This is a Phase 1/2, multicenter, randomized, placebo-controlled, double-blind study to evaluate the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of single and multiple doses of DNL593 in two parts followed by an optional open-label extension (OLE) period. Part A will evaluate the safety, tolerability, PK, and PD of single doses of DNL593 in healthy male and healthy female participants of nonchildbearing potential. Part B will evaluate the safety, tolerability, PK, and PD of multiple doses of DNL593 in participants with frontotemporal dementia (FTD) over 25 weeks. Part B will be followed by Part C, an optional 18-month OLE period available for all participants who complete Part B.