Codon 890 represents a mutational hotspot in CLTC. Specifically, the c.2669C > T (p.P890L) substitution has been identified in four unrelated subjects with a relatively mild DD/ID and MD phenotype (Hamdan et al., 2017; Manti et al., 2019; Nabais Sá et al., 2020). This evidence concerns the gene CLTC and Menkes disease.