Beyond Haploinsufficiency: Protein Domain and Variant Class Shape Language Outcomes in SYNGAP1-DEE

Missense variants in the SynGAP C2 domain (aa248-392; n=28) in PATRE SYNGAP1 registry participants are linked to markedly poorer expressive language (median 1 vs 2; age-adjusted OR 0.16).

• Why it matters: Language development in SYNGAP1-DEE varies despite a common haploinsufficiency framework, and targeted therapies like ASOs make genotype-specific outcome differences critical to interpret.
• What they did: Cross-sectional caregiver-reported outcomes from 440 participants were analyzed by SynGAP protein domain (seven regions) and variant class (missense n=79; truncating/splicing n=255), using age-adjusted regression with Benjamini-Hochberg correction.
• The result: C2 missense variants also showed impaired functional communication (OR 0.23) and reduced two-word phrase acquisition (7.1% vs 52.0%; q=0.0023), while PH truncating/splicing variants (aa103-247; n=50) showed better expressive language (OR 3.52) and higher two-word phrase rates (62.0% vs 31.5%).

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