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). Interpretation The results suggest that haplotypes of GRIN1 may influence responsiveness to ACTH. The findings necessitate further study for confirmation.