Geert R Mortier

University of Antwerp | UA · Department of medical genetics

Achondroplasia is a lifelong condition requiring lifelong management. There is consensus that infants and children with achondroplasia should be managed by a multidisciplinary team experienced in the condition. However, many people are lost to follow-up after the transition from paediatric to adult care, and there is no standardised approach for ma...

Metaphyseal dysplasia with maxillary hypoplasia with or without brachydactyly (MDMHB) is an ultra‐rare skeletal dysplasia caused by heterozygous intragenic RUNX2 duplications, comprising either exons 3 to 5 or exons 3 to 6 of RUNX2. In this study, we describe a 14‐year‐old Belgian boy with metaphyseal dysplasia with maxillary hypoplasia but without...

Pathogenic variants disrupting the binding between sclerostin (encoded by SOST) and its receptor LRP4 have previously been described to cause sclerosteosis, a rare high bone mass disorder. The sclerostin-LRP4 complex inhibits canonical WNT signaling, a key pathway regulating osteoblastic bone formation and a promising therapeutic target for common...

Paget’s disease of bone (PDB) is a common, late-onset bone disorder, characterized by focal increases of bone turnover that can result in bone lesions. Heterozygous pathogenic variants in the Sequestosome 1 (SQSTM1) gene are found to be the main genetic cause of PDB. More recently, PFN1 and ZNF687 have been identified as causal genes in patients wi...

Foramen magnum stenosis is a serious, and potentially life-threatening complication of achondroplasia. The foramen magnum is smaller in infants with achondroplasia, compared with the general population, and both restricted growth in the first 2 years and premature closure of skull plate synchondroses can contribute to narrowing. Narrowing of the fo...

Spondyloepiphyseal dysplasia congenita (SEDC) is a severe non-lethal type 2 collagenopathy caused by pathogenic variants in the COL2A1 gene, which encodes the alpha-1 chain of type II collagen. SEDC is clinically characterized by severe short stature, degenerative joint disease, hearing impairment, orofacial anomalies and ocular manifestations. To...

Introduction: Spondylocostal dysostosis (SCD) is characterized by multiple vertebral abnormalities associated with abnormalities of the ribs. Five genes causative for the disease have been identified. These include DLL3 (OMIM *602768), MESP2 (OMIM #608681), LFNG (OMIM #609813), TBX6 (OMIM *602427), and HES7 (OMIM *608059). Methods: In the curren...

Hemizygous missense variants in the X-linked BGN gene, encoding the extracellular matrix protein biglycan, cause spondyloepimetaphyseal dysplasia (SEMD, biglycan type), which is clinically characterized by short stature, brachydactyly and osteoarthritis. Little is known about the pathomechanisms underlying SEMD, biglycan type. IPSC-derived chondroc...

Background Achondroplasia is the most common form of skeletal dysplasia, with serious comorbidities and complications that may occur from early infancy to adulthood, requiring lifelong management from a multidisciplinary team expert in the condition The European Achondroplasia Forum guiding principles of management highlight the importance of accur...

Varicella-zoster virus (VZV) infection of neuronal cells and the activation of cell-intrinsic antiviral responses upon infection are still poorly understood mainly due to the scarcity of suitable human in vitro models that are available to study VZV. We developed a compartmentalized human-induced pluripotent stem cell (hiPSC)-derived neuronal cultu...

Background Cleidocranial dysplasia (CCD) is a rare skeletal dysplasia with significant clinical variability. CCD patients typically present with delayed closure of fontanels and cranial sutures, dental anomalies, clavicular hypoplasia or aplasia and short stature. RUNX2 is currently the only known disease-causing gene for CCD, but several studies h...

Background Achondroplasia is a genetic condition that can cause complications across the lifespan. While complications in childhood are well documented, the natural history of achondroplasia in adults has, until recently, been relatively lacking, and little is known about the care they receive or how they access it. The European Achondroplasia Foru...

Introduction: The European Registry for Rare Bone and Mineral Conditions (EuRR-Bone) is closely linked to the European Reference Networks on Rare Bone Diseases (ERN BOND) and Rare Endocrine Conditions (Endo-ERN) and with its registry EuRRECa. It is however open to all professionals involved in the care of bone and mineral conditions. In EuRR-Bone w...

