Synonyms: pseudo-vitamin D deficiency rickets Type II, vitamin D-dependent rickets Type II, VDDR II
Inheritance: autosomal recessive
Genetic locus: vitamin D receptor (VDR) gene
Molecular defect: defective binding of vitamin D at its receptor which may be due to several causes. This results in poor absorption of calcium from the GI tract
Clinical features:
(1) normal appearance at birth
(2) onset is during infancy
(3) severe changes in bone with rickets
(4) alopecia in many patients
Laboratory features:
(1) low serum calcium
(2) high serum parathyroid hormone (PTH)
(3) normal to elevated levels of 1,25 dihydroxy vitamin D prior to therapy
Management: Patients respond to massive doses of vitamin D and calcium.
Differential diagnosis:
(1) VDDR I (see previous section)
(2) nutritional deficiency in calcium
(3) nutritional deficiency in phosphate
(4) rickets of severe prematurity
(5) vitamin D deficiency
