Improved growth velocity during thyroid hormone therapy in children with Fanconi anemia and borderline thyroid function

Background. Children with Fanconi anemia (FA) tend to have short stature, mild thyrotropin (TSH) elevation, and borderline low free thyroxine (FT4). Objective was to examine whether thyroid hormone therapy improves linear growth in children with FA and borderline thyroid function tests Procedure. Thyroid function tests were performed in 63 children with FA. Eight subjects participated in a random order, double-blind, cross-over treatment for 7 months with levothyroxine and for 7 months with placebo. Monitoring included growth measurements and laboratory assays at 1, 4 and 7 months of each phase. A 1 month lead in/wash out period was excluded from analysis of each treatment phase. Results. The majority (63%) of FA children had borderline thyroid function tests. All eight FA subjects enrolled in the treatment study had FT4 in the lowest third of the normal range of 0.8-1.8 ng/dL (10.3-23.2 pmol/L) [FT4 0.9 ± 0.1 ng/dL (mean ± SD), range 0.8-1.2 ng/dL (10.3-15.4 pmol/L)]. TSH (optimal range 0.5-3 mU/L) was borderline elevated in six of eight subjects (4.0 ± 1.5 mU/L, 1.9-7.3 mU/L). Growth velocity was slow at baseline and improved significantly during the thyroid phase compared to the placebo phase (2.1 ± 1.2 cm/year vs. 5.4 ± 1.7 cm/year, P < 0.05). Conclusions. Thyroid hormone therapy is safe and may improve linear growth velocity in children with FA who have borderline thyroid function. Subtle hypothyroidism has importance for growth in children. Whether thyroid hormone treatment improves adult height in these children remains to be elucidated.