CHN1 and duane retraction syndrome: Expanding the phenotype to cranial nerves development disease.

Duane retraction syndrome is a congenital eye movement disorder characterized by a failure of abducens nerve to develop normally, resulting in restriction or absence of abduction, adduction, or both, and narrowing of the palpebral fissure and retraction of the globe on attempted adduction. There is a genetic heterogeneity in Duane retraction syndrome (DURS). DURS maps to chromosome 8q13 in some patients, and pathogenic variants in CHN1 and MAFB genes are known to lead to DURS. We report here a child and his father with Duane retraction syndrome, associated to swallowing difficulties and unilateral trapeze aplasia. A whole exome sequencing revealed a heterozygous missense variant in CHN1 gene. This gene encodes GTPase-activating protein and is involved in the assembly of neuronal locomotor circuits. A patient with a 8q deletion has previously been described with a Duane retraction syndrome associated to trapeze aplasia. We provide an additional description to support the role in cranial nerves development of the CHN1 gene.