Hereditary vitamin D resistant rickets: identification of a novel splice site mutation in the vitamin D receptor gene and successful treatment with oral calcium therapy.
OBJECTIVE
To study the vitamin D receptor (VDR) gene in a young girl with severe rickets and clinical features of hereditary vitamin D resistant rickets, including hypocalcemia, hypophosphatemia, partial alopecia, and elevated serum levels of 1,25-dihydroxyvitamin D.


METHODS
We amplified and sequenced DNA samples from blood from the patient, her mother, and the patient's two siblings. We also amplified and sequenced the VDR cDNA from RNA isolated from the patient's blood.


RESULTS
DNA sequence analyses of the VDR gene showed that the patient was homozygous for a novel guanine to thymine substitution in the 5'-splice site in the exon 8-intron J junction. Analysis of the VDR cDNA using reverse transcriptase-polymerase chain reaction showed that exons 7 and 9 were fused, and that exon 8 was skipped. The mother was heterozygous for the mutation and the two siblings were unaffected.


CONCLUSIONS
A novel splice site mutation was identified in the VDR gene that caused exon 8 to be skipped. The mutation deleted amino acids 303-341 in the VDR ligand-binding domain, which is expected to render the VDR non-functional. Nevertheless, successful outpatient treatment was achieved with frequent high doses of oral calcium.
Ma
Nina S
NS
Division of Endocrinology, Diabetes and Metabolism, Department of Pediatrics, Childrens Hospital Los Angeles and Keck School of Medicine of the University of Southern California, Los Angeles, CA 90027, USA. nma@alum.mit.edu
Malloy
Peter J
PJ
Pitukcheewanont
Pisit
P
Dreimane
Daina
D
Geffner
Mitchell E
ME
Feldman
David
D
D000284:Administration, Oral; D000595:Amino Acid Sequence; D001483:Base Sequence; D002118:Calcium / Q000008:administration & dosage* / Q000627:therapeutic use*; D002675:Child, Preschool; D004252:DNA Mutational Analysis; D018076:DNA, Complementary / Q000235:genetics; D005091:Exons / Q000235:genetics; D053098:Familial Hypophosphatemic Rickets / Q000000981:diagnostic imaging / Q000188:drug therapy* / Q000235:genetics*; D005260:Female; D006760:Hospitalization; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D011247:Pregnancy; D022821:RNA Splice Sites / Q000235:genetics*; D011859:Radiography; D018167:Receptors, Calcitriol / Q000737:chemistry / Q000235:genetics*
D018076:DNA, Complementary; D022821:RNA Splice Sites; D018167:Receptors, Calcitriol; D002118:Calcium