Developmental dynamics of voltage-gated sodium channel isoform expression in the human and mouse brain.

BACKGROUND: Genetic variants in the voltage-gated sodium channels SCN1A, SCN2A, SCN3A, and SCN8A are leading causes of epilepsy, developmental delay, and autism spectrum disorder. The mRNA splicing patterns of all four genes vary across development in the rodent brain, including mutually exclusive copies of the fifth protein-coding exon detected in the neonate (5N) and adult (5A). A second pair of mutually exclusive exons is reported in SCN8A only (18N and 18A). We aimed to quantify the expression of individual exons in the developing human brain. METHODS: RNA-seq data from 783 human brain samples across development were analyzed to estimate exon-level expression. Developmental changes in exon utilization were validated by assessing intron splicing. Exon expression was also estimated in RNA-seq data from 58 developing mouse neocortical samples. RESULTS: In the mature human neocortex, exon 5A is consistently expressed at least 4-fold higher than exon 5N in all four genes. For SCN2A, SCN3A, and SCN8A, a brain-wide synchronized 5N to 5A transition occurs between 24 post-conceptual weeks (2nd trimester) and 6 years of age. In mice, the equivalent 5N to 5A transition begins at or before embryonic day 15.5. In SCN8A, over 90% of transcripts in the mature human cortex include exon 18A. Early in fetal development, most transcripts include 18N or skip both 18N and 18A, with a transition to 18A inclusion occurring from 13 post-conceptual weeks to 6 months of age. No other protein-coding exons showed comparably dynamic developmental trajectories. CONCLUSIONS: Exon usage in SCN1A, SCN2A, SCN3A, and SCN8A changes dramatically during human brain development. These splice isoforms, which alter the biophysical properties of the encoded channels, may account for some of the observed phenotypic differences across development and between specific variants. Manipulation of the proportion of splicing isoforms at appropriate stages of development may act as a therapeutic strategy for specific mutations or even epilepsy in general.

Medical Comorbidity of Attention-Deficit/Hyperactivity Disorder in US Adolescents.

Understanding patterns of medical comorbidity in attention-deficit/hyperactivity disorder (ADHD) may lead to better treatment of affected individuals as well as aid in etiologic study of disease. This article provides the first systematic evaluation on the medical comorbidity of ADHD in a nationally representative sample (National Comorbidity Replication Survey-Adolescent Supplement; N = 6483) using formal diagnostic criteria. Survey-weighted odds ratios adjusted for demographics, additional medical, and mental disorders were calculated for associations between ADHD and medical conditions. Models adjusted for demographics revealed significantly increased odds of allergy, asthma, enuresis, headache/migraine, and serious stomach or bowel problems. After adjusting for comorbidity, across the medical conditions, enuresis and serious stomach problems were the strongest correlates of ADHD. These findings confirm the pervasive medical comorbidity of ADHD reported in previous clinical and community-based studies. The intriguing salience of enuresis and serious stomach or bowel conditions may also provide an important clue to multisystem involvement in ADHD.