PRKAG2 and Danon disease: Nineteen probands (3.1%) were diagnosed with metabolic or infiltrative forms closely mimicking sarcomeric HCM (Fig. 3), including transthyretin-related amyloidosis (n = 6, 1%), Fabry disease (n = 5, 0.8%), Danon disease (n = 4, 0.7%) and PRKAG2-related HCM (n = 4, 0.7%), following the identification of variants in group β genes.