Volume 14

Treasury of human inheritance / edited by Karl Pearson, R.A. Fisher, L.S. Penrose.

Date:
1909-
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Treasury of human inheritance / edited by Karl Pearson, R.A. Fisher, L.S. Penrose. Source: Wellcome Collection.

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    muscular organs as the heart and the uterus appear too to show no signs of degeneration; there may be secondary effects upon the heart’s action, due to the slowing up of circulation in the atrophic muscles, but I can recall reading of no case of myocardial degeneration amongst the histories of muscular dystrophy. Of the patients who live to become parents there are no accounts of uterine inertia or of special difficulty in childbirth. Further, no sphincter weakness is reported in association with this disease. Pseudohypertrophy may be very widespread in cases of group A, but only rarely is this so; of the muscles peculiarly prone to exhibit this sign of degeneration I would mention the calves, gluteals, infraspinati and deltoids as the most prominent examples. Of the muscles which appear to waste at an early stage of the disease and only rarely are seen to enlarge I would mention latissimus dorsi, the lower or sternal part of the pectorals, serratus magnus and the muscles of the proximal sections of the limbs. It is difficult to explain this localisation of symptoms as due to anything except genetic deter mination and indeed no environmental condition can be pointed to as contributing to the appearance of the disease or its progressive course; the patients are for the most part healthy, with a sense of well being apart from their localised weakness; on these grounds I have thought it legitimate to regard all single cases of the disease as of genetic etiology and have made use of a number of them to add to my figures concerned with vital statistics, as will be seen below. A number of interesting suggestions have been made from time to time as to the source of this manifest individuality in muscles; in 1925 Bramwell 1 enumerated certain factors which may or may not have a bearing on the question. He considers evidence for differentiation: (a) In the influences to which muscles have been subjected in the process of evolution, (b) In the embryological observation that different muscles of a 5 months foetus vary greatly in their stage of development, those in the most advanced stage tending to be the ones most liable to affection in the muscular dystrophies, (c) In the twofold function of muscles, those concerned in the maintenance of posture being more hable to affection than those concerned with purposive movements. ( d) In the dual innervation of some muscles —a subject concerning which there appears to be little agreement, (e) In the variation in the histo logical structure of different muscles, or in different parts of the same muscle. All these possibilities are of fascinating import and deserve more investigation than has been given to them, but each is a problem for the specialist. A paper bearing on the question of individuality in muscle was published in 1899 by Alexander Meek, 2 who considered the changes which take place in skeletal muscle during growth. He found that during extra-uterine life the growth of voluntary muscle is characterised by a decrease in the number of fibres, some of which atrophy and become completely absorbed, whilst the surviving fibres increase in size and become hypertrophied; this hypertrophy and aplasia does not affect all muscles to the same degree but is at a maximum, and very apparent, in the important muscles of the limbs. The process can be controlled within limits and in fact is controlled by the farmer, whose purpose is to hinder the reduction of fibres; he achieves this by means of nutritious food with relative rest, at the expense of the functional efficiency of the muscle—it is noteworthy that patients with muscular dystrophy are often observed to worsen quickly if they are kept in bed, though well fed. The hypertrophy described by Meek has of course no relationship to the pseudohypertrophy of our cases, but I think the obser vation that “ during extra-uterine life muscle, according to its position, suffers more or less a reduction in its numbers of fibres, the degree of which is expressive of its functional importance ” is an interesting demonstration of individuality in muscle, not without significance perhaps when we consider the genetic basis of muscular manifestations and try to conceive how the determining gene achieves its final results. Meek also points out that muscle spindles, rare except in the extremities, are found to be most numerous in those muscles in which the reduction of the number of fibres is greatest. Meryon, 3 writing in 1852 on fatty degeneration of the voluntary muscles, notes that ostriches are liable to the same disease and that when it appears their keepers know that recovery is hopeless. I sought further 1 Bibl. No. 106. 2 Bibl. No. 35a. 3 Bibl. No. 3.