8q12 Microduplication Syndrome

The newly described 8q12 microduplication syndrome is associated with unusual and characteristic multi-organ clinical features, which include hearing loss, congenital heart defects, intellectual disability, hypotonia in infancy, and Duane anomaly (see this term).

Epidemiology

It has been described in two patients.

Clinical description

The mild facial dysmorphism is characterized by high, arched eyebrows and unilateral narrowing of the palpebral fissure and retraction of the globe caused by Duane anomaly (Duane anomaly is a form of complex strabismus characterized by limited ocular abduction and variably limited adduction accompanied by retraction of the globe, which narrows the palpebral fissure).

Etiology

This microduplication was identified by microarray-based comparative genomic hybridization (aCGH). The lack of recurrent breakpoints in these two cases and the absence of any low-copy repeats (LCR) pairs that flank these de novo events do not support non-allelic homologous recombination as the mutation mechanism. The 8q12 region includes CHD7 and it is proposed that this gene, associated with CHARGE syndrome by haploinsufficiency, causes a different phenotype by gain-of-dosage.