412 VIABILITY OF ENZYMATICALLY ISOLATED BOVINE PRIMORDIAL AND PRIMARY OVARIAN FOLLICLES COLLECTED BY THE BIOPSY PICK-UP TECHNIQUE

Our institution recently developed a new tool for transvaginal, ultrasound-guided collection of ovarian biopsies from living donor cows (Aerts et al. 2005 Theriogenology 64, 947–957). The biopsy pickup (BPU) device consists of a modified needle guidance system, which is equipped with a trocar needle and carries a 60-cm-long true-cut biopsy needle. In a previous experiment, the presence of primordial and preantral follicles in BPU-derived biopsies was demonstrated. As follicular integrity is a prerequisite for further culture or research, the aim of the present study was to assess the viability of enzymatically isolated primordial and primary ovarian follicles collected by the BPU instrument. Four cows were subjected to a one-time BPU procedure. Four cortical biopsies were collected per ovary from each animal. Follicle viability was determined by the dual fluorescent probe technique described by Cortvrindt and Smitz (2001 Fertil. Steril. 75, 588–593). In live cells, calcein-AM is converted into calcein by intracellular esterase enzymes, producing an intense green fluorescence. In dead cells, ethidium homodimer-I is able to penetrate the damaged plasma membrane and, upon binding to nucleic acids, undergo a 40-fold enrichment of fluorescence, thereby producing an intense red signal. Upon retrieval, the biopsies were immersed in HEPES-buffered minimum essential medium (GIBCO, Grand Island, NY, USA) at 4�C. In the laboratory, the tissue samples were transferred to 50-mL conical tubes containing 20 mL PBS supplemented with 1 mg mL-1 collagenase type IA (Sigma-Aldrich NV/SA, Bornem, Belgium) and were incubated in a water bath at 37�C for 60 min. The digestion was terminated by adding an equal volume of cold PBS. The resulting suspension was centrifuged at 300g for 10 min at 8�C. The pellet was resuspended in PBS and transferred to a Petri dish. Each Petri dish was examined under a phase-contrast inverted microscope (Olympus CHX41) equipped with an eyepiece micrometer, and the primordial and primary follicles were collected with a glass micropipette. Isolated follicles were mounted on a slide in 50-�L droplets of PBS containing 2 �mol L-1 calceine-AM and 5 �mol L-1 ethidium homodimer-I (Molecular Probes, Leiden, The Netherlands), and incubated in the dark for 45 min at 37�C. After incubation, the follicles were examined under a fluorescence microscope (Olympus BX61). A total of 95 enzymatically isolated follicles were analyzed for viability with fluorescent probes; 89 (93.7%) of these were viable. Viable follicles were retrieved from all animals. This experiment confirms that viable primordial and primary follicles can be retrieved from living donor cows by the BPU procedure, which makes the technique suited for further culture or research.

A Novel Z-Score–Based Method to Analyze Candidate Genes for Age-Related Hearing Impairment

OBJECTIVE

Approximately half of the variance of Age-Related Hearing Impairment (ARHI) is attributable to environmental risk factors, and the other half to genetic factors. None of these genes has ever been identified, but the genes involved in monogenic nonsyndromic hearing impairment are good candidates. Here we define and validate a quantitative trait value for ARHI, correcting for age and gender, to allow the genetic study of ARHI as a quantitative trait.

DESIGN

Based on the ISO 7029 standard, we convert audiometric data into a Z-score, an age- and gender-independent value expressing to what extent a person is affected by ARHI. The validity of this approach is checked using a test population of randomly collected subjects. The power to evaluate the contribution of a candidate gene to ARHI is assessed using simulated populations. As an example, one ARHI candidate gene is analyzed.

RESULTS

In our test population, Z-scores were normally distributed although the mean did not equal zero. Z-scores were independent of age, and there was no difference between men and women. Power studies using simulated populations indicated that to detect moderate genetic effects, sample sizes of at least 500 random subjects are necessary.

CONCLUSION

The Z-score conversion appears to be a valid method to describe to what extent a subject is affected by ARHI, allowing to compare persons from different age and gender. This method can be the basis of future, powerful studies to identify ARHI genes.

