Aim: 

Recent evidence have demonstrated a causative relation between some mutations of the hHCN4 pacemaker channel gene and disorders of the cardiac rhythm. We therefore screened the hHCN4 channel gene for new mutations in patients affected by bradycardia (B), atrial fibrillation (AF), sinus tachycardia (ST) and inappropriate forms of sudden death (SD).

Methods: 

Genomic DNA was obtained from blood or saliva samples obtained from 85 patients (B, 15; AF, 9; ST, 21; SD, 40). In several cases a familial history of the disease was identified. The HCN4 gene was amplified by RT-PCR and processed by Single Strand Conformational Polymorphism or Denaturing High Performance Liquid Chromatography to identify mutations in the coding region of the hHCN4 gene.

Results: 

To date we have identified a total of 11 mutations (6 of them with a corresponding aminoacid change) which were found according the following scheme: B patients, G36E, E153G, P1117L, L12L, L520L, P1200P; AF patients, G36E, V733I9, L520L; ST patients, V759I, P152P, L520L, P1200P; SD individuals, M1113L, L520L, F613F, and P1200P. Interestingly most of the mutations (9) were found in exons 1 and 8 which code for the N- and C.-terminus regions, respectively. The other two mutations were found in the sixth transmembrane domain and in the cyclic nucleotide binding site. In all cases we collected the familial clinical history of the patients but we failed to find any indication of an association between the mutations and the disease.

Conclusion: 

In the present screening we have found several mutations, but a clear association with a cardiac phenotypic alteration could not be demonstrated. Based on the recent observation that single nucleotide polymorphisms can act as co-factors in diseases of multifactorial origin we plan to continue and extend this research to evaluate this possibility.