A rare autosomal recessive inherited syndrome caused by mutations in the ATR gene, RBBP8 gene, CENPJ gene, CEP152 gene, CEP63 gene, NIN gene, DNA2 gene, or TRAIP gene. It is characterized by intrauterine growth retardation, dwarfism, microcephaly, mental retardation, and a "bird-headed" facial appearance. The disease is Seckel syndrome (Monarch Disease Ontology term MONDO_0019342). Also known as: Harper's syndrome, SCKL, Seckel-type Dwarfism, Virchow-Seckel dwarfism, bird-headed dwarfism, nanocephalic Dwarfism.