Role of Synaptosomal-Associated Protein 25 Gene in Clinical Response to Methylphenidate Among Turkish Pediatric ADHD Cohort

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Introduction: Methylphenidate (MPH) is a first-line treatment for attention-deficit/hyperactivity disorder (ADHD). MPH blocks dopamine and norepinephrine transporters, increasing synaptic catecholamine levels. Neurotransmitter release depends on presynaptic vesicle docking and fusion mediated by synaptosomal-associated protein 25 kDa (SNAP-25), a target-soluble NSF attachment protein receptor (SNARE) protein encoded by the SNAP-25 gene. This study aimed to investigate whether genetic variations in the SNAP-25 gene contribute to variability in clinical response to MPH in pediatric patients with ADHD. Methods: Forty-two children and adolescents aged 6–16 years who presented to the outpatient clinic and were diagnosed with ADHD according to DSM-5-TR criteria were prospectively treated with MPH for two months. Clinical response was assessed using the Conners’ Parent Rating Scale (CPRS) and the Turgay DSM-Based Disruptive Behavior Disorders Rating Scale (T-DBDRS). SNAP-25 exons were sequenced using targeted next-generation sequencing (tNGS). Results: Three common variants in SNAP-25 (rs363006, rs362585, and rs362998) were analyzed. Based on CPRS-defined outcomes, a significant association was observed between the rs362998:C > T polymorphism and response to MPH. In the genotypic model, the CT genotype was more frequent among responders (34.78%) than non-responders (5.26%) (p = 0.026, FDR-adjusted p = 0.049). In the dominant model, CT + TT genotypes were more frequent in responders (p = 0.026, FDR-adjusted p = 0.049). The allelic model showed a higher frequency of the T allele in responders (p = 0.036, FDR-adjusted p = 0.049). Haplotype analysis showed that rs362585, rs362998, and rs363006 formed a single haplotype block. The GC haplotype (rs362585–rs362998) was more frequent among non-responders (p = 0.016), while the GCG haplotype showed a similar trend among non-responders, although it did not reach statistical significance (p = 0.058). However, no haplotype association remained statistically significant after FDR correction. A novel 3′UTR variant (c.*54T > C; chr20:10306251T > C) was also identified. Conclusions: These exploratory findings suggest a potential association between SNAP-25 rs362998:C > T and MPH response in pediatric ADHD; however, the small sample size and wide confidence intervals warrant cautious interpretation and validation in larger, independent cohorts.