A novel locus for autosomal dominant non-syndromic hearing loss, DFNA31, maps to chromosome 6p21.3

BACKGROUND

Non-syndromic hearing loss is the most genetically heterogeneous trait known in humans. To date, 51 loci for autosomal dominant non-syndromic sensorineural hearing loss (NSSHL) have been identified by linkage analysis.

OBJECTIVE

To investigate the genes involved in a Dutch family with NSSHL.

METHODS

Linkage analysis in a large Dutch pedigree with progressive bilateral loss of the mid and high frequencies, in which a novel dominant locus for postlingual NSSHL (DFNA31) has been identified.

RESULTS

DFNA31 was found to be located in a 7.5 cM region of chromosome 6p21.3 between D6S276 (telomeric) and D6S273 (centromeric), with a maximum two point LOD score of 5.99 for D6S1624. DNA sequencing of coding regions and exon/intron boundaries of two candidate genes (POU5F1, GABBR1) in this interval did not reveal disease causing mutations.

CONCLUSIONS

Haplotype analysis indicated that the genetic defect in this family does not overlap the DFNA13 and DFNA21 regions that are also located on 6p. Identification of the disease gene will be of major importance in understanding the pathophysiology of hearing impairment.

Mutational spectrum of the WFS1 gene in Wolfram syndrome, nonsyndromic hearing impairment, diabetes mellitus, and psychiatric disease

WFS1 is a novel gene and encodes an 890 amino-acid glycoprotein (wolframin), predominantly localized in the endoplasmic reticulum. Mutations in WFS1 underlie autosomal recessive Wolfram syndrome and autosomal dominant low frequency sensorineural hearing impairment (LFSNHI) DFNA6/14. In addition, several WFS1 sequence variants have been shown to be significantly associated with diabetes mellitus and this gene has also been implicated in psychiatric diseases. Wolfram syndrome is highly variable in its clinical manifestations, which include diabetes insipidus, diabetes mellitus, optic atrophy, and deafness. Wolfram syndrome mutations are spread over the entire coding region, and are typically inactivating, suggesting that a loss of function causes the disease phenotype. In contrast, only non-inactivating mutations have been found in DFNA6/14 families, and these mutations are mainly located in the C-terminal protein domain. In this paper, we provide an overview of the currently known disease-causing and benign allele variants of WFS1 and propose a potential genotype-phenotype correlation for Wolfram syndrome and LFSNHI.

Progression of low-frequency sensorineural hearing loss (DFNA6/14-WFS1)

OBJECTIVE

To assess the audiometric profile and speech recognition characteristics in affected members of 2 families with DFNA6/14 harboring heterozygous mutations in the WFS1 gene that cause an autosomal dominant nonsyndromic sensorineural hearing impairment trait.

DESIGN

Family study.

SETTING

Tertiary referral center. Patients Thirteen patients from 2 recently identified Dutch families with DFNA6/14 (Dutch III and IV).

METHODS

Cross-sectional and longitudinal analyses of pure-tone thresholds at octave frequencies of 0.25 to 8 kHz were performed, and speech phoneme recognition scores were assessed. Progression was evaluated by linear regression analysis with and without correction for presbycusis.

RESULTS

All individuals showed low-frequency hearing impairment. The 2-kHz frequency was more affected in the Dutch III family than in the Dutch IV family. Progressive hearing loss beyond presbycusis was found in the Dutch IV family and in 3 individuals in the Dutch III family. Annual threshold deterioration was between 0.6 and 1 dB per year at all frequencies. The speech recognition scores in the Dutch III family showed significantly more deterioration at increasing levels of hearing impairment compared with those in the Dutch IV family.

CONCLUSION

Both families showed an autosomal dominant, progressive, low-frequency sensorineural hearing impairment caused by heterozygous WFS1 mutations.

Is DFNA5 a susceptibility gene for age-related hearing impairment?

A mutation in DFNA5 leads to a type of hearing loss that closely resembles the frequently observed age-related hearing impairment (ARHI). The hearing loss is sensorineural, progressive and starts at the high frequencies. As DFNA5 was considered an excellent candidate ARHI susceptibility gene, we performed linkage analysis to a quantitive measure of high frequency hearing loss. However, no significant linkage between ARHI and microsatellite markers from the DFNA5 region could be detected. Subsequently, the DFNA5 coding region was analysed for single nucleotide polymorphisms (SNPs). Two SNPs leading to amino-acid substitutions (P142H and V207M) were selected for further analysis. Using these SNPs, an association study based on a collection of random individuals, and a case-control association study were performed. No significant differences in genotypes between good hearing and hearing impaired individuals could be detected in either study design. We conclude that there exists no strong association between DFNA5 and ARHI.

