The identification of additional larger families with PD in which PLXNA4 p.Ser657Asn or p.Arg302His segregate with the phenotype or the replication of the finding of an excess of very rare variants (MAF≤0.02%) in an independent case/control sample would lend further support to a possible role of modifying or causal variants in PLXNA4 in PD and to the interesting hypothesis of axonal guidance dysfunction in neurodegenerative conditions. The gene discussed is PLXNA4; the disease is Parkinson disease.