Mutations in KIF11 cause autosomal-dominant microcephaly variably associated with congenital lymphedema and chorioretinopathy

Genetic testing for lymphatic malformations with or without primary lymphedema

Lymphatic malformations (LMs) show phenotypic variability, as well as clinical and genetic heterogeneity. Inheritance is autosomal dominant, recessive or X-linked and major genes involved in predisposition for LMs are continuously being discovered. The literature also indicates that somatic mutations play an important role in the development of LMs. In fact, activating somatic mutations in PIK3CA have been reported in lymphatic endothelial cells obtained from patients with different kinds of LM. This Utility Gene Test was developed on the basis of an analysis of the literature and existing diagnostic protocols. It is useful for confirming diagnosis, as well as for differential diagnosis, couple risk assessment and access to clinical trials.

Detection and quantification of a KIF11 mosaicism in a subject presenting familial exudative vitreoretinopathy with microcephaly

Familial exudative vitreoretinopathy (FEVR) is an inherited retinal disorder, which is primarily characterized by abnormal development of retinal vasculature. In this study, we reported a subject presenting the clinical features of FEVR as well as microcephaly. Screening of the KIF11 gene in this patient revealed a novel heterozygous protein-truncating variant (c.2717del, p.(L906*), NM_004523.3). Segregation analysis in the unaffected parents using Sanger sequencing suggested the variant to be present in a mosaic state in the unaffected mother. KIF11 exon 19 which harbors the variant was amplified from the proband and her father, as well as three different tissues of the mother, followed by amplicon-based deep sequencing. This analysis revealed that the variant is present in different tissues of the mother at various rates, i.e. in blood (16.9%), saliva (20.7%), or skin biopsy-derived fibroblast cells (6.6%). These data demonstrate the importance of deep sequencing in unaffected parents upon detection of a genetic defect in isolated cases to detect possible mosaicisms, enabling a  more reliable recurrence risk assessment and thereby improve genetic counseling.

Retinal and optic nerve changes in microcephaly: An optical coherence tomography study

OBJECTIVE

To investigate the morphology of the retina and optic nerve (ON) in microcephaly.

METHODS

This was a prospective case-control study including 27 patients with microcephaly and 27 healthy controls. All participants underwent ophthalmologic examination and handheld optical coherence tomography (OCT) of the macula and ON head. The thickness of individual retinal layers was quantified at the foveal center and the parafovea (1,000 μm nasal and temporal to the fovea). For the ON head, disc diameter, cup diameter, cup-to-disc ratio, cup depth, horizontal rim diameter, rim area, peripapillary retinal thickness, and retinal nerve fiber layer thickness were measured.

RESULTS

Seventy-eight percent of patients had ophthalmologic abnormalities, mainly nystagmus (56%) and strabismus (52%). OCT abnormalities were found in 85% of patients. OCT revealed disruption of the ellipsoid zone, persistent inner retinal layers, and irregular foveal pits. Parafoveal retinal thickness was significantly reduced in patients with microcephaly compared to controls, nasally (307 ± 44 vs 342 ± 19 μm, p = 0.001) and temporally (279 ± 56 vs 325 ± 16 μm, p < 0.001). There was thinning of the ganglion cell layer and the inner segments of the photoreceptors in microcephaly. Total peripapillary retinal thickness was smaller in patients with microcephaly compared to controls for both temporal (275 vs 318 μm, p < 0.001) and nasal sides (239 vs 268 μm, p = 0.013).

CONCLUSIONS

Retinal and ON anomalies in microcephaly likely reflect retinal cell reduction and lamination alteration due to impaired neurogenic mitosis. OCT allows diagnosis and quantification of retinal and ON changes in microcephaly even if they are not detected on ophthalmoscopy.

Utilizing lymphatic cell markers to visualize human lymphatic abnormalities

In vivo visualization of the human lymphatic system is limited by the mode of delivery of tracing agents, depth of field and size of the area examined, and specificity of the cell markers used to distinguish lymphatic endothelium from the blood vessels and the surrounding tissues. These limitations are particularly problematic when imaging human lymphatic abnormalities. First, limited understanding of the lymphatic disease aetiology exists with respect to genetic causes and phenotypic presentations. Second, the ability of a tracer to reach the entire lymphatic network within the diseased tissue is suboptimal. Third, what is known about the expression of lymphatic endothelial cell (LEC) markers, such as podoplanin, lymphatic vessel endothelial hyaluronan receptor, Drosophila melanogaster homeobox gene prospero-1 and vascular endothelial growth factor receptor-3 in rodent lymphatic vessels and healthy human LECs may not necessarily apply in human lymphatic disease settings. The aim of this review is to highlight challenges in visualizing lymphatic vessels in human lymphatic abnormalities with respect to distribution patterns of the cellular markers currently employed to visualize abnormal human lymphatic vessels in experimental settings. Allowing for these limitations within new diagnostic visualization technologies is likely to improve our ability to image human lymphatic diseases.

A Novel Mutation of KIF11 in a Child with 22q11.2 Deletion Syndrome Associated with MCLMR

Microcephaly with or without chorioretinopathy, lymphedema, or mental retardation (MCLMR; OMIM 152950) is a rare autosomal dominantly inherited syndrome. Mutations in the kinesin family member 11 (KIF11) gene have been associated with this condition. Here, we report a de novo novel heterozygous missense mutation in exon 12 of the KIF11 gene [c.1402T>G; p.(Leu468Val)] in a boy with 22q11.2 microdeletion syndrome. His major features were microcephaly, ventricular septal defect, congenital lymphedema of the feet, and distinct facial appearance including upslanting palpebral fissures, a broad nose with rounded tip, anteverted nares, long philtrum with a thin upper lip, pointed chin, and prominent ears. His right eye was enucleated due to subretinal hemorrhage and retinal detachment at age 3 months. Lacunae of chorioretinal atrophy and the pale optic disc were present in the left eye. He also had a de novo 1.6-Mb microdeletion in the Di George/VCFS region of chromosome 22q11.2 in SNP array, which was confirmed by FISH analysis. In this study, for the first time, we describe the co-occurrence of a KIF11 mutation and 22q11.2 deletion syndrome in a patient with MCLMR.

A New Way to Treat Brain Tumors: Targeting Proteins Coded by Microcephaly Genes?: Brain tumors and microcephaly arise from opposing derangements regulating progenitor growth. Drivers of microcephaly could be attractive brain tumor targets

New targets for brain tumor therapies may be identified by mutations that cause hereditary microcephaly. Brain growth depends on the repeated proliferation of stem and progenitor cells. Microcephaly syndromes result from mutations that specifically impair the ability of brain progenitor or stem cells to proliferate, by inducing either premature differentiation or apoptosis. Brain tumors that derive from brain progenitor or stem cells may share many of the specific requirements of their cells of origin. These tumors may therefore be susceptible to disruptions of the protein products of genes that are mutated in microcephaly. The potential for the products of microcephaly genes to be therapeutic targets in brain tumors are highlighted hereby reviewing research on EG5, KIF14, ASPM, CDK6, and ATR. Treatments that disrupt these proteins may open new avenues for brain tumor therapy that have increased efficacy and decreased toxicity.

