NM_000455.5(STK11):c.129_141del is a 13bp frameshift deletion in exon 1 producing p.(Lys44SerfsTer3), predicted to trigger nonsense-mediated decay and complete loss of STK11 protein expression. STK11 loss of function is a well-established mechanism for Peutz-Jeghers syndrome (autosomal dominant).¹ This variant is absent from gnomAD v2.1 and v4.1 population databases, consistent with a rare pathogenic variant.² The variant has not been reported in ClinVar, COSMIC, or any published patient cohort evaluated in this assessment.³ No variant-specific functional studies, segregation data, or de novo observations were identified in the literature. Five OncoKB-curated STK11 publications were reviewed; none mention this variant.⁴ Applying generic ACMG/AMP 2015 classification rules (PMID:25741868): PVS1 (very_strong) + PM2 (moderate) meets the Likely Pathogenic combination threshold (1 Very Strong + 1 Moderate).⁵