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SUMMARYBackgroundKBG syndrome is a highly variable neurodevelopmental disorder and clinical diagnostic criteria have changed as new patients have been published. Both loss-of-function sequence variants and large deletions (CNVs) involving ANKRD11 have been involved in KBG, but no genotype-phenotype correlation has been reported to date. This study presents the clinical and molecular characteristics of 67 new patients with KBG syndrome and the results of the first genotype-phenotype correlation leveraging data on 273 patients previously published.Methods67 patients with KBG syndrome were recruited through a Spanish collaborative effort and were assessed using a custom phenotypic questionnaire. The frequency of all features was calculated. Manifestations present in >50% of the patients and a “severity score” were used to perform a genotype-phenotype correlation in the 340 KBG patients.ResultsNeurodevelopmental delay (95%), comorbidites (82.8%), macrodontia (80.9%), triangular face (71%), characteristic ears (76%), nose (75.9%) and eyebrows (67.3%) were the most prevalent features in the 67 patients. The genotype-phenotype correlation yielded significant associations with the triangular face (71.1% in patients with sequence variants vs 45.2% in CNVs, p=0.015), short stature (62.5% variants in exon 9 vs. 27.8% outside; p=0.009) and macrodontia (with larger deletions, p=0.028), ID/ADHD/ASD (70.4% in c.1903_1907del vs. 89.4%; p=0.012) and a higher phenotypic score in patients with sequence variants compared with CNVs (p=0.005).ConclusionsWe present a detailed phenotypic description of KBG syndrome in the largest series of patients reported to date, provide evidence of a genotype-phenotype correlation between some KBG features and specific ANKRD11 aberrations, and propose updated clinical diagnostic criteria based on our findings.