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Change in Effect Sizes Over Time in Autism Research
There has been a move from categorical toward spectrum-based definitions of autism accompanied by steady increases in its prevalence. In a meta-analysis, Rodgaard and colleagues investigated 11 meta-analyses with data from 27 723 individuals examining group differences on 7 neurocognitive constructs and found downward temporal trends for effect size for all constructs without a similar trend in studies of schizophrenia. Reduction in differences between individuals with and without autism may be owing to changes in the definition of autism. In an Editorial, Harris discusses implications for the field.
Attention-Deficit/Hyperactivity Disorder Risk and Hypomania
Attention-deficit/hyperactivity disorder (ADHD) and bipolar disorder are highly comorbid but the mechanisms accounting for their cooccurrence are unknown. Hosang and colleagues used data on 13 532 twin pairs from Sweden and found significant associations between ADHD and genetic risk for adolescent hypomanic symptoms, more for hyperactivity-impulsivity than for inattention; environmental factors played a negligible role. Thus, more than a quarter of the genetic risk factors for adolescent hypomanic traits were also associated with ADHD symptoms in childhood and adolescence. Moran and colleagues discuss implications for the field in an Editorial.
Posttraumatic Stress Disorder Improvement and Diabetes Risk
Posttraumatic stress disorder (PTSD) is associated with increased risk of type 2 diabetes, but it is unknown whether PTSD improvement is associated with type 2 diabetes risk. Using medical records data from 5916 patients who received PTSD specialty care, Scherrer and colleagues found significant reduction in incident type 2 diabetes during 2 to 6 years of follow-up among patients with but not without clinically meaningful PTSD improvement. These findings suggest that clinically meaningful reductions in PTSD symptoms are associated with a lower risk of type 2 diabetes, whether through treatment or spontaneous improvement.
Meta-analysis of Delay Discounting in Psychiatric Disorders
Delay discounting is a behavioral economic index of impulsive preferences for smaller immediate or larger delayed rewards, which may be abnormal in psychiatric disorders. Amlung and colleagues conducted a meta-analysis of 43 studies on delay discounting in people with 8 diagnostic categories of psychiatric disorders and found significantly steeper discounting for individuals with a psychiatric disorder compared with control individuals except those with anorexia nervosa, who exhibited significantly shallower discounting; data were limited in posttraumatic stress disorder. These results provide empirical support for delay discounting as a transdiagnostic process across most psychiatric disorders.
Poorer Methylation Status and Risk of Dementia
Methylation status, eg, vitamin B12- and folate-dependent conversion from homocysteine to methionine, is important for normal brain function and may also be associated with dementia. Hooshmand and colleagues examined data from 2570 participants of the Swedish National Study on Aging and Care in Kungsholmen and found that a higher methionine to homocysteine ratio in participants was associated with decreased risk of incident dementia and Alzheimer disease. These results support the hypothesis that a better methylation status may be beneficial for the structure and functioning of the brain.
Highlights. JAMA Psychiatry. 2019;76(11):1109. doi:10.1001/jamapsychiatry.2018.3010
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