Iron Supplementation Associated With Loss of Phenotype in Autosomal Dominant Hypophosphatemic Rickets.

CONTEXT: Autosomal dominant hypophosphatemic rickets (ADHR) is the only hereditary disorder of renal phosphate wasting in which patients may regain the ability to conserve phosphate. Low iron status plays a role in the pathophysiology of ADHR. OBJECTIVE: This study reports of a girl with ADHR, iron deficiency, and a paternal history of hypophosphatemic rickets that resolved without treatment. The girl's biochemical phenotype resolved with iron supplementation. SUBJECTS: A 26-month-old girl presented with typical features of hypophosphatemic rickets, short stature (79 cm; -2.82 SDS), and iron deficiency. Treatment with elemental phosphorus and calcitriol improved her biochemical profile and resolved the rickets. The girl's father had presented with rickets at age 11 months but never received medication. His final height was reduced (154.3 cm; -3.51 SDS), he had undergone corrective leg surgery and had an adult normal phosphate, fibroblast growth factor 23, and iron status. Father and daughter were found to have a heterozygous mutation in exon 3 of the FGF23 gene (c.536G>A, p.Arg179Gln), confirming ADHR. INTERVENTION: Withdrawal of rickets medication was attempted off and on iron supplementation. RESULTS: Withdrawal of rickets medication in the girl was unsuccessful in the presence of low-normal serum iron levels at age 5.6 years but was later successful in the presence of high-normal serum iron levels following high-dose iron supplementation. CONCLUSIONS: We report an association between iron supplementation and a complete loss of biochemical ADHR phenotype, allowing withdrawal of rickets medication. Experience from this case suggests that reduction and withdrawal of rickets medication should be attempted only after iron status has been optimized.

A levothyroxine dose recommendation for the treatment of children and adolescents with autoimmune thyroiditis induced hypothyroidism.

OBJECTIVE: To determine a levothyroxine (T4) dose recommendation for the treatment of autoimmune thyroiditis (AIT)-induced hypothyroidism. METHODS: T4 doses in 75 children and adolescents with newly diagnosed AIT were prospectively collected and compared to T4 doses of patients with congenital hypothyroidism (CH, n=22). RESULTS: Sixty-four patients with AIT and 22 patients with CH were included in the analysis. The thyroid-stimulating hormone declined significantly from 25.8 ± 50.1 to 2.1 ± 1.5 µIU/mL (AIT group; p<0.01) and from 338.7 ± 380.7 to 1.9 ± 1.6 µIU/mL (CH group; p<0.01). The required T4 dose for patients with AIT was 1.5 ± 0.5 µg/kg per day (≥ 6 to <10 years: 2.0 ± 0.4 µg T4/kg per day; ≥ 10 to <12 years: 1.6 ± 0.4 µg T4/kg per day; ≥ 12 to <14 years: 1.5 ± 0.6 µg T4/kg per day; ≥ 14 years: 1.4 ± 0.6 µg T4/kg per day). It deviated significantly from the CH patients' mean T4 dose of 2.8 ± 0.7 µg T4/kg per day, p<0.01. CH patients with athyreosis required an average dose of 3.1 ± 0.5 µg T4/kg per day; patients with ectopia, 2.6 ± 0.7 µg T4/kg per day; and patients with dyshormonogenesis, 2.5 ± 0.6 µg T4/kg per day. CONCLUSION: Juvenile patients with AIT require significantly lower T4 doses than patients with CH.