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Next-generation sequencing is a powerful tool for the discovery of genes related to neurodevelopmental disorders (NDDs). Here, we report the identification of a distinct syndrome due to de novo or inherited heterozygous mutations in Tousled-like kinase 2 (TLK2) in 38 unrelated individuals and two affected mothers, using whole-exome and whole-genome sequencing technologies, matchmaker databases, and international collaborations. Affected individuals had a consistent phenotype, characterized by mild-borderline neurodevelopmental delay (86%), behavioral disorders (68%), severe gastro-intestinal problems (63%), and facial dysmorphism including blepharophimosis (82%), telecanthus (74%), prominent nasal bridge (68%), broad nasal tip (66%), thin vermilion of the upper lip (62%), and upslanting palpebral fissures (55%). Analysis of cell lines from three affected individuals showed that mutations act through a loss-of-function mechanism in at least two case subjects. Genotype-phenotype analysis and comparison of computationally modeled faces showed that phenotypes of these and other individuals with loss-of-function variants significantly overlapped with phenotypes of individuals with other variant types (missense and C-terminal truncating). This suggests that haploinsufficiency of TLK2 is the most likely underlying disease mechanism, leading to a consistent neurodevelopmental phenotype. This work illustrates the power of international data sharing, by the identification of 40 individuals from 26 different centers in 7 different countries, allowing the identification, clinical delineation, and genotype-phenotype evaluation of a distinct NDD caused by mutations in TLK2.

Human adenovirus (HAdV) E1B-55K is a multifunctional regulator of productive viral replication and oncogenic transformation in nonpermissive mammalian cells. These functions depend on E1B-55K's posttranslational modification with the SUMO protein and its binding to HAdV E4orf6. Both early viral proteins recruit specific host factors to form an E3 ubiquitin ligase complex that targets antiviral host substrates for proteasomal degradation. Recently, we reported that the PML-NB associated factor Daxx represses efficient HAdV productive infection and is proteasomally degraded via a SUMO-E1B-55K-dependent, E4orf6-independent pathway, the details of which remained to be established. RNF4, a cellular SUMO-targeted ubiquitin ligase (STUbL), induces ubiquitinylation of specific SUMOy lated proteins and plays an essential role during DNA repair. Here, we show that E1B-55K recruits RNF4 to the insoluble nuclear matrix fraction of the infected cell to support RNF4/Daxx association, promoting Daxx PTM and thus inhibiting this antiviral factor. Removing RNF4 from infected cells using RNA interference resulted in blocking the proper establishment of viral replication centers and significantly diminished viral gene expression. These results provide a model for how HAdV antagonize the antiviral host responses by exploiting the functional capacity of cellular STUbLs. Thus, RNF4 and its STUbL function represent a positive factor during lytic infection and a novel candidate for future therapeutic antiviral intervention strategies.IMPORTANCE Daxx is a PML-NB-associated transcription factor that was recently shown to repress efficient HAdV productive infection. To counteract this antiviral measurement during infection, Daxx is degraded via a novel pathway including viral E1B-55K and host proteasomes. This virus-mediated degradation is independent of the classical HAdV E3 ubiquitin ligase complex, which is essential during viral infection to target other host antiviral substrates. To maintain a productive viral life cycle, HAdV E1B-55K early viral protein inhibits the chromatin-remodeling factor Daxx in a SUMO-dependent manner. In addition, viral E1B-55K protein recruits the STUbL RNF4 and sequesters it into the insoluble fraction of the infected cell. E1B-55K promotes complex formation between RNF4-and E1B-55K-targeted Daxx protein, supporting Daxx posttranslational modification prior to functional inhibition. Hence, RNF4 represents a novel host factor that is beneficial for HAdV gene expression by supporting Daxx counteraction. In this regard, RNF4 and other STUbL proteins might represent novel targets for therapeutic intervention.