A case of exudative vitreoretinopathy and chorioretinal coloboma associated with microcephaly in a female with contiguous Xp11.3-11.4 deletion

The constellation of signs including microcephaly, retinal colobomas, and exudative vitreo-retinopathy suggests a mutation of the KIF-11 gene on chromosome 10q. We report a female infant with these features but due, instead, to a contiguous gene deletion on chromosome Xp including the OMIM morbid genes CASK, KDM6A, NDP, MAOA, NYX, and DDX3X. The NDP deletion could account for the exudative retinopathy and the CASK deletion for the microcephaly, while CASK and KDM6A have both been associated with coloboma. This case highlights genetic heterogeneity for the clustering of these signs.

KIF11 microdeletion is associated with microcephaly, chorioretinopathy and intellectual disability

KIF11 mutations are known to cause autosomal dominant microcephaly-lymphedema-chorioretinopathy dysplasia syndrome, associated or not with intellectual disability. We report a father and two children presenting microcephaly, chorioretinopathy and mild intellectual disability associated with a 209-kb microdeletion at 10q23.33. This microdeletion encompasses the entire KIF11 gene. In addition to point mutations, KIF11 haploinsufficiency due to a deletion is causally associated with autosomal dominant microcephaly, chorioretinopathy and mild intellectual disability.

Clinical and genetic characteristics of 251 consecutive patients with macular and cone/cone-rod dystrophy

Macular and cone/cone-rod dystrophies (MD/CCRD) demonstrate a broad genetic and phenotypic heterogeneity, with retinal alterations solely or predominantly involving the central retina. Targeted next-generation sequencing (NGS) is an efficient diagnostic tool for identifying mutations in patient with retinitis pigmentosa, which shows similar genetic heterogeneity. To detect the genetic causes of disease in patients with MD/CCRD, we implemented a two-tier procedure consisting of Sanger sequencing and targeted NGS including genes associated with clinically overlapping conditions. Disease-causing mutations were identified in 74% of 251 consecutive MD/CCRD patients (33% of the variants were novel). Mutations in ABCA4, PRPH2 and BEST1 accounted for 57% of disease cases. Further mutations were identified in CDHR1, GUCY2D, PROM1, CRX, GUCA1A, CERKL, MT-TL1, KIF11, RP1L1, MERTK, RDH5, CDH3, C1QTNF5, CRB1, JAG1, DRAM2, POC1B, NPHP1 and RPGR. We provide detailed illustrations of rare phenotypes, including autofluorescence and optical coherence tomography imaging. Targeted NGS also identified six potential novel genotype-phenotype correlations for FAM161A, INPP5E, MERTK, FBLN5, SEMA4A and IMPDH1. Clinical reassessment of genetically unsolved patients revealed subgroups with similar retinal phenotype, indicating a common molecular disease cause in each subgroup.

Genetic tests in lymphatic vascular malformations and lymphedema

Syndromes with lymphatic malformations show phenotypic variability within the same entity, clinical features that overlap between different conditions and allelic as well as locus heterogeneity. The aim of this review is to provide a comprehensive clinical genetic description of lymphatic malformations and the techniques used for their diagnosis, and to propose a flowchart for genetic testing. Literature and database searches were performed to find conditions characterised by lymphatic malformations or the predisposition to lymphedema after surgery, to identify the associated genes and to find the guidelines and genetic tests currently used for the molecular diagnosis of these disorders. This search allowed us to identify several syndromes with lymphatic malformations that are characterised by a great heterogeneity of phenotypes, alleles and loci, and a high frequency of sporadic cases, which may be associated with somatic mutations. For these disorders, we found many diagnostic tests, an absence of harmonic guidelines for molecular diagnosis and well-established clinical guidelines. Targeted sequencing is the preferred method for the molecular diagnosis of lymphatic malformations. These techniques are easy to implement and have a good diagnostic success rates. In addition, they are relatively inexpensive and permit parallel analysis of all known disease-associated genes. The targeted sequencing approach has improved the diagnostic process, giving patients access to better treatment and, potentially, to therapy personalised to their genetic profiles. These new techniques will also facilitate the prenatal and early postnatal diagnosis of congenital lymphatic conditions and the possibility of early intervention.

An approach to familial lymphoedema

Lymphoedema is the build-up of lymphatic fluid leading to swelling in the tissues. Most commonly it affects the peripheries. Diagnosis is based on clinical assessment and imaging with lymphoscintigraphy. Treatment is supportive with compression garments, massage, good skin hygiene and prompt use of antibiotics to avoid the complication of cellulitis. Most commonly, lymphoedema occurs as a result of damage to the lymphatic system following surgery, trauma, radiation or infection. However, it can be primary, often associated with a genetic defect that causes disruption to the development of the lymphatic system. Common genetic conditions associated with lymphoedema include Turner syndrome and Noonan syndrome; however, there are numerous others that can be classified based on their clinical presentation and associated features. Herein we discuss how to diagnose and classify the known primary lymphoedema conditions and how best to investigate and manage this group of patients.

The evolution of cortical development: the synapsid-diapsid divergence

The cerebral cortex covers the rostral part of the brain and, in higher mammals and particularly humans, plays a key role in cognition and consciousness. It is populated with neuronal cell bodies distributed in radially organized layers. Understanding the common and lineage-specific molecular mechanisms that orchestrate cortical development and evolution are key issues in neurobiology. During evolution, the cortex appeared in stem amniotes and evolved divergently in two main branches of the phylogenetic tree: the synapsids (which led to present day mammals) and the diapsids (reptiles and birds). Comparative studies in organisms that belong to those two branches have identified some common principles of cortical development and organization that are possibly inherited from stem amniotes and regulated by similar molecular mechanisms. These comparisons have also highlighted certain essential features of mammalian cortices that are absent or different in diapsids and that probably evolved after the synapsid-diapsid divergence. Chief among these is the size and multi-laminar organization of the mammalian cortex, and the propensity to increase its area by folding. Here, I review recent data on cortical neurogenesis, neuronal migration and cortical layer formation and folding in this evolutionary perspective, and highlight important unanswered questions for future investigation.

Quantitative Assessment of Microstructural Changes of the Retina in Infants With Congenital Zika Syndrome

Importance

A better pathophysiologic understanding of the neurodevelopmental abnormalities observed in neonates exposed in utero to Zika virus (ZIKV) is needed to develop treatments. The retina as an extension of the diencephalon accessible to in vivo microcopy with spectral-domain optical coherence tomography (SD-OCT) can provide an insight into the pathophysiology of congenital Zika syndrome (CZS).

Objective

To quantify the microstructural changes of the retina in CZS and compare these changes with those of cobalamin C (cblC) deficiency, a disease with potential retinal maldevelopment.

