An ocular presentation of familial tumoral calcinosis

Hyperphosphatemic Tumoral Calcinosis: Pathogenesis, Clinical Presentation, and Challenges in Management

Hyperphosphatemic familial tumoral calcinosis (HFTC) is a rare and disabling disorder of fibroblast growth factor 23 (FGF23) deficiency or resistance. The disorder is manifest by hyperphosphatemia, inappropriately increased tubular reabsorption of phosphate and 1,25-dihydroxy-Vitamin D, and ectopic calcifications. HFTC has been associated with autosomal recessive pathogenic variants in: (1) the gene encoding FGF23; (2) GALNT3, which encodes a protein responsible for FGF23 glycosylation; and (3) KL, the gene encoding KLOTHO, a critical co-receptor for FGF23 signaling. An acquired autoimmune form of hyperphosphatemic tumoral calcinosis has also been reported. Periarticular tumoral calcinosis is the primary cause of disability in HFTC, leading to pain, reduced range-of-motion, and impaired physical function. Inflammatory disease is also prominent, including diaphysitis with cortical hyperostosis. Multiple treatment strategies have attempted to manage blood phosphate, reduce pain and inflammation, and address calcifications and their complications. Unfortunately, efficacy data are limited to case reports and small cohorts, and no clearly effective therapies have been identified. The purpose of this review is to provide a background on pathogenesis and clinical presentation in HFTC, discuss current approaches to clinical management, and outline critical areas of need for future research.

Hyperphosphatemic familial tumoral calcinosis secondary to fibroblast growth factor 23 (FGF23) mutation: a report of two affected families and review of the literature

Hyperphosphatemic familial tumoral calcinosis (HFTC), secondary to fibroblast growth factor 23 (FGF23) gene mutation, is a rare genetic disorder characterized by recurrent calcified masses. We describe young Lebanese cousins presenting with HFTC, based on a retrospective chart review and a prospective case study. In addition, we present a comprehensive review on the topic, based on a literature search conducted in PubMed and Google Scholar, in 2014 and updated in December 2017. While the patients had the same previously reported FGF23 gene mutation (homozygous c.G367T variant in exon 3 leading to a missense mutation), they presented with variable severity and age of disease onset (at 4 years in patient 1 and at 23 years in patient 2). A review of the literature revealed several potential patho-physiologic pathways of HFTC clinical manifestations, some of which may be independent of hyperphosphatemia. Most available treatment options aim at reducing serum phosphate level, by stimulating renal excretion or by inhibiting intestinal absorption. HFTC is a challenging disease. While the available medical treatment has a limited and inconsistent effect on disease symptomatology, surgical resection of calcified masses remains the last resort. Research is needed to determine the safety and efficacy of FGF23 replacement or molecular therapy, targeting the specific genetic aberration. Hyperphosphatemic familial tumoral calcinosis is a rare genetic disorder characterized by recurrent calcified masses, in addition to other visceral, skeletal, and vascular manifestations. It remains a very challenging disease.

Phosphate, fibroblast growth factor 23 and retinopathy in chronic kidney disease: the Chronic Renal Insufficiency Cohort Study

BACKGROUND

Elevated circulating concentrations of phosphate and fibroblast growth factor 23 (FGF23) contribute to the pathogenesis of cardiovascular disease in chronic kidney disease (CKD). Retinopathy is a common manifestation of microvascular disease in CKD, but its associations with phosphate and FGF23 have not been studied. We tested the hypothesis that higher serum phosphate is associated with more severe retinopathy in individuals with CKD, independent of FGF23 and known risk factors for retinopathy.

METHODS

We tested the associations of serum phosphate and plasma FGF23 with retinopathy in a cross-sectional analysis of 1800 participants in the Chronic Renal Insufficiency Cohort Study who underwent fundus photography. Retinopathy severity was graded according to the Early Treatment of Diabetic Retinopathy Severity score, and retinal venous and arterial diameters were measured.

RESULTS

Mean estimated glomerular filtration rate (eGFR) was 46.5 ± 15.4 mL/min/1.73 m(2), mean serum phosphate was 3.7 ± 0.6 mg/dl and median plasma C-terminal FGF23 was 133 RU/mL (interquartile range 87.2, 217.8 RU/mL). In multivariable ordinal logistic regression models, higher serum phosphate was associated with greater retinopathy severity independent of hypertension, diabetes, CKD severity and FGF23 [adjusted odds ratio of being in one higher category of retinopathy severity: 1.19 per 1 standard deviation increase; 95% confidence interval (CI) 1.05, 1.36; P = 0.007]. Presence of diabetes or hypertension did not modify the results. Higher serum phosphate was also independently associated with greater retinal venous diameter (multivariable-adjusted 1.70 µm increase per 1 standard deviation increase in phosphate; 95% CI 0.46, 2.93; P = 0.007). FGF23 levels were not independently associated with retinopathy severity or retinal venous diameter, and neither FGF23 nor phosphate was associated with retinal arterial diameter.

CONCLUSIONS

Among individuals with moderate-to-severe CKD, higher serum phosphate but not FGF23 was independently associated with more severe retinopathy and microvascular retinal venous dilatation.

Hyperphosphatemic familial tumoral calcinosis: genetic models of deficient FGF23 action

Hyperphosphatemic familial tumoral calcinosis (hFTC) is a rare disorder of phosphate metabolism defined by hyperphosphatemia and ectopic calcifications in various locations. To date, recessive mutations have been described in three genes involving phosphate metabolism: FGF23, GALNT3, and α-Klotho, all of which result in the phenotypic presentation of hFTC. These mutations result in either inadequate intact fibroblast growth factor-23 (FGF23) secretion (FGF23 or GALNT3) or resistance to FGF23 activity at the fibroblast growth factor receptor/α-Klotho complex (α-Klotho). The biochemical consequence of limitations in FGF23 activity includes increased renal tubular reabsorption of phosphate, hyperphosphatemia, and increased production of 1,25-dihydroxyvitamin D. The resultant ectopic calcifications can be painful and debilitating. Medical treatments are targeted toward decreasing intestinal phosphate absorption or increasing phosphate excretion; however, results have been variable and generally limited. Treatments that would increase FGF23 levels or signaling would more appropriately target the genetic etiologies of this disease and perhaps be more effective.

Long-term clinical outcome and phenotypic variability in hyperphosphatemic familial tumoral calcinosis and hyperphosphatemic hyperostosis syndrome caused by a novel GALNT3 mutation; case report and review of the literature

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.

RESULTS

We 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.

Ocular involvement in tumoral calcinosis

We report a 32-year-old male who presented with blurring of vision in the right eye since 1.5 years. He had history of swelling over the extensor surfaces of large joints which were migratory in nature. Few of them spontaneously subsided following suppuration of chalky white discharges except over the gluteal region. Ophthalmological examination revealed visual acuity of counting fingers (CF) at 1 m in the right eye and perilimbal conjunctival calcific deposits and retinal angiod streaks in both eyes. There was choroidal neovascular membrane with subretinal hemorrhage in right eye, confirmed by fundus fluorescein angiography (FFA) and optical coherence tomography (OCT). B scan ultrasonography and simultaneous vector A scan detected calcification of the subretinal neovascular membrane and the adjoining sclera.