The couple was extensively counseled before deciding to proceed with PGD. Blood samples from the
proband, the parents and the grandparents were used for genotype and haplotype analysis. From each
sample, both genomic DNA and single lymphocytes were isolated for the standardization of procedures.
For the purpose of PGD, four Short Tandem Repeat (STR) markers closely linked to the HEXA gene were
used as already described elsewhere (Altarescu et al., 2007). These were carefully selected following an
initial workup with a number of STR markers, so that they would be informative for the family and
flanking the HEXA gene (in order, D15S204 and TS-AAAT are 5′ and D15S215 and D15S169 are 3′ to the
gene). Initial multiplex Polymerase Chain Reaction (PCR) amplification of all four STR's was followed by
hemi-nested PCR. The reactions of 50 μl were set up for each step using Multiplex HotStart Taq (Qiagen,
Germany) according to the manufacturer's instructions. In the hemi-nested reactions, the internal forward
primers were labeled with fluorescent dyes and products were analyzed on an ABI 3130XL genetic
analyzer