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Mechanotransduction, the pathway by which mechanical forces are translated to biological signals, plays important but poorly characterized roles in physiology. PIEZOs are recently identified, widely expressed, mechanically activated ion channels that are hypothesized to play a role in mechanotransduction in mammals. Here, we describe two distinct PIEZO2 mutations in patients with a subtype of Distal Arthrogryposis Type 5 characterized by generalized autosomal dominant contractures with limited eye movements, restrictive lung disease, and variable absence of cruciate knee ligaments. Electrophysiological studies reveal that the two PIEZO2 mutations affect biophysical properties related to channel inactivation: both E2727del and I802F mutations cause the PIEZO2-dependent, mechanically activated currents to recover faster from inactivation, while E2727del also causes a slowing of inactivation. Both types of changes in kinetics result in increased channel activity in response to a given mechanical stimulus, suggesting that Distal Arthrogryposis Type 5 can be caused by gain-of-function mutations in PIEZO2 . We further show that overexpression of mutated PIEZO2 cDNAs does not cause constitutive activity or toxicity to cells, indicating that the observed phenotype is likely due to a mechanotransduction defect. Our studies identify a type of channelopathy and link the dysfunction of mechanically activated ion channels to developmental malformations and joint contractures.

This review summarizes the clinical and electromyography (EMG) characteristics and peripheral myelin protein 22 ( PMP22 ) gene-related diseases of hereditary neuropathy with liability to pressure palsies (HNPP). Clinical, EMG, and laboratory data of patients diagnosed with HNPP at our institution from 2022 to 2023 were retrospectively reviewed. Relevant literature from January 2003 to June 2024 was retrieved from PubMed using the keywords “hereditary neuropathy with liability to pressure palsies” and “HNPP.” Clinical manifestations, EMG characteristics, and gene detection results of HNPP were summarized. All patients exhibited transient neurological symptoms and tested positive for the PMP22 deletion. EMG revealed multiple peripheral nerve abnormalities. Sixty-eight studies meeting the inclusion and exclusion criteria were included, comprising 124 HNPP cases (including six from our study), with 67 males and 57 females. The mean age of onset and diagnosis for the 124 cases were 26.5 ± 18 years and 32.7 ± 18.9 years, respectively, with a maximum onset-to-diagnosis interval of 40 years. Typical weakness and numbness in vulnerable areas were observed in 63.7% of cases, with 62% experiencing recurrent episodes. Atypical symptoms were present in 29.8%, while 6.5% were asymptomatic. Patients exhibited pain and muscular dystrophy (17.7%), pes cavus (12.1%), and a family history of HNPP (64.5%). Among symptomatic patients, triggers were traction or compression (57.8%), temperature changes (3.4%), or unclear (38.8%). Heterozygous PMP22 deletions and other PMP22 gene mutations were found in 77.4% and 22.6% of cases, respectively.

Background Individuals with arthrogryposis multiplex congenita (AMC) exhibit a range of modes of ambulation, from walking independently to requiring a wheelchair. Presence of joint contractures and muscle strength plays a crucial role, and, in some patients, orthoses are necessary to facilitate or enable walking. Methods Gait was assessed with a three-dimensional (3D) gait analysis, calculated as a gait deviation index (GDI) of nine kinematic variables, and compared between childhood and adulthood. Results A total of 12 persons, 8 with community and 4 with household ambulation, who had undergone a 3D gait analysis in childhood (CH) and as an adult (follow-up, FU) at the same gait laboratory were enrolled in the study. At the FU, three, five, and four participants respectively were categorized based on need of joint stabilization while walking as AMC1 using knee-ankle-orthoses (KAFOs) with locked knee joints, AMC2 using KAFOs with free-articulating knee joint or ankle–foot-orthoses (AFOs) and AMC3 using insoles or shoes. Two participants in AMC2 had changed from AFOs to insoles or shoes between CH and FU. There were no differences in joint contractures between the AMC groups at CH or FU. Two participants had orthopaedic surgery between CH and FU. The GDI of the leg with the lowest GDI score at CH vs FU was median [min, max] 55.67 [41.79, 65.14] vs 48.4 [42.67, 56.30] ( p  = 1.000) in AMC1, 81.25 [59.42, 84.12] vs 68.96 [47.68, 70.33] ( p  = 0.043) in AMC2, and 73.15 [43.94, 91.72] vs 73.46 [50.82, 75.24] ( p  = 1.000) in AMC3. Time and distance parameters of cadence, walking speed, step length, and step width did not differ between the CH and FU, nor were there differences in satisfaction with the device or the service at the FU. Conclusion A difference in the GDI was found in one of the AMC groups between childhood and adulthood that could not be explained by factors such as contractures or muscle strength. This study reflects that gait is maintained in ambulating persons with AMC who were offered an orthosis program that has been available from childhood into adulthood.

