wie viel gene hat der mensch — what symptoms are typical?

The question combines two distinct aspects: the number of human genes and typical symptoms. The number of protein-coding genes in humans is about 20,000–25,000 (current genome reference). This is well-established but has no direct link to symptoms. Symptoms arise from genetic variants, not from the gene count itself. The provided contexts (BDNF, ACTN3, PPARGC1A, IgE, cortisol) show that specific variants can be associated with certain traits – e.g., BDNF Val66Met with reduced BDNF secretion or elevated IgE with allergies. However, effects are usually small and not diagnostic. Typical symptoms of a genetic predisposition cannot be generalized; they depend on the specific gene and environment. Consumer DNA tests often overstate clinical relevance. For any symptoms, a doctor should be consulted. Evidence for gene count is strong; for the symptom question it is unclear due to vagueness.