Informing & Supporting Thyroid Patients Since 1985
Informing & Supporting Thyroid Patients Since 1985
Thyroid Research 
Thyroid Research Archive Congenital
(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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