Interestingly, one AluYb8 insertion (chrX: 41391772-41391772) that is only commonly polymorphic in the Korean population (Fig. 4) was inserted into the CASK gene, which is closely linked to mental retardation and microcephaly with pontine and cerebellar hypoplasia (MICPCH)84,85. The gene discussed is CASK; the disease is microcephaly.