Collagen XVIII mutation in Knobloch syndrome with acute lymphoblastic leukemia

Whole genome sequencing in a Knobloch syndrome family confirms the molecular diagnosis

BACKGROUND

To establish the molecular diagnosis in two brothers presenting with the ocular features of Knobloch Syndrome using whole genome sequencing (WGS).

METHODS

Clinical examination and ophthalmological phenotyping were completed under general anaesthesia. DNA samples were tested on a targeted retinal dystrophy next-generation sequencing panel. Subsequently, WGS was performed to identify additional variants.

RESULTS

Clinical examination confirmed the diagnosis of Knobloch Syndrome. Targeted sequencing identified a novel heterozygous frameshift pathogenic variant in COL18A1, c.2864dupC; p.(Gly956ArgfsX20), inherited from their mother. A second paternally inherited heterozygous missense variant was identified in both brothers, c.5014 G > A; p.(Asp1672Asn), which was initially considered to have too high frequency to be pathogenic (MAF 8.8%). This led to an in-depth analysis of the COL18A1 locus using WGS data, which confirmed that Asp1672Asn is a likely pathogenic hypomorphic allele.

CONCLUSION

To date, all confirmed genetic diagnoses of Knobloch syndrome are attributable to variants in COL18A1. The family described here has a heterozygous novel loss of function variant. Detailed analysis of WGS data combined with family segregation studies concluded that although Asp1672Asn has a high population frequency, it is the most likely second pathogenic variant in our family. This supports the hypothesis that this is a hypomorphic allele, which, in combination with a loss of function pathogenic variant, leads to Knobloch syndrome.To our knowledge, this is the first time that WGS has been used to confirm a molecular diagnosis of Knobloch syndrome in this way and has provided further insight into the molecular mechanisms in this rare disorder.

Knobloch Syndrome Associated with Novel COL18A1 Variants in Chinese Population

Knobloch syndrome is an inherited disorder characterized by high myopia, retinal detachment, and occipital defects. Disease-causing mutations have been identified in the COL18A1 gene. This study aimed to investigate novel variants of COL18A1 in Knobloch syndrome and describe the associated phenotypes in Chinese patients. We reported six patients with Knobloch syndrome from four unrelated families in whom we identified five novel COL18A1 mutations. Clinical examination showed that all probands presented with high myopia, chorioretinal atrophy, and macular defects; one exhibited rhegmatogenous retinal detachment in one eye. Occipital defects were detected in one patient.

An Early Diagnostic Clue for COL18A1- and LAMA1-Associated Diseases: High Myopia With Alopecia Areata in the Cranial Midline

Background

High myopia with alopecia areata in the occipital region has been observed in patients with Knobloch syndrome caused by COL18A1 mutations. This study investigated other possible genetic causes of high myopia in patients with alopecia areata in the cranial midline.

Methods

Six patients with early onset high myopia and alopecia areata in the cranial midline were recruited. Targeted high-throughput sequencing was performed on the proband’s DNA to detect potential pathogenic variants. Cosegregation analysis was performed for available family members. Minigene assay and RNA Sequencing were used to validate the abnormality of possible splicing change and gross deletion. Ophthalmological and neuroimaging examinations were performed.

Results

Eight novel and one known loss-of-function mutants were detected in all six patients, including a gross deletion detected by RNA sequencing. Four COL18A1 mutants in three patients with scalp leisure in the occipital region; and five LAMA1 mutations in three patients with scalp leisure in the parietal region. Further assessments indicated that patients with COL18A1 mutations had Knobloch syndrome, and the patients with LAMA1 mutations had Poretti–Boltshauser syndrome.

Conclusion

Our study found that early onset high myopia with midline alopecia areata could be caused not only by mutations of the COL18A1 gene but also by mutations in the LAMA1 gene. To our knowledge, we are the first to observe scalp defects in patients with LAMA1 mutations. High myopia with alopecia areata in the cranial midline could be treated as an early diagnostic clue for ophthalmologists to consider the two kinds of rare diseases.

