Severe thyrotoxicosis in an infant revealing familial nonautoimmune hyperthyroidism with a novel (C672W) stimulating thyrotropin receptor germline mutation

A CASE OF FAMILIAL NONAUTOIMMUNE HYPERTHYROIDISM DURING PREGNANCY

Objective

Familial nonautoimmune hyperthyroidism (FNAH) is a rare disease. To date there are few, if any, reports of pregnancies in women with FNAH. Our objective here is to present such a case.

Methods

Free thyroxine (free T4), free triiodothyronine (free T3), thyroid-stimulating hormone (TSH), and antibodies related to the thyroid were measured. Fetal thyroid function indicators including thyroid volume and ossification were checked using ultrasound. Thyroid-stimulating hormone receptor (TSHR) gene analyses were performed.

Results

The patient was a 30-year-old woman with no past medical history. She was introduced to our hospital in the fifth gestational week for pregnancy care because her family history revealed that her mother had nonautoimmune hyperthyroidism with a TSHR-activating germ-line mutation (Asn406Ser). The serum free T4 was 1.88 ng/dL (normal, 0.62 to 1.19 ng/dL), free T3 was 3.27 pg/mL (normal, 2.55 to 3.88 pg/mL), TSH was 0.02 μIU/mL (normal, 0.007 to 3.619 μIU/mL), and TSHR was negative which were considered to be consistent with mild primary hyperthyroidism. Serum free T4, free T3, and TSH concentrations were monitored every 4 to 6 weeks with a peak free T4 of 2.23 ng/dL noted at gestational week 9. The patient had no signs related to hyperthyroidism throughout pregnancy. The patient delivered a 3,518 g girl at 40 weeks of gestation. Genetic analysis of her TSHR gene showed heterozygous Asn406Ser mutation. The offspring did not show any signs of prenatal hyperthyroidism, and thyroid function at day 6 after delivery revealed a free T4 of 2.41 ng/dL (normal, 1.83 to 2.91 ng/dL) and a TSH of 3.55 μIU/mL (normal, 0.51 to 4.57 μIU/mL).

Conclusion

Women with FNAH and mild thyrotoxicosis prior to pregnancy may have continuous hyperthyroidism with additional change due to the series of human chorionic gonadotropin secretion during pregnancy.

Severe thyrotoxicosis in an infant revealing familial nonautoimmune hyperthyroidism with a novel (C672W) stimulating thyrotropin receptor germline mutation

We describe severe thyrotoxicosis in young members of a family with nonautoimmune hyperthyroidism caused by a C672W germline mutation in exon 10 of TSHR gene. In this family, lack of genotype‐phenotype correlation and anticipation across generations could be linked to an increased iodine intake as recently observed in France.