Review of X-linked syndromes with arthrogryposis or early contractures-aid to diagnosis and pathway identification

Perspective: Modulating the integrated stress response to slow aging and ameliorate age-related pathology

Healthy aging requires the coordination of numerous stress signaling pathways that converge on the protein homeostasis network. The Integrated Stress Response (ISR) is activated by diverse stimuli, leading to phosphorylation of the eukaryotic translation initiation factor elF2 in its α-subunit. Under replete conditions, elF2 orchestrates 5' cap-dependent mRNA translation and is thus responsible for general protein synthesis. elF2α phosphorylation, the key event of the ISR, reduces global mRNA translation while enhancing the expression of a signature set of stress response genes. Despite the critical role of protein quality control in healthy aging and in numerous longevity pathways, the role of the ISR in longevity remains largely unexplored. ISR activity increases with age, suggesting a potential link with the aging process. Although decreased protein biosynthesis, which occurs during ISR activation, have been linked to lifespan extension, recent data show that lifespan is limited by the ISR as its inhibition extends survival in nematodes and enhances cognitive function in aged mice. Here we survey how aging affects the ISR, the role of the ISR in modulating aging, and pharmacological interventions to tune the ISR. Finally, we will explore the ISR as a plausible target for clinical interventions in aging and age-related disease.

A novel Xp11.22-22.33 deletion suggesting a possible mechanism of congenital cervical spinal muscular atrophy

BACKGROUND

Congenital cervical spinal muscular atrophy (CCSMA) is a rare, nonprogressive, neurogenic disorder characterized by symmetric arthrogryposis and motor deficits mainly confined to upper extremities. Since its first proposal by Darwish et al. 39 years ago, only few cases have ever been reported. Vascular insult to the anterior horn of cervical spinal cord during fetal development was speculated to be the cause, however, the exact pathogenesis is still not well understood.

METHODS

In this study, whole-exome sequencing (WES) and copy number variation (CNV) analysis were conducted on a definitive CCSMA patient, confirmed by the clinical manifestations and other supplementary examinations.

RESULTS

On physical examination, the patient was mainly characterized by symmetric, congenital, nonprogressive contractures, hypotonia, and muscle weakness mainly confined to the upper limbs, which were further supported by MRI and electromyography. Neuromuscular biopsy of the deltoid muscle demonstrated the type 1 myofiber predominance without any infiltration of inflammatory cells. The WES and CNV analysis unveiled a de novo Xp11.22-22.33 deletion. On further examination of the genes contained within this segment, we recognize UBA1 gene as the most likely pathogenic gene. Ubiquitin-like modifier activating enzyme 1 is encoded by UBA1 gene (MIM 314370) located in Xp11.3 and is a critical protein that plays a vital role in ubiquitin-proteasome system and autophagy. It is well documented that UBA1 gene mutation causes X-linked infantile spinal muscular atrophy (XL-SMA), which manifests phenotypes of arthrogryposis, hypotonia, and myopathic face. Type 2 XL-SMA, which follows a nonprogressive and nonlethal course is very similar to the presentations of CCSMA.

CONCLUSION

The phenotypic similarities between this CCSMA case and XL-SMA prompt us to hypothesize a possible connection between UBA1 gene deficit and the pathogenesis of CCSMA. Our study is the first to demonstrate that CCSMA might have a genetic etiology, thus, expanding our insights into the underlying cause of CCSMA.

A novel de novo nonsense mutation in ZC4H2 causes Wieacker-Wolff Syndrome

Background

Wieacker‐Wolff syndrome (WWS) is a congenital X‐linked neuromuscular disorder, which was firstly reported in 1985. Zinc finger C4H2‐type containing (ZC4H2) gene has been found to be associated with the disease pathogenesis. However, the underlying mechanism remains elusive.

Methods

Whole‐exome sequencing was performed to identify the mutations. Expression plasmids were constructed and cell culture and immune‐biochemical assays were used to examine the effects of the mutation.