Whole exome sequencing revealed novel variants in consanguineous Pakistani families with intellectual disability

BACKGROUND

Intellectual disability (ID) is a heterogeneous disorder affecting 1-3% of the population. Elucidation of monogenic variants for ID is a current challenge. These variants can be better demonstrated in consanguineous affected families.

OBJECTIVE

The study was designed to find the genetic variants of ID in consanguineous families.

METHODS

We analyzed five unrelated consanguineous Pakistani families affected with ID using whole exome sequencing (WES). Data was analyzed using different bioinformatics tools and software.

RESULTS

We mapped four variants including three novels in four different ID known genes. Each variant is found in a different family, co-segregating with a recessive pattern of inheritance. The novel variants found are; c. 2_4del (p.?) mapped in ROS1 and c. 718G>A (p.Gly240Arg) in GRM1. Another novel causative variant, c.2673del (p.Gly892Aspfs*17) identified in COL18A1 in a recessive form, a gene reported for Knobloch syndrome that manifests ID along with typical retinal abnormalities, and this phenotype was confirmed on reverse phenotyping. A mutation c.2134C>T (p.Arg712*) in TRAPPC9 has been found first time in the homozygous recessive form in our enrolled three affected siblings while it was previously reported in compound heterozygous form in a Caucasian descent. While fifth family remained unsolved.

CONCLUSION

These mutations in four different genes with a recessive inheritance would be a contribution to the disease variant database of this devastating disorder.

The extracellular matrix: A key player in the pathogenesis of hematologic malignancies

Hematopoietic stem and progenitor cells located in the bone marrow lay the foundation for multiple lineages of mature hematologic cells. Bone marrow niches are architecturally complex with specific cellular, physiochemical, and biomechanical factors. Increasing evidence suggests that the bone marrow microenvironment contributes to the pathogenesis of hematological neoplasms. Numerous studies have deciphered the role of genetic mutations and chromosomal translocations in the development hematologic malignancies. Significant progress has also been made in understanding how the cellular components and cytokine interactions within the bone marrow microenvironment promote the evolution of hematologic cancers. Although the extracellular matrix is known to be a key player in the pathogenesis of various diseases, it's role in the progression of hematologic malignancies is less understood. In this review, we discuss the interactions between the extracellular matrix and malignant cells, and provide an overview of the role of extracellular matrix remodeling in sustaining hematologic malignancies.

Type XVIII Collagen Modulates Keratohyalin Granule Formation and Keratinization in Oral Mucosa

Epithelial keratinization involves complex cellular modifications that provide protection against pathogens and chemical and mechanical injuries. In the oral cavity, keratinized mucosa is also crucial to maintain healthy periodontal or peri-implant tissues. In this study, we investigated the roles of type XVIII collagen, a collagen-glycosaminoglycan featuring an extracellular matrix component present in the basement membrane, in oral mucosal keratinization. Histological analysis of keratinized and non-keratinized oral mucosa showed that type XVIII collagen was highly expressed in keratinized mucosa. Additionally, a 3D culture system using human squamous carcinoma cells (TR146) was used to evaluate and correlate the changes in the expression of type XVIII collagen gene, COL18A1, and epithelial keratinization-related markers, e.g., keratin 1 (KRT1) and 10 (KRT10). The results showed that the increase in COL18A1 expression followed the increase in KRT1 and KRT10 mRNA levels. Additionally, loss-of-function analyses using silencing RNA targeting COL18A1 mRNA and a Col18-knockout (KO) mouse revealed that the absence of type XVIII collagen induces a dramatic decrease in KRT10 expression as well as in the number and size of keratohyalin granules. Together, the results of this study demonstrate the importance of type XVIII collagen in oral mucosal keratinization.

