Molecular Genetics of Neuromuscular Disease 
ucts from patients who do not have a detectable 
deletion, we have found at least one mutation 
that involves splicing of dystrophin's primary 
transcript. 
PGR amplification yielded a product of abnor- 
mal size that lacked exon 5. Sequence analysis of 
the patient's DNA from the region of this exon 
revealed an identical sequence to that of normals. 
We are currently cloning other surrounding DNA 
to identify the exact point where a mutation 
might effect the splicing of exon 5. We believe 
that mutations in splicing signals may lead to a 
better understanding of how this huge locus is 
processed into a mature mRNA transcript. 
During our screening of different dystrophin 
antibodies for finding cross-reactive proteins, our 
carboxyl domain-directed antibodies detected a 
small protein (approximately 70 kDa). At the 
same time, David Yafife's group in Israel reported 
observing a short dystrophin transcript in non- 
muscle tissues. Our laboratory cloned this tran- 
script from our human brain cDNA library, and 
sequencing of the cDNA clones revealed a diver- 
gence from expected dystrophin sequence at ap- 
proximately exon 62. We are currently preparing 
antibodies against novel peptide sequences to de- 
termine if the shorter protein detected in brain 
tissue with antidystrophin antibodies is indeed a 
product of this novel transcript. 
In addition to the published shorter transcript, 
we have also detected a slightly larger protein 
(approximately 90 kDa) in sciatic nerve. cDNA 
clones have been prepared and shown to diverge 
from expected dystrophin sequence at exon 54. 
Similar studies are under way for this novel tran- 
script to determine the role these smaller pro- 
teins might play in the phenotype of Duchenne 
dystrophy. 
Our aim for the future year is to build on work 
already in progress. We will continue to identify 
dystrophin-related proteins and attempt to deter- 
mine their normal function in muscle. We will 
determine what role, if any, they play in other 
neuromuscular diseases and whether they miti- 
gate the effects of abnormal dystrophin. We will 
continue our analysis of dystrophin-alternative 
transcripts and what role they might play in nor- 
mal development and the phenotype of Du- 
chenne dystrophy. As more human disease genes 
are mapped to specific human chromosomes, we 
believe that our candidate gene approach, which 
builds upon knowledge of abnormal dystrophin, 
should help in the rapid characterization of these 
diseases. 
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