An inducible Cd79b mutation confers ibrutinib sensitivity in mouse models of Myd88-driven diffuse large B-cell lymphoma.

ABSTRACT: Diffuse large B-cell lymphoma (DLBCL) is the most common aggressive lymphoma and constitutes a highly heterogenous disease. Recent comprehensive genomic profiling revealed the identity of numerous molecularly defined DLBCL subtypes, including a cluster which is characterized by recurrent aberrations in MYD88, CD79B, and BCL2, as well as various lesions promoting a block in plasma cell differentiation, including PRDM1, TBL1XR1, and SPIB. Here, we generated a series of autochthonous mouse models to mimic this DLBCL cluster and specifically focused on the impact of Cd79b mutations in this setting. We show that canonical Cd79b immunoreceptor tyrosine-based activation motif (ITAM) mutations do not accelerate Myd88- and BCL2-driven lymphomagenesis. Cd79b-mutant murine DLBCL were enriched for IgM surface expression, reminiscent of their human counterparts. Moreover, Cd79b-mutant lymphomas displayed a robust formation of cytoplasmic signaling complexes involving MYD88, CD79B, MALT1, and BTK. These complexes were disrupted upon pharmacological BTK inhibition. The BTK inhibitor-mediated disruption of these signaling complexes translated into a selective ibrutinib sensitivity of lymphomas harboring combined Cd79b and Myd88 mutations. Altogether, this in-depth cross-species comparison provides a framework for the development of molecularly targeted therapeutic intervention strategies in DLBCL.

wnt10a is required for zebrafish median fin fold maintenance and adult unpaired fin metamorphosis.

BACKGROUND: Mutations of human WNT10A are associated with odonto-ectodermal dysplasia syndromes. Here, we present analyses of wnt10a loss-of-function mutants in the zebrafish. RESULTS: wnt10a mutant zebrafish embryos display impaired tooth development and a collapsing median fin fold (MFF). Rescue experiments show that wnt10a is essential for MFF maintenance both during embryogenesis and later metamorphosis. The MFF collapse could not be attributed to increased cell death or altered proliferation rates of MFF cell types. Rather, wnt10a mutants show reduced expression levels of dlx2a in distal-most MFF cells, followed by compromised expression of col1a1a and other extracellular matrix proteins encoding genes. Transmission electron microscopy analysis shows that although dermal MFF compartments of wnt10a mutants initially are of normal morphology, with regular collagenous actinotrichia, positioning of actinotrichia within the cleft of distal MFF cells becomes compromised, coinciding with actinotrichia shrinkage and MFF collapse. CONCLUSIONS: MFF collapse of wnt10a mutant zebrafish is likely caused by the loss of distal properties in the developing MFF, strikingly similar to the proposed molecular pathomechanisms underlying the teeth defects caused by the loss of Wnt10 in fish and mammals. In addition, it points to thus fur unknown mechanisms controlling the linear growth and stability of actinotrichia and their collagen fibrils.

Distinct Genetically Determined Origins of Myd88/BCL2-Driven Aggressive Lymphoma Rationalize Targeted Therapeutic Intervention Strategies.

Genomic profiling revealed the identity of at least 5 subtypes of diffuse large B-cell lymphoma (DLBCL), including the MCD/C5 cluster characterized by aberrations in MYD88, BCL2, PRDM1, and/or SPIB. We generated mouse models harboring B cell-specific Prdm1 or Spib aberrations on the background of oncogenic Myd88 and Bcl2 lesions. We deployed whole-exome sequencing, transcriptome, flow-cytometry, and mass cytometry analyses to demonstrate that Prdm1- or Spib-altered lymphomas display molecular features consistent with prememory B cells and light-zone B cells, whereas lymphomas lacking these alterations were enriched for late light-zone and plasmablast-associated gene sets. Consistent with the phenotypic evidence for increased B cell receptor signaling activity in Prdm1-altered lymphomas, we demonstrate that combined BTK/BCL2 inhibition displays therapeutic activity in mice and in five of six relapsed/refractory DLBCL patients. Moreover, Prdm1-altered lymphomas were immunogenic upon transplantation into immuno-competent hosts, displayed an actionable PD-L1 surface expression, and were sensitive to antimurine-CD19-CAR-T cell therapy, in vivo. SIGNIFICANCE: Relapsed/refractory DLBCL remains a major medical challenge, and most of these patients succumb to their disease. Here, we generated mouse models, faithfully recapitulating the biology of MYD88-driven human DLBCL. These models revealed robust preclinical activity of combined BTK/BCL2 inhibition. We confirmed activity of this regimen in pretreated non-GCB-DLBCL patients. See related commentary by Leveille et al., p. 8. This article is highlighted in the In This Issue feature, p. 1.

