CASE FILES: BIOCHEMISTRY
A 3-year-old male with coarse facial features, progressive loss of
motor skills, hepatosplenomegaly and chronic diarrhea is suspected of
having Hunter syndrome (MPS II). Which of the following monosac-
charide residues would be expected to be found at the nonreducing end
of glycosaminoglycans in this patient’s urine?
E. Iduronate 2-sulfate
A nsw ers
D. The patient is exhibiting the classic symptoms of Sanfilippo syn-
drome, which is a deficiency in one of four different lysosomal
enzymes that breakdown glycosaminoglycans leading to the buildup
of heparan sulfate and dermatan sulfate in lysosomes.
B. All of the mucopolysaccharidoses are transmitted by autosomal
recessive inheritance except Hunter syndrome (MPS II), a deficiency
in iduronate sulfatase that is X-linked recessive. Since Hunter syn-
drome is X-linked, it is almost exclusively seen in males. Since our
patient is female, she would not be expected to have an X-linked
E. Since this patient is suspected of having Hunter syndrome, a defi-
ciency in iduronate sulfatase, iduronate 2-sulfate would be expected
to be present at the nonreducing end of glycosaminoglycans found in
this patient’s urine. A deficiency of iduronate sulfatase would prevent
the sulfate ester bond of iduronate 2-sulfate residues from being
hydrolyzed and further degradation of the glycosaminoglycan would
B IO C H E M IS T R Y PE A R L S
Often enzyme deficiencies are inherited as autosomal recessive dis-
orders, so that both chromosomes are defective for the individual
to be affected.
Mucopolysaccharidoses occur when there is a genetic deficiency of
the enzymes involved in the lysosomal breakdown of the
In Sanfilippo syndrome, the accumulation of heparan sulfate in lyso-
somes leads to severe neurologic and mental impairment that
result in death usually by the end of the second decade of life.