Overlapping but distinct roles for NOTCH receptors in human cardiovascular disease.

The NOTCH signalling pathway is an essential pathway, involved in many cellular processes, including cell fate decision, cell proliferation, and cell death and important in the development of most organs. Mutations in genes encoding components of the NOTCH signalling pathway lead to a spectrum of congenital disorders. Over the past decades, mutations in human NOTCH signalling genes have been identified in several diseases with cardiovascular involvement. NOTCH1 mutations have been described in bicuspid aortic valve disease, left-sided congenital heart disease, and Adams-Oliver syndrome. NOTCH2 mutations lead to the development of Alagille syndrome, while mutations in NOTCH3 cause cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy. To date, mutations in NOTCH4 have not been associated with cardiovascular disease. This review focuses on the mutations described in NOTCH1, NOTCH2, and NOTCH3 and their associated cardiovascular phenotypes.

Genetics of sudden cardiac death in the young.

Sudden cardiac death (SCD) has an enormous impact on those who are left behind, evoking strong feelings of anxiety and incomprehension because such a dramatic event was not anticipated. Moreover, over the last decade a prominent genetic contribution to the pathogenesis of SCD has been unveiled. As many inherited cardiac diseases show an autosomal dominant pattern of inheritance, the risk of carrying the same inherited predisposition is a real concern for the relatives. In this article, we discuss the major causes of primary electrical disorders, cardiomyopathies and thoracic aortic dissection and address issues in genotype-phenotype correlation, personalized management and cardiogenetic counselling.

Nonsyndromic hearing impairment is associated with a mutation in DFNA5.

Nonsyndromic hearing impairment is one of the most heterogeneous hereditary conditions, with more than 40 loci mapped on the human genome, however, only a limited number of genes implicated in hearing loss have been identified. We previously reported linkage to chromosome 7p15 for autosomal dominant hearing impairment segregating in an extended Dutch family (DFNA5). Here, we report a further refinement of the DFNA5 candidate region and the isolation of a gene from this region that is expressed in the cochlea. In intron 7 of this gene, we identified an insertion/deletion mutation that does not affect intron-exon boundaries, but deletes five G-triplets at the 3' end of the intron. The mutation co-segregated with deafness in the family and causes skipping of exon 8, resulting in premature termination of the open reading frame. As no physiological function could be assigned, the gene was designated DFNA5.

Mutations in the human alpha-tectorin gene cause autosomal dominant non-syndromic hearing impairment.

The tectorial membrane is an extracellular matrix of the inner ear that contacts the stereocilia bundles of specialized sensory hair cells. Sound induces movement of these hair cells relative to the tectorial membrane, deflects the stereocilia, and leads to fluctuations in hair-cell membrane potential, transducing sound into electrical signals. Alpha-tectorin is one of the major non-collagenous components of the tectorial membrane. Recently, the gene encoding mouse alpha-tectorin (Tecta) was mapped to a region of mouse chromosome 9, which shows evolutionary conservation with human chromosome 11q (ref. 3), where linkage was found in two families, one Belgian (DFNA12; ref. 4) and the other, Austrian (DFNA8; unpublished data), with autosomal dominant non-syndromic hearing impairment. We determined the complete sequence and the intron-exon structure of the human TECTA gene. In both families, mutation analysis revealed missense mutations which replace conserved amino-acid residues within the zona pellucida domain of TECTA. These findings indicate that mutations in TECTA are responsible for hearing impairment in these families, and implicate a new type of protein in the pathogenesis of hearing impairment.

Radiostrontium sorption on natural glauconite sands of the Neogene-Paleogene formations in Belgium.

The Neogene-Paleogene glauconite sands are investigated for radionuclide sorption in the framework of the Belgian radioactive waste disposal program. This study was set up to measure the adsorption of radiostrontium (85Sr) on the sands and on glauconite fractions to identify factors explaining variable sorption among different formations. Batch 85Sr sorption experiments were set up with 45 different glauconite sands and glauconite fractions (125-250 µm) in a background solution of 1 mM CaCl2.H2O and 0.5 mM KCl. The distribution coefficients (KD) for 85Sr2+ ranged 23-65 L kg-1 for the intact sands and ranged 50-144 L kg-1 for the glauconite fractions. The KD values strongly correlated with the CEC (R2 = 0.62 for sands and 0.82 for glauconite fractions) and corresponded well with CEC based predictions based on two existing models calibrated to soils. The KD on the complete sand is proportional to the glauconite content and the KD of the glauconite fraction if no other clay minerals are present in significant amounts. Sorption equilibrium was reached within 48 h in the complete sands, in milled complete sands, in glauconite fractions and in milled glauconite fractions, suggesting no diffusive boundaries in the glauconite pellets. It is concluded that glauconite sands have a suitably high retention of radiostrontium and the sorption strength is in line with that of other geological barriers when judged from the CEC.

