Congenital hypothyroidism in a child with unsuspected familial dysalbuminemic hyperthyroxinemia caused by a mutation (R218H) in the human albumin gene

We found familial dysalbuminemic hyperthyroxinemia (FDH) in a 5-month-old boy with congenital hypothyroidism (CH) who had a blood thyrotropin (TSH) level of 479 mU/L but normal total serum thyroxine (T4) and higher than normal total triiodothyronine (T3) levels. Thyroid hormone substitution began at 5 weeks of age when T4 and T3 concentrations were below normal. Until the age of 5 months, treatment with levothyroxine was suboptimal on the basis of high serum TSH levels despite above-normal T4 levels. FDH was confirmed by isoelectric focusing and testing of other family members. DNA analysis of the patient revealed R218H, a mutation in the serum albumin gene associated with FDH, which was al…