Ferroptosis response segregates small cell lung cancer (SCLC) neuroendocrine subtypes.

Loss of TP53 and RB1 in treatment-naïve small cell lung cancer (SCLC) suggests selective pressure to inactivate cell death pathways prior to therapy. Yet, which of these pathways remain available in treatment-naïve SCLC is unknown. Here, through systemic analysis of cell death pathway availability in treatment-naïve SCLC, we identify non-neuroendocrine (NE) SCLC to be vulnerable to ferroptosis through subtype-specific lipidome remodeling. While NE SCLC is ferroptosis resistant, it acquires selective addiction to the TRX anti-oxidant pathway. In experimental settings of non-NE/NE intratumoral heterogeneity, non-NE or NE populations are selectively depleted by ferroptosis or TRX pathway inhibition, respectively. Preventing subtype plasticity observed under single pathway targeting, combined treatment kills established non-NE and NE tumors in xenografts, genetically engineered mouse models of SCLC and patient-derived cells, and identifies a patient subset with drastically improved overall survival. These findings reveal cell death pathway mining as a means to identify rational combination therapies for SCLC.

Human RAD50 deficiency: Confirmation of a distinctive phenotype.

DNA double-strand breaks (DSBs) are highly toxic DNA lesions that can lead to chromosomal instability, loss of genes and cancer. The MRE11/RAD50/NBN (MRN) complex is keystone involved in signaling processes inducing the repair of DSB by, for example, in activating pathways leading to homologous recombination repair and nonhomologous end joining. Additionally, the MRN complex also plays an important role in the maintenance of telomeres and can act as a stabilizer at replication forks. Mutations in NBN and MRE11 are associated with Nijmegen breakage syndrome (NBS) and ataxia telangiectasia (AT)-like disorder, respectively. So far, only one single patient with biallelic loss of function variants in RAD50 has been reported presenting with features classified as NBS-like disorder. Here, we report a long-term follow-up of an unrelated patient with facial dysmorphisms, microcephaly, skeletal features, and short stature who is homozygous for a novel variant in RAD50. We could show that this variant, c.2524G > A in exon 15 of the RAD50 gene, induces aberrant splicing of RAD50 mRNA mainly leading to premature protein truncation and thereby, most likely, to loss of RAD50 function. Using patient-derived primary fibroblasts, we could show abnormal radioresistant DNA synthesis confirming pathogenicity of the identified variant. Immunoblotting experiments showed strongly reduced protein levels of RAD50 in the patient-derived fibroblasts and provided evidence for a markedly reduced radiation-induced AT-mutated signaling. Comparison with the previously reported case and with patients presenting with NBS confirms that RAD50 mutations lead to a similar, but distinctive phenotype.

ATM activity in T cells is critical for immune surveillance of lymphoma in vivo.

The proximal DNA damage response kinase ATM is frequently inactivated in human malignancies. Germline mutations in the ATM gene cause Ataxia-telangiectasia (A-T), characterized by cerebellar ataxia and cancer predisposition. Whether ATM deficiency impacts on tumor initiation or also on the maintenance of the malignant state is unclear. Here, we show that Atm reactivation in initially Atm-deficient B- and T cell lymphomas induces tumor regression. We further find a reduced T cell abundance in B cell lymphomas from Atm-defective mice and A-T patients. Using T cell-specific Atm-knockout models, as well as allogeneic transplantation experiments, we pinpoint impaired immune surveillance as a contributor to cancer predisposition and development. Moreover, we demonstrate that Atm-deficient T cells display impaired proliferation capacity upon stimulation, due to replication stress. Altogether, our data indicate that T cell-specific restoration of ATM activity or allogeneic hematopoietic stem cell transplantation may prevent lymphomagenesis in A-T patients.

Autosomal-Recessive Mutations in MESD Cause Osteogenesis Imperfecta.

