Severe Arthrogryposis Multiplex Congenita Research Articles

The emerging spectrum of fetal acetylcholine receptor antibody-related disorders (FARAD).

In utero exposure to maternal antibodies targeting the fetal acetylcholine receptor isoform (fAChR) can impair fetal movement, leading to arthrogryposis multiplex congenita (AMC). Fetal AChR antibodies have also been implicated in apparently rare, milder myopathic presentations termed fetal acetylcholine receptor inactivation syndrome (FARIS). The full spectrum associated with fAChR antibodies is still poorly understood. Moreover, since some mothers have no myasthenic symptoms, the condition is likely underreported, resulting in failure to implement effective preventive strategies. Here we report clinical and immunological data from a multicentre cohort (n = 46 cases) associated with maternal fAChR antibodies, including 29 novel and 17 previously reported with novel follow-up data. Remarkably, in 50% of mothers there was no previously established myasthenia gravis (MG) diagnosis. All mothers (n = 30) had AChR antibodies and, when tested, binding to fAChR was often much greater than that to the adult AChR isoform. Offspring death occurred in 11/46 (23.9%) cases, mainly antenatally due to termination of pregnancy prompted by severe AMC (7/46, 15.2%), or during early infancy, mainly from respiratory failure (4/46, 8.7%). Weakness, contractures, bulbar and respiratory involvement were prominent early in life, but improved gradually over time. Facial (25/34; 73.5%) and variable peripheral weakness (14/32; 43.8%), velopharyngeal insufficiency (18/24; 75%) and feeding difficulties (16/36; 44.4%) were the most common sequelae in long-term survivors. Other unexpected features included hearing loss (12/32; 37.5%), diaphragmatic paresis (5/35; 14.3%), CNS involvement (7/40; 17.5%) and pyloric stenosis (3/37; 8.1%). Oral salbutamol used empirically in 16/37 (43.2%) offspring resulted in symptom improvement in 13/16 (81.3%). Combining our series with all previously published cases, we identified 21/85 mothers treated with variable combinations of immunotherapies (corticosteroids/intravenous immunoglobulin/plasmapheresis) during pregnancy either for maternal MG symptom control (12/21 cases) or for fetal protection (9/21 cases). Compared to untreated pregnancies (64/85), maternal treatment resulted in a significant reduction in offspring deaths (P < 0.05) and other complications, with treatment approaches involving intravenous immunoglobulin/ plasmapheresis administered early in pregnancy most effective. We conclude that presentations due to in utero exposure to maternal (fetal) AChR antibodies are more common than currently recognized and may mimic a wide range of neuromuscular disorders. Considering the wide clinical spectrum and likely diversity of underlying mechanisms, we propose 'fetal acetylcholine receptor antibody-related disorders' (FARAD) as the most accurate term for these presentations. FARAD is vitally important to recognize, to institute appropriate management strategies for affected offspring and to improve outcomes in future pregnancies. Oral salbutamol is a symptomatic treatment option in survivors.

Loss of Protein Function Causing Severe Phenotypes of Female-Restricted Wieacker Wolff Syndrome due to a Novel Nonsense Mutation in the ZC4H2 Gene.

Pathogenic variants of zinc finger C4H2-type containing (ZC4H2) on the X chromosome cause a group of genetic diseases termed ZC4H2-associated rare disorders (ZARD), including Wieacker-Wolff Syndrome (WRWF) and Female-restricted Wieacker-Wolff Syndrome (WRWFFR). In the current study, a de novo c.352C>T (p.Gln118*) mutation in ZC4H2 (NM_018684.4) was identified in a female neonate born with severe arthrogryposis multiplex congenita (AMC) and Pierre-Robin sequence (cleft palate and micrognathia). Plasmids containing the wild-type (WT), mutant-type (MT) ZC4H2, or GFP report gene (N) were transfected in 293T cell lines, respectively. RT-qPCR and western blot analysis showed that ZC4H2 protein could not be detected in the 293T cells transfected with MT ZC4H2. The RNA seq results revealed that the expression profile of the MT group was similar to that of the N group but differed significantly from the WT group, indicating that the c.352C>T mutation resulted in the loss of function of ZC4H2. Differentially expressed genes (DEGs) enrichment analysis showed that c.352C>T mutation inhibited the expression levels of a series of genes involved in the oxidative phosphorylation pathway. Subsequently, expression levels of ZC4H2 were knocked down in neural stem cells (NSCs) derived from induced pluripotent stem cells (iPSCs) by lentiviral-expressed small hairpin RNAs (shRNAs) against ZC4H2. The results also demonstrated that decreasing the expression of ZC4H2 significantly reduced the growth of NSCs by affecting the expression of genes related to the oxidative phosphorylation signaling pathway. Taken together, our results strongly suggest that ZC4H2 c.352C>T (p.Gln118*) mutation resulted in the loss of protein function and caused WRWFFR.

