CHEK2 and microcephalic primordial dwarfism: Moreover, cells derived from patients with Seckel syndrome, a hereditary form of microcephaly dwarfism caused by an ATR pre-mRNA splicing mutation that reduces ATR protein levels99, F02-98 and DK0064, and DOX-treated GM847-ATRkd cells (Fig. 2F), show normal ATM and Chk2 activation.