A phenotypically normal couple naturally conceives a child with methylmalonic acidemia (MMA). In order to find out the cause of disease, doctors recommend genetic testing of the child first. The results showed that the child carried two heterozygous mutations of MMACHC gene: C. 609G > A and C. 394C > T, which was inherited from their parents. Methylmalonic acidemia (MMA) is an autosomal recessive hereditary disease. Both of the above two loci were identified as pathogenic loci, which could constitute a compound heterozygous pathogenic pattern. In view of the couple's high risk of having another child, doctors recommend that they choose PGD technology to have a normal child. Following that, blastocyst trophoblast cells from 8 embryos were subjected to haplotype linkage analysis (see the figure below).

Two embryos with normal genotype were obtained. After comprehensive evaluation of these two normal embryos, the doctor finally selected embryo Emb3 for implantation. Now this woman is successful pregnant and all test indexes are good.