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Neurology (Expert Forum)
PKU
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PKU
by henry kayanja, Nov 24, 2000 12:00AM
a)if a homozygous woman and heterozygous man have children, what percentage of the offspring will show the symptoms of PKU?
b)what percentage will be heterozygous and thus carry the mutant allele?
c)if both parents are heterozygous for the condition, what chance is there that their offspring will develop PKU?
d) if a woman who is homozygous for the normal allele had children with a man who is homozygous for the disease allele, what percentage of the offspring would develop the condition?
b)what percentage will be heterozygous and thus carry the mutant allele?
c)if both parents are heterozygous for the condition, what chance is there that their offspring will develop PKU?
d) if a woman who is homozygous for the normal allele had children with a man who is homozygous for the disease allele, what percentage of the offspring would develop the condition?
Doctor's Answer
by CCF Neuro[P] MD, RPS, Nov 24, 2000 12:00AM
Dear Henry:
Since PKU is an autosomal recessive disease, for a child to have PKU, both parents must carry the allele(gene) for PKU. If both parents are heterozygous (do not have the disease but carry the gene) then their offspring EACH have a 25% chance of having the disease, 50% chance of being heterzygous for the gene, and 25% chance of being homozygous for being normal without the allele or gene.
If one of the parents is heterozygous for the gene and the other parent is homozygous for the normal gene, there is no chance that the child will have PKU unless a spontaneuous mutation happens (very unlikley). The chance will be 50% chance that the child would be a carrier or heterozygous, and a 50% chance that the child will not carry the gene.
If one parent is homozygous for the gene PKU and the other is not a carrier and normal, then all the children would be heterozygous for the PKU gene or carriers.
I hope this helps.
Sincerely,
CCF Neuro MD
Since PKU is an autosomal recessive disease, for a child to have PKU, both parents must carry the allele(gene) for PKU. If both parents are heterozygous (do not have the disease but carry the gene) then their offspring EACH have a 25% chance of having the disease, 50% chance of being heterzygous for the gene, and 25% chance of being homozygous for being normal without the allele or gene.
If one of the parents is heterozygous for the gene and the other parent is homozygous for the normal gene, there is no chance that the child will have PKU unless a spontaneuous mutation happens (very unlikley). The chance will be 50% chance that the child would be a carrier or heterozygous, and a 50% chance that the child will not carry the gene.
If one parent is homozygous for the gene PKU and the other is not a carrier and normal, then all the children would be heterozygous for the PKU gene or carriers.
I hope this helps.
Sincerely,
CCF Neuro MD
Member Comments (2)
by lavon, Nov 29, 2000 12:00AM
Forgive me for jumping in but I thought the first question was asking if a woman who is homozygous for PKU has children by a man who is heterozygous what are the chances of problems. For EACH child the chances are 50% that the child will have PKU and 50% that the child will be a carrier. No child will be free of the gene.