Intrafamilial Variability of the R694C Variant in BICD2 Presenting with Lethal Severe Arthrogryposis

Arthrogryposis multiplex congenita (AMC) is a heterogeneous condition comprising congenital multiple joint contractures, and it is secondary to decreased fetal mobility following environmental/genetic abnormalities. BICD2 pathogenic variants have been associated with autosomal dominant spinal muscular atrophy with lower extremity predominance (SMALED2). We report the case of a newborn with decreased fetal movements and ventriculomegaly diagnosed in utero, born with severe AMC, multiple bone fractures, congenital hip dislocation, and respiratory insufficiency that led to neonatal death. His mother had AMC diagnosis without established etiology. Her phenotype characterization was key to guide the genetic investigation. A BICD 2 heterozygous variant (NM_001003800.1; c.2080C &gt; T; p. [Arg694Cys]) was detected both in the mother and the newborn. This variant had previously been reported in 3 cases, all having de novo severe SMALED-type 2B (MIM#618291) phenotype. This is the first report of this variant (p. [Arg694Cys]) presenting with an inherited, severe, and lethal phenotype associated to intrafamilial variability, suggesting a more complex phenotype-genotype correlation than previously stated.

Characterizing the molecular etiology of arthrogryposis multiplex congenita in patients with LGI4 mutations.

Disruption of axon-glia interactions in the peripheral nervous system has emerged as a major cause of arthrogryposis multiplex congenita (AMC), a condition characterized by multiple congenital postural abnormalities involving the major joints. Several genes crucially important to the biology of Schwann cells have now been implicated with AMC. One such gene is LGI4 which encodes a secreted glycoprotein. LGI4 is expressed and secreted by Schwann cells and binds its receptor ADAM22 on the axonal membrane to drive myelination. Homozygous mutations in LGI4 or ADAM22 results in severe congenital hypomyelination and joint contractures in mice. Recently bi-allelic LGI4 loss of function mutations has been described in three unrelated families with severe AMC. Two individuals in a fourth, non-consanguineous family were found to be compound heterozygous for two LGI4 missense mutations. It is not known how these missense mutations affect the biology of LGI4. Here we investigated whether these missense mutations affected the secretion of the protein, its ADAM22 binding capacity, or its myelination-promoting function. We demonstrate that the mutations largely affect the progression of the mutant protein through the endomembrane system resulting in severely reduced expression. Importantly, binding to ADAM22 and myelination-promoting activity appear largely unaffected, suggesting that treatment with chemical chaperones to improve secretion of the mutant proteins might prove beneficial.

A mild phenotype of LGI4-Related arthrogryposis multiplex congenita with intrafamilial variability

Arthrogryposis multiplex congenita (AMC) is a heterogeneous group of congenital disorders characterized by multiple joint contractures. We report a family with two children affected with AMC. First child had a severe AMC phenotype and died in infancy. Second child, currently 4-years-old, was ascertained at the age of 30 months with mild AMC phenotype with cognitive and speech delay. On whole exome sequencing, a novel biallelic sequence variant in initiation codon of LGI4 (leucine-rich glioma-inactivated 4) gene was identified in her. Real-Time PCR revealed 50% reduction in mRNA transcript levels in subject as compared to control which explains the milder phenotype. Till date, only four families with nine affected individuals with LGI4-related AMC have been reported. Except for one child surviving up to 6 years, all others were either terminated after prenatal diagnosis or succumbed in neonatal period. This study adds to mutation spectrum of LGI4 and reports the second case of mild AMC with extended phenotype. We review the existing phenotypic and genotypic information for the individuals with this condition and highlight the intrafamilial and interfamilial variability in these individuals.

