A novel missense mutation in the ESRRB gene causes DFNB35 hearing loss in a Tunisian family

Autosomal recessive non-syndromic hearing loss (ARNSHL) is a genetically heterogenous disorder with 41 genes so far identified. Among these genes, ESRRB whose mutations are responsible for DFNB35 hearing loss in Pakistani and Turkish families. This gene encodes the estrogen-related receptor beta. In this study, we report a novel mutation (p.Y305H) in the ESRRB gene in a Tunisian family with ARNSHL. This mutation was not detected in 100 healthy individuals. Molecular modeling showed that the p.Y305H mutation is likely to alter the conformation of the ligand binding-site by destabilizing the coactivator binding pocket. Interestingly, this ligand-binding domain of the ESRRB protein has been affected in 5 out of 6 mutations causing DFNB35 hearing loss. Using linkage and DHPLC analysis, no more mutations were detected in the ESRRB gene in other 127 Tunisian families with ARNSHL indicating that DFNB35 is most likely to be a rare type of ARNSHL in the Tunisian population.

Reinforcement of a minor alternative splicing event in MYO7A due to a missense mutation results in a mild form of retinopathy and deafness

PURPOSE

Recessive mutations of the myosin VIIA (MYO7A) gene are reported to be responsible for both a deaf-blindness syndrome (Usher type 1B [USH1B] and atypical Usher syndrome) and nonsyndromic hearing loss (HL; Deafness, Neurosensory, Autosomal Recessive 2 [DFNB2]). The existence of DFNB2 is controversial, and often there is no relationship between the type and location of the MYO7A mutations corresponding to the USH1B and DFNB2 phenotype. We investigated the molecular determinant of a mild form of retinopathy in association with a subtle splicing modulation of MYO7A mRNA.

METHODS

Affected members underwent detailed audiologic and ocular characterization. DNA samples from family members were genotyped with polymorphic microsatellite markers. Sequencing of MYO7A was performed. Endogenous lymphoid RNA analysis and a splicing minigene assay were used to study the effect of the c.1935G>A mutation.

RESULTS

Funduscopy showed mild retinitis pigmentosa in adults with HL. Microsatellite analysis showed linkage to markers in the region on chromosome 11q13.5. Sequencing of MYO7A revealed a mutation in the last nucleotide of exon 16 (c.1935G>A), which corresponds to a substitution of a methionine to an isoleucine residue at amino acid 645 of the myosin VIIA. However, structural prediction of the molecular model of myosin VIIA shows that this amino acid replacement induces only minor structural changes in the immediate environment of the mutation and thus does not alter the overall native structure. We found that, although predominantly included in mature mRNA, exon 16 is in fact alternatively spliced in control cells and that the mutation at the very last position is associated with a switch toward a predominant exclusion of that exon. This observation was further supported using a splicing minigene transfection assay; the c.1935G>A mutation was found to trigger a partial impairment of the adjacent donor splice site, suggesting that the unique change at the last position of the exon is responsible for the enhanced exon exclusion in this family.

CONCLUSIONS

This study shows how an exonic mutation that weakens the 5' splice site enhances a minor alternative splicing without abolishing a complete exclusion of the exon and therefore causes a less severe retinitis pigmentosa than the USH1B-associated alleles. It would be interesting to examine a possible correlation between intrafamilial phenotypic variability and the subtle variation in exon 16 inclusion, probably related to genetic background specificities.

Identification of candidate regions for a novel Usher syndrome type II locus

PURPOSE

Chronic diseases affecting the inner ear and the retina cause severe impairments to our communication systems. In more than half of the cases, Usher syndrome (USH) is the origin of these double defects. Patients with USH type II (USH2) have retinitis pigmentosa (RP) that develops during puberty, moderate to severe hearing impairment with downsloping pure-tone audiogram, and normal vestibular function. Four loci and three genes are known for USH2. In this study, we proposed to localize the gene responsible for USH2 in a consanguineous family of Tunisian origin.

METHODS

Affected members underwent detailed ocular and audiologic characterization. One Tunisian family with USH2 and 45 healthy controls unrelated to the family were recruited. Two affected and six unaffected family members attended our study. DNA samples of eight family members were genotyped with polymorphic markers. Two-point and multipoint LOD scores were calculated using Genehunter software v2.1. Sequencing was used to investigate candidate genes.

