause of the disorder. We performed linkage analysis in several MRX families, and in one family with four males with MR we mapped the disease to an interval encompassing Xp21.2–22.11 (with a maximum LOD score of 2.71). Subsequent mutation analysis of genes located in this interval allowed us to identify a partial deletion of the IL1RAPL1 gene. Different nonoverlapping deletions involving IL1RAPL1 have been reported previously, suggesting that this region could be deletion‐prone. In this report, we present the results of the molecular analyses and clinical examinations of four affected family members with the deletion in IL1RAPL1. Our data further confirm the importance and usefulness of linkage studies for gene mapping in MRX families and demonstrate that IL1RAPL1 plays an important role in the etiology of MRX. With the development of new methods (aCGH, MLPA), further rearrangements in this gene (including deletions and duplications) might be discovered in the nearest future.

The COL7A1 mutation database

Dystrophic Epidermolysis Bullosa (DEB) is a genetic disease caused by mutations in the COL7A1 gene that is inherited in the autosomal dominant or recessive mode. We have developed a curated, freely accessible COL7A1 specific database (http://www.col7a1‐database.info), which contains more than 730 reported and unpublished sequence variants of the gene. Molecular defects are reported according to HGVS recommendation. The clinical description module is provided with an advanced search tool together with a CSV (comm. separated values) data format download option. This compilation of COL7A1 data and nomenclature is aimed at assisting molecular and clinical geneticists to enhance the collaboration between researchers worldwide. Hum Mutat 33:327–331, 2012.

The ARX mutations: a frequent cause of X-linked mental retardation.

The ARX gene mutations have been demonstrated to cause different forms of mental retardation (MR). Beside FMR1, in families with X‐linked mental retardation (XLMR), the ARX dysfunction was demonstrated to be among the most frequent causes of this heterogeneous group of disorders. Nevertheless, in sporadic cases of MR, ARX mutations are extremely rare. In order to evaluate the frequency of ARX mutation in XLMR, we performed mutational analysis of ARX in 165 mentally retarded probands negative for FRAXA and belonging to families in which the condition segregates as an X‐linked condition. The same recurrent mutation, an in frame 24 bp insertion (c.428‐451dup (24 bp)), was identified in five patients. In one family, the mother of two affected boys was found not to carry the mutation detected in her sons. These data suggest the presence of germline mosaicism for the mutation in the mother. Our results confirm the significant contribution of ARX mutations in the etiology of MR, especially in this group of patients selected for XLMR (3%). These data, together with those reported in the literature, imply that screening for c.428‐451 dup (24 bp) mutation should be recommended in all patients with suspected XLMR.

Novel A18T and pA29S substitutions in α-synuclein may be associated with sporadic Parkinson's disease.

OBJECTIVE Mutations in the α-synuclein-encoding gene SNCA are considered as a rare cause of Parkinsons disease (PD). Our objective was to examine the frequency of the SNCA point mutations among PD patients of Polish origin. METHODS Detection of the known SNCA point mutations A30P (c.88G>C), E46K (c.136G>A) and A53T (c.157A>T) was performed either using the Sequenom MassArray iPLEX platform or by direct sequencing of the SNCA exons 2 and 3. As the two novel substitutions A18T (c.52G>A) and A29S (c.85G>T) were identified, their frequency in a control population of Polish origin was assessed and in silico analysis performed to investigate the potential impact on protein structure and function. RESULTS We did not observe the previously reported point mutations in the SNCA gene in our 629 PD patients; however, two novel potentially pathogenic substitutions A18T and A29S were identified. Each variant was observed in a single patient presenting with a typical late-onset sporadic PD phenotype. Although neither variant was observed in control subjects and in silico protein analysis predicts a damaging effect for A18T and pA29S substitutions, the lack of family history brings into question the true pathogenicity of these rare variants. CONCLUSIONS Larger population based studies are needed to determine the pathogenicity of the A18T and A29S substitutions. Our findings highlight the possible role of rare variants contributing to disease risk and may support further screening of the SNCA gene in sporadic PD patients from different populations.