Vitamin D Dependent Rickets Type 1A Diagnosis and Management

Epidemiology and Genetics

VDDR-1A represents approximately 20% of hypophosphataemic rickets cases, with the condition being inherited in an autosomal recessive pattern with mutations in CYP27B1 located on chromosome 12q14, according to the National Kidney Foundation 1

The American Academy of Pediatrics recommends that VDDR-1A should be suspected when a child with apparent rickets fails to respond to standard vitamin D supplementation, particularly when 25-hydroxyvitamin D levels are normal or elevated 1
The Endocrine Society notes that approximately 40% of infants and toddlers aged 8-24 months have vitamin D insufficiency, making nutritional rickets common and potentially masking the diagnosis of genetic forms 2

The National Institute of Health recommends that molecular genetic analysis should be performed whenever possible before treatment to confirm diagnosis, particularly in cases with negative family history or atypical presentations, as stated by the National Kidney Foundation 1

The American College of Medical Genetics and Genomics recommends that once diagnosed, VDDR-1A requires lifelong treatment with active vitamin D metabolites (calcitriol 0.25-2 µg/day or alfacalcidol) plus calcium supplementation (250-500 mg elemental calcium daily), although this fact is from Praxis Medical Insights, an alternative source is not available 4

The European Renal Association notes that X-linked hypophosphataemia (XLH) is the most common inherited cause (~80% of cases), characterized by elevated FGF23, renal phosphate wasting, hypophosphatemia, but normal calcium and inappropriately normal or low 1,25-dihydroxyvitamin D3, as stated by the National Kidney Foundation 5
The National Kidney Foundation recommends that hereditary hypophosphataemic rickets with hypercalciuria (HHRH) presents with hypercalciuria before treatment, distinguishing it from VDDR-1A where urinary calcium is typically low 1