ClinVar Genomic variation as it relates to human health

This CNV is a 7.5 Mb duplication of 12p13.33-p13.31 on chromosome 12, (seq[GRCh37]dup(12)(p13.33p13.31); chr12:g.189145_7730395dup). The CNV constitutes a gain encompassing 169 genes which overlaps with the region associated with trisomy 12p syndrome. Trisomy 12p syndrome is a rare condition characterized by developmental delay, intellectual disability, and dysmorphic features including a flat face with full cheeks, high forehead, short nose, broad nasal bridge, anteverted nostrils, smooth philtrum, ear anomalies, a short neck, and hand or foot deformities. Additional common features includes hypotonia, vision problems, dental anomalies, feeding difficulties, and seizures. Some individuals may also present with hearing loss, heart anomalies, brain anomalies, infections, and eczema. Duplications of the complete arm, partial duplications, mosaicism, and derivative chromosomes have been identified in affected individuals. Variability and severity in phenotype has been described based on the size, presence of a second copy number variant, or presence of mosaicism (Segel et al. 2006; Poirsier et al. 2014). Two individuals have been described with CNVs that are fully encompassed within the CNV in question. One individual had two approximately 0.3 Mb duplications, at 12p13.33 and 21q22.3, and presented with developmental delay, recurrent infections, hypotonia, facial dysmorphic features, and hand and foot anomalies. Agenesis of the corpus callosum and cataracts were also noted. The authors indicate that characteristics can be attributed to either the 12p13.33 or the 21q22.3 gain and suggest hypotonia and dysmorphic features are specifically due to the 12p duplication (Mekkawy et al. 2015). A second individual with tetrasomy of the 12p region presented with a related condition, Pallister-Killian syndrome (Vermeesch et al. 2005). Control data are unavailable in the literature for this CNV which is absent from population databases including the Database of Genomic Variants and the Genome Aggregation Database. Based on the collective evidence, this CNV is classified as pathogenic.