The Difficult Diagnosis of Hypophosphatemic Rickets-A Review of 8 Clinical Cases

Hypophosphatemic rickets is a rare, usually genetic disease associated with decreased phosphate reabsorption in the proximal renal tubule and vitamin D resistance. Several genetic mutations have been discovered, the most common being the X-linked PHEX mutation with high fibroblast growth factor 23 (FGF23) circulating levels. The hypophosphatemic type osteomalacia is usually hereditary or tumour-induced (TIO). In the past 20 years, we have discovered, treated and followed up overall 8 cases of the disease-3 women and 5 men, aged 18 to 52 years. In all patients the diagnostic process was long (a mean of 2-3 years) and involved multiple clinical consults, laboratory evaluations: Biochemical Standard Research, Hormonal Tests [PTH, 25 (OH) D, 1,25 (OH) 2D], Specialized Research (FGF23), Instrumental Research (Ultrasonography of whole body; Computed tomography; Magnetic resonance imaging; DXA examination with an assessment of T-score and Z-score of spine/hip). All of these studies aimed at ruling out different neurological, hematological, oncological, rheumatic, gastroenterological, urological, nephrological diseases and conditions. One of the patients had Fanconi syndrome, five had X-linked hypophosphatemia (XLH) and two had TIO. In the last two patients, we found a high level of FGF23 secreting a small lung neoplasm in the first case and a mesenchymal tumor in the median upper part of the right thigh in the second case. The surgical removal of the tumor mass lead to a fast decrease in FGF23 levels and correction of metabolic disturbances. We present clinical cases with hypophosphatemic rickets/osteomalacia and discuss the etiopathogenesis and treatment of this rare disease. Historically until now phosphate supplementation and therapy using analogs of highly active vitamin D (calcitriol, alfacalcidol, paricalcitol) have been used to manage conditions involving hypophosphatemia. In recent years there has been a progression of clinical trials for monoclonal anti-FGF23 antibodies for the treatment of XLH. These monoclonal anti-FGF23 antibodies may have potential for treating other conditions associated with FGF23 overactivity. However, clinical trials to support that possibility are not available at present.