In contrast, duplication of NSD1 in the microduplication 5q35 syndrome leads to microcephaly in 74% of cases, with undergrowth, and developmental delay in close to 90% of the cases (Chen et al., 2006; Franco et al., 2010; Dikow et al., 2013; Rosenfeld et al., 2013; Quintero-Rivera et al., 2021). Here, NSD1 is linked to Global developmental delay.