OR08-5 Associations Between Signal Transducer and Activator of Transcription (STAT) Mutations and Galactorrhea

BACKGROUND: Prolactin (PRL) is responsible for the development of mammary glands and milk production. STAT1 and STAT3 are genes that express transcription factors that mediate PRL's intracellular signaling, but an association between their function and galactorrhea has not yet been identified. Here we describe three patients with somatic STAT mutations and galactorrhea. A 27-year-old woman with hyper-IgE syndrome (Job's Syndrome) due to a STAT3 deletion mutation (p.Val463del) associated with recurrent infections reported thin, white, bilateral discharge with breast manipulation beginning in adolescence. She did not have spontaneous leakage or pain. At presentation, PRL was slightly elevated to 27.9 (ref. 2.0-25.0 mcg/L) with otherwise normal levels of anterior pituitary hormones. She was not on any drugs known to cause hyperprolactinemia. MRI showed a 5×4 mm microadenoma without any mass effect. A 32-year-old woman also with Job's syndrome due to a heterozygous loss-of-function STAT3 mutation (p.R382Q) associated with recurrent infections and papillary thyroid cancer described unilateral, chronic, thin, white nipple discharge with light touch of her right breast for "as long as she could remember." She had a history of breast abscesses, but at presentation there was no evidence of abscess or infection. PRL was 15.1 mcg/L, and other anterior pituitary hormones were normal. MRI showed a structurally normal pituitary. A 22-year-old woman with a STAT1 activating mutation (p.E235A) associated with recurrent infections, autoimmune hypothyroidism, T1DM, and hypogonadotropic hypogonadism requiring pubertal induction at age 12y reported bilateral galactorrhea starting at age 18y. A white, milky discharge could be expressed with light manipulation, but no discharge was produced spontaneously. PRL was 16.2 mcg/L with serial dilution and has consistently been in the reference range. Anterior pituitary evaluation was normal except for elevated TSH of 12.5 (ref. 0.27-4.2) consistent with autoimmune hypothyroidism. MRI revealed a diffusely enlarged pituitary gland (12mm in the cranio-caudal dimension) without focal hypo-enhancement. CONCLUSIONS: It is known that PRL signaling involves the JAK/STAT pathway, and an analysis of human milk cells showed upregulated STAT3 and downregulated STAT1 during lactation (PMID 26909879). These three cases provide clinical evidence for a mechanistic connection between STAT signaling and galactorrhea and suggest that STAT3 and STAT1 function in opposite directions to regulate lactation. In our cases, increased STAT1 or decreased STAT3 activity are associated with normal-PRL, inducible galactorrhea. Beyond understanding the specific intracellular signaling pathways leading to galactorrhea, these observations may be utilized for developing therapies for those with impaired lactation. Presentation: Saturday, June 11, 2022 12:30 p.m. - 12:45 p.m.