RESULTS

Haplotype analysis showed no significant linkage to any known USH gene or locus. A genome-wide screen, using microsatellite markers, was performed, allowing the identification of three homozygous regions in chromosomes 2, 4, and 15. We further confirmed and refined these three regions using microsatellite and single-nucleotide polymorphisms. With recessive mode of inheritance, the highest multipoint LOD score of 1.765 was identified for the candidate regions on chromosomes 4 and 15. The chromosome 15 locus is large (55 Mb), underscoring the limited number of meioses in the consanguineous pedigree. Moreover, the linked, homozygous chromosome 15q alleles, unlike those of the chromosome 2 and 4 loci, are infrequent in the local population. Thus, the data strongly suggest that the novel locus for USH2 is likely to reside on 15q.

CONCLUSIONS

Our data provide a basis for the localization and the identification of a novel gene implicated in USH2, most likely localized on 15q.

[Recurrent toxoplasmic retinochoroiditis after clindamycin treatment]

PURPOSE

To evaluate the efficacy and safety of subconjunctival injections of clindamycin associated with oral corticotherapy in the treatment of toxoplasmic retinochoroiditis (TRC) and its effect on recurrence.

PATIENTS AND METHODS

This study investigated 21 patients (10 males and 11 females) who presented to an ophthalmological department from 1995 to 2000, aged 14-55 years (mean, 28 years), with unilateral TRC. They were treated with subconjunctival injections of clindamycin and systemic corticotherapy at a dose of 1 mg/kg/day. Clinical follow-up consisted of assessment of visual acuity and biomicroscopic fundus examination, completed by retinal angiography if necessary.

RESULTS

We observed clinical improvement in 68.75% of patients within 4 days and in all patients healing of the chorioretinal area within 1.6 months. During the follow-up period ranging from 6 to 52 months (mean, 22 months), there have been two recurrences (9%) over the first 18 months. Tolerance of the injections was good. Serious side effects were noted in two patients: one case of conjunctival necrosis and one case of corneal and conjunctival erosion.

CONCLUSION

In treating ocular toxoplasmosis, clindamycin appears to be a safe and effective substitute for the classic protocol (pyrimethamine-sulfadiazine, pyrimethamine-azithromycin), for which a 50% recurrence rate has been reported. It provides relatively good protection against recurrence and warrants testing in further controlled studies.

Localization of a novel autosomal recessive non-syndromic hearing impairment locus DFNB63 to chromosome 11q13.3-q13.4

Hereditary hearing impairment is the most genetically heterogeneous trait known in humans. So far, 50 published autosomal recessive non-syndromic hearing impairment (ARNSHI) loci have been mapped, and 23 ARNSHI genes have been identified. Here, we report the mapping of a novel ARNSHI locus, DFNB63, to chromosome 11q13.3-q13.4 in a large consanguineous Tunisian family. A maximum LOD score of 5.33 was obtained with microsatellite markers D11S916 and D11S4207. Haplotype analysis defined a 5.55 Mb critical region between microsatellite markers D11S4136 and D11S4081. DFNB63 represents the sixth ARNSHI locus mapped to chromosome 11. We positionally excluded MYO7A from being the DFNB63-causative gene. In addition, the screening of two candidate genes, SHANK2 and KCNE3, failed to reveal any disease-causing mutations.

Métastase irienne d’un carcinome folliculaire de la thyroïde: à propos d’un cas

Metastatic carcinoma of the iris is rare and accounts for 5-10% of uveal metastasis and 3% of all iris lesions. Breast and lung carcinoma are the primary sites in 90% of patients. We report here the case of a 66-year-old man treated in 1992 for follicular thyroid carcinoma and hospitalized in 1995 for a pink vascularized mass in the iris. At that time, neither local recurrence nor metastasis in other organs was observed. Histopathologic findings were typical of follicular thyroid metastasis carcinoma. The patient had refused adjuvant treatment but was followed up for 23 months after the diagnosis of the iris metastasis. Through this observation and a literature review, we discuss clinicopathological and prognosis aspects of this exceptional location.

