Monozygotic twins are rarely concordant
for congenital hypothyroidism
(November 2002)
The background of
the study. Absence or abnormal development of the thyroid
accounts for approximately 85 percent of cases of congenital hypothyroidism
in iodine-sufficient regions of the world. The causes of the abnormalities
are not known. To evaluate the role of heredity in the causation
of these abnormalities, the concordance of congenital hypothyroidism
among twins was studied.
How the study was done. The multi-year
records of the Quebec, Canada, and Brussels, Belgium, screening
programs for congenital hypothyroidism were searched to identify
twins with congenital hypothyroidism; the records of the infants
were then reviewed. In addition, pediatric endocrinologists in both
places were surveyed to determine if they knew of any twins with
congenital hypothyroidism missed by the screening programs.
The results of the study. During
the study period, the frequency of congenital hypothyroidism was
1 in 2971 infants in Quebec and 1 in 3167 infants in Brussels. Sixteen
pairs of twins were identified in the two regions; five were monozygotic
twins and 11 were dizygotic twins. No twin of an affected infant
had congenital hypothyroidism; thus, all the twin pairs were discordant
for congenital hypothyroidism. All 16 mothers had normal thyroid
function, and there was no other case of congenital hypothyroidism
in any of the 16 families. The survey did not reveal any twins missed
by the neonatal screening programs.
The conclusions of the study. Monozygotic
twins are rarely concordant for developmental abnormalities of the
thyroid, the most common cause of congenital hypothyroidism, suggesting
that the role of heredity in the disorder is very limited.
The original article. Perry R, Heinrichs
C, Bourdoux P, Khoury K, Szots F, Dussault JH, Vassart G, Van Vliet
G. Discordance of monozygotic twins for thyroid dysgenesis: implications
for screening and for molecular pathophysiology. J Clin Endocrinol
Metab 2002;87:4072-7.
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