Involvement of T-cell receptor-beta alterations in the development of otosclerosis linked to OTSC2.

Otosclerosis is a common form of hearing loss, characterized by disordered bone remodeling in the otic capsule. Within the otosclerotic foci, several immunocompetent cells and immune-modulating factors can be found. Different etiological theories involving the immune system have been suggested. However, a genetic component is clearly present. In large otosclerosis families, seven autosomal-dominant loci have been found, but none of the disease-causing genes has been identified. This study focused on the exploration of the second otosclerosis locus on chromosome 7q34-36 (OTSC2), holding the T-cell receptor beta locus (TRB locus). A significantly lower T-cell receptor-beta (TCR-beta) mRNA expression and percentage of blood circulating TCR-alphabeta(+) T cells was detected in OTSC2 patients compared with controls and patients with the complex form of the disease. Further analysis illustrated more significant disturbances in specific T-cell subsets, including an increased CD28(null) cell population, suggesting a disturbed T-cell development and ageing in OTSC2 patients. These disturbances could be associated with otosclerotic bone remodeling, given the known effects of immunocompetent cells on bone physiology. These data implicate the TRB locus as the causative gene in the OTSC2 region and represent an important finding in the elucidation of the disease pathology.

Radiocaesium sorption on natural glauconite sands is unexpectedly as strong as on Boom Clay.

The Neogene-Paleogene glauconite sands of Belgium cover the Boom Clay deposits that are candidate host for radioactive waste disposal. It is unclear if the highly permeable sand formations may act as an additional barrier for radiocesium (137Cs) or could be added as a complementary sorption sink in a surface disposal concept. Glauconite is an Fe-rich phyllosilicate that is mainly present as 250-125 µm sized pellets in sand, it is unknown to what extent and how fast these pellets may bind 137Cs. Pelletized clays embedded in sand may have poorly accessible high affinity sites for 137Cs. The 137Cs sorption on 11 different glauconite sands was measured in batch in a background solution of 0.1 M CaCl2 and 0.5 mM KCl. The log transformed 137Cs distribution coefficient Kd (L kg-1) after 30 days reaction ranged 3.4-4.3, surprisingly close to the Kd of the Boom Clay (3.5). Isolated glauconite fractions exhibited similar 137Cs sorption potentials (log Kd 4.1-4.3) as the reference Illite du Puy (4.4). The small Kd variation among the Neogene-Paleogene sands was explained by its glauconite content (r = 0.82). The 137Cs sorption kinetics (1-57 days) of milled pellets (<2 µm) confirmed slower reaction with intact pellets than with milled samples. Additionally, the Kd values of milled samples (57 days) sorption are 1.1-1.5 fold larger than the corresponding intact pellets, suggesting that not all Cs binding sites are accessible in intact pellets. Strongly weathered pellets exhibited cracks (visible with SEM). In these pellets the Kd was similar for milled and intact pellets suggesting that cracks increase the accessibility of the inner sorption sites. After 8.5 months the Kd values were 1.6-1.8-fold above corresponding 1 month data and these long-term reactions were more pronounced as total sand K content was larger. An adsorption-desorption experiment illustrated that 137Cs sorption is not fully reversible.

Spondylo-epiphyseal dysplasia in two sibs due to a homozygous splicing variant in COL2A1.

Type 2 collagenopathies encompass a large group of chondrodysplasias ranging from the perinatally lethal achondrogenesis type 2 and hypochondrogenesis at the severe end of the spectrum to early-onset osteoarthritis with normal stature at the milder end of the spectrum. With the exception of a few reported cases, these dysplasias are predominantly caused by heterozygous variants in the COL2A1 gene and hence show an autosomal dominant inheritance pattern. Here we report on two siblings, originating from a consanguineous family, who presented with disproportionate short stature, ocular abnormalities, cleft palate and hearing impairment. The radiographic study showed signs of a spondyloepiphyseal dysplasia, compatible with a type 2 collagen disorder. Indeed, both siblings were homozygous for a c.3111+2T > Cp.(Glu1033Lysfs*5) splice site variant in the COL2A1 gene. cDNA analysis performed on skin fibroblasts from the affected sibs revealed the co-occurrence of the wild-type transcript and an aberrant splice product, the latter believed to be degraded by nonsense-mediated mRNA decay. The parents who were heterozygous for this variant were phenotypically normal. This paper confirms that type 2 collagenopathies can show an autosomal recessive inheritance.

