Tapeto-retinal degenerations with varying clinical features in Aland islanders.

During the period 1959-1962, we investigated families afflicted with blindness in the Aland archipelago, situated in the northern Baltic Sea between Finland and Sweden. Among the natives of the Aland islands we observed various types of tapeto-retinal degeneration: Leber's congenital amaurosis, degeneratio retinae pigmentosa juvenilis, and retinitis punctata albescens. In 1969 we again surveyed the occurrence of poor sight on the Aland islands, and found new cases of dystrophic changes of the fundus in young subjects. We also observed progression in some of the cases we had on record. Some patients were also studied by electroretinography (ERG), electrooculography(EOG), electronystagmography (ENG), anomaloscopy, the Farnsworth 100 Hue Test, fluorescein angiography, etc. The question arose as to whether these clinically different retinal abiotrophies of autosomal recessive type could be due to the same mutant gene, causing a great diversity of clinical manifestations, depending partly on pleiotropy (polypheny) and partly on progression of the tapeto-retinal degeneration. This hypothesis was corroborated by the genealogical data. Many probands showing different kinds of tapeto-retinal degeneration were found to have ancestors in common, particularly in the more distant ascendancy, though some of them were born in quite different parts of the Aland archipelago. (Water excluded, this archipelago comprises 1505 sq. km., water included about 6,000 sq. km., and the distance between some of the inhabited islands is as much as 100 km.) Furthermore it seemed unlikely that the small population of Aland (about 21,000 subjects) would show so many different recessively inherited tapeto-retinal diseases, which are all rare, both in Sweden and in Finland. It should be borne in mind that the atypical forms of degeneratio retinae