SOMATIC MOSAICISM FOR A DMD GENE DELETION

Mosaicism is a mixed state, with two cell populations of different gen etic origins caused by a cell mutation occurring after fertilization, In the present case, DNA analysis of lymphocytes led to a DMD diagnosi s before death, Postmortem immunocytochemical and DNA analysis showed somatic mosaicism, At age 18 years, blood lymphocyte DNA analysis show ed a DMD gene deletion, upstream from exon 7 to the 5' end containing both muscle and brain promoters. As the patient's mother and elder sis ter had no deletions, he was considered to have a new mutation, Immuno cytochemical studies of postmortem tissues showed that dystrophin was absent from the tongue, deltoid, intercostal, psoas and rectus femoris muscles, but there was a mix of dystrophin-positive and negative fibe rs in the rectus abdominis, cardiac, temporalis and sternocleidomastoi d muscles. Ah diaphragm cells were dystrophin positive, Polymerase cha in reaction (PCR) amplification from all tissues except the temporalis and sternocleidomastoid muscles, diaphragm and kidney, in which no de letion was found, showed the deletion from at least exon 6 to the 5' e nd containing both muscle and brain promoters, In this case, a genomic deletion of the DMD gene contributed to the formation of tissues deri ved from both ectoderm and endoderm, and cells of mesodermal origin sh owed genotypic and phenotypic heterogeneity, Our results indicate a mu tation of the present case may have occurred just before the period of germ layer formation. (C) 1995 Wiley-Liss, Inc.