Candidate gene association study for noise-induced hearing loss in two independent noise-exposed populations.

Millions of people are daily exposed to high levels of noise. Consequently, noise-induced hearing loss (NIHL) is one of the most important occupational health hazards worldwide. In this study, we performed an association study for NIHL based on a candidate gene approach. 644 Single Nucleotide Polymorphisms (SNPs) in 53 candidate genes were analyzed in two independent NIHL sample sets, a Swedish set and part of a Polish set. Eight SNPs with promising results were selected and analysed in the remaining part of the Polish samples. One SNP in PCDH15 (rs7095441), resulted in significant associations in both sample sets while two SNPs in MYH14 (rs667907 and rs588035), resulted in significant associations in the Polish sample set and significant interactions with noise exposure level in the Swedish sample set. Calculation of odds ratios revealed a significant association of rs588035 with NIHL in the Swedish high noise exposure level group. Our studies suggest that PCDH15 and MYH14 may be NIHL susceptibility genes, but further replication in independent sample sets is mandatory.

[Influence of exogenic factors on age-related hearing impairment]. / Einfluss exogener Faktoren auf Altersschwerhörigkeit

BACKGROUND: Age-related hearing impairment is a complex disorder, the causes for which have been insufficiently studied. Genetic and environmental factors all play a role. METHODS: A total of 406 persons aged between 53 and 67 years old were interviewed about various causes and audiometric data were collected. The audiometric pure tone data were adjusted for sex and age and tested for association with exposure to risk factors. RESULTS: Significant negative effects of noise exposure, painkillers, overweight, and cardiovascular diseases on hearing loss were found. A positive effect of moderate alcohol consumption could also be shown in the elderly. These results suggest that a healthy lifestyle can positively affect age-related hearing impairment.

Contribution of the N-acetyltransferase 2 polymorphism NAT2*6A to age-related hearing impairment.

BACKGROUND: Age-related hearing impairment (ARHI) is the most common sensory impairment in older people, affecting 50% of those aged 80 years. The proportion of older people is increasing in the general population, and as a consequence, the number of people affected with ARHI is growing. ARHI is a complex disorder, with both environmental and genetic factors contributing to the disease. The first studies to elucidate these genetic factors were recently performed, resulting in the identification of the first two susceptibility genes for ARHI, NAT2 and KCNQ4. METHODS: In the present study, the association between ARHI and polymorphisms in genes that contribute to the defence against reactive oxygen species, including GSTT1, GSTM1 and NAT2, was tested. Samples originated from seven different countries and were combined into two test population samples, the general European population and the Finnish population. Two distinct phenotypes for ARHI were studied, Z(low) and Z(high), representing hearing in the low and high frequencies, respectively. Statistical analysis was performed for single polymorphisms (GSTM1, GSTT1, NAT2*5A, NAT2*6A, and NAT2*7A), haplotypes, and gene-environment and gene-gene interactions. RESULTS: We found an association between ARHI and GSTT1 and GSTM1 in the Finnish population sample, and with NAT2*6A in the general European population sample. The latter finding replicates previously published data. CONCLUSION: As replication is considered the ultimate proof of true associations in the study of complex disorders, this study provides further support for the involvement of NAT2*6A in ARHI.

The complexity of age-related hearing impairment: contributing environmental and genetic factors.

Age-related hearing impairment (ARHI) is the most common sensory impairment seen in the elderly. It is a complex disorder, with both environmental as well as genetic factors contributing to the impairment. The involvement of several environmental factors has been partially elucidated. A first step towards the identification of the genetic factors has been made, which will result in the identification of susceptibility genes, and will provide possible targets for the future treatment and/or prevention of ARHI. This paper aims to give a broad overview of the scientific findings related to ARHI, focusing mainly on environmental and genetic data in humans and in animal models. In addition, methods for the identification of contributing genetic factors as well as possible future therapeutic strategies are discussed.

A new, easy, and rapid high-throughput detection method for the common GJB2 (CX26), 35delG mutation.