Results

We reported a female patient with classical symptoms of WWS and discovered a novel nonsense heterozygous mutation (p.R67X; c.199C>T) in ZC4H2 gene in the patient but not in her parents. The mutation resulted in a 66 amino‐acid truncated ZC4H2 protein. The mutation is located in the key helix domain and it altered the subcellular locations of the mutant ZC4H2 protein. X‐chromosome inactivation (XCI) pattern analysis revealed that the XCI ratio of the proband was 22:78.

Conclusion

Female heterozygous carriers with nonsense mutation with a truncated ZC4H2 protein could lead to the pathogenesis of Wieacker‐Wolff syndrome and our study provides a potential new target for the disease treatment.

Deleterious de novo variants of X-linked ZC4H2 in females cause a variable phenotype with neurogenic arthrogryposis multiplex congenita

Pathogenic variants in the X-linked gene ZC4H2, which encodes a zinc-finger protein, cause an infrequently described syndromic form of arthrogryposis multiplex congenita (AMC) with central and peripheral nervous system involvement. We present genetic and detailed phenotypic information on 23 newly identified families and simplex cases that include 19 affected females from 18 families and 14 affected males from nine families. Of note, the 15 females with deleterious de novo ZC4H2 variants presented with phenotypes ranging from mild to severe, and their clinical features overlapped with those seen in affected males. By contrast, of the nine carrier females with inherited ZC4H2 missense variants that were deleterious in affected male relatives, four were symptomatic. We also compared clinical phenotypes with previously published cases of both sexes and provide an overview on 48 males and 57 females from 42 families. The spectrum of ZC4H2 defects comprises novel and recurrent mostly inherited missense variants in affected males, and de novo splicing, frameshift, nonsense, and partial ZC4H2 deletions in affected females. Pathogenicity of two newly identified missense variants was further supported by studies in zebrafish. We propose ZC4H2 as a good candidate for early genetic testing of males and females with a clinical suspicion of fetal hypo-/akinesia and/or (neurogenic) AMC.

Central nervous system involvement in arthrogryposis multiplex congenita: Overview of causes, diagnosis, and care

Arthrogryposis or AMC, arthrogryposis multiplex congenita, is defined as multiple congenital joint contractures in more than two joints and in different body areas. The common cause of all AMC is lack of movement in utero, which in turn can have different causes, one of which is CNS involvement. Intellectual disability/CNS involvement is found in approximately 25% of all AMC. AMC with CNS involvement includes a large number of genetic syndromes. So far, more than 400 genes have been identified as linked to AMC, with and without CNS involvement. A number of neonatally lethal syndromes and syndromes resulting in severe disability due to CNS malfunction belong to this group of syndromes. There are several X-linked disorders with AMC, which are primarily related to intellectual disability. A number of neuromuscular disorders may include AMC and CNS/brain involvement. Careful clinical evaluation by a geneticist and a pediatrician/pediatric neurologist is the first step in making a specific diagnosis. Further investigations may include MRI of the brain and spinal cord, electroencephalogram, blood chemistry for muscle enzymes, other organ investigations (ophtalmology, cardiology, gastrointestinal, and genitourinary systems). Nerve conduction studies, electromyogram, and muscle pathology may be of help when there is associated peripheral nervous system involvement. But most importantly, genetic investigations with targeted or rather whole exome or genome sequencing should be performed. A correct diagnosis is important in planning adequate treatment, in genetic counselling and also for future understanding of pathogenic mechanisms and possible new treatments. A multidiciplinary team is needed both in investigation and treatment.

