OBJECTIVE: To determine the proportion of the various types of thyroid disorders 
among newborns detected by the neonatal TSH screening programme, with a normally 
located thyroid gland. Patients and methods Of the 882 575 infants screened in 
our centre between 1981 and 2002, 85 infants with a normally located gland had 
persistent elevation of serum TSH values (an incidence of 1/10 383). Six of 
these 85 patients were lost to follow-up and were therefore excluded from the 
study. During follow-up, patients were classified as having permanent or 
transient hypothyroidism.
RESULTS: Among the 79 patients included in the study, transient (n = 30, 38% of 
cases) and permanent (n = 49, 62% of cases) congenital hypothyroidism (CH) was 
demonstrated during the follow-up at the age of 0.7 +/- 0.6 years and 2.6 +/- 
1.8 years (P < 0.0001), respectively. The proportion of premature births was 
significantly higher in the group with transient CH (57%) than in the group with 
permanent CH (2%) (P < 0.0001). A history of iatrogenic iodine overload was 
identified during the neonatal period in 69% of transient cases. Among permanent 
CH cases (n = 49), patients were classified as having a goitre (n = 27, 55% of 
cases), a normal sized and shaped thyroid gland (n = 14, 29% of cases) or a 
hypoplastic gland (n = 8, 16% of cases). The latter patients demonstrated global 
thyroid hypoplasia (n = 3), a right hemithyroid (n = 2), hypoplasia of the left 
lobe (n = 2), or asymmetry in the location of the two lobes (n = 1). Patients 
with a normal sized and shaped thyroid gland showed a significantly less severe 
form of hypothyroidism than those with a goitre or a hypoplastic thyroid gland 
(P < 0.0002). Among permanent CH cases, those with a goitre (n = 27) had an 
iodine organification defect (n = 10), Pendred syndrome (n = 1), a defect of 
thyroglobulin synthesis (n = 8), or a defect of sodium iodine symporter (n = 1), 
and in seven patients no aetiology could be determined. Among permanent cases 
with a normal sized and shaped thyroid gland (n = 14), a specific aetiology was 
found in only one patient (pseudohypoparathyroidism) and two patients had Down's 
syndrome. Among those with a globally hypoplastic gland, a TSH receptor gene 
mutation was found in two patients.
CONCLUSIONS: A precise description of the phenotype can enhance our 
understanding of various forms of neonatal hypothyroidism as well as their 
prevalence and management. It also helps to identify cases of congenital 
hypothyroidism of unknown aetiology, which will need to be investigated in 
collaboration with molecular biologists.