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Choi and colleagues performed oral glucose tolerance tests (OGTT) in 103 patients
with Turner syndrome who had normal fasting and postprandial glucose levels.
Plasma glucose, insulin, C-peptide, and proinsulin were measured every 30 minutes
and insulin resistance was evaluated using a homeostatic model assessment (HOMA)
and a quantitative insulin sensitivity check index (QUICKI). The OGTT was a
standard 1.75 g/kg with a maximum of 75 g of glucose. Impaired glucose tolerance
(IGT) was defined according to ADA criteria of a fasting glucose below 126
mg/dl and a 2-hour level between 140 - 200 mg/dl. Some of the patients were
receiving recombinant growth hormone.
Eighteen of the subjects were noted to have IGT and 2 were diagnosed as having
diabetes mellitus. BMI and positive family history of diabetes were not different
in the IGT group compared to the normal glucose tolerance (NGT) group. There
was no relationship between positive history of growth hormone administration
and duration of therapy in either group as well. During the OGTT plasma glucose
levels were higher in the IGT group than in the NGT group, particularly at
60, 90, and 120 minutes while plasma insulin levels were higher at 0 and 120
minutes. HOMA was similar in both groups, but QUICKI was lower in the IGT group
than in the NGT group. Fasting plasma triglyceride level was higher in the
IGT group while total cholesterol, HDL, LDL and free fatty acid levels were
similar in both groups. Fasting and 2-hour plasma insulin, proinsulin, and
C-peptide, as well as triglycerides and free fatty acid levels showed significant
correlations with 2-hour plasma glucose level. However, only fasting insulin
and plasma triglyceride levels strongly predicted the 2-hour glucose level.
The authors suggested that testing with an oral glucose tolerance test is
superior to the fasting and postprandial glucose test for the early detection
of abnormalities of carbohydrate metabolism in girls with Turner syndrome.
Choi
IK, Kim DH, Kim HS. The abnormalities of carbohydrate metabolism in Turner syndrome:
Analysis of risk factors associated with impaired glucose tolerance. Eur J Pediatr. 2005;164:442-447.
Editor’s Comment: This is a very comprehensive
study of carbohydrate metabolism in patients with Turner syndrome. It is
not entirely surprising that over 10% had impaired glucose tolerance and
that a variety of hormone levels were elevated in the IGT group -
including insulin, C-peptide, and proinsulin. What is not clear is why the
authors claim that the oral glucose tolerance test is superior to the fasting
and postprandial glucose test for the early detection of abnormalities of
carbohydrate metabolism. Clearly their data show that the fasting plasma
insulin and triglycerides most strongly and significantly predicted the 2-hour
glucose level and, in fact, it is the 2-hour glucose level that predicted
the diagnosis of impaired glucose tolerance.
It is interesting that there was no difference between the NGT and IGT
groups with regard to growth hormone administration or duration of growth
hormone, nor lipids other than triglycerides. Pediatric endocrinologists
and geneticists have been aware of the potential for growth hormone to be
associated with impairment in glucose tolerance. Since such metabolic abnormalities
are known to occur in girls without Turner syndrome who have never received
growth hormone, these findings are particularly reassuring. Since BMIs were
not different between the NGT and IGT groups, this suggests that caloric
restriction and increased physical activity may not have the same effects
in girls with Turner syndrome as have been shown in large populations of
allegedly normal chromosomal individuals with IGT.
William L. Clarke, MD
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Current GGH - Vol. 24 No. 1
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