GJB2 (Gap Junction protein beta type 2; Connexin 26, CX26) is known for its contribution to nonsyndromic recessive deafness (NSRD). One particular mutation, 35delG, a deletion of one guanine from a stretch of six leading to a frame shift early in the gene, has a high prevalence in populations from European descent. 35delG testing therefore has become a standard test in genetic diagnostic laboratories. Most of the currently available methods for the detection of 35delG are relatively time consuming, and not suited for high-throughput diagnostic testing. Within this paper we present a real-time PCR genotyping assay based on melting curve analysis, requiring only a single preparation step before the actual analysis. The assay was optimized on a panel of 48 samples with known 35delG genotypes and subsequently tested using a large Belgian population (N = 460) with unknown 35delG status. For the latter set of samples, real-time PCR results were validated with SNAPShot, an assay used in our laboratory for diagnostic purposes. The real-time PCR genotyping method has proven to be highly reliable, rapid, cost-effective, and suitable for high-throughput screening. We believe that this genetic test for 35delG will find widespread applications in the DNA diagnostic field.

Prevalence of tinnitus and audiometric shape.

OBJECTIVES: Studies of tinnitus are often conducted on patient populations presenting for treatment. It is, however, difficult to generalise prevalence numbers and aetiological results from these studies to a healthy, elderly population. The first aim of our study was to determine the prevalence of tinnitus in an otologically screened population between 55 and 65 years old. Secondly, both prevalence and the specific characteristics of tinnitus were compared in subjects with either a flat audiogram, a high-frequency gently sloping audiogram or a high-frequency steeply sloping audiogram. METHODS: 1147 subjects (549 males and 598 females) were recruited through population registers and underwent thorough clinical and audiological examinations. Subjects who reported tinnitus in the general questionnaire about medical history and environmental exposure were invited to complete an additional questionnaire on tinnitus history. RESULTS: The prevalence of tinnitus was 19.3% according to the general questionnaire on medical health and environmental exposure and 11.8% according to the additional detailed tinnitus-specific questionnaire. Furthermore, our results indicate that gender has a significant effect (tinnitus is more common in males than in females), as does audiometric configuration (tinnitus is more common in subjects with a high-frequency steeply sloping audiogram than in subjects with a flat audiogram). Both effects were significant in noise-/solvent-exposed subjects, as well as in non-exposed subjects. Finally, comparison of "tinnitus characteristics" in subjects categorised by audiogram configuration revealed significant differences in loudness, pitch, temporal variability and family history of tinnitus.

Familial aggregation of tinnitus: a European multicentre study.

INTRODUCTION AND AIM: Tinnitus is a common condition affecting approximately 20% of the older population. There is increasing evidence that changes in the central auditory system following cochlear malfunctioning are responsible for tinnitus. To date, few investigators have studied the influence of genetic factors on tinnitus. The present report investigates the presence of a familial effect in tinnitus subjects. METHODS: In a European multicentre study, 198 families were recruited in seven European countries. Each family had at least 3 siblings. Subjects were screened for causes of hearing loss other than presbyacusis by clinical examination and a questionnaire. The presence of tinnitus was evaluated with the question "Nowadays, do you ever get noises in your head or ear (tinnitus) which usually last longer than five minutes". Familial aggregation was tested using three methods: a mixed model approach, calculating familial correlations, and estimating the risk of a subject having tinnitus if the disorder is present in another family member. RESULTS: All methods demonstrated a significant familial effect for tinnitus. The effect persisted after correction for the effect of other risk factors such as hearing loss, gender and age. The size of the familial effect is smaller than that for age-related hearing impairment, with a familial correlation of 0.15. CONCLUSION: The presence of a familial effect for tinnitus opens the door to specific studies that can determine whether this effect is due to a shared familial environment or the involvement of genetic factors. Subsequent association studies may result in the identification of the factors responsible. In addition, more emphasis should be placed on the effect of role models in the treatment of tinnitus.

KCNQ4: a gene for age-related hearing impairment?