Design, Setting, and Participants

This case series included 8 infants with CZS and 8 individuals with cblC deficiency. All patients underwent ophthalmologic evaluation at 2 university teaching hospitals and SD-OCT imaging in at least 1 eye. Patients with cblC deficiency were homozygous or compound heterozygotes for mutations in the methylmalonic aciduria and homocystinuria type C (MMACHC) gene. Data were collected from January 1 to March 17, 2016, for patients with CZS and from May 4, 2015, to April 23, 2016, for patients with cblC deficiency.

Main Outcomes and Measures

The SD-OCT cross-sections were segmented using automatic segmentation algorithms embedded in the SD-OCT systems. Each retinal layer thickness was measured at critical eccentricities using the position of the signal peaks and troughs on longitudinal reflectivity profiles.

Results

Eight infants with CZS (5 girls and 3 boys; age range, 3-5 months) and 8 patients with cblC deficiency (3 girls and 5 boys; age range, 4 months to 15 years) were included in the analysis. All 8 patients with CZS had foveal abnormalities in the analyzed eyes (8 eyes), including discontinuities of the ellipsoid zone, thinning of the central retina with increased backscatter, and severe structural disorganization, with 3 eyes showing macular pseudocolobomas. Pericentral retina with normal lamination showed a thinned (<30% of normal thickness) ganglion cell layer (GCL) that colocalized in 7 of 8 eyes with a normal photoreceptor layer. The inner nuclear layer was normal or had borderline thinning. The central retinal degeneration was similar to that of cblC deficiency.

Conclusions and Relevance

Congenital Zika syndrome showed a central retinal degeneration with severe GCL loss, borderline inner nuclear layer thinning, and less prominent photoreceptor loss. The findings provide the first, to date, in vivo evidence in humans for possible retinal maldevelopment with a predilection for retinal GCL loss in CZS, consistent with a murine model of the disease and suggestive of in utero depletion of this neuronal population as a consequence of Zika virus infection.

Total retinal detachment caused by a KIF11 mutation

PURPOSE

This is a case report of bilateral retinal detachment associated with KIF11 mutation.

METHODS

In our university hospital, an 8-week-old patient presented with a potential bilateral congenital cataract, iris atrophy, and iridocorneal contact in the left eye. An examination revealed microcephaly and edema of the dorsa of the feet. The eye examination showed a clear lens in both eyes with a dislodged anterior chamber in the left eye with vessels drawn from the iris to the lens. A retrolental white bilateral mass with vessels was also observed. The MRI and the ultrasound revealed a potential peritoneal hyperplastic glass body. Bilateral retinal detachment was diagnosed during surgery.

RESULTS

Due to the external appearance of the eyes (microcephaly and edema) and the bilateral retinal detachments, a test for KIF11 mutations was requested, and the results were positive.

CONCLUSIONS

There is a known association between KIF11 mutation and chorioretinopathy. The bilateral retinal detachment in the present case study has not been previously reported in the literature.

Forces and Disease: Electrostatic force differences caused by mutations in kinesin motor domains can distinguish between disease-causing and non-disease-causing mutations

The ability to predict if a given mutation is disease-causing or not has enormous potential to impact human health. Typically, these predictions are made by assessing the effects of mutation on macromolecular stability and amino acid conservation. Here we report a novel feature: the electrostatic component of the force acting between a kinesin motor domain and tubulin. We demonstrate that changes in the electrostatic component of the binding force are able to discriminate between disease-causing and non-disease-causing mutations found in human kinesin motor domains using the receiver operating characteristic (ROC). Because diseases may originate from multiple effects not related to kinesin-microtubule binding, the prediction rate of 0.843 area under the ROC plot due to the change in magnitude of the electrostatic force alone is remarkable. These results reflect the dependence of kinesin’s function on motility along the microtubule, which suggests a precise balance of microtubule binding forces is required.

AKAP95 interacts with nucleoporin TPR in mitosis and is important for the spindle assembly checkpoint

Faithful chromosome segregation during mitosis relies on a proofreading mechanism that monitors proper kinetochore-microtubule attachments. The spindle assembly checkpoint (SAC) is based on the concerted action of numerous components that maintain a repressive signal inhibiting transition into anaphase until all chromosomes are attached. Here we show that A-Kinase Anchoring Protein 95 (AKAP95) is necessary for proper SAC function. AKAP95-depleted HeLa cells show micronuclei formed from lagging chromosomes at mitosis. Using a BioID proximity-based proteomic screen, we identify the nuclear pore complex protein TPR as a novel AKAP95 binding partner. We show interaction between AKAP95 and TPR in mitosis, and an AKAP95-dependent enrichment of TPR in the spindle microtubule area in metaphase, then later in the spindle midzone area. AKAP95-depleted cells display faster prometaphase to anaphase transition, escape from nocodazole-induced mitotic arrest and show a partial delocalization from kinetochores of the SAC component MAD1. Our results demonstrate an involvement of AKAP95 in proper SAC function likely through its interaction with TPR.

Loss-of-Function Mutations in KIF15 Underlying a Braddock-Carey Genocopy

Braddock-Carey Syndrome (BCS) is characterized by microcephaly, congenital thrombocytopenia, Pierre-Robin sequence (PRS), and agenesis of the corpus callosum. BCS has been shown to be caused by a 21q22.11 microdeletion that encompasses multiple genes. Here, we report a BCS genocopy characterized by congenital thrombocytopenia and PRS that is caused by a loss-of-function mutation in KIF15 in a consanguineous Saudi Arabian family. Mutations of mitotic kinesins are a well-established cause of microcephaly. To our knowledge, KIF15 is the first kinesin to be associated with congenital thrombocytopenia.

Exome Sequencing Identifies De Novo DYNC1H1 Mutations Associated With Distal Spinal Muscular Atrophy and Malformations of Cortical Development

Exome sequencing has become a formidable tool for identifying potential de novo variants in causative genes of human diseases, such as neurodegenerative disorders. This article describes a 16-month-old girl with spinal muscular atrophy with lower extremity predominance and a 13-month-old girl with malformations of cortical development. Exome sequencing identified a novel de novo heterozygous missense mutation c.3395G>A (p.Gly1132Glu) and a previously reported de novo heterozygous missense mutation c.10151G>A (p.Arg3384Gln) in the DYNC1H1 gene. Bioinformatics predictions for c.3395G>A and c.10151G>A indicated pathogenicity of the mutations. DYNC1H1 is a pivotal component of cytoplasmic dynein complex, which is a microtubule-related motor involved in retrograde transport. Previous studies indicated that mutant dynein showed decreased run-length of the motor proteins and diminished retrograde transport, which were clearly associated with neuronal death and neurologic diseases. The present findings expand the mutational spectrum of the DYNC1H1 gene, reemphasizing the significance of the DYNC1H1 protein in the functioning of neurons.