Gene ontology analysis of arthrogryposis (multiple congenital contractures)

In 2016, we published an article applying Gene Ontology Analysis to the genes that had been reported to be associated with arthrogryposis (multiple congenital contractures) (Hall & Kiefer, 2016). At that time, 320 genes had been reported to have mutations associated with arthrogryposis. All were associated with decreased fetal movement. These 320 genes were analyzed by biological process and cellular component categories, and yielded 22 distinct groupings. Since that time, another 82 additional genes have been reported, now totaling 402 genes, which when mutated, are associated with arthrogryposis (arthrogryposis multiplex congenita). So, we decided to update the analysis in order to stimulate further research and possible treatment. Now, 29 groupings can be identified, but only 19 groups have more than one gene.

Fetal arthrogryposis: Challenges and perspectives for prenatal detection and management

Antenatal identification of fetuses with multiple congenital contractures or arthrogryposis multiplex congenita (AMC) may be challenging. The first clinical sign is often reduced fetal movement and/or contractures, as seen on prenatal ultrasounds. This can be apparent at any point, from early to late pregnancy, may range from mild to severe involvement, with or without associated other structural anomalies. Possible etiologies and their prognosis need to be interpreted with respect to developmental timing. The etiology of AMC is highly heterogeneous and making the specific diagnosis will guide prognosis, counseling and prenatal and perinatal management. Current ultrasound practice identifies only approximately 25% of individuals with arthrogryposis prenatally before 24 weeks of pregnancy in a general obstetrics care population. There are currently no studies and guidelines that address the question of when and how to assess for fetal contractures and movements during pregnancy. The failure to identify fetuses with arthrogryposis before 24 weeks of pregnancy means that physicians and families are denied reproductive options and interventions that may improve outcome. We review current practice and recommend adjusting the current prenatal imaging and genetic diagnostic strategies to achieve early prenatal detection and etiologic diagnosis. We suggest exploring options for in utero therapy to increase fetal movement for ongoing pregnancies.

MET mutation causes muscular dysplasia and arthrogryposis

Arthrogryposis is a group of phenotypically and genetically heterogeneous disorders characterized by congenital contractures of two or more parts of the body; the pathogenesis and the causative genes of arthrogryposis remain undetermined. We examined a four‐generation arthrogryposis pedigree characterized by camptodactyly, limited forearm supination, and loss of myofibers in the forearms and hands. By using whole‐exome sequencing, we confirmed MET p.Y1234C mutation to be responsible for arthrogryposis in this pedigree. MET p.Y1234C mutation caused the failure of activation of MET tyrosine kinase. A Met p.Y1232C mutant mouse model was established. The phenotypes of homozygous mice included embryonic lethality and complete loss of muscles that originated from migratory precursors. Heterozygous mice were born alive and showed reduction of the number of myofibers in both appendicular and axial muscles. Defective migration of muscle progenitor cells and impaired proliferation of secondary myoblasts were proven to be responsible for the skeletal muscle dysplasia of mutant mice. Overall, our study shows MET to be a causative gene of arthrogryposis and MET mutation could cause skeletal muscle dysplasia in human beings.

Development of a research platform for children with arthrogryposis multiplex congenita: study protocol for a pilot registry

INTRODUCTION

Arthrogryposis multiplex congenita (AMC) describes a heterogeneous group of conditions with multiple congenital contractures. These conditions may be attributed to genetic or other factors inducing decreased fetal movements, including maternal and paternal factors. Discovering the underlying genetic pathways has important repercussions for prevention, gene therapy and genetic counselling. The current literature mainly consists of small-scale, single-site studies, limiting comparability and pooling of findings across individual studies. A pilot registry for children presenting with AMC is proposed to provide the framework for a large-scale AMC registry. This registry will provide the platform to support high-quality studies to inform the distribution, clinical practice and genetics contributing to this group of conditions.

METHODS AND ANALYSIS

The registry will be piloted on 40 families of children from birth to 21 years of age presenting with AMC. Data will be collected on the child (demographic and newborn variables), mother and father (demographic, lifestyle habits and medical history). To promote standardised data collection, a manual of operations will be developed. Descriptive statistics will be used to summarise relevant data, regression analyses will be used to explore associations to generate hypotheses regarding factors contributing to AMC. Qualitative analysis will also be used to better describe the various phenotypes.

