The clinical observations of our patient overlap with the major common findings for published cases. The deletion detected in our patient does not involve the previously suggested candidate genes YAF2 and AMIGO2 . We draw a correlation between proximal deletion 12q and ARID2 deficiency by comparing patients carrying gross deletions with a cohort of patients carrying small intragenic ARID2 deletions as well as patients with single nucleotide variants (SNVs) in ARID2 . Growth retardation <-2 SD is present in cohorts with both gross and small deletions spanning ARID2 . However, ARID2 SNVs do not correlate with severe growth retardation. AbstractProximal deletion of the long arm of chromosome 12 is a rare chromosomal abnormality described in about 20 patients. Known deletions span the region from 12q11 to 12q13 and include the genes YAF2 , AMIGO2 , and NELL2 . These are suggested as candidate genes for the key phenotypic features such as growth and psychomotor retardation. Here, we present a case with a 3.1-Mb interstitial deletion at 12q12q13.11.