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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.

TRF2 is a telomere-binding protein with roles in telomere protection and telomere-length regulation. The fact that TRF2 is up-regulated in some human tumors suggests a role of TRF2 in cancer. Mice that overexpress TRF2 in the skin, K5TRF2 mice, show critically short telomeres and are susceptible to UV-induced carcinogenesis as a result of deregulated XPF/ERCC1 activity, a nuclease involved in UV damage repair. Here we demonstrate that, when in combination with telomerase deficiency, TRF2 acts as a very potent oncogene in vivo. In particular, we show that telomerase deficiency dramatically accelerates TRF2-induced epithelial carcinogenesis in K5TRF2/Terc−/− mice, coinciding with increased chromosomal instability and DNA damage. Telomere recombination is also increased in these mice, suggesting that TRF2 favors the activation of alternative telomere maintenance mechanisms. Together, these results demonstrate that TRF2 increased expression is a potent oncogenic event that along with telomerase deficiency accelerates carcinogenesis, coincidental with a derepression of telomere recombination. These results are of particular relevance given that TRF2 is up-regulated in some human cancers. Furthermore, these data suggest that telomerase inhibition might not be effective to cease the growth of TRF2-overexpressing tumors.