Context Natriuretic peptide receptor-C (NPR-C, encoded by NPR3) belongs to a family of cell membrane-integral proteins implicated in various physiological processes including longitudinal bone growth. NPR-C acts as a clearance receptor of natriuretic peptides, including C-type natriuretic peptide (CNP), which stimulate the cGMP-forming guanylyl cyc...

The induced pluripotent stem cell (iPSC) technology allows pathomechanistic and therapeutic investigation of human heritable disorders affecting tissue types whose collection from patients is difficult or even impossible. Amongst them are cartilage diseases. Over the past decade, iPSC‐chondrocyte disease models have been shown to exhibit several ke...

Antigen recognition through the T cell receptor (TCR) αβ heterodimer is one of the primary determinants of the adaptive immune response. Vaccines activate naïve T cells with high specificity to expand and differentiate into memory T cells. However, antigen-specific memory CD4 T cells exist in unexposed antigen-naïve hosts. In this study, we use hig...

Sclerosteosis is a high bone mass disorder, caused by pathogenic variants in the genes encoding sclerostin or LRP4. Both proteins form a complex that strongly inhibits canonical WNT signaling activity, a pathway of major importance in bone formation. So far, all reported disease-causing variants are located in the third β-propeller domain of LRP4,...

Paget’s disease of bone (PDB) is a common bone disorder characterized by focal lesions caused by increased bone turnover. Monogenic forms of PDB and PDB-related phenotypes as well as genome-wide association studies strongly support the involvement of genetic variation in components of the NF-κB signaling pathway in the pathogenesis of PDB. In this...

Background Primary microcephaly (PM) is defined as a significant reduction in occipitofrontal circumference (OFC) of prenatal onset. Clinical and genetic heterogeneity of PM represents a diagnostic challenge. Methods We performed detailed phenotypic and genomic analyses in a large cohort (n = 169) of patients referred for PM and could establish a...

Infantile Caffey disease is a rare disorder characterized by acute inflammation with subperiosteal new bone formation, associated with fever, pain, and swelling of the overlying soft tissue. Symptoms arise within the first weeks after birth and spontaneously resolve before the age of two years. Many, but not all, affected individuals carry the hete...

The involvement of genetic factors in the pathogenesis of KC has long been recognized but the identification of variants affecting the underlying protein functions has been challenging. In this study, we selected 34 candidate genes for KC based on previous whole-exome sequencing (WES) and the literature, and resequenced them in 745 KC patients and...

Primary microcephaly (PM) is defined as a significant reduction in occipito-frontal circumference (OFC) of prenatal onset. Clinical and genetic heterogeneity of PM represents a diagnostic challenge. We performed detailed phenotypic and genomic analyses in a large cohort (n=169) of patients referred for PM, and could establish a molecular diagnosis...

Aims We identified the first Belgian SCN5A founder mutation, c.4813 + 3_4813 + 6dupGGGT. To describe the clinical spectrum and disease severity associated with this mutation, clinical data of 101 SCN5A founder mutation carriers and 46 non-mutation carrying family members from 25 Belgian families were collected. Methods and results The SCN5A founde...

PRKACA and PRKACB code for two catalytic subunits (Cα and Cβ) of cAMP-dependent protein kinase (PKA), a pleiotropic holoenzyme that regulates numerous fundamental biological processes such as metabolism, development, memory, and immune response. We report seven unrelated individuals presenting with a multiple congenital malformation syndrome in who...

Imaging studies of the brain, head and neck, sinuses, and dental computed tomography are among the most frequently performed procedures in radiologic departments. Systematic evaluation in the bone window may reveal common and uncommon sclerotic osseous abnormalities of the craniofacial skeleton. Most of these findings are incidental and unrelated...

Background: Although carpal tunnel syndrome (CTS) is the most common form of peripheral entrapment neuropathy, its pathogenesis remains largely unknown. An estimated heritability index of 0.46 and an increased familial occurrence indicate that genetic factors must play a role in the pathogenesis. Methods and results: We report on a family in whi...

