An acceptor splice site mutation in the calcium-sensing receptor (CASR) gene in familial hypocalciuric hypercalcemia and neonatal severe hyperparathyroidism.
We studied family members of a large kindred expressing both familial hypocalciuric hypercalcemia (FHH) and neonatal severe hyperparathyroidism (NSHPT) and found, by PCR amplification of the extracellular calcium-sensing receptor (CASR) gene exons and flanking intronic sequences, that FHH individuals were heterozygous for a g to t substitution in the last nucleotide of intron 2 (IVS2-1G>T). Defects in messenger RNA splicing were investigated by illegitimate transcription of the CASR gene in lymphoblastoid cells from an FHH affected individual, as well as by transfection of a CASR minigene harboring this mutation into HEK293 cells. The mutation resulted predominantly in exon III skipping causing a shift in exon IV reading frame and introduction of a premature stop codon leading to a predicted truncated protein of 153 amino acids. Interestingly, it was noted that exon III splicing is not 100% efficient in parathyroid, thyroid, and kidney; an exon III-deleted transcript is produced approximately 15% of the time. This is the first description of a splice site mutation in the CASR gene and provides an explanation of the clinical phenotype of the patients.
D'Souza-Li
L
L
Department of Medicine, McGill University and Royal Victoria Hospital, Montreal, Canada.
Canaff
L
L
Janicic
N
N
Cole
D E
DE
Hendy
G N
GN
D017398:Alternative Splicing / Q000235:genetics*; D001483:Base Sequence; D002460:Cell Line; D018389:Codon, Nonsense / Q000235:genetics; D004252:DNA Mutational Analysis; D005091:Exons / Q000235:genetics; D005260:Female; D006801:Humans; D006934:Hypercalcemia / Q000235:genetics*; D006961:Hyperparathyroidism / Q000235:genetics*; D007231:Infant, Newborn; D007438:Introns / Q000235:genetics; D008297:Male; D009154:Mutation / Q000235:genetics*; D023282:Nuclease Protection Assays; D016366:Open Reading Frames / Q000235:genetics; D010375:Pedigree; D022821:RNA Splice Sites / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017384:Sequence Deletion / Q000235:genetics; D014158:Transcription, Genetic / Q000235:genetics; D014162:Transfection
D018389:Codon, Nonsense; D022821:RNA Splice Sites; D012333:RNA, Messenger; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface