Comparison of Intelligence Quotient between Permanent Congenital Hypothyroid Children and Healthy Children

Congenital hypothyroidism (CH) is the most common curable cause of mental retardation. The aim of this study was to compare the intelligence quotient (IQ) of congenital hypothyroid patients with that of healthy children.
This case-control cross-sectional study was performed on 30 permanent CH children within the age range of 6-12 years referring to the Endocrine Clinic of Imam Reza Hospital, Mashhad, Iran between April 2017-2019. In addition, 32 healthy children of the same age and gender from the family members of the patients were chosen as the control group. The intelligence test was performed using the revised version of the Wechsler Intelligence Scale for Children and the mean verbal, performance, and total IQ were compared between case and control groups.
There was no significant difference between the two groups in terms of age and gender. The mean verbal, performance, and total IQ in the case group were obtained as 104.33±13.30, 93.13±7.42, and 98.03±7.94, respectively. With regard to the healthy group, these mean values were, respectively, estimated at 121.34±16.74, 99.65±11.92, and 110.71±14.15 (the normal range of IQ was 90-109).
Accordingly, the results revealed a significant difference between the two groups in terms of verbal (P=0.000), performance (P=0.013), and total (P=0.000) IQ. Furthermore, a relationship was found between early treatment initiation and higher verbal IQ (r=0.521; P=0.032), as well as between lower thyroid-stimulating hormone and higher performance IQ (r=0.559; P=0.020).
The permanent CH children that had received timely treatment had normal levels of IQ based on the Wechsler Intelligence test. However, it was significantly lower in the CH children than that in healthy children of the same age, gender, and socioeconomic status.