Kabuki syndrome (KS) is one of the classical, clinically well-known multiple anomalies/mental retardation syndromes, mainly characterized by a very distinctive facial appearance in combination with additional clinical signs such as developmental delay, short stature, persistent fingerpads, and urogenital tract anomalies. In our study, we sequenced all 54 coding exons of the recently identified MLL2 gene in 34 patients with Kabuki syndrome. We identified 18 distinct mutations in 19 patients, 11 of 12 tested de novo. Mutations were located all over the gene and included three nonsense mutations, two splice-site mutations, six small deletions or insertions, and seven missense mutations. We compared frequencies of clinical symptoms in MLL2 mutation carriers versus non-carriers. MLL2 mutation carriers significantly more often presented with short stature and renal anomalies (p = 0.026 and 0.031, respectively), and in addition, MLL2 carriers obviously showed more frequently a typical facial gestalt (17/19) compared with non-carriers (9/15), although this result was not statistically significant (p = 0.1). Mutation-negative patients were subsequently tested for mutations in ten functional candidate genes (e.g. MLL, ASC2, ASH2L, and WDR5), but no convincing causative mutations could be found. Our results indicate that MLL2 is the major gene for Kabuki syndrome with a wide spectrum of de novo mutations and strongly suggest further genetic heterogeneity.

Inappropriate nuclear factor (NF) jB activity is one major hallmark of B-cell malignancies and chronic lymphocytic leukemia (CLL). NFjB-dependent genes are involved in antiapoptosis, cell proliferation and metastasis and are responsible for survival and proliferation of tumors. However, the mechanisms of NFjB activity in CLL still need to be elucidated. Previously, we identified translocations in a region on chromosome 6q that encodes tumor necrosis factor alpha-induced protein 3, which is a key player in negative feedback loop regulation of NFjB. Inactivation of this ubiquitin-editing enzyme is involved in immunopathologies and in tumorigenesis. Frequent mutations in the A20 locus-leading to sustained NFjB activity-could be shown to play a dominant role in development of different B-cell malignancies. To check if A20 is involved in upregulation of NFjB activity in CLL, we sequenced Exons 2-9 of the A20 gene in 55 CLL DNA samples. Furthermore, we determined the methylation status of the promoter region in 63 CLL DNA samples and compared to 10 control DNAs of B cells from healthy donors. Contrary to reports from other B-cell malignancies, the A20 region showed neither mutations nor aberrant DNA methylation. Moreover, its expression could be confirmed by immunoblotting and showing comparable results to healthy B cells. These results indicate that malignant development in CLL differs from most of other B-cell malignancies, which show frequent inactivation of A20.