Hyperphosphatemic familial tumoral calcinosis caused by a mutation in GALNT3 in a European kindred.
ABSTRACT Hyperphosphatemic familial tumoral calcinosis (HFTC) is an autosomal recessive metabolic disorder characterized by extensive phenotypic and genetic heterogeneity. HFTC was shown recently to result from mutations in two genes: GALNT3, coding for a glycosyltransferase responsible for initiating O-glycosylation, and FGF23, coding for a potent phosphaturic protein. All GALNT3 mutations reported so far have been identified in patients of either Middle Eastern or African-American extraction, corroborating numerous historical reports of the disorder in Africa and in the Middle East. In the present study, we describe a patient of Northern European origin displaying typical features of HFTC. Mutation analysis revealed that this patient carries a homozygous novel nonsense mutation in GALNT3 predicted to result in the synthesis of a significantly truncated protein. The present results expand the spectrum of known mutations in GALNT3 and demonstrate the existence of HFTC-causing mutations in this gene outside the Middle Eastern and African-American populations.
SourceAvailable from: Corinne Fisher
[Show abstract] [Hide abstract]
ABSTRACT: Renal control of systemic phosphate homeostasis is critical as evident from inborn and acquired diseases causing renal phosphate wasting. At least three transport proteins are responsible for renal phosphate reabsorption: NAPI-IIa (SLC34A1), NAPI-IIc (SLC34A3) and PIT-2 (SLC20A2). These transporters are highly regulated by various cellular mechanisms and factors including acid-base status, electrolyte balance and hormones such as dopamine, glucocorticoids, growth factors, vitamin D3, parathyroid hormone and fibroblast growth factor 23 (FGF23). Whether renal phosphate wasting is caused by inactivating mutations in the NAPI-IIa transporter is controversial. Mutations in the NAPI-IIc transporter cause hereditary hypophosphatemic rickets with hypercalciuria. Besides the primary inherited defects, there are also inherited defects in major regulators of phosphate homeostasis that lead to alterations in phosphate handling. Autosomal dominant hypophosphatemic rickets is due to FGF23 mutations leading to resistance against its own degradation. Similarly, inactivating mutations in the PHEX gene, which causes FGF23 inactivation, cause X-linked hypophosphatemia due to renal phosphate losses. In contrast, mutations in galactosamine:polypeptide N-acetyl-galactosaminyltransferase, responsible for O-glycosylation of FGF23, or in klotho, a cofactor for FGF23 signalling result in hyperphosphatemia. Acquired syndromes of renal phosphate wasting, hypophosphatemia and osteomalacia (tumour-associated osteomalacia) can be due to the excessive synthesis or release of phosphaturic factors (FGF23, FGF-7, MEPE and sFRP4) from mesenchymal tumours. Keywords: bone, FGF23, kidney, phosphate, PTH.Nephrology Dialysis Transplantation 09/2014; 29(suppl 4):iv45-iv54. DOI:10.1093/ndt/gfu217 · 3.49 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: Background Hyperphosphatemic Familial Tumoral Calcinosis (HFTC) and Hyperphosphatemic Hyperostosis Syndrome (HHS) are associated with autosomal recessive mutations in three different genes, FGF23, GALNT3 and KL, leading to reduced levels of fibroblast growth factor 23 (FGF23) and subsequent clinical effects.ResultsWe describe a consanguineous family with two affected siblings with HFTC and HHS caused by a novel homozygous G-to T substitution in exon 3 of GALNT3 (c.767 G¿>¿T; p.Gly256Val), demonstrating great phenotypic variation and long asymptomatic intervals. Calcific tumors appeared at 14 years of age in the male, and the female displayed episodic diaphysitis from age 9 years. Symptoms of eye involvement were present in both from childhood, and progressed into band keratopathy in the female. Abnormal dental roots and tooth loss, as well as myalgia were present in both from their mid-twenties, while the female also had calcifications in the placenta, the iliac vessels and thyroid cartilage. New calcific tumors appeared more than 20 years after the initial episodes, delaying diagnosis and treatment until the ages of 37 and 50 years, respectively. Both siblings had elevated serum phosphate levels, inappropriately elevated tubular maximum phosphate reabsorption per unit glomerular filtration rate (TmP/GFR), reduced levels of intact FGF23 and increased levels of c-terminal FGF23. Review of all 54 previously published cases of GALNT3, FGF23, and KL associated HFTC and HHS demonstrated that more subjects than previously recognized have a combined phenotype.Conclusion We have described HFTC and HHS in a consanguineous Caucasian family with a novel GALNT3 mutation, demonstrating new phenotypic features and significant variability in the natural course of the disease. A review of the literature, show that more subjects than previously recognized have a combined phenotype of HFTC and HHS. HHS and HFTC are two distinct phenotypes in a spectrum of GALNT3 mutation related calcification disorders, where the additional factors determining the phenotypic expression, are yet to be clarified.BMC Genetics 09/2014; 15(1):98. DOI:10.1186/s12863-014-0098-3 · 2.36 Impact Factor