The lymphatic vasculature: development and role in shaping immunity

The lymphatic vasculature is an integral component of the immune system. Lymphatic vessels are a key highway via which immune cells are trafficked, serving not simply as a passive route of transport, but to actively shape and coordinate immune responses. Reciprocally, immune cells provide signals that impact the growth, development, and activity of the lymphatic vasculature. In addition to immune cell trafficking, lymphatic vessels are crucial for fluid homeostasis and lipid absorption. The field of lymphatic vascular research is rapidly expanding, fuelled by rapidly advancing technology that has enabled the manipulation and imaging of lymphatic vessels, together with an increasing recognition of the involvement of lymphatic vessels in a myriad of human pathologies. In this review we provide an overview of the genetic pathways and cellular processes important for development and maturation of the lymphatic vasculature, discuss recent work revealing important roles for the lymphatic vasculature in directing immune cell traffic and coordinating immune responses and highlight the involvement of lymphatic vessels in a range of pathological settings.

Microduplication of the ARID1A gene causes intellectual disability with recognizable syndromic features

PURPOSE

To determine whether duplication of the ARID1A gene is responsible for a new recognizable syndrome.

METHODS

We describe four patients with a 1p36.11 microduplication involving ARID1A as identified by array-comparative genomic hybridization . We performed comparative transcriptomic analysis of patient-derived fibroblasts using RNA sequencing and evaluated the impact of ARID1A duplication on the cell cycle using fluorescence-activated cell sorting. Functional relationships between differentially expressed genes were investigated with ingenuity pathway analysis (IPA).

RESULTS

Combining the genomic data, we defined a small (122 kb), minimally critical region that overlaps the full ARID1A gene. The four patients shared a strikingly similar phenotype that included intellectual disability and microcephaly. Transcriptomic analysis revealed the deregulated expression of several genes previously linked to microcephaly and developmental disorders as well as the involvement of signaling pathways relevant to microcephaly, among which the polo-like kinase (PLK) pathway was especially notable. Cell-cycle analysis of patient-derived fibroblasts showed a significant increase in the proportion of cells in G1 phase at the expense of G2-M cells.

CONCLUSION

Our study reports a new microduplication syndrome involving the ARID1A gene. This work is the first step in clarifying the pathophysiological mechanism that links changes in the gene dosage of ARID1A with intellectual disability and microcephaly.Genet Med advance online publication 01 December 2016.

Lymphatic System in Cardiovascular Medicine

The mammalian circulatory system comprises both the cardiovascular system and the lymphatic system. In contrast to the blood vascular circulation, the lymphatic system forms a unidirectional transit pathway from the extracellular space to the venous system. It actively regulates tissue fluid homeostasis, absorption of gastrointestinal lipids, and trafficking of antigen-presenting cells and lymphocytes to lymphoid organs and on to the systemic circulation. The cardinal manifestation of lymphatic malfunction is lymphedema. Recent research has implicated the lymphatic system in the pathogenesis of cardiovascular diseases including obesity and metabolic disease, dyslipidemia, inflammation, atherosclerosis, hypertension, and myocardial infarction. Here, we review the most recent advances in the field of lymphatic vascular biology, with a focus on cardiovascular disease.

Prolonged Mitosis of Neural Progenitors Alters Cell Fate in the Developing Brain

Embryonic neocortical development depends on balanced production of progenitors and neurons. Genetic mutations disrupting progenitor mitosis frequently impair neurogenesis; however, the link between altered mitosis and cell fate remains poorly understood. Here we demonstrate that prolonged mitosis of radial glial progenitors directly alters neuronal fate specification and progeny viability. Live imaging of progenitors from a neurogenesis mutant, Magoh(+/-), reveals that mitotic delay significantly correlates with preferential production of neurons instead of progenitors, as well as apoptotic progeny. Independently, two pharmacological approaches reveal a causal relationship between mitotic delay and progeny fate. As mitotic duration increases, progenitors produce substantially more apoptotic progeny or neurons. We show that apoptosis, but not differentiation, is p53 dependent, demonstrating that these are distinct outcomes of mitotic delay. Together our findings reveal that prolonged mitosis is sufficient to alter fates of radial glia progeny and define a new paradigm to understand how mitosis perturbations underlie brain size disorders such as microcephaly.

Identification of novel KIF11 mutations in patients with familial exudative vitreoretinopathy and a phenotypic analysis

KIF11 gene mutations cause a rare autosomal dominant inheritable disease called microcephaly with or without chorioretinopathy, lymphedema, or mental retardation (MCLMR). Recently, such mutations were also found to be associated with familial exudative vitreoretinopathy (FEVR). Here, we report 7 novel KIF11 mutations identified by targeted gene capture in a cohort of 142 probands with FEVR who were diagnosed in our clinic between March 2015 and November 2015. These mutations were: p.L171V, c.790-2A>C, p.Q525*, p.Q842*, p.S936*, p.L983fs and p.R1025G. Phenotypic analysis revealed that all of the affected probands had advanced FEVR (stage 4 or above). Three had microcephaly, and one had chorioretinopathy, which indicated a phenotypic overlap with MCLMR. Two mutations were also found in the families of the affected probands. One parent with a p.R1025G mutation had an avascular peripheral retina and abnormal looping vessels. However, one parent with p.L983fs had normal retina, which indicated incomplete penetration of the genotype. Our results further confirmed that KIF11 is causative of FEVR in an autosomal dominant manner. We also suggest the examination of MCLMR-like features, such as microcephaly, chorioretinopathy, for patients with FEVR and wide-field fundus photography for patients with MCLMR in future practice.

Microtubule plus-end tracking proteins in neuronal development

Regulation of the microtubule cytoskeleton is of pivotal importance for neuronal development and function. One such regulatory mechanism centers on microtubule plus-end tracking proteins (+TIPs): structurally and functionally diverse regulatory factors, which can form complex macromolecular assemblies at the growing microtubule plus-ends. +TIPs modulate important properties of microtubules including their dynamics and their ability to control cell polarity, membrane transport and signaling. Several neurodevelopmental and neurodegenerative diseases are associated with mutations in +TIPs or with misregulation of these proteins. In this review, we focus on the role and regulation of +TIPs in neuronal development and associated disorders.

The mitotic spindle: linking teratogenic effects of Zika virus with human genetics?

Background

Recently, an association between Zika virus infection and microcephaly/ocular findings was found to be reasonable e.g. because of the demonstration that the virus was found in the brain of a fetus after presumed maternal infection. Although there is no proof yet for a causal relationship, for an appropriate risk calculation efforts are urgently needed to either establish or disprove this assumption.

Presentation of the hypothesis

On the basis of inherited syndromes combining microcephaly with ocular findings similar to those associated with Zika infections, we have hypothesized that the impairment of the proper function of the mitotic apparatus is a possible mechanism by which Zika can exert teratogenic effects.

