To explore whether mice with the Clp1R140H mutation have degeneration of lower motor neurons as observed in Clp1K127A/K127A mice and suspected in PCH10 patients (2, 4), we counted cervical spinal motor neurons, identified on the basis of their location and choline acetyltransferase (ChAT) positivity (Fig. 1 B and C). Here, CHAT is linked to pontocerebellar hypoplasia type 10.