A clinical and genetic study in myotonic dystrophy

The genetic counselling for myotonic dystrophy patients appears to be relatively simple. The disease is transtnitted as an autosomal dominant trait, and the patients risk of transmitting the abnormal gene to his children is 50%. However, many patients at the age at which genetic counselling is requested have only tnild symptoms. Often there is only myotonia of the hands and tnild weakness of the face and distal limbs. The patient may have a relative who is affected more severely, which causes anxiety for his own future and that of his children. Apart from the information on the genetic risk, he will have two other questions. Firstly: what does the future hold for him, what will be his own prognosis? Secondly: how severe will the disease be in a child if this will become affected? There is no easy answer to these questions. The expression of the myotonic dystrophy gene is variable, both in age of onset as well as in the nature and severity of the signs and symptoms. In some patients the disease is benign, causing only a cataract at an elderly age. More often the disease starts around the age of twenty, and in the course of several decades the patient will be invalidated by muscle weakness and mental symptoms. Still many of these patients are able to lead a more or less independent life, to have a job and a fatnily, until gradually their capabilities are limited by the increasing disability. However, if a child has congenital myotonic dystrophy his mental deficiency is often so severe that there is little chance of an independent life. Thus, for the proper genetic counselling of myotonic dystrophy patients, one needs, apart from the determination of the genetic risk, information on: I. The natural history of the disease and the prognosis in an individual patient. 2. The predictability of the severity of the disease in offspring inheriting the myotonic dystrophy gene. The purpose of this study was to fmd an answer to these two questions. Literature data are summarised in chapters II and III. The families studied and the methods of examination are described in chapter IV. The res nits of the family study (chapter V), the study on the natural history (chapter VI), and on the severity of the disease in parent-child pairs (chapter VII) are given separately. The results will be discussed in chapter VIII and chapter IX gives a summary. Detailed information about the relatives who were examined is given in the two appendices.