You may diagnose the mutation at HEXA gene of chromosome 15 by karyotyping as well as by fluorescence in situ hybridization (FISH). Ypu may take a look at following link
Fine, for pcr you may design primers. to design primer you may take help from ncbi, primer 3 plus, IDT or other online site or other software eg.PrimerSelect, PrimerPrimer 5, Oligo 6, PrimerPrime etc.. I guess you are aware about it. I am giving some links which might help you to solve ur problem.