The genetic work-up of arthrogryposis is challenging due to the diverse clinical and molecular etiologies. We report a-18 -year-old boy, from a 2nd degree consanguineous family, who presented at 3 years with hypotonia, distal laxity, contractures, feeding difficulties at birth. He required surgery for progressive scoliosis at 16 years of age, and walked independently since then with an unstable gait and coordination defects. His latest examination at 18 years of age revealed a proprioceptive defect and loss-of-joint position sense in the upper limbs. Somatosensory evoked potentials supported bilateral involvement of dorsal column-medial lemniscal sensory pathways and nerve conduction studies revealed a mild axonal neuropathy. Muscle biopsy showed myopathic changes with neonatal myosin expression. Mendeliome sequencing led to the discovery of a recessive stop mutation in piezo-type mechanosensitive ion channel component 2 (PIEZO2, NM_022068, c.1384C>T, p.R462*). PIEZO2 is a nonselective cation channel, expressed in sensory endings of proprioceptors innervating muscle spindles and Golgi tendon organs. Dominant PIEZO2 mutations were described in patients with distal arthrogryposis type 5 and Marden-Walker syndrome. Sensory ataxia and proprioception defect with dorsal column involvement together with arthrogryposis, myopathy, scoliosis and progressive respiratory failure may represent a distinct clinical phenotype, and indicate recessive mutations in PIEZO2.

Purpose Arthrogryposis multiplex congenita (AMC) describes a heterogeneous group of rare congenital conditions. Health-related quality of life (HRQL) may be reduced in AMC due to broadly heterogeneous physical impairments and participation limitations. This study described HRQL in children and youth with AMC, compared HRQL between child self- and parent-proxy reports, and identified factors associated with better/worse HRQL. Methods Data on 205 children with AMC (age 8–21 years) from a North American AMC registry across eight hospital sites was used. HRQL was assessed cross-sectionally using the Patient Reported Outcome Measurement Information System (PROMIS) and European Quality of Life-5 Dimensions-Youth-3 Levels (EQ-5D-Y-3 L) by self-report, parent proxy-report or both. Results Mean child-reported PROMIS T-scores were significantly lower than the normal mean for the Upper Extremity (mean = 33.0) and Mobility (mean = 37.2) but in the normal range for Pain Interference (mean = 46.6) and Peer Relationships (mean = 51.7). A lot of problems in EQ-5D-Y-3 L was reported by 37% in Feeling Worried/ Sad/ Unhappy, 46% in Having Pain/Discomfort, 50% in Doing Usual Activities, 56% in Mobility, and 57% in Looking After Myself. Compared to child-report, parents reported significantly worse PROMIS T-scores and higher problems in EQ-5D domains. Wheelchair use, being small for gestational age, prolonged hospitalization after birth, increased number of orthopedic surgeries, and caregiver’s stress were associated with lower HRQL scores. Conclusion Findings indicate the importance of considering both the child’s and parents’ reports of HRQL, and to provide multimodal interventions that focus on the effect of childhood and parental characteristics to promote HRQL among children with AMC. Plain English summary Our study describes health aspects of quality of life (HRQL) in a large sample of children with arthrogryposis multiplex congenita (AMC). Information on HRQL is crucial for clinicians treating AMC to improve treatment outcomes, and for individuals with AMC and their families to understand various aspects of life in AMC. Our results showed that most children with AMC have mild to moderate problems in mobility (e.g., getting around, walking), self-care (e.g., taking shower), and doing usual activities. We found that the parents tend to perceive worsened HRQL for the child with AMC. Our findings also showed that children who had low birthweight for gestational age, were hospitalized for prolonged periods as an infant, had multiple orthopedic surgeries, and use a wheelchair are more likely to have lower HRQL. Children who have a parent who expressed high caretaking stress tend to have lower mobility and physical functioning. Our findings will help develop more personalized care plans for children with AMC considering various individual and familial characteristics.

