MMP1 and Hirschsprung disease: Our investigation revealed the presence of Stromal 4 cells exclusively in the distal ganglionic colon of HSCR patients, supported by the highest expression of the matrix metallopeptidase 1 (MMP1) marker in the same segment (Fig. 6C), but depletion of the stromal cell 2 marker Pdgfrα (Fig. 6E, F).