AIM Adrenocorticotropic hormone (ACTH) has been used as the major therapy for infantile spasms since 1958 because it effectively suppresses seizures; it also normalizes the electroencephalogram in the short-term treatment of infantile spasms. G protein-regulated inducer of neurite outgrowth 1 (GRIN1, also known as N-methyl-D-aspartate receptor 1, NMDAR1), a glutamate receptor, is the main component of functional N-methyl-D-aspartic acid receptors that are involved in the glucocorticoid-induced neuronal damage. Thus, it may be a candidate gene to be tested for responsiveness to ACTH in infantile spasms. In the present study, polymorphisms in the GRIN1 gene in infantile spasms were investigated using a case-control design.METHOD Twelve single nucleotide polymorphisms in the GRIN1 gene were genotyped in a Chinese case-control set consisting of 97 unrelated patients with infantile spasms (60 males, 37 females; mean age 6.4mo, SD 2.7) and 96 healthy individuals (63 males, 33 females; mean age 7.3mo, SD 3.8). Association analysis was performed on the genotyped data.RESULTS Five estimated haplotypes with a frequency of more than 3% were detected. Results of the study showed that responsiveness to treatment with ACTH in homozygous carriers of the CTA haplotype was higher than that in heterozygous carriers and non-carriers (p=0.022). Furthermore, CTG, a rare haplotype, was strongly associated with infantile spasms (p=0.013).
INTERPRETATIONThe results suggest that haplotypes of GRIN1 may influence responsiveness to ACTH. The findings necessitate further study for confirmation.Infantile spasms is an age-specific epileptic encephalopathy that occurs in infancy and is considered refractory to conventional antiepileptic drugs. Adrenocorticotropic hormone (ACTH) has been identified as a drug that is effective in the treatment of infantile spasms.1 However, some patients are clinically resistant to ACTH therapy, and the exact molecular mechanism remains to be explained. Data from pharmacogenetic studies of epilepsy have shown that the variations in some receptor genes can contribute to the pathogenesis and mechanisms of antiepileptic drug resistance towards infantile spasms.Several models and hypotheses have been proposed to explain the pathogenesis of infantile spasms and its unique sensitivity to ACTH.2 However, none of them has been accepted as a satisfactory model for drug testing. Recently, the clinical features of flexion seizures induced by N-methyl-Daspartic acid (NMDA) in rat pups have been shown to be correlated with human infantile spasms. For instance, flexion spasms and electroencephalogram (EEG) in the rat model correlate with ictal electrodecrement, or after discharges in infantile spasms.3 Interestingly, this model, which is based on the prenatally 'stressed' brain, also shows an acute and partial response to ACTH treatment. In addition, an expression peak of the NMDA receptor was observed in the cortex and hippocampus of children aged 1 to 3 years old. In contrast, the axon and dendrite are mostly developed in ...