Characterizing the functional consequences of haploinsufficiency of NELF-A (WHSC2) and SLBP identifies novel cellular phenotypes in Wolf-Hirschhorn syndrome.

Wolf-Hirschhorn syndrome (WHS) is a contiguous gene deletion disorder associated with the distal part of the short arm of chromosome 4 (4p16.3). Employing a unique panel of patient-derived cell lines with differing-sized 4p deletions, we provide evidence that haploinsufficiency of SLBP and/or WHSC2 (NELF-A) contributes to several novel cellular phenotypes of WHS, including delayed progression from S-phase into M-phase, reduced DNA replication in asynchronous culture and altered higher order chromatin assembly. The latter is evidenced by reduced histone-chromatin association, elevated levels of soluble chaperone-bound histone H3 and increased sensitivity to micrococcal nuclease digestion in WHS patient-derived cells. We also observed increased camptothecin-induced inhibition of DNA replication and hypersensitivity to killing. Our work provides a novel pathogenomic insight into the aetiology of WHS by describing it, for the first time, as a disorder of impaired chromatin reorganization. Delayed cell-cycle progression and impaired DNA replication likely underlie or contribute to microcephaly, pre- and postnatal growth retardation, which constitute the core clinical features of WHS.

Optimizing health and nutrition status of migrant construction workers consuming multiple micronutrient fortified rice in Singapore.

INTRODUCTION: A well-nourished workforce is instrumental in eradicating hunger, alleviating poverty, and spurring economic growth. A fifth of the total workforce in high-income countries are migrant workers. Despite the accessibility of nutritious foods in high-income countries, migrant workers often rely on nutrient-poor diets largely consisting of empty calories, which in turn leads to vitamin and mineral deficiency, also called hidden hunger, and resultant productivity loss. Here, we study the magnitude of hidden hunger in male migrant construction workers in Singapore and investigate the impact of consuming fortified rice for 6 consecutive months on the nutrition and health status of these workers. METHODS: 140 male migrant workers aged 20-51 years of either Bangladeshi or Indian ethnicity from a single dormitory in Singapore volunteered to participate in the study. In total, 133 blood samples were taken at the start of the study and were used to assess vitamin B12, hemoglobin, ferritin, folate, and zinc levels; a sub-sample underwent for homocysteine testing. Anthropometric measurements and vital signs, such as blood pressure, were recorded before and after the intervention. RESULTS: The results show that vitamin and mineral deficiency was present, especially folate (59% of workers deficient) and vitamin B12 (7% deficient, 31% marginally deficient). The consumption of fortified rice significantly improved the vitamin, iron and zinc level in the workers and significantly reduced the systolic blood pressure amongst the Bangladeshi migrant workers, specifically. CONCLUSION: Our study demonstrates that fortified rice may have a positive impact on male migrant construction worker health and nutrition status at the workplace.

A microdeletion proximal of the critical deletion region is associated with mild Wolf-Hirschhorn syndrome.

It is generally accepted that the facial phenotype of Wolf-Hirschhorn syndrome is caused by deletions of either Wolf-Hirschhorn critical regions 1 or 2 (WHSCR 1-2). Here, we identify a 432 kb deletion located 600 kb proximal to both WHSCR1-2 in a patient with a WHS facial phenotype. Seven genes are underlying this deletion region including FAM193a, ADD1, NOP14, GRK4, MFSD10, SH3BP2, TNIP2. The clinical diagnosis of WHS facial phenotype was confirmed by 3D facial analysis using dense surface modeling. Our results suggest that the WHSCR1-2 flanking sequence contributes directly or indirectly to the severity of WHS. Sequencing the Wolf-Hirschhorn syndrome candidate 1 and 2 genes did not reveal any mutations. Long range position effects of the deletion that could influence gene expression within the WHSCR were excluded in EBV cell lines derived from patient lymphoblasts. We hypothesize that either (1) this locus harbors regulatory sequences which affect gene expression in the WHSCR1-2 in a defined temporal and spatial developmental window or (2) that this locus is additive to deletions of WHSCR1-2 increasing the phenotypic expression.

Telomere healing following DNA polymerase arrest-induced breakages is likely the main mechanism generating chromosome 4p terminal deletions.

Constitutional developmental disorders are frequently caused by terminal chromosomal deletions. The mechanisms and/or architectural features that might underlie those chromosome breakages remain largely unexplored. Because telomeres are the vital DNA protein complexes stabilizing linear chromosomes against chromosome degradation, fusion, and incomplete replication, those terminal-deleted chromosomes acquired new telomeres either by telomere healing or by telomere capture. To unravel the mechanisms leading to chromosomal breakage and healing, we sequenced nine chromosome 4p terminal deletion boundaries. A computational analysis of the breakpoint flanking region, including 12 previously published pure terminal breakage sites, was performed in order to identify architectural features that might be involved in this process. All terminal 4p truncations were likely stabilized by telomerase-mediated telomere healing. In the majority of breakpoints multiple genetic elements have a potential to induce secondary structures and an enrichment in replication stalling site motifs were identified. These findings suggest DNA replication stalling-induced chromosome breakage during early development is the first mechanistic step leading toward terminal deletion syndromes.

