Introduction

One of the ultimate objectives of research in human genetics is to elucidate the biochemical effect of pathological genes. Great progress has been made in this respect during recent years, but we still know very little of the biochemical defects in the majority of hereditary diseases. Biochemical genetic research is considerably facilitated if it can be applied to syndromes which are identified as genetic units. The qualitative and quantitative divergences found in these may also throw light on the normal biochemical processes. It is therefore of very great importance that various rare genetic diseases, e.g. neurological and psychiatric diseases, should be registered and analysed with regard to their occurrence, prevalence and mode of inheritance as well as their clinical picture. Sweden offers excellent opportunities for such an analysis of genetic diseases, for the following reasons. (1) The official registration of individuals by the parish offices is very thorough. It is therefore possible to trace ancestors through many generations, often, indeed, as far as the 16th and 17th centuries. (2) The country still contains relatively isolated areas with a sparse population, especially in the northernmost parts, where there are thus increased possibilities of the appearance of rare genetic diseases which manifest themselves in homozygotic form. For several decades past, however, there has been in progress a marked internal migration of the population, which is due among other things to improved communications and social regrouping-cf. T. Larsson (1957). These circumstances can be presumed to result in a spreading of pathological genes in heterozygotic form and to diminished homozygotization. The good opportunities which now exist in Sweden for the study of genetic syndromes have been utilized by inter alia T. Sjogren and T. Larsson in a series of works on different subjects and by C. H. Alstrom and J. A. Book. In 1951 the present author was encouraged by Professor Torsten Sjogren to go systematically through his diagnosis register from the Institution for Blind Persons with a Complicating Disability, Lund. Subsequently all the records at this institution were examined. The scrutiny revealed 25 cases of retinitis pigmentosa combined with congenital deafness; some of these cases also suffered from psychiatric abnormality. Later it was possible to expand this material substan-