IQSEC2 and free sialic acid storage disease: Hypomyelination was found in seven different diseases: Salla disease, 18q deletion syndrome, Cockayne syndrome (type B), mucolipidosis II, neurodegeneration with brain iron accumulation (NBIA5), developmental and epileptic encephalopathy 44 (DEE44), and X‐linked intellectual disability 1 (MRX1) (Figure 4 and Figure S1).