Mutations in the WFS1 gene that cause low-frequency sensorineural hearing loss are small non-inactivating mutations

Hereditary hearing impairment is an extremely heterogeneous trait, with more than 70 identified loci. Only two of these loci are associated with an auditory phenotype that predominantly affects the low frequencies (DFNA1 and DFNA6/14). In this study, we have completed mutation screening of the WFS1 gene in eight autosomal dominant families and twelve sporadic cases in which affected persons have low-frequency sensorineural hearing impairment (LFSNHI). Mutations in this gene are known to be responsible for Wolfram syndrome or DIDMOAD (diabetes insipidus, diabetes mellitus, optic atrophy, and deafness), which is an autosomal recessive trait. We have identified seven missense mutations and a single amino acid deletion affecting conserved amino acids in six families and one sporadic case, indicating that mutations in WFS1 are a major cause of inherited but not sporadic low-frequency hearing impairment. Among the ten WFS1 mutations reported in LFSNHI, none is expected to lead to premature protein truncation, and nine cluster in the C-terminal protein domain. In contrast, 64% of the Wolfram syndrome mutations are inactivating. Our results indicate that only non-inactivating mutations in WFS1 are responsible for non-syndromic low-frequency hearing impairment.

Vestibular dysfunction in the epistatic circler mouse is caused by phenotypic interaction of one recessive gene and three modifier genes

Vestibular dysfunction is a frequent clinical problem, leading to dizziness and imbalance. Genes play an important role in its etiology, but the genetics are complex and poorly understood. In this study we have analyzed the complex inheritance pattern in the Epistatic circler mouse, which shows circling behavior indicative of vestibular dysfunction in the mouse. This phenotype exists in a proportion of the F2-generation from an intercross between C57L/J and SWR/J mouse strains. Genetic investigation indicates that the circling behavior is caused by a major recessively inherited gene derived from the SWR/J strain (the Ecs-gene) in combination with at least three different modifier genes derived from C57L/J (the Ecl-genes). Genetic mapping made it possible to localize the Ecs-gene to chromosome 14 and the Ecl-genes to chromosome 3, 4, and 13. This study illustrates the feasibility of identifying genes for multifactorial traits in mice.

The ABCA4 2588G>C Stargardt mutation: single origin and increasing frequency from South-West to North-East Europe

Inherited retinal dystrophies represent the most important cause of vision impairment in adolescence, affecting approximately 1 out of 3000 individuals. Mutations of the photoreceptor-specific gene ABCA4 (ABCR) are a common cause of retinal dystrophy. A number of mutations have been repeatedly reported for this gene, notably the 2588G>C mutation which is frequent in both patients and controls. Here we ascertained the frequency of the 2588G>C mutation in a total of 2343 unrelated random control individuals from 11 European countries and 241 control individuals from the US, as well as in 614 patients with STGD both from Europe and the US. We found an overall carrier frequency of 1 out of 54 in Europe, compared with 1 out of 121 in the US, confirming that the 2588G>C ABCA4 mutation is one of the most frequent autosomal recessive mutations in the European population. Carrier frequencies show an increasing gradient in Europe from South-West to North-East. The lowest carrier frequency, 0 out of 199 (0%), was found in Portugal; the highest, 11 out of 197 (5.5%), was found in Sweden. Haplotype analysis in 16 families segregating the 2588G>C mutation showed four intragenic polymorphisms invariably present in all 16 disease chromosomes and sharing of the same allele for several markers flanking the ABCA4 locus in most of the disease chromosomes. These results indicate a single origin of the 2588G>C mutation which, to our best estimate, occurred between 2400 and 3000 years ago.

