Vitamin D Hydroxylation-Deficient Rickets, Type 1A

Alternative Names

  • VDDR-IA
  • 1-Alpha-Hydroxylase Deficiency
  • PDDRI
  • Pseudovitamin D-Deficient Rickets
  • VDDI
  • VDDR-I
  • Vitamin D Dependent Rickets, Type I
  • Vitamin D-Dependency, Type I
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WHO-ICD-10 version:2010

Endocrine, nutritional and metabolic diseases

Metabolic disorders

OMIM Number

264700

Mode of Inheritance

Autosomal recessive

Gene Map Locus

12q14.1

Description

Disorders of vitamin D metabolism include vitamin D deficiency, resistance, and biosynthesis, which include mutations in CYP27B1 and CYP2R1.  These disorders result in the clinical and biochemical manifestations of rickets.  There are two forms of vitamin D dependent rickets, type 1 (VDDR-I) and 2 (VDDR-II).  VDDR-IA is common in French-Canadians from the Charlevoix-Saguenay-Lac Saint Jean area of Quebec with a carrier frequency of 1 in 26.  It is characterized clinically by hypotonia, delayed motor development, seizures; due to hypocalcemia in early infancy, growth retardation, rickets and osteomalacia.  The age of onset of clinical symptoms is 2 years of age.  

Laboratory findings include hypocalcemia, elevated serum PTH, markedly decreased or absent serum 1,25-dihydroxyvitamin D3 and normal serum 25-hydroxyvitamin D3.  VDDR-I can be treated with physiologic levels of 1,25-dihydroxyvitamin D3 or 1-alpha-hydroxyvitamin D3.  Some studies had reported relatively strong genotype-phenotype correlation.  In addition, the presence of a residual enzyme activity may contribute to the mild phenotype in some affected individuals.

Molecular Genetics

VDDR-IA is caused by an enzymatic defect in synthesis of the active form of vitamin D due to mutation in the CYP27B1 gene.  Several missense mutations were reported in patients from various ethnicities and some mutations are more frequent in certain ethnic groups.

Epidemiology in the Arab World

View Map
Subject IDCountrySexFamily HistoryParental ConsanguinityHPO TermsVariantZygosityMode of InheritanceReferenceRemarks
264700.G.1.1United Arab Emirates Low levels of vitamin DNM_000782.4:c.733-149=, NC_000020.11:g.54125940=, NC_000012.12:g.57768302=, NM_000785.4:c.1137-29=HomozygousAl Anouti et al. 2017 Cohort involving 162...
264700.G.1.3United Arab Emirates Low levels of vitamin DNC_000012.12:g.[57764205=;57768302=] NC_000020.11:g.[54164712=;54125940=], NC_000012.12:g.[57764205A>G;57768302G>T] NC_000020.11:g.[54164712=;54125940=]Al Anouti et al. 2017 Cohort involving 162...

Other Reports

Morocco

Kim et al (2007) described a Moroccan patient with 1-Alpha-Hydroxylase Deficiency born to unrelated parents.  The male patient presented at the age of 22-months with severe malnutrition, hypotonia and respiratory distress.  Physical and radiological findings were consistent with a diagnosis of severe rickets and pneumonia with pleural effusion.  He had hypocalcemia, and high concentrations of alkaline phosphatase and PTH, while level of 1,25(OH)2D was low.  He died of multiple organ failure following development of bilateral pneumothoraces.  Genetic analysis identified a novel homozygous mutation in the CYP27B1 gene.

Saudi Arabia

Alzahrani et al. (2010) described a 23-year-old woman who presented at the age of 16 years with significant growth retardation, bone pain and severe deformities of lower limbs.  Her general condition gradually deteriorated over the years with impaired walking and generalized bone pain.  Her family history was positive with five of her siblings suffering a similar condition.  Her parents are first degree cousins.  The patient and her affected siblings were treated with calcitroil 0.5-1 mg twice daily and calcium carbonate 600-1200 mg twice daily.  All affected individuals in this family showed remarkable improvement with complete normalization of calcium, phosphate, alkaline phosphatase, and PTH over 2-3 years of treatment.  Molecular genetic testing identified (p.G102E) mutation in the CYP27B1 gene.

Babiker et al. (2014) reported a 13-month old Saudi girl, who presented with multiple fractures resulting from minor traumas.  The patient was born to first-cousin consanguineous parents, with no family history of a similar condition.  The clinical, biochemical, and radiological findings were consistent with previously reported cases of CYP27B1 mutations.  Radiological features were severe and included generalized osteopenia with multiple fractures.  Mutation analysis revealed a novel pathogenic mutation in the CYP27B1 gene.

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