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Vitamin D-Dependent Rickets Type 1B (25-Hydroxylase Deficiency): A Rare Condition or a Misdiagnosed Condition?

Abstract : Vitamin D requires a two-step activation by hydroxylation: The first step is catalyzed by hepatic 25-hydroxylase (CYP2R1, 11p15.2) and the second one is catalyzed by renal 1α-hydroxylase (CYP27B1, 12q13.1), which produces the active hormonal form of 1,25-(OH)2 D. Mutations of CYP2R1 have been associated with vitamin D-dependent rickets type 1B (VDDR1B), a very rare condition that has only been reported to affect 4 families to date. We describe 7 patients from 2 unrelated families who presented with homozygous loss-of-function mutations of CYP2R1. Heterozygous mutations were present in their normal parents. We identified a new c.124_138delinsCGG (p.Gly42_Leu46delinsArg) variation and the previously published c.296T>C (p.Leu99Pro) mutation. Functional in vitro studies confirmed loss-of-function enzymatic activity in both cases. We discuss the difficulties in establishing the correct diagnosis and the specific biochemical pattern, namely, very low 25-OH-D suggestive of classical vitamin D deficiency, in the face of normal/high concentrations of 1,25-(OH)2 D. Siblings exhibited the three stages of rickets based on biochemical and radiographic findings. Interestingly, adult patients were able to maintain normal mineral metabolism without vitamin D supplementation. One index case presented with a partial improvement with 1alfa-hydroxyvitamin D3 or alfacalcidol (1α-OH-D3 ) treatment, and we observed a dramatic increase in the 1,25-(OH)2 D serum concentration, which indicated the role of accessory 25-hydroxylase enzymes. Lastly, in patients who received calcifediol (25-OH-D3 ), we documented normal 24-hydroxylase activity (CYP24A1). For the first time, and according to the concept of personalized medicine, we demonstrate dramatic improvements in patients who were given 25-OH-D therapy (clinical symptoms, biochemical data, and bone densitometry). In conclusion, the current study further expands the CYP2R1 mutation spectrum. We note that VDDR1B could be easily mistaken for classical vitamin D deficiency.
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Contributor : Hélène Bouraïma-Lelong Connect in order to contact the contributor
Submitted on : Thursday, June 13, 2019 - 11:08:42 AM
Last modification on : Saturday, August 27, 2022 - 2:12:58 PM

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Arnaud Molin, Arnaud Wiedemann, Nick Demers, Martin Kaufmann, Jérémy Do Cao, et al.. Vitamin D-Dependent Rickets Type 1B (25-Hydroxylase Deficiency): A Rare Condition or a Misdiagnosed Condition?. Journal of Bone and Mineral Research, 2017, 32 (9), pp.1893-1899. ⟨10.1002/jbmr.3181⟩. ⟨hal-02154934⟩



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