Clinical innovations and future directions of nanoparticles in the treatment of psychiatric and neurological disorders.

Anorexia nervosa (AN) is a psychiatric disorder characterized by severe underweight, an intense fear of weight gain, and a distorted body image (American Psychiatric Association ). The lifetime prevalence of AN in women is estimated up to 3.6% (van Eeden et al. ). Among eating disorders (EDs), AN has the highest mortality rate (Arcelus et al. ). Treatment options for AN are predominantly psychotherapeutic, and for adolescents, family‐based treatment is the first choice (NICE ). A positive outcome is largely dictated by early change, that is, weight gain within the first weeks of treatment (Le Grange et al. ). Detecting AN at an early stage is therefore imperative for remission. Even though AN is a severe and well‐studied psychiatric disorder, the knowledge regarding the initial, or premorbid stages is still very limited. As a result, little is known about potential psychopathological vulnerabilities preceding the AN onset. Extensive research on the acute and recovered stages of AN shows a strong association with psychiatric comorbidity in adults (Treasure et al. ). In adolescents, research is scarcer. However, approximately 50% of adolescents with AN have at least one psychiatric comorbidity, affective and anxiety disorders being the most common (Bühren et al. ; Mairhofer et al. ; Råstam ; Trainor et al. ). Posttreatment, comorbidity frequencies decrease. However, the decline appears to differ between diagnoses, showing anxiety disorders to be more persistent than depression (Dobrescu et al. ; Trainor et al. ). It has been suggested that depression emerges post AN debut, while anxiety disorders tend to exist prior to the AN onset. This may partly explain why treatment is associated with greater improvement in depressive symptoms compared to anxiety symptoms (Hughes ). Previous research supports elevated autistic traits in adults with AN compared with healthy controls (Anckarsäter et al. ; Nielsen et al. ; Nilsson et al. ; Tchanturia et al. ), and comorbid autism in AN is associated with greater ED severity (Zhang et al. ). Although to a lesser extent, elevated autistic traits have been reported among adolescents with AN (Anckarsäter et al. ; Baron‐Cohen et al. ; Nielsen et al. ; Nilsson et al. ; Rhind et al. ), and evidence of increased autistic traits during the acute stages of AN has been reported (Nuyttens et al. ). A longitudinal study of teenage‐onset AN reported reduced, but remaining autistic traits after the recovery of AN in 25% of the sample (Nuyttens et al. ). In contrast, a prospective twin cohort study found no overrepresentation of autistic traits in children with later onset AN (Dinkler et al. ). Regarding other neuropsychiatric disorders, comorbid attention‐deficit/hyperactivity disorder (ADHD) has previously been more closely associated with ED subtypes comprising binge‐purging behaviors (Fernández‐Aranda et al. ; Wentz et al. ). However, a relatively recent review reported the risk of ADHD as two‐folded across all EDs and age groups (Nazar et al. ).