Testing the hypothesis

A bundle of well-known cytogenetic and molecular-cytogenetic methods (e.g. formation of micronuclei, chromosomal lagging, immunofluorescence of centrosomes) to evaluate proper function, maintenance, and establishment of the mitotic spindle poles can be applied on infected cells. Also, the viral proteins can be tested for their possible interaction with proteins encoded by genes involved in inherited syndromes with microcephaly and ocular findings resembling those in presumed cases of intrauterine ZIKV infection.

Implications of the hypothesis

Once proved, this hypothesis allows for a targeted approach into mechanisms of possible relevance as e.g. if different strains of the virus are implicated in the teratogenic effects to the same or a different extent.

ALFY-Controlled DVL3 Autophagy Regulates Wnt Signaling, Determining Human Brain Size

Primary microcephaly is a congenital neurodevelopmental disorder of reduced head circumference and brain volume, with fewer neurons in the cortex of the developing brain due to premature transition between symmetrical and asymmetrical cellular division of the neuronal stem cell layer during neurogenesis. We now show through linkage analysis and whole exome sequencing, that a dominant mutation in ALFY, encoding an autophagy scaffold protein, causes human primary microcephaly. We demonstrate the dominant effect of the mutation in drosophila: transgenic flies harboring the human mutant allele display small brain volume, recapitulating the disease phenotype. Moreover, eye-specific expression of human mutant ALFY causes rough eye phenotype. In molecular terms, we demonstrate that normally ALFY attenuates the canonical Wnt signaling pathway via autophagy-dependent removal specifically of aggregates of DVL3 and not of Dvl1 or Dvl2. Thus, autophagic attenuation of Wnt signaling through removal of Dvl3 aggregates by ALFY acts in determining human brain size.

One of the major events in human evolution is the significant increase in brain volume in the transition from primates to humans. The molecular pathways determining the larger size of the human brain are not fully understood. Hereditary primary microcephaly, a neurodevelopmental disorder in which infants are born with small head circumference and reduced brain volume with intellectual disability, offers insights to the embryonic molecular pathways determining human brain size. Previous studies have shown that human microcephaly can be caused by mutations in genes affecting cell division processes, such as cell cycle regulation, DNA replication, primary cilia formation and centriole and centrosome duplication. We now show a novel molecular pathway determining human brain size: human primary microcephaly can be caused by a mutation in ALFY, a gene that encodes an autophagy scaffold protein. In fact, transgenic flies over expressing the mutant form of human ALFY recapitulate the human disease phenotype of microcephaly. We show the molecular pathway through which ALFY regulates cell division and differentiation: we demonstrate that ALFY normally controls removal of aggregate of DVL3, and through this regulates Wnt signaling, a major molecular pathway in embryogenesis. Thus, Wnt signaling, controlled by ALFY-mediated aggregate removal of DVL3, determines human brain size and human microcephaly.

Whole-exome sequencing is a powerful approach for establishing the etiological diagnosis in patients with intellectual disability and microcephaly

Background

Clinical and genetic heterogeneity in monogenetic disorders represents a major diagnostic challenge. Although the presence of particular clinical features may aid in identifying a specific cause in some cases, the majority of patients remain undiagnosed.

Here, we investigated the utility of whole-exome sequencing as a diagnostic approach for establishing a molecular diagnosis in a highly heterogeneous group of patients with varied intellectual disability and microcephaly.

Methods

Whole-exome sequencing was performed in 38 patients, including three sib-pairs, in addition to or in parallel with genetic analyses that were performed during the diagnostic work-up of the study participants.

Results

In ten out of these 35 families (29 %), we found mutations in genes already known to be related to a disorder in which microcephaly is a main feature. Two unrelated patients had mutations in the ASPM gene. In seven other patients we found mutations in RAB3GAP1, RNASEH2B, KIF11, ERCC8, CASK, DYRK1A and BRCA2. In one of the sib-pairs, mutations were found in the RTTN gene. Mutations were present in seven out of our ten families with an established etiological diagnosis with recessive inheritance.

Conclusions

We demonstrate that whole-exome sequencing is a powerful tool for the diagnostic evaluation of patients with highly heterogeneous neurodevelopmental disorders such as intellectual disability with microcephaly. Our results confirm that autosomal recessive disorders are highly prevalent among patients with microcephaly.

Electronic supplementary material

The online version of this article (doi:10.1186/s12920-016-0167-8) contains supplementary material, which is available to authorized users.

Ocular manifestations of microcephaly with or without chorioretinopathy, lymphedema or intellectual disability (MCLID) syndrome associated with mutations in KIF11

PURPOSE

Microcephaly with or without chorioretinopathy, lymphedema or intellectual disability (MCLID) is an autosomal dominant condition. Mutations in KIF11 have been found to be causative in approximately 75% of cases. This study describes the ocular phenotype in patients with confirmed KIF11 mutations.

METHODS

Standard ophthalmic examination and investigation including visual acuity, refraction and fundus examination was carried out in all patients. Fundus autofluorescence imaging (FAF) was performed in three patients, and four patients underwent spectral domain optical coherence tomography (OCT). Flash electroretinography (ERG) was performed in seven patients, and five underwent additional pattern electroretinography (PERG).

RESULTS

The patients ranged in age from 2 to 10 years. Most presented with visual acuity loss. Fundus examination revealed lacunae of chorioretinal atrophy. Pigmentary macular changes and optic disc pallor were present in three of seven patients. Fundus autofluorescence demonstrated hypoautofluorescence at the macula in two of three patients. The lacunae of chorioretinal atrophy were hypoautofluorescent. The OCT showed atrophic maculae in three of four patients. Follow-up in one patient showed no deterioration of the vision over a 9-year period. The lesions appear not to be progressive on the follow-up imaging. Electrophysiology showed generalized rod and cone dysfunction and severe macular dysfunction. Inner retinal dysfunction was evident in three of seven patients.

CONCLUSIONS

Patients with KIF11 mutations show a specific ocular phenotype with variable expressivity and intrafamilial variability. Macular atrophy and dysfunction have not been consistently documented before. The fundus lesions appear non-progressive. The findings assist in providing an accurate diagnosis and thus improving the management and follow-up of patients with this syndrome.

Neue syndromale Krankheitsbilder mit Mikrozephalie

Die Mikrozephalie ist definiert als Kopfumfang unterhalb der dritten Perzentile bzw. ein Kopfumfang, der mehr als zwei Standardabweichungen unterhalb des Mittelwerts unter Berücksichtigung von Alter und Geschlecht liegt. Auch wenn es isolierte Formen der Mikrozephalie gibt, so ist eine Kombination mit anderen klinischen Zeichen doch häufig zu beobachten. Hierbei handelt es sich dann um syndromale Mikrozephalien. Die Tatsache, dass in der London Medical Database fast 1000 Entitäten eingetragen sind, die mit einer Mikrozephalie einhergehen, zeigt, wie komplex dieses Thema ist. Dieser Artikel hat deshalb auch nicht den Anspruch, einen kompletten Überblick zu dieser Thematik zu geben, sondern fokussiert auf einzelne neue Mikrozephaliesyndrome, deren molekulare Ursachen erst kürzlich identifiziert wurden. Anhand von kurzen Beschreibungen des klinischen und molekularen Spektrums unter Einbeziehung von Fotografien sollen diese neuen Syndrome vorgestellt werden.

