Suppose in a hospital in the United Kingdom out of 98 543 of

Suppose in a hospital in the United Kingdom, out of 98, 543 of babies born in the last 20 years, 13 children were born with myotonic dystrophy. Myotonic dystrophy is caused by an autosomal dominant mutation in the dystrophia myotonica protein kinase gene, DMPK. Myotonic dystrophy causes progressive muscle weakness, cataracts, and difficulty relaxing clenched hands. Of the 13 affected children, only 3 were born to a parent with a DMPK mutation. Given this information, what is the mutation rate of the DMPK gene?

Solution

Mutation rate is number of mutations per cell division.

Let the gene for the disease be “A”.

3 children out of 13 children were born to parents having “A” allele.

Rest 10 children had the mutated gene.

Please note that the number of cell divisions is equal to the total number of babies born (= 98543). Every time a baby is born, cell division or meiosis takes place, which may or may not result in mutation.

So, mutation rate = (10/98543) = 1.01*10^-4 per cell division or per baby born.