Embryology

Question:

A 10-year-old boy complains of increasing weakness in his legs. His mother notes that the patient is no longer as active as he once was and no longer can participate in gym class due to fatigue. On physical exam, it is noted that the patient uses his hands to help him raise himself off the floor, first getting on his knees then walking his hands back to his legs. His blood tests are notable for an elevate CPK. Which protein is most likely decreased in this patient?

Correct Answer: D.  Dystrophin

The patient is suffering from Duchenne muscular dystrophy which is caused by a mutation of the dystrophin (option D) gene on the X chromosome. It is X-linked recessive so it mainly seen in males. The elevated CPK is a sign that there is muscle breakdown which is the reason for the fatigue. The description of the patient raising himself is called the Gowers’ Sign.

A deficiency of alpha-1 antitrypsin (option B) is the caused of liver failure and early-onset panacinar emphysema.

A deficiency in type I collagen (option C) is seen in osteogenesis imperfecta.

A mutation in the fibrillin gene is the cause of Marfan syndrome notable for tall patients with severe nearsightedness, lens subluxation, arachnodactyly, hyperextensible joints, and risk of aortic dissection. It is thought to be due to unopposed action of TGFbeta (since fibrillin inhibits TGF-beta in normal patients).

Actin is found in all eukaryotic organisms and primary building blocks in microfilaments and thin filaments (in sarcomere attach to Z line).