STIM1 GoF Mutants: Genotype-Phenotype Relationships Across the Stormorken/TAM/YPS Spectrum.

Store-operated Calcium (Ca2+) entry (SOCE), mediated by stromal interaction molecule 1 (STIM1) and Orai1, is a central pathway controlling intracellular Ca2+ homeostasis. Gain-of-function (GoF) mutations in STIM1 cause a spectrum of clinically overlapping disorders historically classified as Stormorken Syndrome (STK), tubular aggregate myopathy (TAM), and York Platelet Syndrome (YPS). However, increasing evidence indicates that these entities could represent a shared disease spectrum rather than distinct conditions. At the molecular level, STIM1 activation is governed by a series of autoinhibitory checkpoints that maintain the protein in a tightly controlled resting state. GoF mutations disrupt these regulatory constraints, leading to dysregulated SOCE activity that is frequently, but not uniformly, associated with constitutive channel activation depending on the specific mutation and cellular context. While many disease-associated variants localize to the EF hand, a highly conserved helix-loop-helix Ca2+ binding motif, and the CC1 (coiled-coil 1) domain involved in molecular regulation of STIM1 activation, an increasing number of mutations in the C-terminal region further expands the mechanistic and clinical spectrum. In this review, we summarize current concepts of molecular STIM1 activation and discuss how distinct mutations perturb specific regulatory elements of the protein. By systematically integrating published case reports into a comprehensive overview, including a mutation-phenotype correlation table, we highlight the remarkable variability in and incomplete penetrance of clinical manifestations.