Calculate the population carrier frequency
Using the Hardy-Weinberg equation, p2 +2pq + q2 =1, we can estimate the frequency of the carrier state (2pq) for an autosomal recessive trait. p2 is 0.99003 (homozygous wild type); q2 is 0.00003 (homozygous mutation); 2pq is 0.00995 or 1 in 100.5 (1%).
Calculate the risk for the healthy sibling of an affected individual to have a child with Pompe disease
2/3 (risk of being a carrier) x 1/100 (population frequency) x 1/4 (both carriers and then have an affected child) = 1/600