USH2A mutation analysis in 70 Dutch families with Usher syndrome type II.

Usher syndrome type II (USH2) is characterised by moderate to severe high-frequency hearing impairment, progressive visual loss due to retinitis pigmentosa and intact vestibular responses. Three loci are known for USH2, however, only the gene for USH2a (USH2A) has been identified. Mutation analysis of USH2A was performed in 70 Dutch USH2 families. Ten mutations in USH2A were detected, of which three are novel, c.949C>A, c.2242C>T (p.Gln748X) and c.4405C>T (p.Gln1468X). Including 9 previously published Dutch USH2a families, estimates of the prevalence of USH2a in the Dutch USH2 population were made. Mutations were identified in 62% of the families. In 28% both mutated alleles were identified, whereas in 34% the mutation in only one allele was found. It is estimated that about 28% of the Dutch USH2 families have a different causative gene. Analysis of deduced haplotypes suggests that c.1256G>T (p.Cys419Phe) is a Dutch ancestral mutation, occurring in 16% of the alleles.

Pure tone hearing thresholds and speech recognition scores in Dutch patients carrying mutations in the USH2A gene.

OBJECTIVE: To establish the audiometric profile and speech recognition characteristics in 36 Usher IIa patients, carrying one (A) or two (B) pathogenic mutations in the gene. STUDY DESIGN: Family study. SETTING: Tertiary referral center. PATIENTS: Thirty six Usher IIa patients from 21 Dutch families. METHODS: Ophthalmologic, vestibular, and audiometric examinations were performed on all patients. Cross-sectional analysis was performed on pure tone threshold data at 0.25 to 8 kHz and on speech phoneme recognition scores. Progression was evaluated using linear regression analysis on raw and presbyacusis corrected data. RESULTS: A downsloping audiogram was found, with a mean threshold slope of -9 dB per octave, that was mildly progressive, i.e., by approximately 0.5 dB per year. Individual monaural maximum phoneme recognition scores (% correct) were analyzed in 30 patients in relation to the patient's age and level of hearing impairment characterized by a pure tone average (PTA(1-4 kHz)). The speech recognition score started to deteriorate from a score of 90% at 38 years at a rate of 0.4% per year. The 90% level was attained at 69 dB hearing level (PTA(1-4 kHz)); at higher levels of impairment, the score deteriorated at a slope of 0.6% per dB hearing level. There was no significant difference between group A and B in pure tone threshold, with or without presbyacusis correction, or phoneme recognition score as related to age or PTA(1-4 kHz). CONCLUSIONS: Patients with various mutations in have moderate to severe hearing impairment showing mild progression at approximately 0.5 dB hearing level per year.

Evaluation of visual impairment in Usher syndrome 1b and Usher syndrome 2a.

PURPOSE: To evaluate visual impairment in Usher syndrome 1b (USH1b) and Usher syndrome 2a (USH2a). METHODS: We carried out a retrospective study of 19 USH1b patients and 40 USH2a patients. Cross-sectional regression analyses of the functional acuity score (FAS), functional field score (FFS) and functional vision score (FVS) related to age were performed. Statistical tests relating to regression lines and Student's t-test were used to compare between (sub)groups of patients. Parts of the available individual longitudinal data were used to obtain individual estimates of progressive deterioration and compare these to those obtained with cross-sectional analysis. Results were compared between subgroups of USH2a patients pertaining to combinations of different types of mutations. RESULTS: Cross-sectional analyses revealed significant deterioration of the FAS (0.7% per year), FFS (1.0% per year) and FVS (1.5% per year) with advancing age in both patient groups, without a significant difference between the USH1b and USH2a patients. Individual estimates of the deterioration rates were substantially and significantly higher than the cross-sectional estimates in some USH2a cases, including values of about 5% per year (or even higher) for the FAS (age 35-50 years), 3-4% per year for the FFS and 4-5% per year for the FVS (age > 20 years). There was no difference in functional vision score behaviour detected between subgroups of patients pertaining to different biallelic combinations of specific types of mutations. CONCLUSIONS: The FAS, FFS and FVS deteriorated significantly by 0.7-1.5% per year according to cross-sectional linear regression analysis in both USH1b and USH2a patients. Higher deterioration rates (3-5% per year) in any of these scores were attained, according to longitudinal data collected from individual USH2a patients. Score behaviour was similar across the patient groups and across different biallelic combinations of various types of mutations. However, more elaborate studies, preferably covering longitudinal data, are needed to obtain conclusive evidence.