L-thyroxine therapy and growth processes in children with Down syndrome

Subclinical hypothyroidism is more frequent in newborns with DS (Down syndrome) than in the population of healthy children. The lack of appropriate treatment can deepen the children's retardation as well as affecting the process of their growth.

Evaluation of the impact of hypothyroidism substitution treatment on the process of growth and physical development in children with DS.

The study group included 61 children (25 girls, 36 boys) with DS aged 1-22 years, the average age was 5.13 ± 5.06 years. 49.18% of them were children with congenital cardiac defects (CD). Hypothyroidism was diagnosed on the basis of clinical symptoms and an elevated serum level of TSH (thyroid stimulation hormone) and incorrect levels of fT4 (free thyroxine) and fT3 (free triiodothyronine). In 42 children hypothyroidism substitution treatment was initiated in the first year of life, the rest of the children started the therapy at an older age. Height and body weight measurements were taken at every check-up visit in the Outpatient Clinic. Body weight, height and BMI were expressed as SDS (Standard Deviation Score).

In the whole study group, height SDS was -2.27 ± 1.82. The authors showed a significant correlation between increase in annual height velocity and TSH levels (r = -0.34; p < 0.05). Higher doses of L-thyroxine/kg of body weight had a positive impact on the weight reduction and height velocity and BMI SDS decrease. A significant difference between the annual growth velocity and age of the treatment initiation (up to the 3rd month and between 3-6 months) was found (16.95 ± 4.1cm vs. 12.19 ± 2.95cm in the first year of treatment). In the whole group the authors observed a positive correlation between height velocity and weight velocity in the 1st year of the treatment (r = 0.5; p < 0.001), a negative correlation between height velocity in the 1st year of the treatment and time of the treatment initiation (r = -0.68; p < 0.001) and a positive correlation between the average annual height and weight velocity during whole time of the treatment (r = 0.26; p < 0.05). The birth weight positively correlated with height SDS (r = 0.27; p < 0.0001) and negatively with BMI SDS (r = -0.12; p < 0.01). The authors showed a statistically negative influence of cardiac defects on weight and height velocities.

It is advisable to monitor thyroid function in patients with DS. Early administration of L-thyroxine results in significant improvement in the growth of these children. Optimizing the therapy affects the children's annual growth increases and makes it possible to improve the process of equalization of the growth deficiency.