Question

Parents of a kidney transplant candidate were tested for a potential compatible kidney because the candidate demonstrated HLA antibodies. The patient's HLA antigens were typed as A1, A2, B27, B50, DR17, and DR11. Antibodies identified were specific for A3, B18, and DR7 antigens.

1.  If the mother's HLA typingis A1, A3, B35, B27, DR4, and DR11, and the father's typing is A2, A24, B50, B44, DR11, and DR17, what antigens did the father contribute?

2. List the probable HLA types of the candidate's three siblings. Select the kidney or kidneys with the best match.

Answer 1

MHC genes contain 33 to 44 genes grouped in 3 regions: class I, Class II and class III. Class A has HLA-A, HLA-B and HLA-C molecules; Class II has HLA-Dr, HLA-DP and HLA-DQ and class II includes complement proteins C3 and C4 and cytokines. There is linkage disequilibrium as most genes are linked. HLA are inherited as haplotypes. Each sibling can share at least one haplotypes with the sibling and has a 25% chance of the same HLA typing. The child inherits one haplotypes for each parent.

Mothers Haplotype: A1, A3, B35, B27, DR4, and DR11

Father’s haplotypes: A2, A24, B50, B44, DR11, and DR17

Child’s haplotypes: A1, A2, B27, B50, DR17, and DR11

1. The Child inherits A1 and A2 from either parent. Mother has A1. So A2 (not present in mother) is inherited from father.

Similarly B27 is inherited from mother. So B50 (not present in mother) is inherited from father.

DR11 is inherited from mother. DR17 (not present in mother) is inherited from father. Although DR11 is present in father, this haplotype is obtained from father, as mother lacks DR17.

The child inherited A2, B50 and DR 17 from father.

2.

Mother                                              Father

A1          A3                                                        A2       A24

B27       B35                                                      B44        B50

DR4       DR11                                                   DR11     DR17

Sibling Types:

Sibling 1; A1, A24, B27, B44, DR4, DR11

Sibling 2: A3, A2, B35, B44, DR 11, DR11

Sibling 3: A3, A24, B35, B50, DR4, DR17

Kidneys with best match:

Sibling 1 and 2 matches for 2 haplotypes out of 6, sibling 3 shares 3 haplotypes out of 6.

Sibling 3 is the best match for kidney donation as it matches for 3/6= 50% match