On suspicion of a neurodegenerative disorder in addition to her PWS diagnosis, an urgent trio-WES was performed and detected the homozygous pathogenic variant p.Tyr142fs (NM_017882.3:c.424dup) in the CLN6 gene, consistent with an infantile form of neuronal ceroid lipofuscinosis (OMIM #601708). Here, CLN6 is linked to Prader-Willi syndrome.