Nance-Horan syndrome (NHS; OMIM 302350) is a rare, X-linked syndrome characterized by bilateral congenital cataracts leading to profound vision loss, specific dental anomalies including characteristic screwdriver blade-shaped incisors, facial anomalies, and intellectual disability. It is caused by deleterious loss of function variants or deletions involving the NHS gene at Xp22.13. Heterozygous females often present with similar, but less severe features than affected males. We describe a relatively large cohort of eight new patients with NHS, including two patients with microdeletions including NHS who had classical presentations, and provide detailed descriptions of the clinical findings for both affected males and females. The spectrum of clinical features in NHS is variable and can be mild, in particular for females, and the condition can remain undiagnosed. This report contributes to the delineation of the phenotypic and genotypic findings associated with this condition.

The molecular mechanisms underlying cell migration remain incompletely understood. Here, we show that knock-out cells for NHSL3, the most recently identified member of the Nance-Horan Syndrome family, are more persistent than parental cells in single cell migration, but that, in wound healing, follower cells are impaired in their ability to follow leader cells. The NHSL3 locus encodes several isoforms. We identify the partner repertoire of each isoform using proteomics and predict direct partners and their binding sites using an AlphaFold2-based pipeline. Rescue with specific isoforms, and lack of rescue when relevant binding sites are mutated, establish that the interaction of a long isoform with MENA/VASP proteins is critical at cell-cell junctions for collective migration, while the interaction of a short one with 14-3-3θ in lamellipodia is critical for single cell migration. Taken together, these results demonstrate that NHSL3 regulates single and collective cell migration through distinct mechanisms.

Congenital cataracts (CCs) are a leading cause of preventable childhood blindness, with genetic factors playing a crucial role in their etiology. Nance-Horan syndrome (NHS) is a rare X-linked dominant disorder associated with CCs but is often underdiagnosed due to variable expressivity, particularly in female carriers. Objective: This study aimed to explore the genetic landscape of CCs in a Swiss cohort, focusing on two novel NHS and one novel GJA8 variants and their phenotypic presentation. Methods: Whole-exome sequencing (WES) was conducted on 20 unrelated Swiss families diagnosed with CCs. Variants were analyzed for pathogenicity using genetic databases, and segregation analysis was performed. Clinical data, including cataract phenotype and associated systemic anomalies, were assessed to establish genotype-phenotype correlations. Results: Potentially pathogenic DNA sequence variants were identified in 10 families, including three novel variants, one in GJA8 (c.584T>C) and two NHS variants (c.250_252insA and c.484del). Additional previously reported variants were detected in CRYBA1, CRYGC, CRYAA, MIP, EPHA2, and MAF, reflecting genetic heterogeneity in the cohort. Notably, NHS variants displayed significant phenotypic variability, suggesting dose-dependent effects and X-chromosome inactivation in female carriers. Conclusions: NHS remains underdiagnosed due to its variable expressivity and the late manifestation of systemic features, often leading to misclassification as isolated CC. This study highlights the importance of genetic testing in unexplained CC cases to improve early detection of syndromic forms. The identification of novel NHS and GJA8 variants provides new insights into the genetic complexity of CCs, emphasizing the need for further research on genotype-phenotype correlations.

Nance-Horan Syndrome (NHS) is a rare genetic disorder caused by pathogenic variants in the NHS gene. Phenotypically, NHS is characterized by severe congenital cataracts, dental anomalies, distinct facial features, and developmental defects. Here, we document a novel variant in the NHS gene and investigate the consequent phenotypic manifestations. Ophthalmologic findings along with medical history were gathered through clinical examination and chart review, slit-lamp biomicroscopy, optical coherence tomography, and physical exam alongside genetic testing. Genetic testing through Next-Generation Sequencing (NGS) was performed to investigate the molecular etiology, with variant confirmation and familial segregation analysis conducted using Sanger sequencing. We identified a novel hemizygous frameshift variant in the NHS gene (c.1861_1862del; p.Met621Glyfs *5), resulting from a dinucleotide deletion, in a patient with bilateral congenital cataracts. Segregation analysis revealed that this variant was maternally inherited. The underlying genetic etiology and op`hthalmic consequences associated with this variant are detailed in this study. This case presents a novel variant in the NHS gene in a symptomatic hemizygous patient, exhibiting significant cataract findings and contributing to the phenotypic spectrum of NHS. This case underscores the importance of genetic testing for NHS and highlights the need for further research on the genetics of NHS.

Cell migration is crucial for development and deregulation causes diseases. The Scar/WAVE complex promotes mesenchymal cell migration through Arp2/3 mediated lamellipodia protrusion. We previously discovered that all isoforms of Nance-Horan Syndrome-like 1 (NHSL1) protein interact directly with the Scar/WAVE complex and the NHSL1-F1 isoform negatively regulates Scar/WAVE-Arp2/3 activity thereby inhibiting 2D random cell migration. Here, we investigate the NHSL1-A1 isoform, which contains a Scar homology domain (SHD). The SHD in Scar/WAVE mediates the formation of the Scar/WAVE complex. We found that the SHD of NHLS1-A is sufficient for the formation of an NHSL1-A complex composed of the same proteins as the Scar/WAVE complex, but NHSL1-A replaces Scar/WAVE. NHSL1-A SHD recruits the NHSL1-A complex to lamellipodia, where also the Scar/WAVE complex resides. Scar/WAVE contains a WCA domain, which is phosphorylated by CK2 and recruits and activates the Arp2/3 complex to nucleate branched actin networks supporting lamellipodial protrusion. We identified a WCA domain in NHSL1 which interacts with the Arp2/3 complex. The NHSL1 WCA domain is phosphorylated by GSK3, and this increases the interaction with the Arp2/3 complex. In contrast to NHSL1-F1, the NHSL1-A complex promotes cell migration speed but not cell persistence via the Scar/WAVE complex and potentially via its WCA domain. In addition, the NHSL1-A complex is required for chemotaxis. Mechanistically, the NHSL1-A complex may increase lamellipodial Arp2/3 activity and lamellipodial speed while reducing lamellipodial persistence. Our findings reveal an additional layer of Arp2/3 complex control essential for mesenchymal cell migration highly relevant for development and disease.