N-Acetylcysteine provides limited efficacy as treatment option for skin picking in Prader-Willi syndrome.

Prader-Willi syndrome (PWS) is a rare neurodevelopmental disorder based on a loss of paternally expressed genes in chromosome region 15q11-13. In addition to typical characteristics such as hyperphagia, PWS is evidenced by a certain behavioral phenotype. Common indicators are repetitive behaviors, temper tantrums, and self-injurious behaviors such as skin- and/or rectal picking. N-Acetylcysteine (NAC) was previously described as a promising therapeutic option for skin picking in PWS. In this case series, we retrospectively investigated the effect of pharmacotherapy with NAC in 14 individuals with PWS suffering from skin- and/or rectal picking. Treatment success was determined using the Clinical Global Impression-Improvement scale (CGI-I). The Clinical Global Impression-Efficacy index (CGI-EI) was used to put treatment success and side effects into perspective. Six of fourteen patients, all of which were female, showed improvement in symptoms (dosage 1800-2400 mg/day), whereas six patients did not show any change during treatment. Moreover, two male patients treated for solitary rectal picking showed new onset of skin picking. Across all cases, a CGI-I of 3 (corresponding to minimal improvement) was seen after 3 months of treatment, with a CGI-EI of 1.6 (corresponding to moderate efficacy). NAC remains a reasonable therapeutic option in certain cases of skin picking in PWS but provides only limited efficacy compared to previous studies on the topic. There was a higher rate of adverse drug reactions than previously reported. The results particularly suggest caution in future treatment in individuals with solitary rectal picking and reduced efficacy when coadministered with neuroleptics.