An experimental loop design for the detection of constitutional chromosomal aberrations by array CGH.

BACKGROUND: Comparative genomic hybridization microarrays for the detection of constitutional chromosomal aberrations is the application of microarray technology coming fastest into routine clinical application. Through genotype-phenotype association, it is also an important technique towards the discovery of disease causing genes and genomewide functional annotation in human. When using a two-channel microarray of genomic DNA probes for array CGH, the basic setup consists in hybridizing a patient against a normal reference sample. Two major disadvantages of this setup are (1) the use of half of the resources to measure a (little informative) reference sample and (2) the possibility that deviating signals are caused by benign copy number variation in the "normal" reference instead of a patient aberration. Instead, we apply an experimental loop design that compares three patients in three hybridizations. RESULTS: We develop and compare two statistical methods (linear models of log ratios and mixed models of absolute measurements). In an analysis of 27 patients seen at our genetics center, we observed that the linear models of the log ratios are advantageous over the mixed models of the absolute intensities. CONCLUSION: The loop design and the performance of the statistical analysis contribute to the quick adoption of array CGH as a routine diagnostic tool. They lower the detection limit of mosaicisms and improve the assignment of copy number variation for genetic association studies.

Pathogenic significance of deletions distal to the currently described Wolf-Hirschhorn syndrome critical regions on 4p16.3.

Within recent years, numerous individuals have been identified with terminal 4p microdeletions distal to the currently described critical regions for the Wolf-Hirschhorn syndrome (WHS). Some of these individuals do not display features consistent with WHS whereas others have a clinical phenotype with some overlap to the WHS phenotype. In this review we discuss the genetic and clinical presentation of these cases in an attempt to understand the consequence of monosomy of the genes distal to the proposed critical regions and identify the distal boundary for pathogenic genes involved in components of the WHS phenotype.

Fine-grained facial phenotype-genotype analysis in Wolf-Hirschhorn syndrome.

Wolf-Hirschhorn syndrome is caused by anomalies of the short arm of chromosome 4. About 55% of cases are due to de novo terminal deletions, 40% from unbalanced translocations and 5% from other abnormalities. The facial phenotype is characterized by hypertelorism, protruding eyes, prominent glabella, broad nasal bridge and short philtrum. We used dense surface modelling and pattern recognition techniques to delineate the milder facial phenotype of individuals with a small terminal deletion (breakpoint within 4p16.3) compared to those with a large deletion (breakpoint more proximal than 4p16.3). Further, fine-grained facial analysis of several individuals with an atypical genotype and/or phenotype suggests that multiple genes contiguously contribute to the characteristic Wolf-Hirschhorn syndrome facial phenotype.

Duplication of the Wolf-Hirschhorn syndrome critical region causes neurodevelopmental delay.

Wolf-Hirschhorn Syndrome (WHS) is caused by deletions on chromosome 4p and is clinically well defined. Genotype-phenotype correlations of patients with WHS point to a critical locus to be responsible for the main characteristics of this disorder. Submicroscopic duplications of this region, however, are not known. Here we report a patient with an interstitial 560 kb duplication overlapping this critical locus. The present case shows that not only deletions but also duplications of the Wolf-Hirshhorn critical region cause mental retardation and multiple congenital anomalies. Interestingly, the duplication phenotype overlaps partially with the deletion phenotype. However, his facial phenotype differs from the typical WHS gestalt.

Nuclear speckles and nucleoli targeting by PIP2-PDZ domain interactions.

PDZ (Postsynaptic density protein, Disc large, Zona occludens) domains are protein-protein interaction modules that predominate in submembranous scaffolding proteins. Recently, we showed that the PDZ domains of syntenin-1 also interact with phosphatidylinositol 4,5-bisphosphate (PIP2) and that this interaction controls the recruitment of the protein to the plasma membrane. Here we evaluate the general importance of PIP2-PDZ domain interactions. We report that most PDZ proteins bind weakly to PIP2, but that syntenin-2, the closest homolog of syntenin-1, binds with high affinity to PIP2 via its PDZ domains. Surprisingly, these domains target syntenin-2 to nuclear PIP2 pools, in nuclear speckles and nucleoli. Targeting to these sites is abolished by treatments known to affect these PIP2 pools. Mutational and domain-swapping experiments indicate that high-affinity binding to PIP2 requires both PDZ domains of syntenin-2, but that its first PDZ domain contains the nuclear PIP2 targeting determinants. Depletion of syntenin-2 disrupts the nuclear speckles-PIP2 pattern and affects cell survival and cell division. These findings show that PIP2-PDZ domain interactions can directly contribute to subnuclear assembly processes.