We have investigated the possibility of mutations in the calcitonin/calcitonin 
gene related peptide (CGRP) gene in children with Williams syndrome. Involvement 
of the calcitonin/CGRP gene in Williams syndrome is postulated on the basis that 
Williams syndrome children often have infantile hypercalcemia and deficient 
expression of calcitonin, a hormone that lowers serum calcium levels. To test 
the hypothesis that mutations in the calcitonin/CGRP gene might be responsible 
for the reduced calcitonin levels, we examined the calcitonin/CGRP gene 
structure in Williams syndrome children. Analysis of white blood cell DNA by 
Southern blot hybridizations in 5 individuals did not show any detectable large 
deletions or rearrangements in the calcitonin/CGRP gene locus. The possibility 
of small deletions or point mutations within the exon encoding the mature 
calcitonin hormone is unlikely based on ribonuclease protection assays with 
patient DNA amplified by the polymerase chain reaction (PCR) technique. These 
findings suggest that the calcitonin deficiency might be due either to mutations 
elsewhere in the gene or to defects in the cellular machinery needed for 
calcitonin synthesis and/or secretion.