Mutations in the Wolfram syndrome 1 gene (WFS1) are a common cause of low frequency sensorineural hearing loss

Non-syndromic low frequency sensorineural hearing loss (LFSNHL) affecting only 2000 Hz and below is an unusual type of hearing loss that worsens over time without progressing to profound deafness. This type of LFSNHL may be associated with mild tinnitus but is not associated with vertigo. We have previously reported two families with autosomal dominant LFSNHL linked to adjacent but non-overlapping loci on 4p16, DFNA6 and DFNA14. However, further study revealed that an individual with LFSNHL in the DFNA6 family who had a recombination event that excluded the DFNA14 candidate region was actually a phenocopy, and consequently, DFNA6 and DFNA14 are allelic. LFSNHL appears to be genetically nearly homogeneous, as only one LFSNHL family is known to map to a different chromosome (DFNA1). The DFNA6/14 critical region includes WFS1, the gene responsible for Wolfram syndrome, an autosomal recessive disorder characterized by diabetes mellitus and optic atrophy, and often, deafness. Herein we report five different heterozygous missense mutations (T699M, A716T, V779M, L829P, G831D) in the WFS1 gene found in six LFSNHL families. Mutations in WFS1 were identified in all LFSNHL families tested, with A716T arising independently in two families. None of the mutations was found in at least 220 control chromosomes with the exception of V779M, which was identified in 1/336 controls. This frequency is consistent with the prevalence of heterozygous carriers for Wolfram syndrome estimated at 0.3-1%. An increased risk of sensorineural hearing loss has been reported in such carriers. Therefore, we conclude that mutations in WFS1 are a common cause of LFSNHL.

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.

Determination of the carrier frequency of the common GJB2 (connexin-26) 35delG mutation in the Belgian population using an easy and reliable screening method

Mutations in the gene GJB2, encoding the gap-junction protein connexin-26, have been shown to be a major cause of nonsyndromic recessive deafness (NSRD). A single mutation in the GJB2 gene accounts for the majority of NSRD in many different populations. This mutation represents a deletion of a guanine within a stretch of six Gs between nucleotide positions +30 and +35 of the GJB2 cDNA (35delG). Molecular detection of the 35delG mutation is usually performed by direct sequencing analysis of PCR products, or by allele-specific PCR analysis. To screen for this mutation, we developed an easier and more reliable method, based on the principle of PCR-mediated site-directed mutagenesis (PSDM), followed by a BsiYI digestion. We tested 360 unrelated unaffected Belgian individuals for heterozygosity of the 35delG mutation and found a carrier frequency of 1 in 40 (95% CI, 1 in 30 to 1 in 60). As our new screening method is simple and reliable in use, and detects a mutation responsible for a significant part of NSRD, it may find widespread use in DNA diagnostics.

A gene for autosomal dominant hearing impairment (DFNA14) maps to a region on chromosome 4p16.3 that does not overlap the DFNA6 locus

Non-syndromic hearing impairment is one of the most heterogeneous hereditary conditions, with more than 40 reported gene localisations. We have identified a large Dutch family with autosomal dominant non-syndromic sensorineural hearing impairment. In most patients, the onset of hearing impairment is in the first or second decade of life, with a slow decline in the following decades, which stops short of profound deafness. The hearing loss is bilateral, symmetrical, and only affects low and mid frequencies up to 2000 Hz. In view of the phenotypic similarities of this family with an American family that has been linked to chromosome 4p16.3 (DFNA6), we investigated linkage to the DFNA6 region. Lod score calculations confirmed linkage to this region with two point lod scores above 6. However, as haplotype analysis indicated that the genetic defect in this family is located in a 5.6 cM candidate region that does not overlap the DFNA6 region, the new locus has been named DFNA14.

A gene for autosomal dominant hearing impairment (DFNA14) maps to a region on chromosome 4p16.3 that does not overlap the DFNA6 locus

Non-syndromic hearing impairment is one of the most heterogeneous hereditary conditions, with more than 40 reported gene localisations. We have identified a large Dutch family with autosomal dominant non-syndromic sensorineural hearing impairment. In most patients, the onset of hearing impairment is in the first or second decade of life, with a slow decline in the following decades, which stops short of profound deafness. The hearing loss is bilateral, symmetrical, and only affects low and mid frequencies up to 2000 Hz. In view of the phenotypic similarities of this family with an American family that has been linked to chromosome 4p16.3 (DFNA6), we investigated linkage to the DFNA6 region. Lod score calculations confirmed linkage to this region with two point lod scores above 6. However, as haplotype analysis indicated that the genetic defect in this family is located in a 5.6 cM candidate region that does not overlap the DFNA6 region, the new locus has been named DFNA14.