USMLE Step 1 Question 330

Question:

A 6-year-old boy had meconium ileus at birth. He has now developed chronic productive cough and bulky, fat-containing stools.

Which of the following is he most at risk for?

Correct Answer: C.  Rickets

The most common cause of meconium ileus is cystic fibrosis. The abnormal CFTR channel in cystic fibrosis causes a pancreatic enzyme deficiency that prevents fat digestion and leads to fat excretion, or steatorrhea. In addition to fats themselves, the fatsoluble vitamins, K, A, D, and E, cannot be absorbed. Developing children are at risk for Vitamin D deficiency, or rickets (Answer C).

The rest of the choices are water-soluble vitamins. Malabsorption syndromes affect these vitamins as well, although not as severely.

Beriberi, aka B1 or thiamine deficiency, is often associated with alcoholism.

Pellagra, aka Vitamin B3 or niacin deficiency causes the 3 Ds: diarrhea, dermatitis, and dementia.

Scurvy aka Vitamin C or ascorbic acid deficiency, develops in fruit and vegetable deficient diets.

Vitamin B12 deficiency causes anemia and neurologic symptoms, and can be due to autoimmune attack of parietal cells of the stomach (which secrete intrinsic factor, which is necessary for B12 absorption), surgical resection of the ileum (where B12 absorption takes place), or inadequate B12 intake.