No evidence of locus heterogeneity in familial microcephaly with or without chorioretinopathy, lymphedema, or mental retardation syndrome

BACKGROUND

Microcephaly with or without chorioretinopathy, lymphedema, or mental retardation syndrome (MCLMR) is a rare autosomal dominant disorder with variable expressivity. It is characterized by mild-to-severe microcephaly, often associated with intellectual disability, ocular defects and lymphedema. It can be sporadic or inherited. Eighty-seven patients have been described to carry a mutation in KIF11, which encodes a homotetrameric motor kinesin, EG5.

METHODS

We tested 23 unreported MCLMR index patients for KIF11. We also reviewed the clinical phenotypes of all our patients as well as of those described in previously published studies.

RESULTS

We identified 14 mutations, 12 of which are novel. We detected mutations in 12 affected individuals, from 6 out of 6 familial cases, and in 8 out of 17 sporadic patients. Phenotypic evaluation of patients (our 26 + 61 earlier published = 87) revealed microcephaly in 91%, eye anomalies in 72%, intellectual disability in 67% and lymphedema in 47% of the patients. Unaffected carriers were rare (4 out of 87: 5%). Family history is not a requisite for diagnosis; 31% (16 out of 52) were de novo cases.

CONCLUSIONS

All inherited cases, and 50% of sporadic cases of MCLMR are due to germline KIF11 mutations. It is possible that mosaic KIF11 mutations cause the remainder of sporadic cases, which the methods employed here were not designed to detect. On the other hand, some of them might have another mimicking disorder and genetic defect, as microcephaly is highly heterogeneous. In aggregate, KIF11 mutations likely cause the majority, if not all, of MCLMR.

Between Rho(k) and a hard place: the relation between vessel wall stiffness, endothelial contractility, and cardiovascular disease

Vascular stiffness is a mechanical property of the vessel wall that affects blood pressure, permeability, and inflammation. As a result, vascular stiffness is a key driver of (chronic) human disorders, including pulmonary arterial hypertension, kidney disease, and atherosclerosis. Responses of the endothelium to stiffening involve integration of mechanical cues from various sources, including the extracellular matrix, smooth muscle cells, and the forces that derive from shear stress of blood. This response in turn affects endothelial cell contractility, which is an important property that regulates endothelial stiffness, permeability, and leukocyte-vessel wall interactions. Moreover, endothelial stiffening reduces nitric oxide production, which promotes smooth muscle cell contraction and vasoconstriction. In fact, vessel wall stiffening, and microcirculatory endothelial dysfunction, precedes hypertension and thus underlies the development of vascular disease. Here, we review the cross talk among vessel wall stiffening, endothelial contractility, and vascular disease, which is controlled by Rho-driven actomyosin contractility and cellular mechanotransduction. In addition to discussing the various inputs and relevant molecular events in the endothelium, we address which actomyosin-regulated changes at cell adhesion complexes are genetically associated with human cardiovascular disease. Finally, we discuss recent findings that broaden therapeutic options for targeting this important mechanical signaling pathway in vascular pathogenesis.

Mutations in TUBGCP4 alter microtubule organization via the γ-tubulin ring complex in autosomal-recessive microcephaly with chorioretinopathy

We have identified TUBGCP4 variants in individuals with autosomal-recessive microcephaly and chorioretinopathy. Whole-exome sequencing performed on one family with two affected siblings and independently on another family with one affected child revealed compound-heterozygous mutations in TUBGCP4. Subsequent Sanger sequencing was performed on a panel of individuals from 12 French families affected by microcephaly and ophthalmic manifestations, and one other individual was identified with compound-heterozygous mutations in TUBGCP4. One synonymous variant was common to all three families and was shown to induce exon skipping; the other mutations were frameshift mutations and a deletion. TUBGCP4 encodes γ-tubulin complex protein 4, a component belonging to the γ-tubulin ring complex (γ-TuRC) and known to regulate the nucleation and organization of microtubules. Functional analysis of individual fibroblasts disclosed reduced levels of the γ-TuRC, altered nucleation and organization of microtubules, abnormal nuclear shape, and aneuploidy. Moreover, zebrafish treated with morpholinos against tubgcp4 were found to have reduced head volume and eye developmental anomalies with chorioretinal dysplasia. In summary, the identification of TUBGCP4 mutations in individuals with microcephaly and a spectrum of anomalies in eye development, particularly photoreceptor anomalies, provides evidence of an important role for the γ-TuRC in brain and eye development.

Impaired angiogenesis and tumor development by inhibition of the mitotic kinesin Eg5

Kinesin motor proteins exert essential cellular functions in all eukaryotes. They control mitosis, migration and intracellular transport through interaction with microtubules. Small molecule inhibitors of the mitotic kinesin KiF11/Eg5 are a promising new class of anti-neoplastic agents currently evaluated in clinical cancer trials for solid tumors and hematological malignancies. Here we report induction of Eg5 and four other mitotic kinesins including KIF20A/Mklp2 upon stimulation of in vivo angiogenesis with vascular endothelial growth factor-A (VEGF-A). Expression analyses indicate up-regulation of several kinesin-encoding genes predominantly in lymphoblasts and endothelial cells. Chemical blockade of Eg5 inhibits endothelial cell proliferation and migration in vitro. Mitosis-independent vascular outgrowth in aortic ring cultures is strongly impaired after Eg5 or Mklp2 protein inhibition. In vivo, interfering with KIF11/Eg5 function causes developmental and vascular defects in zebrafish and chick embryos and potent inhibition of tumor angiogenesis in experimental tumor models. Besides blocking tumor cell proliferation, impairing endothelial function is a novel mechanism of action of kinesin inhibitors.

Evidence for SH2 domain-containing 5'-inositol phosphatase-2 (SHIP2) contributing to a lymphatic dysfunction

The lymphatic vasculature plays a critical role in a number of disease conditions of increasing prevalence, such as autoimmune disorders, obesity, blood vascular diseases, and cancer metastases. Yet, unlike the blood vasculature, the tools available to interrogate the molecular basis of lymphatic dysfunction/disease have been lacking. More recently, investigators have reported that dysregulation of the PI3K pathway is involved in syndromic human diseases that involve abnormal lymphatic vasculatures, but there have been few compelling results that show the direct association of this molecular pathway with lymphatic dysfunction in humans. Using near-infrared fluorescence lymphatic imaging (NIRFLI) to phenotype and next generation sequencing (NGS) for unbiased genetic discovery in a family with non-syndromic lymphatic disease, we discovered a rare, novel mutation in INPPL1 that encodes the protein SHIP2, which is a negative regulator of the PI3K pathway, to be associated with lymphatic dysfunction in the family. In vitro interrogation shows that SHIP2 is directly associated with impairment of normal lymphatic endothelial cell (LEC) behavior and that SHIP2 associates with receptors that are associated in lymphedema, implicating its direct involvement in the lymphatic vasculature.

