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CASE FILES: BIOCHEMISTRY
[29.3]
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?
A. A-Acetylglucosamine
B. A-Acetylgalactosamine
C. Glucuronate
D. Iduronate
E. Iduronate 2-sulfate
A nsw ers
[29.1]
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.
[29.2]
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
disorder.
[29.3]
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
be halted.
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
glycosaminoglycans.
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.
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