Exploring the roles of MACIT and multiplexin collagens in stem cells and cancer

The extracellular matrix (ECM) is ubiquitously involved in neoplastic transformation, tumour growth and metastatic dissemination, and the interplay between tumour and stromal cells and the ECM is now considered crucial for the formation of a tumour-supporting microenvironment. The 28 different collagens (Col) form a major ECM protein family and display extraordinary functional diversity in tissue homeostasis as well as in pathological conditions, with functions ranging from structural support for tissues to regulatory binding activities and storage of biologically active cryptic domains releasable through ECM proteolysis. Two subfamilies of collagens, namely the plasma membrane-associated collagens with interrupted triple-helices (MACITs, including ColXIII, ColXXIII and ColXXV) and the basement membrane-associated collagens with multiple triple-helix domains with interruptions (multiplexins, including ColXV and ColXVIII), have highly interesting regulatory functions in tissue and organ development, as well as in various diseases, including cancer. An increasing, albeit yet sparse, data suggest that these collagens play crucial roles in conveying regulatory signals from the extracellular space to cells. We summarize here the current knowledge about MACITs and multiplexins as regulators of stemness and oncogenic processes, as well as their roles in influencing cell fate decisions in healthy and cancerous tissues. In addition, we present a bioinformatic analysis of the impacts of MACITs and multiplexins transcript levels on the prognosis of patients representing a wide array of malignant diseases, to aid future diagnostic and therapeutic efforts.

Knobloch syndrome caused by homozygous frameshift mutation of the COL18A1 gene in a Chinese pedigree

AIM

To explore the clinical feature and genetic etiology of a Chinese Knobloch syndrome family.

METHODS

Ocular examinations and magnetic resonance imagings (MRIs) were performed on the family. Whole exome sequencing was conducted on the two patients. Sanger sequencing was utilized to validate the presence of variation in the family as well as in 100 normal controls. Real-time quantitative polymerase chain reaction (PCR) was used to detect the expression level of COL18A1 in peripheral blood lymphocytes of the patients and normal carriers.

RESULTS

The affected subjects presented with vision loss, exotropia, cataracts, retinal detachment, and other complications. A homozygous c.4759_4760delCT (p.Leu1587ValfsX72) mutation (rs398122391) in COL18A1 was identified in the two patients, cosegregating with the phenotypes, and did not be detected in 100 normal controls. This mutation caused significant decreased expression of COL18A1 mRNA in the patients.

CONCLUSION

The findings strongly indicate that this mutation is the disease-causing mutation. Moreover, this is the first Knobloch syndrome pedigree reported in the Chinese population.

Collagen XVIII in tissue homeostasis and dysregulation - Lessons learned from model organisms and human patients

Collagen XVIII is a ubiquitous basement membrane (BM) proteoglycan produced in three tissue-specific isoforms that differ in their N-terminal non-collagenous sequences, but share collagenous and C-terminal non-collagenous domains. The collagenous domain provides flexibility to the large collagen XVIII molecules on account of multiple interruptions in collagenous sequences. Each isoform has a complex multi-domain structure that endows it with an ability to perform various biological functions. The long isoform contains a frizzled-like (Fz) domain with Wnt-inhibiting activity and a unique domain of unknown function (DUF959), which is also present in the medium isoform. All three isoforms share an N-terminal laminin-G-like/thrombospondin-1 sequence whose specific functions still remain unconfirmed. The proteoglycan nature of the isoforms further increases the functional diversity of collagen XVIII. An anti-angiogenic domain termed endostatin resides in the C-terminus of collagen XVIII and is proteolytically cleaved from the parental molecule during the BM breakdown for example in the process of tumour progression. Recombinant endostatin can efficiently reduce tumour angiogenesis and growth in experimental models by inhibiting endothelial cell migration and proliferation or by inducing their death, but its efficacy against human cancers is still a subject of debate. Mutations in the COL18A1 gene result in Knobloch syndrome, a genetic disorder characterised mainly by severe eye defects and encephalocele and, occasionally, other symptoms. Studies with gene-modified mice have elucidated some aspects of this rare disease, highlighting in particular the importance of collagen XVIII in the development of the eye. Research with model organisms have also helped in determining other structural and biological functions of collagen XVIII, such as its requirement in the maintenance of BM integrity and its emerging roles in regulating cell survival, stem or progenitor cell maintenance and differentiation and inflammation. In this review, we summarise current knowledge on the properties and endogenous functions of collagen XVIII in normal situations and tissue dysregulation. When data is available, we discuss the functions of the distinct isoforms and their specific domains.

