Simon P. Brooks

X-linked cataract and Nance-Horan syndrome are allelic disorders

Nance-Horan syndrome (NHS) is an X-linked developmental disorder characterized by congenital cataract, dental anomalies, facial dysmorphism and, in some cases, mental retardation. Protein truncation mutations in a novel gene (NHS) have been identified in patients with this syndrome. We previously mapped X-linked congenital cataract (CXN) in one family to an interval on chromosome Xp22.13 which encompasses the NHS locus; however, no mutations were identified in the NHS gene. In this study, we show that NHS and X-linked cataract are allelic diseases. Two CXN families, which were negative for mutations in the NHS gene, were further analysed using array comparative genomic hybridization. CXN was found to be caused by novel copy number variations: a complex duplication–triplication re-arrangement and an intragenic deletion, predicted to result in altered transcriptional regulation of the NHS gene. Furthermore, we also describe the clinical and molecular analysis of seven families diagnosed with NHS, identifying four novel protein truncation mutations and a novel large deletion encompassing the majority of the NHS gene, all leading to no functional protein. We therefore show that different mechanisms, aberrant transcription of the NHS gene or no functional NHS protein, lead to different diseases. Our data highlight the importance of copy number variation and non-recurrent re-arrangements leading to different severity of disease and describe the potential mechanisms involved.

The Nance-Horan Syndrome protein encodes a functional WAVE Homology Domain (WHD) and is important for co-ordinating actin remodelling and maintaining cell morphology

Nance–Horan syndrome (NHS) is an X-linked developmental disorder, characterized by bilateral congenital cataracts, dental anomalies, facial dysmorphism and mental retardation. Null mutations in a novel gene, NHS, cause the syndrome. The NHS gene appears to have multiple isoforms as a result of alternative transcription, but a cellular function for the NHS protein has yet to be defined. We describe NHS as a founder member of a new protein family (NHS, NHSL1 and NHSL2). Here, we demonstrate that NHS is a novel regulator of actin remodelling and cell morphology. NHS localizes to sites of cell–cell contact, the leading edge of lamellipodia and focal adhesions. The N-terminus of isoforms NHS-A and NHS-1A, implicated in the pathogenesis of NHS, have a functional WAVE homology domain that interacts with the Abi protein family, haematopoietic stem/progenitor cell protein 300 (HSPC300), Nap1 and Sra1. NHS knockdown resulted in the disruption of the actin cytoskeleton. We show that NHS controls cell morphology by maintaining the integrity of the circumferential actin ring and controlling lamellipod formation. NHS knockdown led to a striking increase in cell spreading. Conversely, ectopic overexpression of NHS inhibited lamellipod formation. Remodelling of the actin cytoskeleton and localized actin polymerization into branched actin filaments at the plasma membrane are essential for mediating changes in cell shape, migration and cell contact. Our data identify NHS as a new regulator of actin remodelling. We suggest that NHS orchestrates actin regulatory protein function in response to signalling events during development.

New mutations in the NHS gene in Nance-Horan Syndrome families from the Netherlands

Mutations in the NHS gene cause Nance–Horan Syndrome (NHS), a rare X-chromosomal recessive disorder with variable features, including congenital cataract, microphthalmia, a peculiar form of the ear and dental anomalies. We investigated the NHS gene in four additional families with NHS from the Netherlands, by dHPLC and direct sequencing. We identified an unique mutation in each family. Three out of these four mutations were not reported before. We report here the first splice site sequence alteration mutation and three protein truncating mutations. Our results suggest that X-linked cataract and NHS are allelic disorders.

Another look at follicular lymphoma: Immunophenotypic and molecular analyses identify distinct follicular lymphoma subgroups

The aim of this study was to analyse the immunophenotypic and molecular features of a large series of follicular lymphomas, focusing in particular on atypical cases that fail to express CD10 and/or bcl‐2. Such cases present diagnostic pitfalls, especially with regard to the differential diagnosis from follicular hyperplasia and marginal zone B‐cell lymphoma. Therefore, we also included an immunohistochemical evaluation of stathmin, which is strongly expressed by germinal centre B cells, as a putative new marker for follicular lymphomas, particularly those with an atypical phenotype.

Refinement of the X-linked cataract locus (CXN) and gene analysis for CXN and Nance-Horan syndrome (NHS).

The X-linked congenital cataract (CXN) locus has been mapped to a 3-cM (approximately 3.5 Mb) interval on chromosome Xp22.13, which is syntenic to the mouse cataract disease locus Xcat and encompasses the recently refined Nance-Horan syndrome (NHS) locus. A positional cloning strategy has been adopted to identify the causative gene. In an attempt to refine the CXN locus, seven microsatellites were analysed within 21 individuals of a CXN family. Haplotypes were reconstructed confirming disease segregation with markers on Xp22.13. In addition, a proximal cross-over was observed between markers S3 and S4, thereby refining the CXN disease interval by approximately 400 Kb to 3.2 Mb, flanked by markers DXS9902 and S4. Two known genes (RAI2and RBBP7) and a novel gene (TL1) were screened for mutations within an affected male from the CXN family and an NHS family by direct sequencing of coding exons and intron-exon splice sites. No mutations or polymorphisms were identified, therefore excluding them as disease-causative in CXN and NHS. In conclusion, the CXN locus has been successfully refined and excludes PPEF1as a candidate gene. A further three candidates were excluded based on sequence analysis. Future positional cloning efforts will focus on the region of overlap between CXN, Xcat, and NHS.