Antigen recognition through the T cell receptor (TCR) αβ heterodimer is one of the primary determinants of the adaptive immune response. Vaccines activate naïve T cells with high specificity to expand and differentiate into memory T cells that allow for a quick and robust T cell response upon exposure to the pathogen or re-exposure to the vaccine a...

Purpose In a significant proportion of children born small-for-gestational age (SGA) with failure of catch-up growth, the etiology of short stature remains unclear after routine diagnostic work-up. We wanted to investigate if extensive analysis of the (epi)genome can unravel the cause of growth failure in a significant portion of these children. P...

Although at first glance chondrodysplasia and aneurysmal thoracic aortopathy seem oddly dissimilar, recent lines of evidences indicate that they share molecular similarities. Chondrodysplasias are a group of skeletal disorders characterized by genetic defects in hyaline cartilage. Aneurysmal thoracic aortopathy is the pathological enlargement of th...

Melorheostosis is a very rare sclerosing bone dysplasia characterized by asymmetrical and progressive cortical hyperostosis, usually with involvement of soft tissues surrounding the lesions. Recently Kang et al. identified somatic mosaicism for variantsc (p.Gln56Pro, p.Lys57Asn, or p.Lys57Glu) in the negative regulatory domain of MAP2K1, resulting...

Skeletal dysplasias are a diverse group of heritable diseases affecting bone and cartilage growth. Throughout the years, the molecular defect underlying many of the diseases has been identified. These identifications led to novel insights in the mechanisms regulating bone and cartilage growth and homeostasis. One of the pathways that is clearly imp...

In the past years, WNT16 became an interesting target in the field of skeletal research, as it was identified as an essential regulator of the cortical bone compartment, with the ability to increase both cortical and trabecular bone mass and strength in vivo. Even though there are indications that these advantageous effects are coming from canonica...

Thanks to the recommendation of a combined Measles/Mumps/Rubella (MMR) vaccine, like Priorix®, these childhood diseases are less common now. This is beneficial to limit the spread of these diseases and work towards their elimination. However, the measles, mumps and rubella antibody titers show a large variability in short- and long-term immunity. T...

Introduction: Spondylo-epi-metaphyseal dysplasia (SEMD) represents a group of osteo-chondrodysplasias characterized by vertebral, epiphyseal as well as metaphyseal abnormalities. Several genes have been identified underlying the different forms. Methodology and results: Two relatives (cousins) in a family were found to have disproportionate shor...

Background: Meningitis can be caused by several viruses and bacteria. Identifying the causative pathogen as quickly as possible is crucial to initiate the most optimal therapy, as acute bacterial meningitis is associated with a significant morbidity and mortality. Bacterial meningitis requires antibiotics, as opposed to enteroviral meningitis, whi...

Paget’s disease of bone (PDB) is a common, late-onset bone disorder characterized by focal increase of bone turnover. Mutations in the SQSTM1 gene are found in up to 40% of patients and recent GWAS have led to novel associations with several loci. RIN3, the candidate gene located at the associated 14q32 locus, has recently been studied in a British...

Camurati–Engelmann disease or progressive diaphyseal dysplasia is a rare autosomal dominant sclerosing bone dysplasia. Mainly the skull and the diaphyses of the long tubular bones are affected. Clinically, the patients suffer from bone pain, easy fatigability, and decreased muscle mass and weakness in the proximal parts of the lower limbs resulting...

Osteogenesis imperfecta (OI) is the commonest form of heritable bone fragility. It is mainly characterized by fractures, hearing loss and dentinogenesis imperfecta. OI patients are at increased risk of cardiovascular disease of variable severity. Aortic aneurysm/dissection is one of the rarer but potentially serious cardiovascular complications of...

Pathogens of past and current infections have been identified directly by means of PCR or indirectly by measuring a specific immune response (e.g., antibody titration). Using a novel approach, Emerson and colleagues showed that the cytomegalovirus serostatus can also be accurately determined by using a T cell receptor repertoire data mining approac...