Osteogenesis imperfecta (OI) comprises a genetically heterogeneous group of skeletal fragility diseases. Here, we report on five independent families with a progressively deforming type of OI, in whom we identified four homozygous truncation or frameshift mutations in MESD. Affected individuals had recurrent fractures and at least one had oligodontia. MESD encodes an endoplasmic reticulum (ER) chaperone protein for the canonical Wingless-related integration site (WNT) signaling receptors LRP5 and LRP6. Because complete absence of MESD causes embryonic lethality in mice, we hypothesized that the OI-associated mutations are hypomorphic alleles since these mutations occur downstream of the chaperone activity domain but upstream of ER-retention domain. This would be consistent with the clinical phenotypes of skeletal fragility and oligodontia in persons deficient for LRP5 and LRP6, respectively. When we expressed wild-type (WT) and mutant MESD in HEK293T cells, we detected WT MESD in cell lysate but not in conditioned medium, whereas the converse was true for mutant MESD. We observed that both WT and mutant MESD retained the ability to chaperone LRP5. Thus, OI-associated MESD mutations produce hypomorphic alleles whose failure to remain within the ER significantly reduces but does not completely eliminate LRP5 and LRP6 trafficking. Since these individuals have no eye abnormalities (which occur in individuals completely lacking LRP5) and have neither limb nor brain patterning defects (both of which occur in mice completely lacking LRP6), we infer that bone mass accrual and dental patterning are more sensitive to reduced canonical WNT signaling than are other developmental processes. Biologic agents that can increase LRP5 and LRP6-mediated WNT signaling could benefit individuals with MESD-associated OI.

Dual Inhibition of GLUT1 and the ATR/CHK1 Kinase Axis Displays Synergistic Cytotoxicity in KRAS-Mutant Cancer Cells.

The advent of molecularly targeted therapeutic agents has opened a new era in cancer therapy. However, many tumors rely on nondruggable cancer-driving lesions. In addition, long-lasting clinical benefits from single-agent therapies rarely occur, as most of the tumors acquire resistance over time. The identification of targeted combination regimens interfering with signaling through oncogenically rewired pathways provides a promising approach to enhance efficacy of single-agent-targeted treatments. Moreover, combination drug therapies might overcome the emergence of drug resistance. Here, we performed a focused flow cytometry-based drug synergy screen and identified a novel synergistic interaction between GLUT1-mediated glucose transport and the cell-cycle checkpoint kinases ATR and CHK1. Combined inhibition of CHK1/GLUT1 or ATR/GLUT1 robustly induced apoptosis, particularly in RAS-mutant cancer cells. Mechanistically, combined inhibition of ATR/CHK1 and GLUT1 arrested sensitive cells in S-phase and led to the accumulation of genotoxic damage, particularly in S-phase. In vivo, simultaneous inhibition of ATR and GLUT1 significantly reduced tumor volume gain in an autochthonous mouse model of KrasG12D -driven soft tissue sarcoma. Taken together, these findings pave the way for combined inhibition of GLUT1 and ATR/CHK1 as a therapeutic approach for KRAS-driven cancers. SIGNIFICANCE: Dual targeting of the DNA damage response and glucose transport synergistically induces apoptosis in KRAS-mutant cancer, suggesting this combination treatment for clinical validation in KRAS-stratified tumor patients.

UBQLN4 Represses Homologous Recombination and Is Overexpressed in Aggressive Tumors.

Genomic instability can be a hallmark of both human genetic disease and cancer. We identify a deleterious UBQLN4 mutation in families with an autosomal recessive syndrome reminiscent of genome instability disorders. UBQLN4 deficiency leads to increased sensitivity to genotoxic stress and delayed DNA double-strand break (DSB) repair. The proteasomal shuttle factor UBQLN4 is phosphorylated by ATM and interacts with ubiquitylated MRE11 to mediate early steps of homologous recombination-mediated DSB repair (HRR). Loss of UBQLN4 leads to chromatin retention of MRE11, promoting non-physiological HRR activity in vitro and in vivo. Conversely, UBQLN4 overexpression represses HRR and favors non-homologous end joining. Moreover, we find UBQLN4 overexpressed in aggressive tumors. In line with an HRR defect in these tumors, UBQLN4 overexpression is associated with PARP1 inhibitor sensitivity. UBQLN4 therefore curtails HRR activity through removal of MRE11 from damaged chromatin and thus offers a therapeutic window for PARP1 inhibitor treatment in UBQLN4-overexpressing tumors.

The Cdkn1aSUPER Mouse as a Tool to Study p53-Mediated Tumor Suppression.

