Any Seckel syndrome in which the cause of the disease is a mutation in the ATR gene. The disease is Monarch Disease Ontology id MONDO_0008869 (Seckel syndrome 1). Also known as: ATR Seckel syndrome, SCKL1, Seckel syndrome 3, Seckel syndrome caused by mutation in ATR, Seckel syndrome type 1, microcephalic primordial dwarfism I.