Neonatal brachial plexus injury (NBPI) causes disabling and incurable muscle contractures that are driven by impaired growth of denervated muscles. A rare form of NBPI, which maintains afferent muscle innervation despite motor denervation, does not cause contractures. As afferent innervation regulates various aspects of skeletal muscle homeostasis through NRG/ErbB signaling, our current study investigated the role of this pathway in modulating contracture development. Through pharmacologic modification with an ErbB antagonist and NRG1 isoforms, we discovered that NRG/ErbB signaling does not modulate the development of contractures in neonatal mice. Instead, ErbB inhibition impeded growth in nondenervated skeletal muscles, whereas increased ErbB activation exacerbated denervation‐induced skeletal muscle atrophy. This potential regulatory effect of NRG/ErbB signaling on neonatal muscle growth warrants deeper investigation.

Background and Aims: Genetic risk can influence disease progression. We measured the impact of genetic risk for substance use disorders (SUDs) on substance use onset and progression of symptoms.Design, Setting, Participants: Using findings from genome-wide association studies (GWASs) of alcohol use disorder (AUD), opioid use disorder (OUD) and smoking trajectory (SMK) as discovery samples, we calculated polygenic risk scores (PRSs) in a deeply

Background: Charting the clinical course of substance use disorders (SUDs) to identify etiologic contributors to milestone onset and progression could inform intervention efforts. Methods: We calculated polygenic risk scores (PRS) in 5,692 European-ancestry individuals (EUR) (56.2% male) and 4,918 African-ancestry (AFR) individuals (54.9% male) using genome-wide association studies (GWAS) of alcohol use disorder (AUD), opioid use disorder (OUD), and smoking trajectory (SMK). Using Cox regression, we examined the association of polygenic risk with age of first substance use, regular use, reported problems, and dependence diagnosis and with progression from regular use to onset of problems and dependence. Results: EUR and males reported earlier onset and shorter progression times than AFR and females, respectively. Among EUR, higher AUD PRS predicted earlier onset and more rapid progression to alcohol-related milestones (p<0.0001) and although a stronger moderator of problem onset among females (p=0.0165), it was more predictive of the progression to problems among males (p=0.0054). OUD and SMK PRS in EUR also predicted earlier onset of the respective milestones (p=0.0002). Among AFR, where power is lower, AUD PRS predicted age of regular alcohol use (p=0.039) and dependence (p=0.001) and progression from regular use to diagnosis (p=0.045), while SMK PRS predicted earlier age of initiation (p=0.036). Conclusions: Genetic risk for SUDs predicts milestones and symptom progression in EUR and, to a lesser extent, among AFR. Larger, diverse discovery GWAS and target samples are needed to enhance the power of PRS to personalize interventions for individuals at genetic risk of serious substance-related outcomes.