HCN4 and chronic obstructive pulmonary disease: It is however important to note that, to our knowledge, none of the patients already described with cardiac arrhythmias due to HCN4 mutations has been reported to also present an epileptic phenotype, suggesting that the HCN4 R550C mutation reported here is likely to be a contributing factor requiring other mechanisms or a still unidentified genetic background to express an epileptic phenotype.