An improved <i>SMS</i> p.Gly56Ser mouse model of Snyder-Robinson syndrome reveals phenotypic parallels with clinical features

Snyder-Robinson syndrome (SRS), a rare X-linked disorder caused by pathogenic variants in spermine synthase (SMS), results in spermine deficiency and excessive spermidine accumulation. Previously reported mouse models exhibited reduced birthrate and survival of affected males, greatly limiting their experimental utility. Here we describe a new mouse model carrying the clinically relevant Sms p.Gly56Ser (SmsG56S) allele in which viable males are recovered at Mendelian ratios, enabling generation of adequately powered cohorts. Hemizygous males produce markedly reduced SMS protein across tissues, recreating the biochemical hallmark of SRS, an elevated spermidine:spermine ratio. SmsG56S/Y males exhibit reduced body size, altered body composition, decreased locomotor and exploratory behaviors, and reduced seizure threshold, aligning with clinical features reported in SRS patients. Serum LDL, HDL, and cholesterol levels were reduced, while brain histology revealed modest region-specific astrocytic changes. Comprehensive polyamine profiling revealed tissue-specific biochemical disturbances, highlighting putrescine elevation in the brain and informing development of translational strategies and windows for intervention. Overall, this improved model reproduces multiple key aspects of the human SRS phenotype and provides a robust platform for mechanistic studies and preclinical evaluation of therapies.