Treatment of Rickets in Vitamin D-Dependent Rickets Type 1A (CYP27B1 Mutation / 1-Alpha-Hydroxylase Deficiency)

Vitamin D-dependent rickets type 1A (VDDR1A) is caused by mutations in CYP27B1, the gene encoding the enzyme 1-alpha-hydroxylase. Because this enzyme is required to activate vitamin D, patients cannot generate adequate active hormone regardless of conventional vitamin D intake, resulting in rickets that requires a specific lifelong management approach.

Clinical scenario

Rickets in the setting of confirmed vitamin D-dependent rickets type 1A — a CYP27B1 mutation causing 1-alpha-hydroxylase deficiency. This enzymatic block means standard vitamin D supplementation is insufficient; the protocol addresses this specific pathophysiology.

Treatment approach (partial)

Management involves lifelong replacement with an active vitamin D compound to bypass the deficient hydroxylation step, with an initial higher-dose phase and oral calcium supplementation in the early period — full dosing, agent selection, and phase structure are in the complete protocol.

Treatment goals

Serum PTH in the mid-normal range
Serum calcium in the mid-normal range

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References

DOI: 10.1007/s00467-022-05505-5

In patients with vitamin D-dependent rickets type 1A, which is due to mutations in CYP27B1, the gene encoding 1-alpha hydroxylase, patients are treated lifelong with physiologic 1,25-dihydroxyvitamin D (1,25(OH)2D) doses, given twice daily due to its short half-life.

In addition, oral calcium supplementation (50 mg per kg body weight per day of elemental calcium) is recommended during the early phase of treatment to prevent aggravation of hypocalcemia due to bone remineralization.

Dosages of active vitamin D should be tailored to keep serum PTH and calcium levels in the mid-normal range.

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