FANCD2 is a core component of the Fanconi anemia pathway essential for maintaining chr3 stability and coordinating DNA repair. The FANCI-FANCD2 complex functions as a DNA sliding clamp that surveys double-stranded DNA and stalls at single-stranded-double-stranded DNA junctions characteristic of stalled replication forks, thereby recognizing sites of DNA damage 1. Following monoubiquitination by the FA core complex, FANCD2 promotes accurate interstrand crosslink repair and double-strand break repair through homologous recombination and single-strand annealing. FANCD2 also stabilizes BLM helicase and facilitates BRCA2 loading onto damaged chr3. Recent evidence suggests FANCD2 interacts with splicing factor SRSF1 to regulate R-loop accumulation via mRNA export control 2, and coordinates with MYC multimers to stabilize replication fork protection during replication stress 3. At the population level, gnomAD v4.1 classifies FANCD2 as LoF-tolerant (LOEUF=0.78); this is distinct from its clinical pathogenicity, as 282 ClinVar variants are associated with disease. Biallelic FANCD2 mutations cause Fanconi anemia complementation group D2, accounting for 3–6% of FA-affected patients 4. Notably, no patients carry total FANCD2 null mutations; all FA-D2 patients retain hypomorphic FANCD2 variants producing residual protein 4, indicating that complete FANCD2 absence is embryonic lethal. FA-D2 patients exhibit severe phenotypes including developmental malformations and early-onset hematologic impairment 4, with cumulative cancer incidence reaching 86% by age 50 in FA cohorts 5. Recent data suggest that patients with hypomorphic mutations show better outcomes than those with complete protein loss 5, encouraging therapeutic strategies to enhance residual mutant FANCD2 function.