Cdkn1a, which encodes p21, functions as a major route for p53-mediated cell-cycle arrest. However, the consequence of Cdkn1a gene dosage on tumor suppression has not been systematically investigated. Here, we employed BAC transgenesis to generate a Cdkn1aSUPER mouse, which harbors an additional Cdkn1a allele within its natural genomic context. We show that these mice display enhanced cell-cycle arrest and reduced apoptosis in response to genotoxic stress. Furthermore, using a chemically induced skin cancer model and an autochthonous Kras-driven lung adenocarcinoma model, we show that Cdkn1aSUPER mice display a cancer protection phenotype that is indistinguishable from that observed in Tp53SUPER animals. Moreover, we demonstrate that Tp53 and Cdkn1a cooperate in mediating cancer resistance, using a chemically induced fibrosarcoma model. Overall, our Cdkn1aSUPER allele enabled us to assess the contribution of Cdkn1a to Tp53-mediated tumor suppression.

Specific combinations of biallelic POLR3A variants cause Wiedemann-Rautenstrauch syndrome.

BACKGROUND: Wiedemann-Rautenstrauch syndrome (WRS) is a form of segmental progeria presenting neonatally, characterised by growth retardation, sparse scalp hair, generalised lipodystrophy with characteristic local fatty tissue accumulations and unusual face. We aimed to understand its molecular cause. METHODS: We performed exome sequencing in two families, targeted sequencing in 10 other families and performed in silico modelling studies and transcript processing analyses to explore the structural and functional consequences of the identified variants. RESULTS: Biallelic POLR3A variants were identified in eight affected individuals and monoallelic variants of the same gene in four other individuals. In the latter, lack of genetic material precluded further analyses. Multiple variants were found to affect POLR3A transcript processing and were mostly located in deep intronic regions, making clinical suspicion fundamental to detection. While biallelic POLR3A variants have been previously reported in 4H syndrome and adolescent-onset progressive spastic ataxia, recurrent haplotypes specifically occurring in individuals with WRS were detected. All WRS-associated POLR3A amino acid changes were predicted to perturb substantially POLR3A structure/function. CONCLUSION: Biallelic mutations in POLR3A, which encodes for the largest subunit of the DNA-dependent RNA polymerase III, underlie WRS. No isolated functional sites in POLR3A explain the phenotype variability in POLR3A-related disorders. We suggest that specific combinations of compound heterozygous variants must be present to cause the WRS phenotype. Our findings expand the molecular mechanisms contributing to progeroid disorders.

Targeting a non-oncogene addiction to the ATR/CHK1 axis for the treatment of small cell lung cancer.

Small cell lung cancer (SCLC) is a difficult to treat subtype of lung cancer. One of the hallmarks of SCLC is its almost uniform chemotherapy sensitivity. However, chemotherapy response is typically transient and patients frequently succumb to SCLC within a year following diagnosis. We performed a transcriptome analysis of the major human lung cancer entities. We show a significant overexpression of genes involved in the DNA damage response, specifically in SCLC. Particularly CHEK1, which encodes for the cell cycle checkpoint kinase CHK1, is significantly overexpressed in SCLC, compared to lung adenocarcinoma. In line with uncontrolled cell cycle progression in SCLC, we find that CDC25A, B and C mRNAs are expressed at significantly higher levels in SCLC, compared to lung adenocarcinoma. We next profiled the efficacy of compounds targeting CHK1 and ATR. Both, ATR- and CHK1 inhibitors induce genotoxic damage and apoptosis in human and murine SCLC cell lines, but not in lung adenocarcinoma cells. We further demonstrate that murine SCLC tumors were highly sensitive to ATR- and CHK1 inhibitors, while Kras G12D -driven murine lung adenocarcinomas were resistant against these compounds and displayed continued growth under therapy. Altogether, our data indicate that SCLC displays an actionable dependence on ATR/CHK1-mediated cell cycle checkpoints.

Two mouse models reveal an actionable PARP1 dependence in aggressive chronic lymphocytic leukemia.

Chronic lymphocytic leukemia (CLL) remains an incurable disease. Two recurrent cytogenetic aberrations, namely del(17p), affecting TP53, and del(11q), affecting ATM, are associated with resistance against genotoxic chemotherapy (del17p) and poor outcome (del11q and del17p). Both del(17p) and del(11q) are also associated with inferior outcome to the novel targeted agents, such as the BTK inhibitor ibrutinib. Thus, even in the era of targeted therapies, CLL with alterations in the ATM/p53 pathway remains a clinical challenge. Here we generated two mouse models of Atm- and Trp53-deficient CLL. These animals display a significantly earlier disease onset and reduced overall survival, compared to controls. We employed these models in conjunction with transcriptome analyses following cyclophosphamide treatment to reveal that Atm deficiency is associated with an exquisite and genotype-specific sensitivity against PARP inhibition. Thus, we generate two aggressive CLL models and provide a preclinical rational for the use of PARP inhibitors in ATM-affected human CLL.ATM and TP53 mutations are associated with poor prognosis in chronic lymphocytic leukaemia (CLL). Here the authors generate mouse models of Tp53- and Atm-defective CLL mimicking the high-risk form of human disease and show that Atm-deficient CLL is sensitive to PARP1 inhibition.

