Refinement of the critical 7p22.1 deletion region: Haploinsufficiency of ACTB is the cause of the 7p22.1 microdeletion-related developmental disorders.

Non-recurrent microdeletion (≤2 Mb in size) in 7p22.1 is a rarely described cytogenetic aberration, only recently reported in patients with developmental delay/intellectual disability, short stature and microcephaly. The size of the deletions ranged from 0.37 to 1.5 Mb, and reported genotype-phenotype correlations identified a minimum deleted region of 0.37 Mb involving the FBLX18, ACTB, FSCN1, RNF216 and ZNF815P genes. The authors suggested that deletion of ACTB, which encodes β-actin, an essential component of the cytoskeleton, could be responsible for the clinical features observed in the patients with a 7p22.1 microdeletion. Here, we describe a 23-month-old child displaying developmental delay, short stature, microcephaly and distinctive facial features. Chromosomal microarray analysis performed using high-resolution SNP-array platform revealed a de novo interstitial 60 Kb microdeletion in the 7p22.1 region (from 5,509,127 bp to 5,569,096 bp, hg19) encompassing only two genes: FBXL18 and ACTB. To the best of our knowledge, this is the smallest deletion at 7p22.1 to date reported in medical literature (Pubmed). Combining our data with phenotypic and genotypic data of cases from literature, we were able to narrow the minimal critical region, which contained only two genes, i.e., FBXL18 and ACTB. Our finding is useful to perform a more accurate genotype-phenotype correlation and strongly strengthen the hypothesis that haploinsufficiency of ACTB is the main cause of the clinical phenotype observed in the patients with 7p22.1 microdeletions, facilitating genetic diagnosis and counseling.