Introduction: As the hepatitis B virus is widely spread and responsible for considerable morbidity and mortality, WHO recommends vaccination from infancy to reduce acute infection and chronic carriers. However, current subunit vaccines are not 100% efficacious and leave 5-10% of recipients unprotected. Methods: To evaluate immune responses after...

Around 30% of individuals will develop herpes zoster (HZ), caused by the varicella zoster virus (VZV), during their life. While several risk factors for HZ, such as immunosuppressive therapy, are well known, the genetic and molecular components that determine the risk of otherwise healthy individuals to develop HZ are still poorly understood. We cr...

Purpose of review: The group of sclerosing bone disorders encompasses a variety of disorders all marked by increased bone mass. In this review, we give an overview of the genetic causes of this heterogeneous group of disorders and briefly touch upon the value of these findings for the development of novel therapeutic agents. Recent findings: Adv...

Case report A newborn girl presented with a small thorax, short limbs, bilateral postaxial polydactyly with cutaneous syndac-tyly and dystrophic nails. Further clinical examination revealed a small indentation on the middle part of the upper lip, hypertrophic gingiva and a prominent frenu-lum. Neonatal radiographic evaluation showed dysplasia of mu...

Author summary Osteoporosis is a skeletal disorder affecting hundreds of millions of people, and is characterized by a low bone mineral density (BMD) and increased susceptibility to fracture. Genetic factors are the greatest determinants of BMD, but only a small fraction of these have been identified through genome-wide association studies. Studyin...

Structural and cellular properties of the skeletal phenotype of conditional Zip14L438R female knock-in mice. (A) Representative undecalcified spine (upper row) and tibia sections (bottom row) from Zip14fl/-, Zip14fl/-; Runx2-Cre and Zip14fl/-; CtsK-Cre mice stained with von Kossa/van Gieson. Vertebrae of Zip14fl/-; Runx2-Cre mice show less trabecul...

Dynamic histomorphometric analysis of conditional Zip14L438R female knock-in mice. (A) Dynamic histomorphometry of the tibial endocortical (Ct), (B) tibial periosteal (P) and (C) trabecular (Tb) bone surface measuring the mineralizing surface (MS/BS), bone formation rate (BFR/BS) and mineral apposition rate (MAR) in Zip14fl/-; Runx2-Cre and Zip14fl...

Quantitative structural histomorphometry of spine sections from controls (Zip14fl/-) and conditional Zip14L438R knock-in mice. Quantitative analysis of trabecular (Tb) bone parameters on lumbar spine sections stained with Von Kossa/Van Gieson confirms a significantly decreased trabecular bone volume (BV/TV), number (Tb.N), and increased separation...

Dynamic histomorphometric analysis of the tibial periosteal (P) bone surface of conditional Zip14L438R male knock-in mice. Dynamic histomorphometry of the tibial periosteal (P) bone surface indicates. N = 6 animals/genotype; *: p<0.05; **: p<0.025 by 2-tailed Student’s t-test (compared to Zip14fl/- mice). (TIF)

Negative control for immunohistochemistry experiments. Immunohistochemistry of osteoblastoma and giant cell tumor tissue with a rabbit IgG isotype control shows no positive signal in osteoblasts (black line), in giant osteoclast-like cells (arrowheads) and in osteocytes. Scale bars upper figures, 500μm; scale bars lower figures, 100μm. (TIF)

Generation and genotyping of a floxed Zip14L438R mouse model. (A) A mouse model with floxed Zip14L438R was generated through targeted insertion within the ROSA26 locus. A loxP-flanked transcriptional STOP cassette is incorporated between Zip14L438R and its CAG promoter to allow the expression of the resulting transgene to be dependent upon the Cre...

Subcellular localization of wildtype and mutant (L441R) ZIP14 in the Golgi apparatus and in early and late endosomes of HEK293T cells. Red fluorescent staining of markers for the Golgi apparatus (golgin-97, left panel) and early (EEA1, central panel) and late endosomes (Rab7, right panel) was performed after transfection of a green fluorescent prot...

