Neurotransmission Specification of synaptic action

compared to the transmission pattern of the DMD gene. If the DNA sequence homologous to hRC8 were located at a great distance from the DMD gene, then there should be no relationship in the pattern of segregation of the hRC8 polymorphism and the DMD gene. The segregation pattern of the two genetic loci was, however, far from random. The two characteristics (DMD and hRC8 polymorphism) were inherited together with a probability of almost 90%. This result means that hRC8 and the DMD gene are in the same region of the X chromosome. How will this result lead to the identification of the DMD gene itself? Two possible strategies may lead to this end-point. One approach will involve the isolation of other cloned DNA sequences in the Xp21 region, which will lead to the DMD gene by a series of successive approximations. Eventually the DMD gene will be hounded within a sufficiently small (perhaps 500 000 base pairs) DNA segment that it will be possible to isolate and characterize all the DNA sequences between these boundaries and determine which polypeptide chains are coded for by the DNA within these regions. These five or ten polypeptide chains will then form a short-list of candidates for the gene product of the DMD gene. Physiological tests will be necessary to determine which of these properties is the actual product of the DMD gene. An alternative possibility is presented by the results of Wrogemann and co-workers 3. This group, working at the University of Manitoba in Winnipeg, Canada, reports the identification of a 56 000 mol. wt polypeptide which is absent in the fibroblasts of DMD patients but present in the fibroblasts of normal individuals. If this polypeptide chain were found to be the actual gene product of the DMD gene, then the pathway to the understanding of DMD will have advanced markedly. One of the key tests to determine whether the missing polypeptide is the direct product of the DMD gene locus will be to demonstrate that the coding information for this polypeptide chain resides at Xp21. Experiments are in progress in Winnipeg to explore this possibility. Reading i/st 1 Davies, K. E., Young, B. D., Elles, R. G., Hill, M. E. and WiUiamson, R. (1981) Nature (London)