To the Editor: Subtelomeric screening and FISH analysis of a 13-year-old girl with severe mental retardation, intrauterine growth retardation, microcephaly, facial dysmorphisms, hypoplastic kidney, and short hands and feet but without congenital diaphragmatic hernia (CDH [MIM 142340]) allowed us to find a de novo deletion in 15q26.1–26.2. That region, as shown by Klaassens et al. (2005) in a study published in the May issue of the Journal, contains a candidate region for CDH, a condition that occurrs in ∼1 of 3,000 newborns and is associated with a 30%–60% mortality rate, with significant morbidity among survivors (Harrison et al. 1994; Nobuhara et al. 1996). The etiology of this condition is barely known and, in most cases, is considered idiopathic, whereas ∼15% of patients with CDH show chromosomal abnormalities. Recently, Biggio et al. (2004) reported on a child with a 15q26.1 deletion showing CDH, coarctation of the aorta, and dysmorphic features, suggesting this region as the possible candidate locus for CDH. Furthermore, the authors proposed myocyte-specific enhancer factor–2A (MEF2A [MIM 600660]) as a candidate gene for CDH, coding for a protein playing a critical role in the control of muscle differentiation and development. Klaassens et al. (2005) found 7% numerical and 5% structural chromosome abnormalities in 200 CDH patients. The most frequent chromosome abnormality was 15q deletion. Eventually, they determined the size of the deletions in seven patients with CDH. They incorporated data from two patients with terminal 15q deletions without CDH, and data from one patient with a small 15q interstitial deletion and CDH. A minimal deletion region, spanning ∼5 Mb at chromosome bands 15q26.1–15q26.2, has been suggested by these authors. Two of the known genes of this region, namely, NR2F2 (MIM 107773) and CDH2 (MIM 602119), were considered to be the best candidates for CDH. To better define the deletion in our patient, FISH experiments were carried out with a set of linearly ordered BACs selected by human NCBI Map Viewer (build 35.1) and provided by the Sanger Institute. This analysis showed that the BAC RP11-386M24, localized to chromosome band 15q26.1 (∼9.0 Mb from the end of the chromosome), was the closest to the telomere that hybridized on both chromosomes in all examined metaphases. The immediately more centromeric CTD—2313J17 BAC showed signals of different intensities on the 15q telomeres, suggesting that the breakpoint lay within this BAC, whereas the overlapping RP11-437B10 BAC and all the distally placed BACs showed no hybridization signal (data not shown). We thus compared our results with the most significant previously characterized 15q deletions, including ring chromosome 15, unbalanced translocations, and pure 15qter monosomies, either associated with the CDH phenotype or not. As shown in figure 1, no clear critical region can be drawn from these data, essentially because case 12 with CDH carried a ring (15) resulting in a smaller deletion than cases 1, 2, and 3, without CDH. At least two hypotheses can be made to explain these contradictory data. First, it is possible that haploinsufficiency of the CDH locus has a reduced penetrance and that data from patients without CDH could be useless in establishing the critical region. If this is true, the candidate region is restricted to ∼3.5 Mb (fig. 1) and includes the NR2F2 gene, but its telomeric limit is more distal than that defined by Klaassens et al. (2005), which was derived from a deletion of a patient without CDH (fig. 1, case 13). On the other hand, drawing genotype-phenotype relationships may be difficult in ring carriers because of the potential instability of ring chromosomes that can be associated with gain or loss of genetic material in other tissues (Tumer et al. 2004). If we omit ring cases from the analysis, then the critical region would be narrowed to a 0.7-Mb genomic portion (fig. 1). The NR2F2 gene, in this case, would be located outside this putative critical region. Figure 1 Graphical representation of 15q deletions in patients with and without CDH. The most significant BAC clones analyzed are shown on the left. Solid boxes represent deleted regions, hatched boxes indicate the uncertainty of the breakpoints, and open boxes ... The ST8 alpha-N-acetyl-neuraminide alpha-2, 8-sialyltransferase 2 gene (ST8SIA2 [MIM 602546]) is the unique known gene in this region and encodes for a type II membrane protein that catalyzes the transfer of sialic acid from CMP-sialic acid to the neural cell adhesion molecules (NCAMs) (Ong et al. 1998). The ST8SIA2 gene is expressed in many tissues during development (Angata et al. 1997). Evidence suggests that polysialylated NCAMs promote cell migration and, thus, they are thought to play a critical role in development. More specifically, it has been shown that, during diaphragmatic morphogenesis, the expression of polysialylated NCAMs is tightly modulated along each stage of myogenesis (Allan and Greer 1998). Finally, although it is less likely, we cannot exclude the possibility that both the mentioned hypotheses are true. In this case, the critical region would be represented by the extent of the deletion in patient 8 (fig. 1). Additional findings are needed to refine the search for a CDH gene in 15q chromosome. However, it seems likely that NR2F2 and ST8SIA2 are the best candidates.