SIBLING NON-IDENTITY DETECTED AT C LOCUS - A CASE STUDY.
          M Williams, P Casey, D Hartzell, M Hoffman, M Wetmore and B Carver, HLA Laboratory, Lehigh Valley Hospital, Allentown, PA.
          Three siblings presented for HLA typing. The serologic results were:-Patient: A2, 24, B44, 62, Cw3,-,DR4,-,DQ3. Donor #1: A2, 31, B44, 51, Cw5,-, DR4, 14, DQ1,7.  Donor #2: A2, 24, B44, 62, Cw3, w5, DR4,-, DQ3 (probable 7&8).  From the serologic results, donor #2 appeared to be phenotypically identical to the patient except for the C locus.  The donor was a Cw3 & Cw5, but the recipient only demonstrated a Cw3.  At a later date, a third donor was typed who was identical to donor #2, including the C locus.  The reactivity of these siblings with the DQ3 antisera also led us to believe the donors were DQ7 & 8, but the recipient was only a DQ8.  Renal patients don't always react as well as normal donors; but it was unclear whether this was the case, whether there were shared parental antigens or whether a crossover was involved.  We then requested that the parents be typed.  The father's HLA phenotype is A2,-, B44,-, Cw5, -DR4,-, DQ3 (probable 7&8). The mother's HLA phenotype is A24, 31, B51, 62, Cw3,-, DR4,1 4, DQ1, 8. Review of the family typings indicated the possibility that the father was homozygous A, B, & DR and that the recipient had inherited the opposite haplotype from the father as had donors 2 & 3. Since immune suppression is handled somewhat differently for patients receiving a kidney from an HLA identical sibling, it was imperative that this be clarified. Donor #3 was ABO compatible, therefore, blood from both him and the recipient was sent for typing by DNA with the following results:- Pt.: A2, 24, B44, 1524, Cw9, w16, DRB1*0401,0402, DRB4*0103, DQB1*0302.  Don.: 2, 24, B44, 1524, Cw5, w9, DRB1*0401, DRB4*0103, DQB1*0301, 0302.  Although the donor and recipient appeared to be identical A, B & DR, the C locus difference lead us to question the haplotypic identity and further testing revealed this pair to be a one haplotype match with no major mismatches on the A, B or DR loci.