PTH and hypophosphatemia: The VDDR1A patients usually develop growth retardation, hypotonia, muscle weakness, motor delay, seizures, and skeletal deformities during the first 2 years of life, characterized by hypocalcemia, hypophosphatemia, elevated serum levels of alkaline phosphatase (ALP) and parathyroid hormone (PTH), normal to elevated 25-hydroxyvitamin D [25(OH)D], and decreased or inappropriately normal 1,25(OH)2D3 (4, 5).