New gain-of-function mutation shows CACNA1D as recurrently mutated gene in autism spectrum disorders and epilepsy.

CACNA1D encodes the pore-forming α1-subunit of Cav1.3, an L-type voltage-gated Ca2+-channel. Despite the recent discovery of two de novo missense gain-of-function mutations in Cav1.3 in two individuals with autism spectrum disorder (ASD) and intellectual disability CACNA1D has not been considered a prominent ASD-risk gene in large scale genetic analyses, since such studies primarily focus on likely-disruptive genetic variants. Here we report the discovery and characterization of a third de novo missense mutation in CACNA1D (V401L) in a patient with ASD and epilepsy. For the functional characterization we introduced mutation V401L into two major C-terminal long and short Cav1.3 splice variants, expressed wild-type or mutant channel complexes in tsA-201 cells and performed whole-cell patch-clamp recordings. Mutation V401L, localized within the channel's activation gate, significantly enhanced current densities, shifted voltage dependence of activation and inactivation to more negative voltages and reduced channel inactivation in both Cav1.3 splice variants. Altogether, these gating changes are expected to result in enhanced Ca2+-influx through the channel, thus representing a strong gain-of-function phenotype. Additionally, we also found that mutant channels retained full sensitivity towards the clinically available Ca2+ -channel blocker isradipine. Our findings strengthen the evidence for CACNA1D as a novel candidate autism risk gene and encourage experimental therapy with available channel-blockers for this mutation. The additional presence of seizures and neurological abnormalities in our patient define a novel phenotype partially overlapping with symptoms in two individuals with PASNA (congenital primary aldosteronism, seizures and neurological abnormalities) caused by similar Cav1.3 gain-of-function mutations.

Heterozygous HNRNPU variants cause early onset epilepsy and severe intellectual disability.

Pathogenic variants in genes encoding subunits of the spliceosome are the cause of several human diseases, such as neurodegenerative diseases. The RNA splicing process is facilitated by the spliceosome, a large RNA-protein complex consisting of small nuclear ribonucleoproteins (snRNPs), and many other proteins, such as heterogeneous nuclear ribonucleoproteins (hnRNPs). The HNRNPU gene (OMIM *602869) encodes the heterogeneous nuclear ribonucleoprotein U, which plays a crucial role in mammalian development. HNRNPU is expressed in the fetal brain and adult heart, kidney, liver, brain, and cerebellum. Microdeletions in the 1q44 region encompassing HNRNPU have been described in patients with intellectual disability (ID) and other clinical features, such as seizures, corpus callosum abnormalities (CCA), and microcephaly. Recently, pathogenic HNRNPU variants were identified in large ID and epileptic encephalopathy cohorts. In this study, we provide detailed clinical information of five novels and review two of the previously published individuals with (likely) pathogenic de novo variants in the HNRNPU gene including three non-sense and two missense variants, one small intragenic deletion, and one duplication. The phenotype in individuals with variants in HNRNPU is characterized by early onset seizures (6/7), severe ID (6/6), severe speech impairment (6/6), hypotonia (6/7), and central nervous system (CNS) (5/6), cardiac (4/6), and renal abnormalities (3/4). In this study, we broaden the clinical and mutational HNRNPU-associated spectrum, and demonstrate that heterozygous HNRNPU variants cause epilepsy, severe ID with striking speech impairment and variable CNS, cardiac, and renal anomalies.

Smith-Kingsmore syndrome: A third family with the MTOR mutation c.5395G>A p.(Glu1799Lys) and evidence for paternal gonadal mosaicism.

