Young boys with Duchenne muscular dystrophy (DMD) often demonstrate a distinctive way of rising from the floor using their hands and arms to walk up their bodies. This is called:
Gower’s sign
Correct! Gower’s sign or maneuver is a classic finding in a young boy with DMD.
Frontal release sign
Incorrect
Genetic testing in DMD is most likely to find which of the following mutations in the DMD gene if DMD is present:
Trinucleotide repeat sequences
Incorrect
Deletion of one or more exons
Correct! The most common mutations in DMD are deletions of one or more exons.
Large insertions mutations
Incorrect
Substitution of valine for glutamate in the beta-chain
Incorrect
Mrs. M has one male biological relative with DMD on her mother’s side of the family. Her 17 year old brother also has DMD. Mrs. M is concerned about the possibility of having a child with DMD. She notes no other history of DMD in the family and we have no genetic testing information. What are the chances that that Mrs. M would have an affected son?
8.3%
Correct! You can assume that Mrs M’s mother is an obligate carrier as there is a family history of one other male biological relative with DMD (this makes it unlikely that the mutation in Mrs. M’s brother is caused by a de novo mutation, but we still are accounting for possibility of de novo in our calculation as it is so common). The risk of having an affected child can be roughly calculated as: 2/3 (chance of her brother having an inherited mutation; 1/3 are do novo) X ½ (chance of Mrs. M being a carrier) X ¼ (chance of a carrier having an affected child) = 1/12 or 8.3%. This is really a rough calculation since the probability that her brother has an inherited mutation is a bit higher than 2/3 since we know there is a positive family history of one other affected relative.