Long-term clinical outcome and the identification of homozygous CYP27B1 gene mutations in a patient with vitamin D hydroxylation-deficient rickets type 1A

Siblings with vitamin D-dependent rickets type 1A: Importance of genetic testing and a review of genotype-phenotype correlations

Vitamin D-dependent rickets type 1A (VDDR1A) is a rare condition caused by biallelic pathogenic variants in CYP27B1, which encodes 25-hydroxyvitamin D3-1-α-hydroxylase. Inadequate activity of this enzyme results in deficient 1α-hydroxylation of inactive 25-hydroxyvitamin D to biologically active 1,25-dihydroxyvitamin D, with consequent adverse effects on calcium and phosphate metabolism. A female child was clinically diagnosed at 18 months old with hypophosphatemic rickets based on phenotype and biochemical testing, with neither parent affected. A subsequent affected male sibling led to the reconsideration of the diagnosis. Exome sequencing showed a homozygous CYP27B1 c.1040T>A (p.Ile347Asn) variant for both children. No variants were found in genes associated with hypophosphatemic rickets. A review of published cases of VDDR1A with homozygous CYP27B1 variants indicates variable clinical presentation, lack of genotype-phenotype correlation, and low serum phosphate at diagnosis in most cases. These findings emphasize the clinical importance of molecular testing as part of the diagnostic evaluation for cases of non-nutritional rickets.

Vitamin D and Toxic Metals in Pregnancy - a Biological Perspective

Purpose of Review

To discuss the potential biological mechanisms between vitamin D and toxic metals and summarize epidemiological studies examining this association in pregnant women.

Recent Findings

We identified four plausible mechanisms whereby vitamin D and toxic metals may interact: nephrotoxicity, intestinal absorption of metals, endocrine disruption, and oxidative stress. Few studies have examined the association between vitamin D and toxic metals in pregnant women. North American studies suggest that higher vitamin D status early in pregnancy are associated with lower blood metals later in pregnancy. However, a trial of vitamin D supplementation in a pregnant population, with higher metal exposures and lower overall nutritional status, does not corroborate these findings.

Summary

Given ubiquitous exposure to many toxic metals, nutritional intervention could be a means for prevention of adverse outcomes. Future prospective studies are needed to establish a causal relationship and clarify the directionality of vitamin D and metals.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40471-024-00348-0.

Clinical spectrum and diagnostic challenges of vitamin D dependent rickets type 1A (VDDR1A) caused by CYP27B1 mutation in resource limited countries

OBJECTIVES

Vitamin D dependent rickets type 1A (VDDR1A) is a rare autosomal recessive condition due to inactivating mutation of CYP27B1. It mimics clinically, biochemically and rediologically to nutritional and hypophosphatemic rickets. In developing countries like Pakistan, VDDR1A is often misdiagnosed as nutritional rickets or hypophosphatemic rickets due lack of free access to 1,25 (OH) 2 D level and genetic testing. This study was aimed to determine the clinical spectrum and diagnostic challenges of VDDR1A due to CYP27B1 mutation in developing countries.

METHODS

Retrospective review of all cases of VDDR1A due to CYP27B1 mutation over a period of two years presenting in the Pediatric Endocrine clinic of Hameed Latif Hospital, Lahore, Pakistan.

RESULTS

Six cases of VDDR1A (4 males) were identified. Mean age of clinical manifestation was 14 (9-24) months. Mean age of presentation to endocrine department was 5.5 (1.5-11.8) years. Growth failure and bony deformities were the most common presentation (n=6), followed by repeated diarrheas and abdominal distension (n=3) and recurrent fractures (n=1). All cases shared same biochemical profile of low/normal calcium, hypophosphatemia, raised alkaline phosphatase, raised PTH, normal/high 25(OH)D and tubular reabsorption of phosphate (TRP) <85%. Patients treated with calcitriol showed rapid healing as compared to those treated with 1-alfacalcidol.

CONCLUSIONS

We should have a high index of suspicion of VDDR1A in rickets not responding to cholecalciferol therapy.

A case of vitamin D hydroxylation-deficient rickets type 1A caused by 2 novel pathogenic variants in CYP27B1 gene

Vitamin D hydroxylation-deficient rickets type 1A (VDDR1A, OMIM 264700) is a rare autosomal recessive inherited disorder. Pathogenic variants in the CYP27B1 gene lead to loss of 1α-hydroxylase activity. We report the case of a 22-month-old toddler who presented with growth retardation and delayed development. The patient exhibited the typical laboratory findings of VDDR1A, including hypocalcemia (calcium: 5.2 mg/dL), elevated serum level of alkaline phosphatase (2,600 U/L), elevated serum level of intact-parathyroid hormone (238 pg/mL), low 1,25(OH)2D3 level (11.2 pg/mL), and normal 25(OH)D3 level (40.7 ng/mL). His height and weight were 76.5 cm and 9.5 kg, respectively (both &lt;3rd percentile). The Bayley Scales of Infant and Toddler Development II indicated significantly delayed development (mental development index &lt;50, psychomotor development index &lt;50). The patient was a compound heterozygous for two novel pathogenic variants in the CYP27B1 gene: c.57_69del (p.Glu20Profs*2) and c.171dupG (p.Leu58Alafs*275), inherited from his mother and father, respectively. The patient showed remarkable improvement after treatment with calcitriol and calcium carbonate.