PAX9 and tooth agenesis: Bearing in mind the information presented above on the influence of various mutations in the coding area of the MSX1 gene homeodomain, it is worth emphasizing that the functional analysis of the remaining five missense mutations in the same region of the MSX1 gene, correlated with hypodontia (Met61Lys, Ala194Val, Arg196Pro, Ala219Thr, and Ala221Glu), revealed none of the previously known molecular mechanisms (such as a disturbance of the interaction of MSX1 with PAX9 or other regulatory proteins).