Everyone inherits two sets of chromosomes containing HLA genes, four genes per set. One set comes from their father and one from their mother, for a total of eight genes. There is a one in four, or 25 percent, chance that any brother or sister will have inherited the same two sets of HLA genes as the patient. For a parent to be "matched" with his or her child, both parents must by chance have some HLA genes in common with each other. It is very unlikely, about a one in a million chance, for two unrelated individuals to have the same HLA genes in common, and there is only a one in 200 chance that a parent and child will be HLA matched.
A much higher chance for a parent (or both parents) and children to be HLA matched in case the parents and grandparents are siblings (having same biological father and mother).
Don't know how PMLN will sell this idea (of Maryam being HLA match of her father) to the nation.