Background The rarity of pregnancies in women with arthrogryposis multiplex congenita (AMC) could lead to healthcare providers having limited exposure to these cases. Consequently, they may be less familiar with the possibilities and challenges associated with pregnancies in women affected by AMC. AMC is an umbrella term for a disorder with multiple contractures at birth, having a broad spectrum of causes, onset and severity of expression. A clinical classification describing the phenotype is Group 1 with primary limb involvement, Group 2 with musculoskeletal involvement plus other system anomalies, and Group 3 with musculoskeletal involvement plus central nervous system dysfunction and/or intellectual disability. A scoping review was conducted to review available literature on documented cases of pregnancies in women with AMC, with the following aims: (1) to outline the maternal, fetal and neonatal outcomes; (2) to describe AMC stability during and after pregnancy (worsening of symptoms due to contractures, increased muscle weakness, pain or lung involvement); and (3) to summarize counselling aspects during pregnancy for expecting mothers who have AMC. Results This scoping review included 27 manuscripts reporting on 43 women with 82 pregnancies, of whom 18 in Group 1, 20 in Group 2, 2 in Group 3, and 3 with an unknown type. Details on pregnancy-related outcomes could be depicted from 26 of the 43 women concerning 31 pregnancies. Among these pregnancies, 74% (23/31) had a cesarean section delivery, of which 74% (17/23) were elective. Children were born preterm before week 37 in 7 of 31 pregnancies (22%). A birth weight below the 10th percentile was seen in 6 of the 24 (25%) with a reported birth weight. The course of the pregnancy was uneventful in 16 of the 26 women (62%). Pregnancy had a limited negative influence on AMC stability except for three cases with a transient worsening of lung function. Conclusions Gathering the information of the case histories revealed that the majority of the reported women had Distal Arthrogryposis with stable AMC during pregnancy and after delivery. The risk to have a cesarean section, preterm labour or a small for gestational age child is higher in this group than in the general population. Insights obtained by this review emphasized to offer (pre)pregnancy counselling and care by a multidisciplinary team tailored to the women’s type of AMC, to ensure optimal preparation for both obstetric, genetic, neurologic, pulmonary and anesthetic care during pregnancy, delivery and postpartum period.

Nucleoporins build the nuclear pore complex (NPC), which, as sole gate for nuclear-cytoplasmic exchange, is of outmost importance for normal cell function. Defects in the process of nucleocytoplasmic transport or in its machinery have been frequently described in human diseases, such as cancer and neurodegenerative disorders, but only in a few cases of developmental disorders. Here we report biallelic mutations in the nucleoporin NUP88 as a novel cause of lethal fetal akinesia deformation sequence (FADS) in two families. FADS comprises a spectrum of clinically and genetically heterogeneous disorders with congenital malformations related to impaired fetal movement. We show that genetic disruption of nup88 in zebrafish results in pleiotropic developmental defects reminiscent of those seen in affected human fetuses, including locomotor defects as well as defects at neuromuscular junctions. Phenotypic alterations become visible at distinct developmental stages, both in affected human fetuses and in zebrafish, whereas early stages of development are apparently normal. The zebrafish phenotypes caused by nup88 deficiency are rescued by expressing wild-type Nup88 but not the disease-linked mutant forms of Nup88. Furthermore, using human and mouse cell lines as well as immunohistochemistry on fetal muscle tissue, we demonstrate that NUP88 depletion affects rapsyn, a key regulator of the muscle nicotinic acetylcholine receptor at the neuromuscular junction. Together, our studies provide the first characterization of NUP88 in vertebrate development, expand our understanding of the molecular events causing FADS, and suggest that variants in NUP88 should be investigated in cases of FADS.