Heterozygous germline mutations in MTOR have been shown to underlie Smith-Kingsmore syndrome, a rare autosomal dominant syndrome characterized by macrocephaly, developmental delay, and dysmorphic facial features. Recently, two unrelated families with the MTOR mutation, c.5395G>A p.(Glu1799Lys), were reported. Here, we describe siblings from a non-consanguineous German family in whom we identified the same heterozygous missense mutation in MTOR. Remarkably, in all reported families with Smith-Kingsmore syndrome and the MTOR c.5395G>A mutation, including the family described herein, healthy parents of recurrently affected children do not have detectable levels of the mutation in tested tissues, lending credence to gonadal mosaicism as the underlying mechanism. Furthermore, the glutamic acid at position 1799 was shown to present a recurrent somatic mutation site in several cancers, including colon cancer, pointing to a somatic mutational hotspot in MTOR. Importantly, we highlight the occurrence of multiple intestinal polyps in the older sibling. Further patients are required to establish definitively whether polyp formation forms part of the SKS clinical spectrum. © 2016 Wiley Periodicals, Inc.

An unusual presentation of Kabuki syndrome with orbital cysts, microphthalmia, and cholestasis with bile duct paucity.

Kabuki syndrome (KS) is a rare developmental disorder characterized by multiple congenital malformations, postnatal growth retardation, intellectual disability, and recognizable facial features. It is mainly caused by mutations in either KMT2D or KDM6A. We describe a 14-year-old boy with KS presenting with an unusual combination of bilateral microphthalmia with orbital cystic venous lymphatic malformation and neonatal cholestasis with bile duct paucity, in addition to the typical clinical features of KS. We identified the novel KMT2D mutation c.10588delC, p.(Glu3530Serfs*128) by Mendeliome (Illumina TruSight One®) sequencing, a next generation sequencing panel targeting 4,813 genes linked to human genetic disease. We analyzed the Mendeliome data for additional mutations which might explain the exceptional clinical presentation of our patient but did not find any, leading us to suspect that the above named symptoms might be part of the KMT2D-associated spectrum of anomalies. We thus extend the range of KS-associated malformations and propose a hypothetical connection between KMT2D and Notch signaling. © 2016 Wiley Periodicals, Inc.

Tumor suppression in basal keratinocytes via dual non-cell-autonomous functions of a Na,K-ATPase beta subunit.

The molecular pathways underlying tumor suppression are incompletely understood. Here, we identify cooperative non-cell-autonomous functions of a single gene that together provide a novel mechanism of tumor suppression in basal keratinocytes of zebrafish embryos. A loss-of-function mutation in atp1b1a, encoding the beta subunit of a Na,K-ATPase pump, causes edema and epidermal malignancy. Strikingly, basal cell carcinogenesis only occurs when Atp1b1a function is compromised in both the overlying periderm (resulting in compromised epithelial polarity and adhesiveness) and in kidney and heart (resulting in hypotonic stress). Blockade of the ensuing PI3K-AKT-mTORC1-NFκB-MMP9 pathway activation in basal cells, as well as systemic isotonicity, prevents malignant transformation. Our results identify hypotonic stress as a (previously unrecognized) contributor to tumor development and establish a novel paradigm of tumor suppression.

Papillon-Lefèvre syndrome: report of six patients and identification of a novel mutation.

Papillon-Lefèvre syndrome is an autosomal recessive genodermatosis typically manifesting with the constellation of palmoplantar keratoderma and progressive early-onset periodontitis. The cutaneous phenotype can be strikingly psoriasiform, possibly posing a diagnostic challenge. This rare disorder is caused by loss-of-function mutations in the CTSC gene, which encodes cathepsin C. We report six patients with Papillon-Lefèvre syndrome from five consanguineous Turkish families, in whom genetic analysis of the CTSC gene revealed four recurrent mutations (c.415G>A; c.1015C>T; c.1019A>G; and c.103-105delCTG) and a novel missense mutation (c.117G>T) in the homozygous state.

A syndrome of microcephaly, short stature, polysyndactyly, and dental anomalies caused by a homozygous KATNB1 mutation.

Using whole-exome sequencing, we identified a homozygous acceptor splice-site mutation in intron 6 of the KATNB1 gene in a patient from a consanguineous Turkish family who presented with congenital microcephaly, lissencephaly, short stature, polysyndactyly, and dental abnormalities. cDNA analysis revealed complete loss of the natural acceptor splice-site resulting either in the usage of an alternative, exonic acceptor splice-site inducing a frame-shift and premature protein truncation or, to a minor extent, in complete skipping of exon 7. Both effects most likely lead to complete loss of KATNB1 function. Homozygous and compound heterozygous mutations in KATNB1 have very recently been described as a cause of microcephaly with brain malformations and seizures. We extend the KATNB1 associated phenotype by describing a syndrome characterized by primordial dwarfism, lissencephaly, polysyndactyly, and dental anomalies, which is caused by a homozygous truncating KATNB1 mutation.