Thioredoxin Reductase 2 Variant as a Cause of Micropenis, Undescended Testis, and Selective Glucocorticoid Deficiency

Variants in genes that play a role in maintaining cellular redox homeostasis in adrenocortical cells may be associated with glucocorticoid deficiency, and it is unclear whether these cases may be associated with a wider phenotype. However, to date, only 1 case of a genetic variant in thioredoxin reductase type 2 (TXNRD2) in a South Asian kindred with familial glucocorticoid deficiency has been reported.

The index case was diagnosed with selective glucocorticoid deficiency at 10 years of age. He had a history of a small penis and a right undescended testis, which subsequently required an orchidopexy. The parents were of Pakistani origin and first cousins. The boy's gonadal function was normal and autosomal recessive missense homozygous variants p.Val361Met;Val361Met in TXNRD2 were identified in him by whole-genome sequencing. Functional studies were performed using peripheral blood mononuclear cells from the patient, unaffected parents, and four age-matched healthy boys. Compared to the carriers and controls, the case had lower TXNRD2 protein on immunoblotting using anti-TXNRD2 antibody (1.3-fold), 95% CI: 1.8 (1.5-2.1), lower mRNA expression of TXNRD2 on quantitative RT-PCR (1.6-fold), 95% CI: 1.1 (0.7-1.4), and a lower glutathione:oxidized glutathione ratio (6.7-fold), 95% CI: 2.0 (1.6-2.4).

In addition to confirming the critical role that TXNRD2 serves in maintaining adrenal function, by reporting the findings of atypical genitalia, this case further extends the phenotype.