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Editor,—Little information is available on the aetiology of primary not transient congenital hypothyroidism due to thyroid malformations. Usually it is considered to be a sporadic disease; however, to date, there are no reliable studies to identify some possible family risk factors for the disease.1 2Therefore between April and September 1996, during therapeutic follow up of affected children, we examined the mothers of 19 consecutive infants with congenital hypothyroidism (group A) screened through our regional newborn screening program (Emilia-Romagna, Italy) and 17 age matched volunteer mothers of unaffected children (group B). At the time of this examination the chronological age of the infants with congenital hypothyroidism was 5.5±3.8 years; in all cases the diagnosis of congenital hypothyroidism was confirmed and all had malformations (15 ectopic thyroid glands, three athyrosis, one hypoplasia). All the mothers examined were resident in our region, clinically euthyroid, and had not previously had any thyroid investigations. In all subjects a thyroid ultrasound was performed by the same blind operator using a 10 MHz probe and blood samples were taken to determine serum concentrations of thyroid stimulating hormone, free triiodothyronine, and free thyroxine and antithyroid antibodies.
At the ultrasound examination three mothers in group A (15.8%) showed congenital thyroid abnormalities that were pathological asymmetries of the gland (agenesis of the left lobe and of the isthmus in one case and severe hypoplasia of the left lobe in the other two cases). Their incidence was 33.4% (1/3 cases) in the mothers of athyrotic children and 13.3% (2/15 cases) in the mothers of children with ectopic glands. None of the mothers in group B showed the same abnormalities. Thyroid enlargement on ultrasound examination was found in 8/19 cases in group A and in 7/17 cases in group B; the percentage of nodular goitres was 75.0% and 85.7% respectively.
All subjects examined showed thyroid hormone values within the normal range; positive antithyroid antibody titres were found in 2/19 subjects of group A and in 1/17 subjects of group B.
Congenital thyroid hemiagenesis is thought to be a rare developmental anomaly of the gland and its exact incidence is unknown as the data are usually skewed toward selected patients.3 The only data in literature from a large necropsy series reported a prevalence of 0.34‰.4 The preliminary results of our study seem to indicate that the ultrasound findings of a pathological thyroid asymmetry represent a possible risk factor for fetal congenital hypothyroidism. Further family studies are needed to evaluate the thyroid transcription factor-1 gene which is probably responsible for thyroid development. In our region (Emilia-Romagna, Italy) we have observed an elevated incidence of ‘asymptomatic’ goitres in women of fertile age. This disease, however, does not appear to be related to a higher risk for thyroid malformation in the offspring.