ETHICS AND DISSEMINATION

Ethics approval was obtained at the participating sites. The pilot registry will provide the platform for multisite AMC registry that will generate multiple research avenues to enhance current care and establish new therapies. Following this pilot study, the participant selection criteria will be refined and datasets will be expanded to include rehabilitation and surgical interventions, and genetic sequencing. The best timing for the questionnaire administration and frequency of follow-up prior to the implementation of a multisite AMC registry will be determined.

A severe female case of arthrogryposis multiplex congenita with brain atrophy, spastic quadriplegia and intellectual disability caused by ZC4H2 mutation

Arthrogryposis multiplex congenita (AMC) is characterized by heterogeneous multiple congenital contractures appearing at birth. Mutations in X-linked zinc-finger gene ZC4H2 were recently identified in some families and individuals with variable forms of AMC associated with dysmorphic signs, intellectual disability and spastic paresis. We present a non-consanguineous Japanese female presenting AMC with severe intellectual disability and spastic quadriplegia who also had progressive brain atrophy. Microarray-based comparative genomic hybridization identified 395 kb microdeletions at Xq11.2 which only included ZC4H2 gene. Previous reports showed that affected females have lesser symptoms and slight abnormality on brain MRI compared to male due to X-inactivation. Our case, however, showed severe manifestation than as ever reported as well as progressive diffuse brain atrophy, which implicated contribution of other genetic or environmental factors or extremely skewed X inactivation.

The Clinic Is My Laboratory: Life as a Clinical Geneticist

Clinical genetics is the application of advances in genetics and medicine to real human families. It involves diagnosis, care, and counseling concerning options available to affected individuals and their family members. Advances in medicine and genetics have led to dramatic changes in the scope and responsibilities of clinical genetics. This reflection on the last 50+ years of clinical genetics comes from personal experience, with an emphasis on the important contributions that clinical geneticists have made to the understanding of disease/disorder processes and mechanisms. The genetics clinic is a research laboratory where major advances in knowledge can and have been made.

Mutations in ERGIC1 cause Arthrogryposis multiplex congenita, neuropathic type

Arthrogryposis multiplex congenita (AMC) is heterogeneous group of disorders characterized by non-progressive joint contractures from birth that involve more than 1 part of the body. There are various etiologies for AMC including genetic and environmental depends on the specific type, however, for most types, the cause is not fully understood. We previously reported large Israeli Arab kindred consisting of 16 patients affected with AMC neuropathic type, and mapped the locus to a 5.5 cM interval on chromosome 5qter. Using whole exome sequencing, we have now identified homozygous pathogenic variant in the ERGIC1 gene within the previously defined linked region. ERGIC1 encodes a cycling membrane protein which has a possible role in transport between endoplasmic reticulum and Golgi. We further show that this mutation was absent in more than 200 samples of healthy unrelated individuals of the Israeli Arab population. Thus, our findings expand the spectrum of hereditary AMC and suggest that abnormalities in protein trafficking may underlie AMC-related disorders.

Arthrogryposis as a Syndrome: Gene Ontology Analysis

Arthrogryposis by definition has multiple congenital contractures. All types of arthrogryposis have decreased in utero fetal movement. Because so many things are involved in normal fetal movement, there are many causes and processes that can go awry. In this era of molecular genetics, we have tried to place the known mutated genes seen in genetic forms of arthrogryposis into biological processes or cellular functions as defined by gene ontology. We hope this leads to better identification of all interacting pathways and processes involved in the development of fetal movement in order to improve diagnosis of the genetic forms of arthrogryposis, to lead to the development of molecular therapies, and to help better define the natural history of various types of arthrogryposis.

