A patient with congenital hypothyroidism due to a frameshift variant accompanying a urogenital malformation.

PAX8 is a transcription factor that is expressed in the thyroid gland and kidneys. Monoallelic loss-of-function variants cause congenital hypothyroidism (CH), and urogenital malformations are infrequent complications seen in less than 10% of variant carriers. Herein, we report the case of a 3-yr-old female patient with CH who was diagnosed during newborn screening. She was treated with levothyroxine, and she showed normal growth and development at a minimal dose (0.7 µg/kg/d of levothyroxine at 3 yr of age). At 5 mo of age, she visited an emergency department for fever and was incidentally found to have differently sized kidneys by ultrasonography, which was subsequently diagnosed as unilateral multicystic dysplastic kidney. Her serum creatinine and cystatin C levels were normal. Next-generation sequencing-based genetic analysis revealed that the patient was heterozygous for a frameshift variant (p.Thr320ProfsTer106) and a missense variant (p.Arg885Gln). Our patient is the first truncating variant carrier to have a urogenital malformation with CH. Genetic analysis for should be considered in patients with CH and urogenital malformations.