Genetic Polymorphisms Associated to Folate Transport as Predictors of Increased Risk for Acute Lymphoblastic Leukemia in Mexican Children

Acute lymphoblastic leukemia (ALL) is a frequent neoplasia occurring in children. The most commonly used drug for the treatment of ALL is methotrexate (MTX), an anti-folate agent. Previous studies suggest that folate transporters play a role in ALL prognosis and that genetic polymorphism of genes encoding folate transporters may increase the risk of ALL. Therefore, the main goal of this study was to determine the associations among six genetic polymorphisms in four genes related with the folate transporter pathway to determine a relationship with the occurrence of ALL in Mexican children. A case-control study was performed in 73 ALL children and 133 healthy children from Northern and Northwestern Mexico. COL18A1 (rs2274808), SLC19A1 (rs2838956), ABCB1 (rs1045642 and rs1128503), and ABCC5 (rs9838667 and rs3792585). Polymorphisms were assayed through qPCR. Our results showed an increased ALL risk in children carrying CT genotype (OR = 2.55, CI 95% 1.11–5.83, p = 0.0001) and TT genotype (OR = 21.05, CI 95% 5.62–78.87, p < 0.0001) of COL18A1 rs2274808; in SLC19A1 rs2838956 AG carriers (OR = 44.69, CI 95% 10.42–191.63, p = 0.0001); in ABCB1 rs1045642 TT carriers (OR = 13.76, CI 95% 5.94–31.88, p = 0.0001); in ABCC5 rs9838667 AC carriers (OR = 2.61, CI 95% 1.05–6.48, p < 0.05); and in ABCC5 rs3792585 CC carriers (OR = 9.99, CI 95% 3.19–31.28, p = 0.004). Moreover, several combinations of genetic polymorphisms were found to be significantly associated with a risk for ALL. Finally, two combinations of ABCC5 polymorphisms resulted in protection from this neoplasia. In conclusion, certain genetic polymorphisms related to the folate transport pathway, particularly COL18A1 rs2274808, SLC19A1 rs2838956, ABCB1 rs1045642, and ABCC5 rs3792585, were associated with an increased risk for ALL in Mexican children.

2,3,7,8 Tetrachlorodibenzo-p-dioxin-induced RNA abundance changes identify Ackr3, Col18a1, Cyb5a and Glud1 as candidate mediators of toxicity

2,3,7,8 Tetrachlorodibenzo-p-dioxin (TCDD) is an aromatic, long-lived environmental contaminant. While the pathogenesis of TCDD-induced toxicity is poorly understood, it has been shown that the aryl hydrocarbon receptor (AHR) is required. However, the specific transcriptomic changes that lead to toxic outcomes have not yet been identified. We previously identified a panel of 33 genes that respond to TCDD treatment in two TCDD-sensitive rodent species. To identify genes involved in the onset of hepatic toxicity, we explored 25 of these in-depth using liver from two rat strains: the TCDD-resistant Han/Wistar (H/W) and the TCDD-sensitive Long–Evans (L–E). Time course and dose–response analyses of mRNA abundance following TCDD insult indicate that eight genes are similarly regulated in livers of both strains of rat, suggesting that they are not central to the severe L–E-specific TCDD-induced toxicities. The remaining 17 genes exhibited various divergent mRNA abundances between L–E and H/W strains after TCDD treatment. Several genes displayed a biphasic response where the initial response to TCDD treatment was followed by a secondary response, usually of larger magnitude in L–E liver. This secondary response was most often an exaggeration of the original TCDD-induced response. Only cytochrome b5 type A (microsomal) (Cyb5a) had equivalent TCDD sensitivity to the prototypic AHR-responsive cytochrome P450, family 1, subfamily a, polypeptide 1 (Cyp1a1), while six genes were less sensitive. Four genes showed an early inter-strain difference that was sustained throughout most of the time course (atypical chemokine receptor 3 (Ackr3), collagen, type XVIII, alpha 1 (Col18a1), Cyb5a and glutamate dehydrogenase 1 (Glud1)), and of those genes examined in this study, are most likely to represent genes involved in the pathogenesis of TCDD-induced hepatotoxicity in L–E rats.

