Thyroid receptor alpha (THRA) gene mutation causes thyroid hormone resistance syndrome characterized by near normal thyroid function tests and tissue-specific hypothyroidism.
Case: A 4-year-old male patient was admitted with short stature, motor-mental retardation, and constipation. Motor-mental retardation has been assessed at the age of one year and no etiologic cause was found. In past medical history, he was born at 38 weeks gestational age with a birth weight of 2900 g. His motor-mental milestones were delayed. He had transient hypogammaglobulinemia. Mother and father were first-degree relatives. In his physical examination, height, weight, and head circumference were 17.4 kg (SDS: -0.12), 96.4 cm (SDS: -2.47), and 54.5 cm (SDS: 2.08), respectively. Pubertal stage was A1P1, testes were 2+2 mL palpable. He had edema in the eyelids, face was coarse, and umbilical hernia was found. In the lab exam, Hb was 10.4 g/dL, MCV 88.5 fL, RDW 14.7%, electrolytes, liver and kidney function tests were normal, CK and CK-MB were 396 IU/L (41-277) and 55.3 U/L (0-24), respectively. fT3 was 5.04 pg/mL (2.3-4.2), fT4 0.93 ng/dL (0.89-1.76), and TSH was 3.89 µIU/mL (0.35-5.5); bone age was 2 years. Craniography revealed thickness of the scalp. Phenotypically hypothyroid findings and at moderate elevation of fT3 levels, normochrome normocytic anemia and elevation of CK and CK-MB levels were consistent with primary thyroid hormone resistance. In the mutation analysis, a novel de novo p.G291S heterozygous mutation in the THRA gene was detected. Na-L thyroxin replacement therapy was initiated.
THRA gene mutation should be considered in patients who are clinically hypothyroid with increased/moderately increased fT3, decreased/normal fT4, normal TSH levels, and increased muscle enzymes.