Atelis syndrome-1 (ATELS1) is an autosomal recessive neurodevelopmental disorder characterized by global developmental delay with learning difficulties and poor overall growth with short stature and microcephaly. Most patients have anemia, some have immunologic defects, and some have congenital heart septal defects. More variable features may include hypotonia, dysmorphic facial features, skin pigmentary anomalies, and mild skeletal defects. Patient cells show multiple chromosomal abnormalities due to impaired DNA replication and disrupted mitosis (Grange et al., 2022). See also ATELS2 (620185), caused by mutation in the SMC5 gene (609386) on chromosome 9q21. For a discussion of genetic heterogeneity of MVA, see MVA1 (257300).