Comorbidities, including gastric bypass surgery, can exacerbate phosphate malabsorption in up to 30% of affected individuals, while FCM administration triggers transient FGF-23 elevation in 50%-92% of cases, typically resolving within 3-6 months; prolonged symptoms beyond this period should raise suspicion for FGF-23-mediated hypophosphatemia, which includes both acquired (e.g., TIO) and genetic causes [4-6]. This evidence concerns the gene FGF23 and hypophosphatemia.