Mo. Rev. Stat. § 630.120: No presumptions.

No patient or resident, either voluntary or involuntary, shall be presumed to be incompetent, to forfeit any legal right, responsibility or obligation or to suffer any legal disability as a citizen, unless otherwise prescribed by law, as a consequence of receiving evaluation, care, treatment, habilitation or rehabilitation for a mental disorder, mental illness, intellectual disability, developmental disability, alcohol problem or drug problem.