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 hypoc alciuric hypercalcemia (FHH) and neonatal severe hyperparathyroidism (NSHPT ) and found, by PCR amplification of the extracellular calcium-sensing rece ptor (CASR) gene exons and flanking intronic sequences, that FHH individual s were heterozygous for a g to t substitution in the last nucleotide of int ron 2 (IVS2-1G>T). Defects in messenger RNA splicing were investigated by i llegitimate transcription of the CASR gene in lymphoblastoid cells from an FHH affected individual, as well as by transfection of a CASR minigene harb oring this mutation into HEK293 cells. The mutation resulted predominantly in exon III skipping causing a shift in exon IV reading frame and introduct ion of a premature stop codon leading to a predicted truncated protein of 1 53 amino acids. Interestingly, it was noted that exon III splicing is not 1 00% efficient in parathyroid, thyroid, and kidney; an exon III-deleted tran script is produced approximately 15% of the time. This is the first descrip tion of a splice site mutation in the CASR gene and provides an explanation of the clinical phenotype of the patients. Hum Mutat 18:411-421, 2001. (C) 2001 Wiley-Liss, Inc.