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Central nervous system stimulants are a commonly used first-line treatment option for attention-deficit/hyperactivity disorder (ADHD). Stimulants are generally well tolerated, with anorexia and insomnia the most common adverse effects. However, there are some concerns with long-term use of stimulants, such as potential growth delay. Historically, data regarding this long-term adverse effect have been conflicting. In this article, we review the newer data surrounding the effects of central nervous system stimulants on growth parameters in children with ADHD. We conducted a literature search of the PubMed database; only articles using ADHD criteria from the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition; Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision; and Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, were included to ensure the most up-to-date review of literature. Nine articles were identified for relevance and quality and are discussed in this review, describing clinical observations of height and weight of adolescent or pediatric patients receiving stimulant medications for ADHD therapy. In summary, this review points toward potential associations between duration of treatment and higher doses of stimulants with decreased weight and body mass index. Furthermore, this review demonstrates that evidence is still conflicting regarding the relationship between stimulant use and significant height decreases. Future studies with higher quality of evidence are needed to observe this potential adverse effect of stimulants in children and adolescents.

DNA damage encountered by DNA replication forks poses risks of genome destabilization, a precursor to carcinogenesis. Damage checkpoint systems cause cell cycle arrest, promote repair and induce programed cell death when damage is severe. Checkpoints are critical parts of the DNA damage response network that act to suppress cancer. DNA damage and perturbation of replication machinery causes replication stress, characterized by accumulation of single-stranded DNA bound by replication protein A (RPA), which triggers activation of ataxia telangiectasia and Rad3 related (ATR) and phosphorylation of the RPA32, subunit of RPA, leading to Chk1 activation and arrest. DNA-dependent protein kinase catalytic subunit (DNA-PKcs) [a kinase related to ataxia telangiectasia mutated (ATM) and ATR] has well characterized roles in DNA double-strand break repair, but poorly understood roles in replication stress-induced RPA phosphorylation. We show that DNA-PKcs mutant cells fail to arrest replication following stress, and mutations in RPA32 phosphorylation sites targeted by DNA-PKcs increase the proportion of cells in mitosis, impair ATR signaling to Chk1 and confer a G2/M arrest defect. Inhibition of ATR and DNA-PK (but not ATM), mimic the defects observed in cells expressing mutant RPA32. Cells expressing mutant RPA32 or DNA-PKcs show sustained H2AX phosphorylation in response to replication stress that persists in cells entering mitosis, indicating inappropriate mitotic entry with unrepaired damage.

Genotoxins and other factors cause replication stress that activate the DNA damage response (DDR), comprising checkpoint and repair systems. The DDR suppresses cancer by promoting genome stability, and it regulates tumor resistance to chemo- and radiotherapy. Three members of the phosphatidylinositol 3-kinase-related kinase (PIKK) family, ATM, ATR, and DNA-PK, are important DDR proteins. A key PIKK target is replication protein A (RPA), which binds single-stranded DNA and functions in DNA replication, DNA repair, and checkpoint signaling. An early response to replication stress is ATR activation, which occurs when RPA accumulates on ssDNA. Activated ATR phosphorylates many targets, including the RPA32 subunit of RPA, leading to Chk1 activation and replication arrest. DNA-PK also phosphorylates RPA32 in response to replication stress, and we demonstrate that cells with DNA-PK defects, or lacking RPA32 Ser4/Ser8 targeted by DNA-PK, confer similar phenotypes, including defective replication checkpoint arrest, hyper-recombination, premature replication fork restart, failure to block late origin firing, and increased mitotic catastrophe. We present evidence that hyper-recombination in these mutants is ATM-dependent, but the other defects are ATM-independent. These results indicate that DNA-PK and ATR signaling through RPA32 plays a critical role in promoting genome stability and cell survival in response to replication stress.