Recessive NEK9 mutation causes a lethal skeletal dysplasia with evidence of cell cycle and ciliary defects

Skeletal dysplasias are a clinically and genetically heterogeneous group of bone and cartilage disorders. Whilst >450 skeletal dysplasias have been reported, 30% are genetically uncharacterized. We report two Irish Traveller families with a previously undescribed lethal skeletal dysplasia characterized by fetal akinesia, shortening of all long bones, multiple contractures, rib anomalies, thoracic dysplasia, pulmonary hypoplasia and protruding abdomen. Single nucleotide polymorphism homozygosity mapping and whole exome sequencing identified a novel homozygous stop-gain mutation in NEK9 (c.1489C>T; p.Arg497*) as the cause of this disorder. NEK9 encodes a never in mitosis gene A-related kinase involved in regulating spindle organization, chromosome alignment, cytokinesis and cell cycle progression. This is the first disorder to be associated with NEK9 in humans. Analysis of NEK9 protein expression and localization in patient fibroblasts showed complete loss of full-length NEK9 (107 kDa). Functional characterization of patient fibroblasts showed a significant reduction in cell proliferation and a delay in cell cycle progression. We also provide evidence to support possible ciliary associations for NEK9. Firstly, patient fibroblasts displayed a significant reduction in cilia number and length. Secondly, we show that the NEK9 orthologue in Caenorhabditis elegans, nekl-1, is almost exclusively expressed in a subset of ciliated cells, a strong indicator of cilia-related functions. In summary, we report the clinical and molecular characterization of a lethal skeletal dysplasia caused by NEK9 mutation and suggest that this disorder may represent a novel ciliopathy.

Molecular etiology of arthrogryposis in multiple families of mostly Turkish origin

BACKGROUND

Arthrogryposis, defined as congenital joint contractures in 2 or more body areas, is a clinical sign rather than a specific disease diagnosis. To date, more than 400 different disorders have been described that present with arthrogryposis, and variants of more than 220 genes have been associated with these disorders; however, the underlying molecular etiology remains unknown in the considerable majority of these cases.

METHODS

We performed whole exome sequencing (WES) of 52 patients with clinical presentation of arthrogryposis from 48 different families.

RESULTS

Affected individuals from 17 families (35.4%) had variants in known arthrogryposis-associated genes, including homozygous variants of cholinergic γ nicotinic receptor (CHRNG, 6 subjects) and endothelin converting enzyme-like 1 (ECEL1, 4 subjects). Deleterious variants in candidate arthrogryposis-causing genes (fibrillin 3 [FBN3], myosin IXA [MYO9A], and pleckstrin and Sec7 domain containing 3 [PSD3]) were identified in 3 families (6.2%). Moreover, in 8 families with a homozygous mutation in an arthrogryposis-associated gene, we identified a second locus with either a homozygous or compound heterozygous variant in a candidate gene (myosin binding protein C, fast type [MYBPC2] and vacuolar protein sorting 8 [VPS8], 2 families, 4.2%) or in another disease-associated genes (6 families, 12.5%), indicating a potential mutational burden contributing to disease expression.

CONCLUSION

In 58.3% of families, the arthrogryposis manifestation could be explained by a molecular diagnosis; however, the molecular etiology in subjects from 20 families remained unsolved by WES. Only 5 of these 20 unrelated subjects had a clinical presentation consistent with amyoplasia; a phenotype not thought to be of genetic origin. Our results indicate that increased use of genome-wide technologies will provide opportunities to better understand genetic models for diseases and molecular mechanisms of genetically heterogeneous disorders, such as arthrogryposis.

FUNDING

This work was supported in part by US National Human Genome Research Institute (NHGRI)/National Heart, Lung, and Blood Institute (NHLBI) grant U54HG006542 to the Baylor-Hopkins Center for Mendelian Genomics, and US National Institute of Neurological Disorders and Stroke (NINDS) grant R01NS058529 to J.R. Lupski.