Genetics of hemangiomas, vascular malformations, and primary lymphedema

With improved genetic testing and genomic sequencing, abnormalities are increasingly being identified in affected or germline tissues in DNA of patients with vascular tumors, vascular malformations, and lymphedema. Recognition of the genetics of vascular anomalies should help clinicians make more specific diagnoses, anticipate diagnosis-specific morbidities, provide better genetic counseling, and have a better understanding of the pathogenesis of these anomalies. Growing pharmacologic options, including therapies targeted to specific mutations, with obvious parallels to cancer treatment now allow the pediatric hematologist-oncologist to assume a more prominent role in clinical care and research for patients with these diagnoses. We summarize genes and genetic loci that have been associated with vascular anomalies and offer guidelines for patient evaluations.

Congenital microcephaly and chorioretinopathy due to de novo heterozygous KIF11 mutations: five novel mutations and review of the literature

The microcephaly-lymphedema-chorioretinal dysplasia (MLCRD) syndrome is a distinct microcephaly syndrome. The hallmark features, microcephaly, chorioretinopathy, and lymphedema are frequently recognized at birth. Another clinical entity, the chorioretinal dysplasia, microcephaly and mental retardation syndrome (CDMMR) is a highly overlapping syndrome characterized by more variable lymphedema. Recently, heterozygous mutations in KIF11, a gene encoding a critical spindle motor protein of the Kinesin family, have been reported in individuals with MLCRD, and in individuals with CDMMR. This finding is suggestive of a single clinically variable spectrum. Here, we report on de novo novel mutations of KIF11 in five individuals with severe microcephaly, marked simplification of the gyral pattern on neuroimaging, bilateral chorioretinopathy, and developmental delay. Three patients had congenital lymphedema, and one had congenital bilateral sensorineural hearing loss. This report, therefore, further expands the clinical and molecular spectrum of KIF11-associated microcephaly.

Genetics of vascular malformations

Vascular anomalies are developmental defects of the vasculature and encompass a variety of disorders. The majority of these occur sporadically, yet a few are reported to be familial. The identification of genes mutated in the different malformations provides insight into their etiopathogenic mechanisms and the specific roles the associated proteins play in vascular development and maintenance. It is becoming evident that somatic mosaicism plays a major role in the formation of vascular lesions. The importance of utilizing Next-Generating Sequencing (NGS) for high-throughput and "deep" screening of both blood and lesional DNA and RNA is thus emphasized, as the somatic changes are present in low quantities. There are several examples where NGS has already accomplished discovering these changes. The identification of all the causative genes and unraveling of a holistic overview of the pathogenic mechanisms should enable generation of in vitro and in vivo models and lead to development of more effective treatments, not only targeted on symptoms.

Microcephaly with or without chorioretinopathy, lymphoedema, or mental retardation (MCLMR): review of phenotype associated with KIF11 mutations

Microcephaly with or without chorioretinopathy, lymphoedema, or mental retardation (MCLMR) (MIM No.152950) is a rare autosomal dominant condition for which a causative gene has recently been identified. Mutations in the kinesin family member 11 (KIF11) gene have now been described in 16 families worldwide. This is a review of the condition based on the clinical features of 37 individuals from 22 families. This report includes nine previously unreported families and additional information for some of those reported previously. The condition arose de novo in 8/20 families (40%). The parental results were not available for two probands. The mutations were varied and include missense, nonsense, frameshift, and splice site and are distributed evenly throughout the KIF11 gene. In our cohort, 86% had microcephaly, 78% had an ocular abnormality consistent with the diagnosis, 46% had lymphoedema, 73% had mild-moderate learning difficulties, 8% had epilepsy, and 8% had a cardiac anomaly. We identified three individuals with KIF11 mutations but no clinical features of MCLMR demonstrating reduced penetrance. The variable expression of the phenotype and the presence of mildly affected individuals indicates that the prevalence may be higher than expected, and we would therefore recommend a low threshold for genetic testing.

Involvement of the kinesin family members KIF4A and KIF5C in intellectual disability and synaptic function

INTRODUCTION

Kinesin superfamily (KIF) genes encode motor proteins that have fundamental roles in brain functioning, development, survival and plasticity by regulating the transport of cargo along microtubules within axons, dendrites and synapses. Mouse knockout studies support these important functions in the nervous system. The role of KIF genes in intellectual disability (ID) has so far received limited attention, although previous studies have suggested that many ID genes impinge on synaptic function.

METHODS

By applying next-generation sequencing (NGS) in ID patients, we identified likely pathogenic mutations in KIF4A and KIF5C. To further confirm the pathogenicity of these mutations, we performed functional studies at the level of synaptic function in primary rat hippocampal neurons.

RESULTS AND CONCLUSIONS

Four males from a single family with a disruptive mutation in the X-linked KIF4A (c.1489-8_1490delins10; p.?- exon skipping) showed mild to moderate ID and epilepsy. A female patient with a de novo missense mutation in KIF5C (c.11465A>C; p.(Glu237Lys)) presented with severe ID, epilepsy, microcephaly and cortical malformation. Knock-down of Kif4a in rat primary hippocampal neurons altered the balance between excitatory and inhibitory synaptic transmission, whereas the mutation in Kif5c affected its protein function at excitatory synapses. Our results suggest that mutations in KIF4A and KIF5C cause ID by tipping the balance between excitatory and inhibitory synaptic excitability.

Genetics of lymphatic anomalies

Lymphatic anomalies include a variety of developmental and/or functional defects affecting the lymphatic vessels: sporadic and familial forms of primary lymphedema, secondary lymphedema, chylothorax and chylous ascites, lymphatic malformations, and overgrowth syndromes with a lymphatic component. Germline mutations have been identified in at least 20 genes that encode proteins acting around VEGFR-3 signaling but also downstream of other tyrosine kinase receptors. These mutations exert their effects via the RAS/MAPK and the PI3K/AKT pathways and explain more than a quarter of the incidence of primary lymphedema, mostly of inherited forms. More common forms may also result from multigenic effects or post-zygotic mutations. Most of the corresponding murine knockouts are homozygous lethal, while heterozygotes are healthy, which suggests differences in human and murine physiology and the influence of other factors.

New developments in clinical aspects of lymphatic disease

The lymphatic system is fundamentally important to cardiovascular disease, infection and immunity, cancer, and probably obesity--the four major challenges in healthcare in the 21st century. This Review will consider the manner in which new knowledge of lymphatic genes and molecular mechanisms has demonstrated that lymphatic dysfunction should no longer be considered a passive bystander in disease but rather an active player in many pathological processes and, therefore, a genuine target for future therapeutic developments. The specific roles of the lymphatic system in edema, genetic aspects of primary lymphedema, infection (cellulitis/erysipelas), Crohn's disease, obesity, cancer, and cancer-related lymphedema are highlighted.

