Uncovering genetic causes of hypophosphatemia.

BACKGROUND: Chronic hypophosphatemia can result from a variety of acquired disorders, such as malnutrition, intestinal malabsorption, hyperparathyroidism, vitamin D deficiency, excess alcohol intake, some drugs, or organ transplantation. Genetic disorders can be a cause of persistent hypophosphatemia, although they are less recognized. We aimed to better understand the prevalence of genetic hypophosphatemia in the population. METHODS: By combining retrospective and prospective strategies, we searched the laboratory database of 815,828 phosphorus analyses and included patients 17-55 years old with low serum phosphorus. We reviewed the charts of 1287 outpatients with at least 1 phosphorus result ≤2.2 mg/dL. After ruling out clear secondary causes, 109 patients underwent further clinical and analytical studies. Among them, we confirmed hypophosphatemia in 39 patients. After excluding other evident secondary causes, such as primary hyperparathyroidism and vitamin D deficiency, we performed a molecular analysis in 42 patients by sequencing the exonic and flanking intronic regions of a panel of genes related to rickets or hypophosphatemia (CLCN5, CYP27B1, dentin matrix acidic phosphoprotein 1, ENPP1, FAM20C, FGFR1, FGF23, GNAS, PHEX, SLC34A3, and VDR). RESULTS: We identified 14 index patients with hypophosphatemia and variants in genes related to phosphate metabolism. The phenotype of most patients was mild, but two patients with X-linked hypophosphatemia (XLH) due to novel PHEX mutations had marked skeletal abnormalities. CONCLUSION: Genetic causes should be considered in children, but also in adult patients with hypophosphatemia of unknown origin. Our data are consistent with the conception that XLH is the most common cause of genetic hypophosphatemia with an overt musculoskeletal phenotype.

Analysis of the influence of the T393C polymorphism of the GNAS gene on the clinical expression of primary hyperparathyroidism / Análisis de la influencia del polimorfismo T393C del gen GNASen la expresión clínica del hiperparatiroidismo primario

Background: The receptor of parathyroid hormone and parathyroid hormone-related-protein (PTH/PTHrp) is located in the cell membrane of target tissues - kidney and osteoblasts. It is a G protein-coupled-receptor whose Gsα subunit is encoded by the GNAS gene. Our aim was to study whether the single nucleotide polymorphism (SNP) T393C of the GNAS gene is associated with renal stones, bone mineral density (BMD), or bone remodelling markers in primary hyperparathyroidism (PHPT).Methods: An analysis was made of clinical and biochemical parameters and densitometric values in three areas and their relationship with the T393C SNP of the GNAS gene in 261 patients with primary hyperparathyroidism and in 328 healthy controls. Genotyping was performed using the Custom Taqman(R) SNP Genotyping assay. Results: The genotype frequencies of GNAS T/C 393 were similar in the control and PHPT groups. No association was found between genotypes and clinical expression of PHPT (renal stones and bone fractures). A nonstatistically significant trend was seen to lower BMD in the lumbar spine, femoral neck, and total hip in both PHPT and control C homozygote subjects. Conclusion: Genetic susceptibility to PHPT related to the GNAS T393C polymorphism or a major influence in its development and clinical expression were found. A C allele-related susceptibility to lower BMD in trabecular bone in both PHPT and control subjects is not sufficient to suggest a more severe clinical expression of PHPT. This trend may be considered as a basis for further studies with larger sample sizes and complementary functional evaluation (AU)

Introducción: El receptor de la hormona paratiroidea y de la proteína relacionada con la hormona paratiroidea (PTH/PTHrp) está situado en la membrana celular de sus tejidos diana: riñón y osteoblastos. Se trata de un receptor unido a proteina G cuya subunidad Gsα está codificada por el gen GNAS. Nuestro objetivo fue estudiar si el polimorfismo de un sólo nucleótido (SNP) T393C del gen GNAS se asociaba con litiasis renal, densidad mineral ósea (DMO) o marcadores de remodelado óseo en el hiperparatiroidismo primario (HPTP). Métodos: Analizamos parámetros clínicos, bioquímicos y densitométricos en 3 zonas y su relación con el SNP T393C del gen GNAS en 261 pacientes con HPTP y en 328 controles sanos. El genotipado se realizó utilizando el ensayo Custom Taqman(R). Resultados: Las frecuencias genotípicas del SNP T/C 393 del GNAS fueron similares en ambos grupos control y HPTP. No encontramos ninguna asociación entre los genotipos y la expresión clínica del HPTP (litiasis renal y fracturas óseas). Encontramos una tendencia no estadísticamente significativa hacia una menor DMO en columna lumbar, cuello femoral y cadera en los sujetos control y HPTP portadores del alelo C. Conclusiones: No encontramos susceptibilidad genética para el desarrollo de PHPT relacionada con el polimorfismo T393C del gen GNAS ni influencia en su expression clínica. Sí hallamos una tendencia hacia niveles menores de DMO en el hueso trabecular relacionada con el alelo C en pacientes con PHPT y en sujetos control sin ser suficiente para sugerir una expresión clínica más grave. Estos resultados pueden ser considerados como un punto de partida para futuros estudios con mayor tamaño muestral y con evaluación funcional complementaria (AU)

Analysis of the influence of the T393C polymorphism of the GNAS gene on the clinical expression of primary hyperparathyroidism.

BACKGROUND: The receptor of parathyroid hormone and parathyroid hormone-related-protein (PTH/PTHrp) is located in the cell membrane of target tissues - kidney and osteoblasts. It is a G protein-coupled-receptor whose Gsα subunit is encoded by the GNAS gene. Our aim was to study whether the single nucleotide polymorphism (SNP) T393C of the GNAS gene is associated with renal stones, bone mineral density (BMD), or bone remodelling markers in primary hyperparathyroidism (PHPT). METHODS: An analysis was made of clinical and biochemical parameters and densitometric values in three areas and their relationship with the T393C SNP of the GNAS gene in 261 patients with primary hyperparathyroidism and in 328 healthy controls. Genotyping was performed using the Custom Taqman® SNP Genotyping assay. RESULTS: The genotype frequencies of GNAS T/C 393 were similar in the control and PHPT groups. No association was found between genotypes and clinical expression of PHPT (renal stones and bone fractures). A nonstatistically significant trend was seen to lower BMD in the lumbar spine, femoral neck, and total hip in both PHPT and control C homozygote subjects. CONCLUSION: Genetic susceptibility to PHPT related to the GNAS T393C polymorphism or a major influence in its development and clinical expression were found. A C allele-related susceptibility to lower BMD in trabecular bone in both PHPT and control subjects is not sufficient to suggest a more severe clinical expression of PHPT. This trend may be considered as a basis for further studies with larger sample sizes and complementary functional evaluation.