In: Biology
1. A woman is affected with Alpha-1 antitrypsin deficiency, an autosomal recessive condition with a carrier frequency of 1 in 13. As they are planning on having children, her partner undergoes carrier testing for the condition. The result was negative, indicating that he was not found to be a carrier. The reported sensitivity of the carrier testing is 95%. What is the chance that their first child will be affected with Alpha-1 antitrypsin deficiency?
Given, alpha-1-antitrypsin is Autosomal Recessive disease means it will affect only in Homozygous Recessive condition.
Also given that woman is affected = means she is Homozygous Recessive for this condition. As the Homozygous Dominant and Heterozygous dominant are not affected in Autosomal Recessive disease. And the woman has carrier frequency of 1/13 means transmit it to next generation by this frequency.
Total frequency = 1/13(transmit) * 1(affected )
= 1/13 = female
She and her partner are planning to have children so, her partner is undergone testing for the condition. He is not found to be a carrier and report sensitivity is 95%. It means her partner is not a carreir by 95% but can be a carrier by 5%.
Her partner = 5/100(carrier frequency) * 1/2( 1 chance of being a carreir for total = carrier + not a carrier)
= 5/100 * 1/2
= 1/40
Probability/Chance that they have their first child as affected for alpha-1-antitrypsin =
Probability of recessive allele from mother * Probability of recessive allele from Father
= 1/13 * 1/40
= 1/520
So, they can have their first child as affected by the Probability or chance of 1/520.