HAPLN2 and early-onset autosomal dominant Alzheimer disease: Hapln2, a hyaluronan and proteoglycan link protein 2, also known as brain-derived connexin 1 (Bral1), is essential for neuronal conductivity and extracellular matrix (ECM) formation and has been identified to be involved in a variety of neurological disease pathologies, such as schizophrenia (Martins-de-Souza et al., 2009) and Alzheimer’s disease (Minjarez et al., 2013).