Interstitial 9p24.3 deletion involving only DOCK8 and KANK1 genes in two patients with non-overlapping phenotypic traits

Chromosome 9p deletion represents a clinically and genetically heterogeneous condition characterized by a wide spectrum of phenotypic manifestations and a variable size of the deleted region. The deletion breakpoint occurs from 9p22 to 9p24 bands, and the large majority of cases have either terminal deletions or translocations involving another chromosome. Here we report on two patients with similar inherited interstitial 9p24.3 deletion involving only DOCK8 and KANK1 genes. Interestingly, the two patients showed non-overlapping phenotypic traits ranging from a complex phenotype in one to only trigonocephaly with minor dysmorphic features and hand anomalies in the other one. The factors underlying the phenotypic variation associated with seemingly identical genomic alterations are not entirely clear, even if smaller variants, single-nucleotide changes, and epigenetic or stochastic factors altering the expression of genes within functionally relevant pathways have been recently shown to contribute to phenotypic variation. We discuss the role of the two genes and propose possible explanations for the clinical heterogeneity of the phenotype of the two patients.