RFLP of the HLA-DQ alpha region: a diallelic DX alpha polymorphism, not linked to DR and DQ specificities.

HLA-DQ alpha DNA polymorphism was studied by Southern blot analysis in a panel of 117 individuals, consisting of 56 randomly selected and 61 HLA-DR homozygous individuals. Hybridizing fragments representing DQ alpha genes correlate with DR specificities owing to linkage disequilibrium between DQ and DR. Two fragments representing DX alpha genes were identified with the restriction enzymes PvuII and TaqI and a DQ alpha cDNA probe. The two fragments of PvuII-DQ alpha hybridization (a 7200 and a 7000 basepair fragment) and the two of TaqI-DQ alpha (2200 and 1900 basepairs) have an identical distribution in the panel, and reveal gene frequencies of 49.1% and 50.9%; they behave as alleles of the putative DX alpha locus. The panel study shows that the DX alpha fragments are not linked with the DR or DQ specificities but segregate along with HLA as shown in family studies.