μCT analysis of femora of controls (Zip14fl/-) and conditional Zip14L438R female knock-in mice. (A) 3D reconstruction of whole femora of Zip14fl/- controls, Zip14fl/-; Runx2-Cre and Zip14fl/-; CtsK-Cre mice. Femora of Zip14fl/-; Runx2-Cre mice show an increased cortical thickness and decreased midshaft diameter along with a decreased trabecular bon...

Table S1. Clinical Details for 162 Individuals with an NF1 Missense Mutation Affecting One of Five Codons 844–848 from 129 Different Families

La mucolipidose de type III est une maladie de surcharge lysosomale rare et héréditaire qui se caractérise, sur le plan radiologique, par une forme légère à modérée de dysostosis multiplex congenita. D’un point de vue clinique, elle se manifeste par une raideur et des douleurs osseuses. Des troubles systémiques peuvent survenir. Les anomalies radio...

Neurofibromatosis type 1 (NF1), a common genetic disorder with a birth incidence of 1:2,000–3,000, is characterized by a highly variable clinical presentation. To date, only two clinically relevant intragenic genotype-phenotype correlations have been reported for NF1 missense mutations affecting p.Arg1809 and a single amino acid deletion p.Met922de...

Varicella zoster virus (VZV) typically causes chickenpox upon primary infection. In rare cases, VZV can give rise to life-threatening disease in otherwise healthy people, but the immunological basis for this remains unexplained. We report 4 cases of acute severe VZV infection affecting the central nervous system or the lungs in unrelated, otherwise...

Smith-Lemli-Opitz syndrome (SLOS; OMIM 270400) is a well known autosomal recessively inherited multiple congenital malformation syndrome. Typical limb malformations seen in individuals with SLOS include post-axial polydactyly and 2-3 toe cutaneous syndactyly. We present 2 unrelated 20-week fetuses with striking abnormalities involving the hands and...

Primary electrical disease (PED) is characterized by cardiac arrhythmias, which can lead to sudden cardiac death in the absence of detectable structural heart disease. PED encompasses a diversity of inherited syndromes, predominantly Brugada syndrome, early repolarization syndrome, long QT syndrome, short QT syndrome, arrhythmogenic right ventricul...

Intellectual disability (ID) affects approximately 1–2% of the general population and is characterized by impaired cognitive abilities. ID is both clinically as well as genetically heterogeneous, up to 2000 genes are estimated to be involved in the emergence of the disease with various clinical presentations. For many genes, only a few patients hav...

Purpose: Thoracic aortic aneurysm and dissection (TAAD) is typically inherited in an autosomal dominant manner, but rare X-linked families have been described. So far, the only known X-linked gene is FLNA, which is associated with the periventricular nodular heterotopia type of Ehlers-Danlos syndrome. However, mutations in this gene explain only a...

In approximately 20% of individuals with Kagami-Ogata syndrome (KOS14, MIM 608149), characterized by a bell-shaped thorax with coat-hanger configuration of the ribs, joint contractures, abdominal wall defects and polyhydramnios during the pregnancy, the syndrome is caused by a maternal deletion of the imprinted gene cluster in chromosome 14q32.2. M...

Whole genome sequencing of a severely affected dizygotic twin with an autism spectrum disorder and intellectual disability revealed a compound heterozygous mutation in the HTR7 gene as the only variation not detected in control databases. Each parent carries one allele of the mutation, which is not present in an unaffected stepsister. The HTR7 gene...

Autosomal-dominant tubulo-interstitial kidney disease (ADTKD) encompasses a group of disorders characterized by renal tubular and interstitial abnormalities, leading to slow progressive loss of kidney function requiring dialysis and kidney transplantation. Mutations in UMOD, MUC1, and REN are responsible for many, but not all, cases of ADTKD. We re...

Background and aim: Osteogenesis imperfecta (OI), also called brittle bone disease, is a clinically and genetically heterogeneous disorder characterized by decreased bone density. Autosomal dominant forms result from mutations in either the COL1A1 (collagen type I alpha-1 chain) or COL1A2 (collagen type I alpha-2 chain) genes encoding the type I c...