Assessment of Efficacy and Safety of Z-Shaped Skin Flap, Posterior Release Combined with External Fixation for Severe Arthrogryposis Multiplex Congenita and Flexion Deformity

Objective: To evaluate the efficacy and safety of Z-shaped skin flap, posterior release combined with external fixation for children diagnosed with severe arthrogryposis multiplex congenita and flexion deformity. Methods: Five children (10 knees) with AMC complicated with severe flexion contracture of &gt;40 degrees were enrolled and subject to posterior Z-shaped flap, posterior release combined with external fixator technique. After the operation, external fixation bracket was used to fix the knee joint. Results: The degree of average knee extension was increased up to 25.5 degrees after the soft tissue release. The knee joint could be completely straightened after using wearing the external fixator for 12.3 d on average. No distal femur osteotomy was performed. The average time of wearing the external fixator was 43.1 d. During an average of 19.2-month follow-up, children could independently walk in the community area and 1 case could walk at home. No child recurred during postoperative follow-up. Conclusion: The combined technique of Z-shaped skin flap, posterior release and external fixation is an efficacious and safe for children diagnosed with severe arthrogryposis multiplex congenita and flexion deformity. During the short-term follow-up, the time of external fixator wear is significantly shortened, the incidence of postoperative complications is lowered and the recurrence rate is equally reduced.

Loss-of-Function Mutations in LGI4, a Secreted Ligand Involved in Schwann Cell Myelination, Are Responsible for Arthrogryposis Multiplex Congenita

Arthrogryposis multiplex congenita (AMC) is a developmental condition characterized by multiple joint contractures resulting from reduced or absent fetal movements. Through genetic mapping of disease loci and whole-exome sequencing in four unrelated multiplex families presenting with severe AMC, we identified biallelic loss-of-function mutations in LGI4 (leucine-rich glioma-inactivated 4). LGI4 is a ligand secreted by Schwann cells that regulates peripheral nerve myelination via its cognate receptor ADAM22 expressed by neurons. Immunolabeling experiments and transmission electron microscopy of the sciatic nerve from one of the affected individuals revealed a lack of myelin. Functional tests using affected individual-derived iPSCs showed that these germline mutations caused aberrant splicing of the endogenous LGI4 transcript and in a cell-based assay impaired the secretion of truncated LGI4 protein. This is consistent with previous studies reporting arthrogryposis in Lgi4-deficient mice due to peripheral hypomyelination. This study adds to the recent reports implicating defective axoglial function as a key cause of AMC.

G.O.4 - Autosomal recessive mutations of GPR126 are responsible for severe arthrogryposis multiplex congenita

ophthalmoplegia. The OPA1 protein is essential for normal mitochondrial fusion. In mouse DOA (such as OPA1Q285STOP), autophagy (recycling of spent cellular components) is dysregulated in retinal ganglion cells (RGCs), and mitophagy (mitochondrial recycling) has been implicated. Quantifying mitophagy is technically demanding. The hallmarks of mitophagy are organelles called autophagosomesis, co-localisating with, and then engulfing mitochondria. We validated and used two high throughput imaging systems [Imagestream (Amnis) and InCell analyser (GE)] to quantify mitophagy in fibroblasts. Co-localisation of mitochondria and autophagosomes was increased in fibroblasts in five patients from four families with severe OPA1 phenotypes indicating increased mitophagy. ImageStream also showed that basal mitophagy was increased when control cultures were depleted of Opa1 by siRNA. Western blotting confirmed increased basal autophagy and autophagic flux in the presence of activators. Increased mitochondrial fragmentation, mitophagy and failure of mitochondrial transport may together cause local depletion of mitochondria in critical regions of the affected neurons, such as axons or synapses. To investigate mitophagy in a DOA model we crossed the OPA1Q285STOP mouse with our RedMIT/GFP-LC3 mouse harbouring red fluorescent mitochondria and green fluorescent autophagosomes. We showed increased co-localisation between mitochondria and autophagosomes in both cell types investigated, confirming increased mitophagy in this model. The role of mitophagy in mitochondrial disease remains controversial, but appears to be excessive and poorly selective in OPA1 mutants. We intend to use our model to identify drug modulators of mitophagy for treating OPA1 and other mitochondrial patients.

Mutations of GPR126 Are Responsible for Severe Arthrogryposis Multiplex Congenita

Arthrogryposis multiplex congenita is defined by the presence of contractures across two or more major joints and results from reduced or absent fetal movement. Here, we present three consanguineous families affected by lethal arthrogryposis multiplex congenita. By whole-exome or targeted exome sequencing, it was shown that the probands each harbored a different homozygous mutation (one missense, one nonsense, and one frameshift mutation) in GPR126. GPR126 encodes G-protein-coupled receptor 126, which has been shown to be essential for myelination of axons in the peripheral nervous system in fish and mice. A previous study reported that Gpr126(-/-) mice have a lethal arthrogryposis phenotype. We have shown that the peripheral nerves in affected individuals from one family lack myelin basic protein, suggesting that this disease in affected individuals is due to defective myelination of the peripheral axons during fetal development. Previous work has suggested that autoproteolytic cleavage is important for activating GPR126 signaling, and our biochemical assays indicated that the missense substitution (p.Val769Glu [c.2306T>A]) impairs autoproteolytic cleavage of GPR126. Our data indicate that GPR126 is critical for myelination of peripheral nerves in humans. This study adds to the literature implicating defective axoglial function as a key cause of severe arthrogryposis multiplex congenita and suggests that GPR126 mutations should be investigated in individuals affected by this disorder.

