Duchenne muscular dystrophy due to familial Xp21 deletion detectable by DNA analysis and flow cytometry

We report two male cousins with Duchenne muscular dystrophy (DMD) in whom cytogenetic studies have shown a small interstitial deletion at Xp21. The lesion is readily detectable in patients and carriers by flow cytometry which indicates that approximately 6000 kb of DNA are deleted in each case. The DNA markers OTC, C7, and B24 are present in the deleted X chromosome but 87-8, 87-1, and 754 are absent. Despite apparently identical deletions one affected boy has profound mental handicap while the other is only mildly retarded. The results confirm the assignment of familial DMD to Xp21 and illustrate the value of flow cytometry in improving the precision of chromosome analysis. We have also undertaken flow cytometry in a cell line from a previously reported DMD patient with a de novo Xp21 deletion who had, in addition, chronic granulomatous disease, retinitis pigmentosa, and the McLeod syndrome. The results indicate that the amount of DNA deleted from the X is similar in both families despite the striking differences in phenotype.