A novel autosomal recessive non-syndromic deafness locus, DFNB66, maps to chromosome 6p21.2-22.3 in a large Tunisian consanguineous family

Hereditary non-syndromic deafness is extremely heterogeneous. Autosomal recessive forms account for approximately 80% of genetic cases. Autosomal recessive non-syndromic sensorineural deafness segregating in a large consanguineous Tunisian family was mapped to chromosome 6p21.2-22.3. A maximum lod score of 5.36 at theta=0 was obtained for the polymorphic microsatellite marker IR2/IR4. Haplotype analysis defined a 16.5-Mb critical region between microsatellite markers D6S1602 and D6S1665. The screening of 3 candidate genes, COL11A2, BAK1 and TMHS, did not reveal any disease causing mutation, suggesting that this is a novel deafness locus, which has been named DFNB66. A search in the Human Cochlear EST Library for ESTs located in this critical interval allowed us to identify several candidates. Further investigations on these candidates are needed in order to identify the deafness-causing gene in this Tunisian family.

Blépharite mycosique à Malassezia : à propos d’un cas

PURPOSE

Blepharitis is a very common disorder but the role of certain mycoses in the etiopathogenesis of blepharitis remains controversial.

OBSERVATION

We report the case of a 29-year-old man presenting with bilateral redness and intense itching of the edge of the eyelid. Slit-lamp examination showed vasodilation of the vessels of the edge of the eyelid associated with seborrhea and a sticky yellowish substance at the roots of the eyelashes. When the substance dried and fell, microulcerations were seen at the base of the eyelids, characteristic of follicular-seborrheic blepharitis. Otherwise the ophthalmological examination was normal. Treatment with eye drops (antibiotics, antiseptics, corticoids, antihistamines) was tried several times. The blepharoconjunctivitis regressed during these treatments without totally disappearing, recurring after the treatment was discontinued. Bacteriological and fungal exams were conducted, showing numerous Malassezia furfur spores and hyphae. Given that there was no antifungal eye drop preparation on the market, topical ketoconazole (Nizoral) was prescribed. Two weeks later, the condition had cleared, with no recurrence after 5 months of follow-up.

DISCUSSION

Malassezia is a saprophyte species that may play a role in certain cases of chronic blepharitis, either through a reaction of intolerance and hypersensitivity or occasional proliferation. Treatment consists in eradicating the causal fungus using an antifungal agent associated with symptomatic treatment. We stress that fungal exams should be conducted whenever blepharitis recurs.

[Palpebral seborrheic keratosis: a case study]

INTRODUCTION

Seborrheic keratosis is the most frequent palpebral tumor, observed for the most part in the second half of life. It may be confused clinically with a basal cell carcinoma or a melanoma. The histopathological study confirms the diagnosis.

OBSERVATION

A 69-year-old man presented with a giant superior palpebral tumor leading to ptosis of the eyelid, which had evolved over 5 years. Examination found a pigmented cerebriform multilobed granulated mass, with a smooth surface and a more or less seborrheic aspect, pedicled in places, covering the entire eyelid but sparing the internal angle. This aspect suggested melanoma, basal cell carcinoma or seborrheic keratosis. Histological biopsy revealed basal cell carcinoma. Excision with palpebral reconstitution using palpebral flaps was performed. The histopathological analysis of the tumor concluded in seborrheic keratosis.

DISCUSSION

Seborrheic keratosis is a frequent tumor of the face and eyelids. Its highly pigmented clinical aspect can be confounded with a nevus or a melanoma, whereas the histological aspect can suggest basal cell carcinoma or squamous cell carcinoma, but the basal membrane is always intact. Several treatments have been proposed, including electrocoagulation, cryotherapy, dermabrasion, as well as CO2 laser treatment. However, when there is doubt with regard to the histological nature, surgery is preferred.

CONCLUSION

This was a case of seborrheic keratosis, atypical in that it covered the entire upper eyelid and produced a highly disfiguring aspect and functional problems, requiring surgical treatment with eyelid reconstruction.

[Changes in cerebral calcium, sodium and potassium after single or repeated administration of lithium in the rat]

A single administration (IP) of lithium chloride in the rat induces a decrease in erythrocyte calcium, proportional to the lithium level (p less than 0.01) and a diminution in cerebral calcium (p less than 0.001) which is accompanied by decrease in cerebral sodium and potassium levels (p less than 0.001). Repeated administration (IP + VO) has the same cerebral effects. The authors report that the reversible decrease in calcium, sodium and potassium, resulting from an increase in cerebral lithium levels, can be demonstrated on sampling at 1.30 and 3 hours (IP), or at 12 hours (VO). These results are relevant to the treatment of manic illnesses using calcium antagonists.