Background: Osteosclerotic metaphyseal dysplasia (OSMD) is a unique form of osteopetrosis characterised by severe osteosclerosis localised to the bone ends. The mode of inheritance is autosomal recessive. Its genetic basis is not known. Objective: To identify the disease gene for OSMD. Methods and results: By whole exome sequencing in a boy wi...

Although there are nearly 100 different causative genes identified for nonsyndromic hearing loss (NSHL), Sanger sequencing based DNA diagnostics usually only analyses three, namely GJB2, SLC26A4 and OTOF. As this is seen as inadequate, there is a need for high throughput diagnostic methods to detect disease-causing variations, including single nucl...

The 22q11.2 deletion syndrome is the most common microdeletion disorder, with wide phenotypic variability. To investigate variation within the non-deleted allele we performed targeted resequencing of the 22q11.2 region for 127 patients, identifying multiple deletion sizes, including two deletions with atypical breakpoints. We cataloged ~12,000 hemi...

Mutations in the LRP4 gene, coding for a Wnt signaling coreceptor, have been found to cause several allelic conditions. Among these, two are characterized by a strong skeletal involvement, namely sclerosteosis and Cenani-Lenz syndrome. In this work, we evaluated the role of LRP4 in the pathophysiology of these diseases. First, we report a novel LRP...

Recurrent rearrangements of chromosome 1q21.1 that occur as a consequence of non-allelic homologous recombination (NAHR) show considerable variability in phenotypic expression and penetrance. Chromosome 1q21.1 deletions (OMIM 612474) have been associated with microcephaly, intellectual disability, autism, schizophrenia, cardiac abnormalities and ca...

At least 14 causative genes have been identified for both syndromic and non-syndromic forms of thoracic aortic aneurysm/dissection (TAA), an important cause of death in the industrialized world. Molecular confirmation of the diagnosis is increasingly important for gene-tailored patient management but consecutive, conventional molecular TAA gene scr...

Inherited dental malformations constitute a clinically and genetically heterogeneous group of disorders. Here, we report on four families, three of them consanguineous, with an identical phenotype, characterized by significant short stature with brachyolmia and hypoplastic amelogenesis imperfecta (AI) with almost absent enamel. This phenotype was f...

Nephronophthisis (NPHP) is an autosomal recessive cystic kidney disease that is the most frequent monogenic cause of end-stage renal disease in children. Infantile NPHP, often in combination with other features like situs inversus, are commonly caused by mutations in the INVS gene. INVS encodes the ciliary protein inversin, and mutations induce dys...

Sclerosing bone dysplasias are a group of rare, monogenic disorders characterized by increased bone density resulting from the disturbance in the fragile equilibrium between bone formation and resorption. Over the last decade, major contributions have been made toward better understanding of the pathogenesis of these conditions. These studies provi...

Desbuquois dysplasia (DBQD) is a severe condition characterized by short stature, joint laxity, and advanced carpal ossification. Based on the presence of additional hand anomalies, we have previously distinguished DBQD type 1 and identified CANT1 (calcium activated nucleotidase 1) mutations as responsible for DBQD type 1. We report here the identi...

Cornelia de Lange syndrome (CdLS) is a multisystem genetic disorder with distinct facies, growth failure, intellectual disability, distal limb anomalies, gastrointestinal and neurological disease. Mutations in NIPBL, encoding a cohesin regulatory protein, account for >80% of cases with typical facies. Mutations in the core cohesin complex proteins,...

Camurati-Engelmann disease (CED, OMIM 131300), or progressive diaphyseal dysplasia, is a rare autosomal dominant skeletal dysplasia, caused by mutations in the transforming growth factor-β1 (TGFβ1) gene. We describe the first Indian CED family with genetic confirmation and presenting manifestations. The proband is a 17-year-old woman who presented...

Recently, microarrays have replaced karyotyping as a first tier test in patients with idiopathic intellectual disability and/or multiple congenital abnormalities (ID/MCA) in many laboratories. Although in about 14-18% of such patients, DNA copy-number variants (CNVs) with clinical significance can be detected, microarrays have the disadvantage of m...