C Asteria, L Persani, M Ferrari and P Beck-Peccoz
This study analyzed the structural differences of the carbohydrate chains of circulating free alpha-submit (alpha-SU) hypersecreted in various non-tumoral (primary hypothyroids, postmenopausal women, patients with chronic uremia, normal fetuses) and tumoral (gut carcinoids, TSH-, GH- and pure alpha-secreting pituitary adenomas) clinical conditions. Carbohydrate structures of free alpha-SU were investigated by means of lectin affinity chromatography using Concanavalin A (Con-A), which allows the separation of free alpha-SU in three different fractions (unbound = UB, weakly bound = WB and firmly bound = FB) depending on the nature and maturation of glycosylated chains. The concentrations of alpha-SU in serum and in Con-A fractions were measured by a sensitive and specific IRMA. Free alpha-SU hypersecreted from postmenopausal women, primary hypothyroids, and patients with chronic uremia showed similar binding patterns to Con-A, the percentage of UB fractions (UB: 44.5 +/- 1.9%, 39.5 +/- 3.8%, 48.2 +/- 5.6% respectively) being higher than both WB and FB fractions (WB: 33.2 +/- 1.4%, 30.7 +/- 4.6%, 28.5 +/- 2.1%; FB: 22.3 +/- 0.7%, 29.8 +/- 6.6%, 23.3 +/- 4.2% respectively). In normal fetuses the amount of UB fraction was very high (UB: 70.7 +/- 5.4%). Free alpha-SU from patients with TSH- and GH-secreting adenomas showed a binding pattern to Con-A significantly different from that observed in postmenopausal women taken as controls, the WB fractions being significantly higher (WB: 56.9 +/- 16.8% and 71 +/- 12.4% respectively, P < 0.001). A typical pattern of elution on Con-A, characterized by a prevalence of immature alpha-SU molecules eluted in the FB fraction, was found in patients with pure alpha-secreting adenomas. This chromatographic behavior was significantly different from that seen in the controls, as well as in other pituitary tumors and in gut carcinoids (FB: 41.8 +/- 5.0%, 22.3 +/- 0.7%, 16.8 +/- 6.6%, 10.6 +/- 2.0% respectively). Moreover, in these latter patients the pattern of free alpha-SU binding was exactly the opposite of that observed in pure alpha-secreting adenomas, with a prevalence of mature alpha-SU molecules (UB: 59.1 +/- 4.4 vs 18.3 +/- 7.2%). In conclusion, our data on Con-A affinity chromatography clearly demonstrate that carbohydrate branching of circulating free alpha-SU varies in patients with pituitary adenomas as compared with patients with gut carcinoids or other non-tumoral conditions. Moreover, the finding of a greater proportion of circulating free alpha-SU forms that firmly bind to Con-A in patients with pure alpha-secreting adenomas, seems to be pathognomonic of non-functioning pituitary adenomas.
C Asteria, JH Oliveira, J Abucham and P Beck-Peccoz
BACKGROUND: One of the causes of combined pituitary hormone deficiency (CPHD) is represented by Prophet of Pit-1 (PROP-1) gene inactivating mutations. This disorder is generally characterized by GH, TSH, prolactin (PRL), and gonadotropin deficiency, but recent papers have described a concomitant alteration of the corticotrope function. OBJECTIVE: To make a detailed investigation of the hypothalamic-pituitary-adrenal axis in two sisters with PROP-1 gene mutations. PATIENTS: Two female siblings (17 and 16 years old) with CPHD, belonging to a Brazilian family of consanguineous parents, presented with growth retardation and central hypothyroidism during childhood, and showed central hypogonadism at the age of puberty. No clear clinical symptoms and signs of hypocortisolism were present. METHODS: GH, TSH, free thyroxine, total tri-iodothyronine, PRL, LH, FSH, ACTH and cortisol were measured in basal condition and after appropriate testing. The molecular study was performed by PCR amplification and sequencing analysis of PROP-1 gene. RESULTS: Both patients showed GH, PRL, LH and FSH deficiencies, associated with absent responses to an insulin tolerance test (ITT), TRH and GnRH injection. Circulating concentrations of TSH were normal in basal conditions, but failed to respond to a TRH test. Plasma ACTH concentrations were normal, but serum cortisol concentrations were below the lower limit of the normal range, showing a trend to decrease during 6 years of follow-up. The serum ACTH response to ITT was impaired, whereas its response to CRH was normal and prolonged. The cortisol response to both tests, and to the ACTH test, was clearly impaired. In both sisters, the genetic analysis showed the presence of a homozygous 2-bp deletion (296delGA) of PROP-1 gene, which results in the synthesis of a protein with no residual functional activity. CONCLUSION: In addition to GH, TSH, PRL and gonadotropin deficiency, patients with PROP-1 gene mutations can present with late-onset central hypocortisolism, possibly beause of the lack of important paracrine factors normally produced by the cells surrounding the corticotropes and absent in the pituitary of these patients, or because of progressive corticotrope apoptosis. This finding indicates the need for life-long endocrine monitoring of PROP-1-deficient patients.