wie viele gene hat ein mensch — what are common causes?

The number of human genes is currently estimated at around 20,000–25,000 protein-coding genes, though the exact count remains debated due to non-coding RNAs, pseudogenes, and regulatory elements. The phrase 'common causes' is ambiguous: it could refer to common causes of genetic variation (e.g., SNPs, mutations) or common causes of disease. The provided context does not contain specific information about gene count or common causes. The included texts discuss DNA tests for stress, COMT, BDNF, FADS1, APOA2, and ADH1B, but not the fundamental gene number or general causes. Therefore, an evidence-based answer from the given context is not possible. Without clear context, any answer remains speculative. For precise statements, more specific sources or a clearer question would be required.