Proteomic insight into the molecular function of the vitreous

The human vitreous contains primarily water, but also contains proteins which have yet to be fully characterized. To gain insight into the four vitreous substructures and their potential functions, we isolated and analyzed the vitreous protein profiles of three non-diseased human eyes. The four analyzed substructures were the anterior hyaloid, the vitreous cortex, the vitreous core, and the vitreous base. Proteins were separated by multidimensional liquid chromatography and identified by tandem mass spectrometry. Bioinformatics tools then extracted the expression profiles, signaling pathways, and interactomes unique to each tissue. From each substructure, a mean of 2,062 unique proteins were identified, with many being differentially expressed in a specific substructure: 278 proteins were unique to the anterior hyaloid, 322 to the vitreous cortex, 128 to the vitreous base, and 136 to the vitreous core. When the identified proteins were organized according to relevant functional pathways and networks, key patterns appeared. The blood coagulation pathway and extracellular matrix turnover networks were highly represented. Oxidative stress regulation and energy metabolism proteins were distributed throughout the vitreous. Immune functions were represented by high levels of immunoglobulin, the complement pathway, damage-associated molecular patterns (DAMPs), and evolutionarily conserved antimicrobial proteins. The majority of vitreous proteins detected were intracellular proteins, some of which originate from the retina, including rhodopsin (RHO), phosphodiesterase 6 (PDE6), and glial fibrillary acidic protein (GFAP). This comprehensive analysis uncovers a picture of the vitreous as a biologically active tissue, where proteins localize to distinct substructures to protect the intraocular tissues from infection, oxidative stress, and energy disequilibrium. It also reveals the retina as a potential source of inflammatory mediators. The vitreous proteome catalogues the dynamic interactions between the vitreous and surrounding tissues. It therefore could be an indirect and effective method for surveying vitreoretinal disease for specific biomarkers.

The dynamic sclera: extracellular matrix remodeling in normal ocular growth and myopia development

Myopia is a common ocular condition, characterized by excessive elongation of the ocular globe. The prevalence of myopia continues to increase, particularly among highly educated groups, now exceeding 80% in some groups. In parallel with the increased prevalence of myopia, are increases in associated blinding ocular conditions including glaucoma, retinal detachment and macular degeneration, making myopia a significant global health concern. The elongation of the eye is closely related to the biomechanical properties of the sclera, which in turn are largely dependent on the composition of the scleral extracellular matrix. Therefore an understanding of the cellular and extracellular events involved in the regulation of scleral growth and remodeling during childhood and young adulthood will provide future avenues for the treatment of myopia and its associated ocular complications.

Homozygosity mapping and whole exome sequencing reveal a novel homozygous COL18A1 mutation causing Knobloch syndrome

The aim of this study was to identify the genetic basis of a chorioretinal dystrophy with high myopia of unknown origin in a child of a consanguineous marriage. The proband and ten family members of Iranian ancestry participated in this study. Linkage analysis was carried out with DNA samples of the proband and her parents by using the Human SNP Array 6.0. Whole exome sequencing (WES) was performed with the patients' DNA. Specific sequence alterations within the homozygous regions identified by whole exome sequencing were verified by Sanger sequencing. Upon genetic analysis, a novel homozygous frameshift mutation was found in exon 42 of the COL18A1 gene in the patient. Both parents were heterozygous for this sequence variation. Mutations in COL18A1 are known to cause Knobloch syndrome (KS). Retrospective analysis of clinical records of the patient revealed surgical removal of a meningocele present at birth. The clinical features shown by our patient were typical of KS with the exception of chorioretinal degeneration which is a rare manifestation. This is the first case of KS reported in a family of Iranian ancestry. We identified a novel disease-causing (deletion) mutation in the COL18A1 gene leading to a frameshift and premature stop codon in the last exon. The mutation was not present in SNP databases and was also not found in 192 control individuals. Its localization within the endostatin domain implicates a functional relevance of endostatin in KS. A combined approach of linkage analysis and WES led to a rapid identification of the disease-causing mutation even though the clinical description was not completely clear at the beginning.