A synthetic lethal interaction between APC/C and topoisomerase poisons uncovered by proteomic screens

The Anaphase-promoting complex/cyclosome (APC/C) cofactor Cdh1 modulates cell proliferation by targeting multiple cell-cycle regulators for ubiquitin-dependent degradation. Lack of Cdh1 results in structural and numerical chromosome aberrations, a hallmark of genomic instability. By using a proteomic approach in Cdh1-null cells and mouse tissues, we have identified kinesin Eg5 and topoisomerase 2α as Cdh1 targets involved in the maintenance of genomic stability. These proteins are ubiquitinated and degraded through specific KEN and D boxes in a Cdh1-dependent manner. Whereas Cdh1-null cells display partial resistance to Eg5 inhibitors such as monastrol, lack of Cdh1 results in a dramatic sensitivity to Top2α poisons as a consequence of increased levels of trapped Top2α-DNA complexes. Chemical inhibition of the APC/C in cancer cells results in increased sensitivity to Top2α poisons. This work identifies in vivo targets of the mammalian APC/C-Cdh1 complex and reveals synthetic lethal interactions of relevance in anticancer treatments.

Exome sequencing greatly expedites the progressive research of Mendelian diseases

The advent of whole-exome sequencing (WES) has facilitated the discovery of rare structure and functional genetic variants. Combining exome sequencing with linkage studies is one of the most efficient strategies in searching disease genes for Mendelian diseases. WES has achieved great success in the past three years for Mendelian disease genetics and has identified over 150 new Mendelian disease genes. We illustrate the workflow of exome capture and sequencing to highlight the advantages of WES. We also indicate the progress and limitations of WES that can potentially result in failure to identify disease-causing mutations in part of patients. With an affordable cost, WES is expected to become the most commonly used tool for Mendelian disease gene identification. The variants detected cumulatively from previous WES studies will be widely used in future clinical services.

Exome sequencing identifies mutations in KIF14 as a novel cause of an autosomal recessive lethal fetal ciliopathy phenotype

Gene discovery using massively parallel sequencing has focused on phenotypes diagnosed postnatally such as well-characterized syndromes or intellectual disability, but is rarely reported for fetal disorders. We used family-based whole-exome sequencing in order to identify causal variants for a recurrent pattern of an undescribed lethal fetal congenital anomaly syndrome. The clinical signs included intrauterine growth restriction (IUGR), severe microcephaly, renal cystic dysplasia/agenesis and complex brain and genitourinary malformations. The phenotype was compatible with a ciliopathy, but not diagnostic of any known condition. We hypothesized biallelic disruption of a gene leading to a defect related to the primary cilium. We identified novel autosomal recessive truncating mutations in KIF14 that segregated with the phenotype. Mice with autosomal recessive mutations in the same gene have recently been shown to have a strikingly similar phenotype. Genotype-phenotype correlations indicate that the function of KIF14 in cell division and cytokinesis can be linked to a role in primary cilia, supported by previous cellular and model organism studies of proteins that interact with KIF14. We describe the first human phenotype, a novel lethal ciliary disorder, associated with biallelic inactivating mutations in KIF14. KIF14 may also be considered a candidate gene for allelic viable ciliary and/or microcephaly phenotypes.

Vascular endothelial growth factor receptor-2 promotes the development of the lymphatic vasculature

Vascular endothelial growth factor receptor 2 (VEGFR2) is highly expressed by lymphatic endothelial cells and has been shown to stimulate lymphangiogenesis in adult mice. However, the role VEGFR2 serves in the development of the lymphatic vascular system has not been defined. Here we use the Cre-lox system to show that the proper development of the lymphatic vasculature requires VEGFR2 expression by lymphatic endothelium. We show that Lyve-1^wt/Cre;Vegfr2^flox/flox mice possess significantly fewer dermal lymphatic vessels than Vegfr2^flox/flox mice. Although Lyve-1^wt/Cre;Vegfr2^flox/flox mice exhibit lymphatic hypoplasia, the lymphatic network is functional and contains all of the key features of a normal lymphatic network (initial lymphatic vessels and valved collecting vessels surrounded by smooth muscle cells (SMCs)). We also show that Lyve-1^Cre mice display robust Cre activity in macrophages and in blood vessels in the yolk sac, liver and lung. This activity dramatically impairs the development of blood vessels in these tissues in Lyve-1^wt/Cre;Vegfr2^flox/flox embryos, most of which die after embryonic day14.5. Lastly, we show that inactivation of Vegfr2 in the myeloid lineage does not affect the development of the lymphatic vasculature. Therefore, the abnormal lymphatic phenotype of Lyve-1^wt/Cre;Vegfr2^flox/flox mice is due to the deletion of Vegfr2 in the lymphatic vasculature not macrophages. Together, this work demonstrates that VEGFR2 directly promotes the expansion of the lymphatic network and further defines the molecular mechanisms controlling the development of the lymphatic vascular system.

Mutations in the VEGFR3 signaling pathway explain 36% of familial lymphedema

Lymphedema is caused by dysfunction of lymphatic vessels, leading to disabling swelling that occurs mostly on the extremities. Lymphedema can be either primary (congenital) or secondary (acquired). Familial primary lymphedema commonly segregates in an autosomal dominant or recessive manner. It can also occur in combination with other clinical features. Nine mutated genes have been identified in different isolated or syndromic forms of lymphedema. However, the prevalence of primary lymphedema that can be explained by these genetic alterations is unknown. In this study, we investigated 7 of these putative genes. We screened 78 index patients from families with inherited lymphedema for mutations in FLT4, GJC2, FOXC2, SOX18, GATA2, CCBE1, and PTPN14. Altogether, we discovered 28 mutations explaining 36% of the cases. Additionally, 149 patients with sporadic primary lymphedema were screened for FLT4, FOXC2, SOX18, CCBE1, and PTPN14. Twelve mutations were found that explain 8% of the cases. Still unidentified is the genetic cause of primary lymphedema in 64% of patients with a family history and 92% of sporadic cases. Identification of those genes is important for understanding of etiopathogenesis, stratification of treatments and generation of disease models. Interestingly, most of the proteins that are encoded by the genes mutated in primary lymphedema seem to act in a single functional pathway involving VEGFR3 signaling. This underscores the important role this pathway plays in lymphatic development and function and suggests that the unknown genes also have a role.

The classification and diagnostic algorithm for primary lymphatic dysplasia: an update from 2010 to include molecular findings

Historically, primary lymphoedema was classified into just three categories depending on the age of onset of swelling; congenital, praecox and tarda. Developments in clinical phenotyping and identification of the genetic cause of some of these conditions have demonstrated that primary lymphoedema is highly heterogenous. In 2010, we introduced a new classification and diagnostic pathway as a clinical and research tool. This algorithm has been used to delineate specific primary lymphoedema phenotypes, facilitating the discovery of new causative genes. This article reviews the latest molecular findings and provides an updated version of the classification and diagnostic pathway based on this new knowledge.