Three family members presented with FHH-1 and short QT interval (< 360 ms), a condition that could lead to cardiac arrhythmias, and the effects of cinacalcet, an allosteric modulator of the CaSR, in rectifying the abnormal sensitivity of the mutant CaSR and in correcting the short QT interval were determined. Here, CASR is linked to cardiac arrhythmia.