Direct detection of 4q35 rearrangements implicated in facioscapulohumeral muscular dystrophy (FSHD)

The p13E-11 probe has been shown to detect DNA rearrangements in sporadic and familial cases of FSHD. Its use, however, has been hampered by the fact that it detects at least two pairs of EcoRI alleles, one derived from the 4q35 region (D4F104S1), the other from 10q26 (D10F104S2). We have cloned p13E-11 EcoRI fragments from the 4q35 and 10q26 subtelomeric regions and shown the presence of several restriction site differences within the KpnI tandem repeat units. The two loci present a different distribution of restriction sites for the enzyme BlnI which allows differential cleavage of the KpnI units derived from 10q26, leaving intact the 4q35 pair of alleles. This method of differential restriction greatly facilitates the interpretation of Southern blots obtained from affected and unaffected subjects, with an important improvement in reliability for diagnosis and genetic counselling. In addition, this method can be used to investigate the molecular mechanism of the 4q35 rearrangement implicated in the disease and to ascertain whether the rearrangement is because of inter-chromosomal exchange between 4qter and 10qter KpnI repeats.