Association of prolactin receptor (PRLR) variants with prolactinomas.

Prolactinomas are the most frequent type of pituitary tumors, which represent 10-20% of all intracranial neoplasms in humans. Prolactinomas develop in mice lacking the prolactin receptor (PRLR), which is a member of the cytokine receptor superfamily that signals via Janus kinase-2-signal transducer and activator of transcription-5 (JAK2-STAT5) or phosphoinositide 3-kinase-Akt (PI3K-Akt) pathways to mediate changes in transcription, differentiation and proliferation. To elucidate the role of the PRLR gene in human prolactinomas, we determined the PRLR sequence in 50 DNA samples (35 leucocytes, 15 tumors) from 46 prolactinoma patients (59% males, 41% females). This identified six germline PRLR variants, which comprised four rare variants (Gly57Ser, Glu376Gln, Arg453Trp and Asn492Ile) and two low-frequency variants (Ile76Val, Ile146Leu), but no somatic variants. The rare variants, Glu376Gln and Asn492Ile, which were in complete linkage disequilibrium, and are located in the PRLR intracellular domain, occurred with significantly higher frequencies (P < 0.0001) in prolactinoma patients than in 60 706 individuals of the Exome Aggregation Consortium cohort and 7045 individuals of the Oxford Biobank. In vitro analysis of the PRLR variants demonstrated that the Asn492Ile variant, but not Glu376Gln, when compared to wild-type (WT) PRLR, increased prolactin-induced pAkt signaling (>1.3-fold, P < 0.02) and proliferation (1.4-fold, P < 0.02), but did not affect pSTAT5 signaling. Treatment of cells with an Akt1/2 inhibitor or everolimus, which acts on the Akt pathway, reduced Asn492Ile signaling and proliferation to WT levels. Thus, our results identify an association between a gain-of-function PRLR variant and prolactinomas and reveal a new etiology and potential therapeutic approach for these neoplasms.

Clinical variability of familial tumoral calcinosis caused by novel GALNT3 mutations.

The GALNT3 gene encodes GalNAc-T3, which prevents degradation of the phosphaturic hormone, fibroblast growth factor 23 (FGF23). Biallelic mutations in either GALNT3 or FGF23 result in hyperphosphatemic familial tumoral calcinosis or its variant, hyperostosis-hyperphosphatemia syndrome. Tumoral calcinosis is characterized by the presence of ectopic calcifications around major joints, whereas hyperostosis-hyperphosphatemia syndrome is characterized by recurrent long bone lesions with hyperostosis. Here we investigated four patients with hyperphosphatemia and clinical manifestations including tumoral calcinosis and/or hyperostosis-hyperphosphatemia syndrome to determine underlying genetic cause and delineate phenotypic heterogeneity of these disorders. Mutational analysis of FGF23 and GALNT3 in these patients revealed novel homozygous mutations in GALNT3. Although the presence of massive calcifications, cortical hyperostosis, or dental anomalies was not shared by all patients, all had persistent hyperphosphatemia. Three of the patients also had inappropriately normal 1,25-dihyroxyvitamin D [1,25(OH)(2)D] and confirmed low circulating intact FGF23 concentrations. The four novel GALNT3 mutations invariably resulted in hyperphosphatemia as a result of low intact FGF23, but other clinical manifestations were variable. Therefore, tumoral calcinosis and hyperostosis-hyperphosphatemia syndrome represent a continuous spectrum of the same disease caused by increased phosphate levels, rather than two distinct disorders.

Vitamin D deficiency in white, apparently healthy, free-living adults in a temperate region.

OBJECTIVE: The precise incidence of vitamin D deficiency is not known, primarily because there is no consensus on the optimal levels of serum 25(OH)Vitamin D. The aim of the present study was to determine the incidence of vitamin D deficiency in a large group of normal adult volunteers residing in a typical temperate region. DESIGN-METHODS: In 625 healthy, free living adults (553 women, 72 men, aged 18-85 years), serum 25(OH)Vitamin D and 1-25(OH)2 Vitamin D (RIA), plasma intact PTH (ECLIA) and routine chemistries (multianalyser) were determined at baseline once during a whole year. In a subgroup of 36 subjects, a vitamin D loading (suppression) test was also performed to define the lower normal values for these two Vitamin D metabolites. RESULTS: The estimated lower normal values, based on the results of the vitamin D2 loading test, were 22 ng/ml (55 nmol/L) for 25(OH)Vitamin D and 24.6 pg/ml (59 pmol/l) for 1-25(OH)2 Vitamin D. During the whole year, the incidence of low values was 57.7% for 25(OH)Vitamin D and 33.2% for 1-25(OH)2 Vitamin D. A highly significant (p<0.001) positive linear correlation of serum 25(OH)Vitamin D with 1-25(OH)2 Vitamin D values and a negative correlation of 25(OH)Vitamin D with intact PTH was observed in the entire group and separately in women without or with osteoporosis and osteopenia. CONCLUSION: Most of the white normal adults living in a temperate region were vitamin D deficient. The observed correlations between serum concentrations of 25(OH)Vitamin D and 1-25(OH)2 Vitamin D as well as of 25(ΟΗ)Vitamin D and intact PTH, suggest that 25(OH)Vitamin D is implicated not only in 1-25(OH)2 Vitamin D production but also in PTH secretion.