No abstract

The study was undertaken to procure population‐based prevalence data on the various types of Usher syndrome and other retinal dystrophy‐hearing impairment associations. The medical files on 646 patients with a panretinal pigmentary dystrophy aged 20–49 years derived from the Danish Retinitis Pigmentosa (RP) register were scrutinised. The data were supplemented by a prior investigation on hearing ability in a part of the study population. After exclusion of patients with possibly extrinsic causes of hearing impairments, 118 patients, including 89 cases of Usher syndrome were allocated to one of five clinically defined groups. We calculated the following prevalence rates: Usher syndrome type I: 1.5/100000, Usher syndrome type II: 2.2/100000, and Usher syndrome type III: 0.1/100000 corresponding to a 2:3 ratio between Usher syndrome type I and II. The overall prevalence rate of Usher syndrome was estimated to 5/100000 in the Danish population, devoid of genetic isolates. The material comprised 11 cases with retinal dystrophy, hearing impairment, and additional syndromic features. Finally, 18 subjects with various retinal dystrophy‐hearing impairment associations without syndromic features were identified, corresponding to a prevalence rate of 0.8/100000. This group had a significant overrepresentation of X‐linked RP, including two persons harboring a mutation in the retinitis pigmentosa GTP‐ase regulator (RPGR) gene.

X-linked infantile myopia is described in a family of 273 members of whom 87 were examined in the National Eye Clinic. The disease may represent a new ocular syndrome, constituted by myopia combined with astigmatism, impaired vision, hypoplasia of the optic nerve heads, and deuteranopia. Obligate carriers presented slight retinal changes. Linkage studies are in progress.

The aim of this study was a complete survey of all patients in Denmark with a diagnosis of retinitis pigmentosa. The study was performed during the period 1986-1989 and included all persons living in Denmark from 1850 to 1989. We describe the methods of registration from medical and non-medical sources, based on defined criteria. The inclusion criteria were fulfilled by 1890 persons, 1056 males and 834 females. Evaluation of this 'Danish Retinitis Pigmentosa Register' demonstrates an overall completeness of about 80%, increasing from 40% for birth cohorts before 1911 to 90% for patients born since 1981. Concerning diagnostic confidence, 73% of the probands were characterized as certain, 16% as probable, and 11% as possible. Non-systemic cases comprised 61% of all probands and 31% had systemic disease, the rest being unclassified with respect to systemic involvement. The material is considered very suitable for epidemiological treatment and continuous clinical and genetic investigations.

In a nation-wide study we utilized all available sources to characterize the prevalence rates of retinitis pigmentosa. 1301 persons, 715 males and 586 females, were identified, with a diagnosis of retinitis pigmentosa or some other tapetoretinal dystrophy, and living in Denmark per January 1, 1988. The corresponding completeness corrected prevalence rate of retinitis pigmentosa was 1:3026. All cases were classified as 'certain', 'probable', or 'possible'. The age specific prevalence rates increased until 40-50 years, reaching a level of 35-40 male cases per 100,000 and 25-30 female cases per 100,000. Age specific prevalence rates were standardized to the WHO World Standard Population and compared to rates reported from Britain and The United States. World standardized prevalence rate for males was 25.29 per 100,000 and for females 19.31 per 100,000. The preponderance of males was highly statistically significant, (P less than 0.01).