60.A 6-month-old boy is brought into the pediatric clinic. He weighs 12 lb,
2 oz and is 22 in. tall. Neither his height nor his weight is on the growth
chart for his age; mean weight and height for a 6-month-old are 17 lb, 4 oz
and 26.5 in., respectively. Through functional tests, you determine that he is
suffering from an inherited condition known as I-cell disease and is missing
UDP N-acetylglucosamine: lysosomal enzyme N-acetylglucosamine-1-
phosphotransferase, which is more conveniently referred to as phospho-
transferase. You recall from your cell biology that the phosphotransferase
enzymes phosphorylate mannose to form mannose-6-phosphate. Electron
microscopy is performed on a biopsy, and blood tests are completed. Which
of the following explains the altered cell biological processes in this patient?
a. Lysosomal enzymes missorted back to the Golgi apparatus
b. Peroxisomal proteins missorted to other organelles
c. Abnormal KDEL sequence on vesicles
d. Absence of SNARE proteins on vesicles
e. Secretion of lysosomal enzymes into the blood
132 Anatomy, Histology, and Cell Biology