Specific collagen XVIII isoforms promote adipose tissue accrual via mechanisms determining adipocyte number and affect fat deposition

Collagen XVIII is an evolutionary conserved ubiquitously expressed basement membrane proteoglycan produced in three isoforms via two promoters (P). Here, we assess the function of the N-terminal, domain of unknown function/frizzled-like sequences unique to medium/long collagen XVIII by creating P-specific null mice. P2-null mice, which only produce short collagen XVIII, developed reduced bulk-adiposity, hepatic steatosis, and hypertriglyceridemia. These abnormalities did not develop in P1-null mice, which produce medium/long collagen XVIII. White adipose tissue samples from P2-null mice contain larger reserves of a cell population enriched in early adipocyte progenitors; however, their embryonic fibroblasts had ∼ 50% lower adipocyte differentiation potential. Differentiating 3T3-L1 fibroblasts into mature adipocytes produced striking increases in P2 gene-products and dramatic falls in P1-transcribed mRNA, whereas Wnt3a-induced dedifferentiation of mature adipocytes produced reciprocal changes in P1 and P2 transcript levels. P2-derived gene-products containing frizzled-like sequences bound the potent adipogenic inhibitor, Wnt10b, in vitro. Previously, we have shown that these same sequences bind Wnt3a, inhibiting Wnt3a-mediated signaling. P2-transcript levels in visceral fat were positively correlated with serum free fatty acid levels, suggesting that collagen α1 (XVIII) expression contributes to regulation of adipose tissue metabolism in visceral obesity. Medium/long collagen XVIII is deposited in the Space of Disse, and interaction between hepatic apolipoprotein E and this proteoglycan is lost in P2-null mice. These results describe a previously unidentified extracellular matrix-directed mechanism contributing to the control of the multistep adipogenic program that determines the number of precursors committing to adipocyte differentiation, the maintenance of the differentiated state, and the physiological consequences of its impairment on ectopic fat deposition.

Mutations in extracellular matrix genes NID1 and LAMC1 cause autosomal dominant Dandy-Walker malformation and occipital cephaloceles

We performed whole-exome sequencing of a family with autosomal dominant Dandy-Walker malformation and occipital cephaloceles and detected a mutation in the extracellular matrix (ECM) protein-encoding gene NID1. In a second family, protein interaction network analysis identified a mutation in LAMC1, which encodes a NID1-binding partner. Structural modeling of the NID1-LAMC1 complex demonstrated that each mutation disrupts the interaction. These findings implicate the ECM in the pathogenesis of Dandy-Walker spectrum disorders.

Rat-tail tendon fiber SAXS high-order diffraction peaks recovered by a superbright laboratory source and a novel restoration algorithm

The nanoscale structural order of air-dried rat-tail tendon is investigated using small-angle X-ray scattering (SAXS). SAXS fiber diffraction patterns were collected with a superbright laboratory microsource at XMI-LAB [Altamura, Lassandro, Vittoria, De Caro, Siliqi, Ladisa & Giannini (2012).J. Appl. Cryst.45, 869–873] for increasing integration times (up to 10 h) and a novel algorithm was used to estimate and subtract background, and to deconvolve the beam-divergence effects. Once the algorithm is applied, the peak visibility improves considerably and reciprocal space information up to the 22nd diffraction order is retrieved (q= 0.21 Å−1,d= 29 Å) for an 8–10 h integration time. The gain in the visibility is already significant for patterns collected for 0.5 h, at least on the more intense peaks. This demonstrates the viability of detecting structural changes on a molecular/nanoscale level in tissues with state-of-the-art laboratory sources and also the technical feasibility to adopt SAXS fiber diffraction as a future potential clinical indicator for disease.

Cataract surgery in Knobloch syndrome: a case report

Knobloch syndrome is an autosomal recessive disorder associated with early-onset ocular abnormalities and central nervous system malformations. Ocular abnormalities are usually severe, and include high myopia, vitreoretinal degeneration, retinal detachment, macular abnormalities, and cataract. The most frequent systemic changes are midline malformations of the brain, ventricular dilation, and occipital encephalocele. Cognitive delay may occur. We report a case of cataract in a child with Knobloch syndrome. Cataract surgery and follow-up are described.