Mutations in CNTNAP1 and ADCY6 are responsible for severe arthrogryposis multiplex congenita with axoglial defects

Non-syndromic arthrogryposis multiplex congenita (AMC) is characterized by multiple congenital contractures resulting from reduced fetal mobility. Genetic mapping and whole exome sequencing (WES) were performed in 31 multiplex and/or consanguineous undiagnosed AMC families. Although this approach identified known AMC genes, we here report pathogenic mutations in two new genes. Homozygous frameshift mutations in CNTNAP1 were found in four unrelated families. Patients showed a marked reduction in motor nerve conduction velocity (<10 m/s) and transmission electron microscopy (TEM) of sciatic nerve in the index cases revealed severe abnormalities of both nodes of Ranvier width and myelinated axons. CNTNAP1 encodes CASPR, an essential component of node of Ranvier domains which underlies saltatory conduction of action potentials along the myelinated axons, an important process for neuronal function. A homozygous missense mutation in adenylate cyclase 6 gene (ADCY6) was found in another family characterized by a lack of myelin in the peripheral nervous system (PNS) as determined by TEM. Morpholino knockdown of the zebrafish orthologs led to severe and specific defects in peripheral myelin in spite of the presence of Schwann cells. ADCY6 encodes a protein that belongs to the adenylate cyclase family responsible for the synthesis of cAMP. Elevation of cAMP can mimic axonal contact in vitro and upregulates myelinating signals. Our data indicate an essential and so far unknown role of ADCY6 in PNS myelination likely through the cAMP pathway. Mutations of genes encoding proteins of Ranvier domains or involved in myelination of Schwann cells are responsible for novel and severe human axoglial diseases.

Plasma from human mothers of fetuses with severe arthrogryposis multiplex congenita causes deformities in mice.

Arthrogryposis multiplex congenita (AMC) is characterized by fixed joint contractures and other deformities, sometimes resulting in fetal death. The cause is unknown in most cases, but some women with fetuses affected by severe AMC have serum antibodies that inhibit fetal acetylcholine receptor (AChR) function, and antibodies to fetal antigens might play a pathogenic role in other congenital disorders. To investigate this possibility, we have established a model by injecting pregnant mice with plasma from four anti-AChR antibody-positive women whose fetuses had severe AMC. We found that human antibodies can be transferred efficiently to the mouse fetus during the last few days of fetal life. Many of the fetuses of dams injected with AMC maternal plasmas or Ig were stillborn and showed fixed joints and other deformities. Moreover, similar changes were found in mice after injection of a serum from one anti-AChR antibody-negative mother who had had four AMC fetuses. Thus, we have confirmed the role of maternal antibodies in cases of AMC associated with maternal anti-AChR, and we have demonstrated the existence of pathogenic maternal factors in one other case. Importantly, this approach can be used to look at the effects of other maternal human antibodies on development of the fetus.

CT-scanning of skeletal muscle in arthrogryposis multiplex congenita

CT-scanning of skeletal muscles was performed on 14 patients with arthrogryposis multiplex congenita (AMC), according to an eight-slice protocol. Adipose tissue replacement and atrophy of muscles was found in six patients with neurogenic or myopathic origin of AMC, associated with severe muscle weakness. In the remaining patients with other forms of AMC, in which muscle weakness was less marked or absent, muscular CT-scanning was normal. It is stated that muscular CT-scanning is not a routine investigation in a screening procedure of all cases of AMC. However, CT-scanning appears to be useful in cases of severe AMC with associated muscle weakness in detecting the neurogenic and myopathic forms. It also facilitates the selection of a suitable site for EMG and biopsy and may provide important information for orthopaedic management.

Arthrogryposis multiplex congenita: neurogenic type with autosomal recessive inheritance.

An infant affected by severe arthrogryposis multiplex congenita leading to death in infancy due to neurogenic atrophy is described. Six other sibs were similarly affected. An autosomal recessive mode of inheritance is suggested.