Review Question - QID 100097

This woman's presentation is consistent Marfan syndrome. This autosomal dominant condition is due to a mutation in fibrillin-1. Normally, fibrillin binds to individual tropoelastin molecules to form the protein elastin, which is defective in Marfan syndrome.

Signs of Marfan syndrome include detached lenses, aortic dilatation, stretchy skin, arachnodactyly and tall stature, scoliosis, and the thumb and wrist signs (a person is able to wrap their thumb over the nail of the fifth finger encircling their opposite wrist, and thumbs protrude out opposite from clenched fists, see images below). Mitral valve prolapse may also be seen. Death is due to cardiac causes: aortic dissection or heart failure due to aortic insufficiency.

Figure A shows arachnodactyly, a typical sign of Marfan syndrome. Illustration A shows the thumb and wrist signs, which are part of the diagnostic criteria for Marfan syndrome.

Incorrect Answers:
Answer 1: Type 1 collagen is found in bone, skin, and tendons. Defects in Type I collagen may cause osteogenesis imperfecta or Ehlers Danlos syndrome.
Answer 2: Troponin is the protein involved in muscle contraction. It lies in the actin groove and prevents myosin binding unless there is Ca+ present.
Answer 4: Microtubules are hollow tubules made of a- and B-tubulin. They are deficient in Chediek-Higashi syndrome leading to recurrent pyogenic infections due to decreased neutrophil chemotaxis.
Answer 5: Collagen is formed of repetitive Gly-,Pro-X sequences. The small size of the glycine molecule allows tight packing of adjacent peptide chains.