Unmeasurable low vitamin D levels caused by a novel, homozygote loss-of-function variant in the group-specific component gene.

A 29-year-old female, born to consanguineous parents, was found with unmeasurable levels of vitamin D (<10 nmol/L) after routine biochemical screening during her first pregnancy. She did not respond to either oral or intramuscular vitamin D supplementation and was an otherwise healthy young woman, with no signs of rickets, osteomalacia, osteoporosis, or secondary hyperparathyroidism. Western blot analysis revealed total lack of vitamin D binding protein, and next generation sequencing confirmed a novel, pathogenic homozygote loss-of-function mutation in exon 13 of the group-specific component gene, that encodes the poly A tail for vitamin D binding protein. She was therefore diagnosed with hereditary DBP deficiency, and vitamin D supplementation was diminished to life-long regular vitamin D supplementation (25 µg per day). This case is extremely interesting, as it expands our knowledge of vitamin D physiology and supports the free hormone hypothesis, given that the patient was asymptomatic despite no measurable levels of vitamin D.

Analytical validation of the Roche 25-OH Vitamin D Total assay.

BACKGROUND: Vitamin D deficiency is considered a major health issue and therefore there is a need for reliable routine tests for measurement of the vitamin in blood samples. Here we present a validation of the recently released Roche 25-OH Vitamin D Total assay (Vitamin D Total). METHODS: We analyzed control materials (2 levels) and patient serum pools (3 levels) ranging from 34 to 123 nmol/L 84 times over a period of 21 days, and we analyzed five serum pools in 10 separate runs to verify the limit of quantification. We also analyzed 53 paired samples of serum and Li-heparin plasma. We evaluated the 25-OH Vitamin D Total assay in comparison to our in-house liquid chromatography tandem mass spectrometry (LC-MS/MS) method [194 patient samples without 25-hydroxy vitamin D(2) (25OHD(2)) and 23 patient samples containing 25OHD(2)]. RESULTS: At concentrations of 34 and 56 nmol/L within-run CVs were 4.8% and 1.9% and total CVs were 8.3% and 6.1%. We verified that the limit of quantification was 22.5 nmol/L, as stated by the manufacturer. No significant difference was observed between serum and plasma samples (Li-heparin). Comparison with LC-MS/MS using 194 samples containing 25OHD(3) only (no 25OHD(2)) showed Vitamin D Total nmol/L=1.07×(LC-MS/MS) nmol/L+4.7 nmol/L, whereas comparison of 25OHD(2) using 23 patient samples showed Vitamin D Total nmol/L=0.55×(LC-MS/MS) nmol/L-2.38 nmol/L (Demings regression). CONCLUSIONS: The Roche Vitamin D Total assay is judged suitable for measurement of 25OHD in serum and Li-heparin plasma. Results for 25OHD(3) are comparable to those obtained by LC-MS/MS, while results for 25OHD(2) are around half of those obtained by LC-MS/MS.

Vitamin D depletion does not affect key aspects of the preeclamptic phenotype in a transgenic rodent model for preeclampsia.

Maternal vitamin D deficiency is proposed as a risk factor for preeclampsia in humans. We tested the hypothesis that vitamin D depletion aggravates and high supplementation ameliorates the preeclampsia phenotype in an established transgenic rat model of human renin-angiotensin system-mediated preeclampsia. Adult rat dams, transgenic for human angiotensinogen (hAGT) and mated with male rats transgenic for human renin (hREN), were fed either vitamin D-depleted chow (VDd) or enriched chow (VDh) 2 weeks before mating and during pregnancy. Mean blood pressure was recorded by tail-cuff, and 24-hour urine samples were collected in metabolic cages at days 6 and 18 of gestation. Rats were sacrificed at day 21 of gestation. Depleted dams (VDd) had negligible serum 25-hydroxyvitamin D2+3 levels (mean ± SEM; 2.95 ± 0.45 nmol/l vs. VDh 26.20 ± 2.88 nmol/l, P = .01), but in both groups, levels of 1,25(OH)2D3 remained below detection level of 25 pmol/l. Dietary vitamin D depletion did not aggravate hypertension (mean ± SEM BP, day 20 of gestation: 151.38 ± 5.65 mmHg VDd vs. 152.00 ± 4.10 mmHg VDh) or proteinuria. Fetal anthropometrics were similar between the groups, whereas VDd displayed lower placental:fetal weight ratios (0.15 vs. 0.16 g/g, P = .01) and increased sFlt-1/PlGF ratio. Expression of hREN was lower in placenta of VDd dams (0.82 ± 0.44 AU vs. 1.52 ± 0.15 AU, P = .04). Expression of key vitamin D metabolizing enzymes was unchanged. Dietary vitamin D intervention did not alter key aspects of the preeclampsia phenotype using the transgenic rodent model of human renin-angiotensin system-mediated pre-eclampsia, plausibly due to altered vitamin D metabolism or excretion in the transgenic rats.