Age-related hearing impairment (ARHI) is the most common sensory impairment among the elderly. It is a complex disorder influenced by genetic as well as environmental factors. SNPs in a candidate susceptibility gene, KCNQ4, were examined in two independent Caucasian populations. Two quantitative trait locus (QTL) values were investigated: Zhigh and Zlow, a measure of high and respectively low frequency hearing loss. In the first population, the statistical analysis of 23 genotyped SNPs spread across KCNQ4 resulted in significant p-values for two SNPs for Zhigh-SNP9 (NT_004511:g.11244177A > T) and SNP15 (NT_004511:g.11257005C > T; NP_004691:p.Ala259Ala), and one SNP for Zlow-SNP12 (NT_004511:g.11249550A > T). The linkage disequilibrium (LD) structure of KCNQ4 was subsequently determined in a 34-kb region surrounding the significant SNPs, resulting in three LD-blocks. LD-block 1 contains SNP9 and covers an area of 5 kb, LD-block 2 measures 5 kb and surrounds SNP13 (NT_004511:g.11253513A > G) to SNP18 (NT_004511:g.11257509G > A; NP_004691:p.Thr293Thr), and LD-block 3 spans 7 kb. Five tag-SNPs of block 1 and 2, and 2 extra SNPs were subsequently genotyped in the second population. Again, several SNPs were positively associated with ARHI: one SNP (SNP18) for the high frequencies and three SNPs (SNP9, SNP12, and SNP18) for the low frequencies, although only a single SNP (SNP12) resulted in significant p-values in both populations. Nevertheless, the associated SNPs of both populations were all located in the same 13-kb region in the middle of the KCNQ4 gene.

Calmodulin-binding proteins in granule and plasma membranes from bovine chromaffin cells.

Calmodulin-binding proteins in chromaffin granule membrane and chromaffin cell plasma membranes have been investigated and compared. Chromaffin granules were purified by centrifugation over a 1.7 M sucrose layer. Plasma membranes were obtained in a highly purified form by differential and isopycnic centrifugation. Enzymatic determinations of 5'-nucleotidase, a generally accepted plasma membrane marker, showed a 40-50-fold enrichment as compared to the cell homogenate. Marker enzyme studies demonstrated only minimal contamination by other subcellular organelles. After solubilization with Triton X-100, calmodulin-binding proteins were isolated from chromaffin granule membranes and plasma membranes by affinity chromatography on a calmodulin/Sepharose 4B column. On two-dimensional polyacrylamide gelelectrophoresis a prominent protein (Mr = 65,000, pI ranging from 5.1 to 6) consisting of multiple spots, was present in the calmodulin-binding fraction from chromaffin granule membranes as well as from plasma membranes. Besides this 65 kDa protein both fractions had at least four groups of proteins in common. Also, proteins typical for either preparation were observed. In the calmodulin-binding protein preparations from chromaffin granule membranes a prominent spot with Mr = 80,000 and a pH ranging from 5.0 to 5.7 was present. This protein was enzymatically and immunologically identified as dopamine-beta-monooxygenase.

DFNA5: hearing impairment exon instead of hearing impairment gene?

BACKGROUND: Three mutations in the DFNA5 gene have been described in three families with autosomal dominant non-syndromic hearing impairment. Although these mutations are different at the genomic DNA level, they all lead to skipping of exon 8 at the mRNA level. We hypothesise that hearing impairment associated with DFNA5 is caused by a highly unusual mechanism, in which skipping of one specific exon leads to disease that is not caused by other mutations in this gene. We hypothesise that this represents a very specific "gain of function" mutation, with the truncated protein exerting a deleterious new function. METHODS: We performed transfection experiments in mammalian cell lines (HEK293T and COS-1) with green fluorescent protein (GFP) tagged wildtype and mutant DFNA5 and analysed cell death with flow cytometry and fluorescence microscopy. RESULTS: Post-transfection death of HEK293T cells approximately doubled when cells were transfected with mutant DFNA5-GFP compared with wildtype DFNA5-GFP. Cell death was attributed to necrotic events and not to apoptotic events. CONCLUSION: The transfection experiments in mammalian cell lines support our hypothesis that the hearing impairment associated with DFNA5 is caused by a "gain of function" mutation and that mutant DFNA5 has a deleterious new function.

A common founder for the 35delG GJB2 gene mutation in connexin 26 hearing impairment.

Fifty to eighty percent of autosomal recessive congenital severe to profound hearing impairment result from mutations in a single gene, GJB2, that encodes the protein connexin 26. One mutation of this gene, the 35delG allele, is particularly common in white populations. We report evidence that the high frequency of this allelic variant is the result of a founder effect rather than a mutational hot spot in GJB2, which was the prevailing hypothesis. Patients homozygous for the 35delG mutation and normal hearing controls originating from Belgium, the UK, and the USA were genotyped for different single nucleotide polymorphisms (SNPs). Four SNPs mapped in the immediate vicinity of GJB2, while two were positioned up to 76 kb from it. Significant differences between the genotypes of patients and controls for the five SNPs closest to GJB2 were found, with nearly complete association of one SNP allele with the 35delG mutation. For the most remote SNP, we could not detect any association. We conclude that the 35delG mutation is derived from a common, albeit ancient founder.