Introduction: Heterozygous pathogenic variants in MYH3 are known to be responsible for distal arthrogryposis. Case report: We report a consanguineous family of four children with two likely pathogenic MYH3 homozygous variants associated with complex movement disorders, especially prominent lingual dystonia, along with skeletal abnormalities. The two variants in MYH3 (c.3445G>A and c.4760T>C) have already been described in patients with congenital arthrogryposis. No other significant variation was found using long-read whole genome sequencing. Discussion: We have extended the phenotype of MYH3-associated arthrogryposis to include movement disorders, which may have been underdiagnosed to date. Highlights This article extends the phenotype of MYH3-associated arthrogryposis to include movement disorders, illustrating a family of four children presenting MYH3 skeletal disorders and lingual dystonia. Two homozygous likely pathogenic variants have been identified in the four sibs and appear to be causative for both skeletal and neurological phenotypes.

Introduction. Distal arthrogryposis type 5D (DA5D) is an autosomal recessive disease. The clinical symptoms include contractures of the joints of limbs, especially camptodactyly of the hands and/or feet, unilateral ptosis, a round-shaped face, arched eyebrows, and micrognathia, without ophthalmoplegia. ECEL1 is a DA5D causative gene that encodes a membrane-bound metalloprotease. ECEL1 plays important roles in the final axonal arborization of motor nerves in limb skeletal muscles and neuromuscular junction formation during prenatal development. Methods. A DA5D family with webbing of the elbows and fingers was recruited. We performed whole-exome sequencing (WES) and filtered mutations by disease-causing genes of arthrogryposis multiplex congenita (AMC). Mutational analysis and cosegregation confirmation were then performed. Results. We identified novel compound heterozygous mutations of ECEL1 (NM_004826: c.69C>A, p.C23∗ and c.1810G>A, p.G604R) in the proband. Conclusions. We detected causative mutations in a DA5D family, expanding the spectrum of known ECEL1 mutations and contributing to the clinical diagnosis of DA5D.

Objective To provide a comprehensive clinical and genetic characterization of individuals with arthrogryposis multiplex congenita (AMC), focusing on the distribution of genetic etiologies across the neuromuscular spectrum and comparing myogenic and neurogenic subtypes. Methods A total of 105 individuals with AMC were clinically and genetically evaluated in a single‐center study. Participants were stratified based on the primary site of involvement, and further classification was performed for neuromuscular cases into neurogenic and myogenic subtypes. Genetic diagnoses were made through using a range of next‐generation sequencing techniques, including exome sequencing (42 individuals), gene panel testing (40 individuals), genome sequencing (24 individuals), and targeted‐gene testing in selected cases. In most individuals who underwent genome sequencing, this was preceded by exome or gene panel testing. Results Of the 105 individuals, 4 were classified as Amyoplasia and 1 as FARAD. Among the remaining 100 cases, 81 (81%) presented with neuromuscular AMC, with defects involving motor neurons/peripheral nerves (52%, 42/81), neuromuscular junctions (7%, 6/81), and skeletal muscle (41%, 33/81). A genetic diagnosis was achieved in 55% (55/100) of the entire cohort and in 58% (47/81) of individuals with neuromuscular AMC. The most frequently implicated genes were TTN (16%, 9/55), CHRNG (10.9%, 6/55), PIEZO2 (9.1%, 5/55), ZC4H2 (9.1%, 5/55), DYNC1H1 (7.2%, 4/55), MYH3 (5.4%, 3/55), and RYR1 (5.4%, 3/55). Diagnostic yield varied significantly between subgroups, with 84.6% (33/39) of myogenic AMC cases genetically resolved, compared to 33.3% (14/42) of neurogenic cases. TTN was the most common gene in myogenic AMC, while ZC4H2 and DYNC1H1 were predominant in neurogenic AMC. Interpretation This study provides a detailed phenotypic and genetic characterization of neuromuscular AMC, highlighting the most frequently affected genes and their associated phenotypes. The findings underscore the challenges in diagnosing a significant proportion of cases, especially within the neurogenic subgroup, and emphasize the importance of integrating detailed phenotypic data with genetic analysis to enhance diagnosis, prognosis, and management of family expectations.