Figure 2. Preimplantation HLA matching in combination with PGD for b-thalassaemia, resulting in the birth of two twins, HLA matched with the affected sibling. Specific haplotypes were determined by genomic DNA analysis of HLA STR markers and Beta globin (HBB) linked markers from father, mother (upper panel) and affected child (lower panel-left side, black square). Informative STR markers are ordered from telomere (top) to centromere (bottom). The numbers in STR markers represent the size of PCR products in base pair. Paternally and maternally derived HLA haplotypes matched to the affected child are shown in boldface. STR alleles linked to the paternal and maternal mutations are also represented boldfaced. Examples of different results of HBB mutation analysis and HLA haplotyping from biopsied blastomeres are shown in the lower panel. Paternally and maternally derived haplotypes from each embryo are shown on the left and the right, respectively. The HLA identity of the embryos with the affected sibling has been ascertained evaluating the inheritance of the matching haplotypes. Embryos 1, 2 (carriers) and 8 (affected) represent HLA non-identical embryos. Embryos 3 and 6 were diagnosed as normal, and embryo 7 as carrier, HLA matched with the affected sibling, and were transferred resulting in a HLA matched unaffected birth of two twins (babies have been originated from embryos 3 and 6). ET = Embryo Transfer.