Identification of a novel pathogenic mutation of the MYH3 gene in a family with distal arthrogryposis type 2B.

Distal arthrogryposis (DA) type 2B (DA2B) is an autosomal dominant congenital disorder, characterized by camptodactyly, thumb adduction, ulnar deviation and facial features, including small mouth, down­slanting palpebral fissure and slight nasolabial fold. It has been reported that four genes are associated with DA2B, including troponin I, fast­twitch skeletal muscle isoform, troponin T3, fast skeletal, myosin heavy chain 3 (MYH3) and tropomyosin 2, which are all associated with embryonic limb morphogenesis and skeletal muscle contraction. In the present study, three affected family members and five unaffected individuals were identified through clinical and radiological assessment. Genomic DNA was obtained from the three patients, which then underwent whole­exome sequencing, and candidate mutations were verified by Sanger sequencing in all available family members and 100 healthy volunteers. Then, the spatial models of embryonic MYH were further constructed. In the clinic, the three patients recruited to the present study were diagnosed with DA2B. Mutation analysis indicated that there was a novel heterogeneous missense mutation c.2506 A>G (p.K836E) in the MYH3 gene among the affected individuals, which was highly conserved and was not identified in the unaffected family members and healthy controls. Furthermore, protein modeling revealed that the altered position interacted with regulatory light chain. Thus, the present study identified a novel pathogenic mutation of the MYH3 gene in a Chinese family with DA2B, which expanded the mutational spectrum of MYH3 and provided additional information regarding the association between mutation locations and different types of DA.

[Clinical features and VPS33B mutations in a family affected by arthrogryposis, renal dysfunction, and cholestasis syndrome].

Arthrogryposis, renal dysfunction, and cholestasis (ARC) syndrome is an autosomal recessive disorder caused by mutations in the VPS33B or VIPAS39 gene. The aim of this study was to investigate the clinical features and VPS33B gene mutations of an infant with ARC syndrome. A 47-day-old female infant was referred to the hospital with the complaint of jaundiced skin and sclera for 45 days and abnormal liver function for 39 days. The patient had been managed in different hospitals, but the therapeutic effects were unsatisfactory due to undetermined diagnosis. Physical examination showed jaundice of the skin and sclera. Systemic skin was dry with desquamation in the limbs and trunk. There were no positive signs on cardiopulmonary examination. The liver was palpable 2.0 cm under the right subcostal margin. The hips and knees were flexed, and the extension was limited, with low muscular tone in the four limbs. Biochemical analysis demonstrated raised serum total bile acids, bilirubin (predominantly conjugated bilirubin) and transaminases, but the γ-glutamyl transpeptidase level was normal. Routine urine test revealed increased glucose as well as red and white blood cells. On genetic analysis, the infant was proved to be homologous for a VPS33B mutation c.1594C>T(p.R532X). She was definitely diagnosed to have ARC syndrome. Symptomatic and supportive therapy was given, but no improvement was observed, and the infant finally died at 3 months and 29 days of life.

Haematological manifestations of arthrogryposis-renal dysfunction-cholestasis (ARC) syndrome: a case report.

Arthrogryposis multiplex congenita, renal dysfunction, and cholestasis (ARC) syndrome is a rare, fatal, multisystem disorder. Bleeding problems, which occur spontaneously and post organ biopsies, have been reported in these patients. We report the case of an infant who had life-threatening spontaneous nasal bleeding. A detailed assessment of her platelet function and morphology is presented.

Fetal arthrogryposis and maternal serum antibodies.

Arthrogryposis multiplex congenital (AMC) describes multiple joint contractures resulting from lack of movement in utero. Antibodies directed at the fetal isoform of the muscle acetylcholine receptor (AChR) have been reported in a small number of asymptomatic mothers of AMC babies. We examined sera from 179 mothers of AMC babies and 20 parous and non-parous controls to look for antibodies to AChR or undefined muscle or neuronal proteins. We found positive AChR antibodies in only three sera (1.5%) from asymptomatic AMC mothers. However, there was reactivity with muscle or with neuronal antigens in 33% of the sera, and reactivity to undefined neuronal antigens was more common in sera from mothers of AMC babies with CNS involvement (p=0.001) than those without. The offspring of mothers with AChR antibodies may benefit from treatment during pregnancy. Other maternal antibodies require further study, but these observations add to the emerging literature on maternal antibodies associated with developmental intrauterine disorders.

Teratogen update: maternal myasthenia gravis as a cause of congenital arthrogryposis.

BACKGROUND: Arthrogryposis multiplex congenita (AMC) is defined as nonprogressive congenital contractures that generally result from lack of fetal movement in utero. AMC is a feature of many congenital disorders caused by genetic, environmental, or other factors. One rare cause of AMC is maternal myasthenia gravis (MG). This is an autoimmune disorder, caused by antibodies to the nicotinic acetylcholine receptor (AChR), and resulting in weakness of voluntary muscles. In 10-15% of babies born to MG mothers, transient signs of MG are noted after placental transfer of anti-AChR antibodies. In a few cases, AMC predominates. METHODS: We review the role of antibodies to AChR in MG and in AMC associated with maternal antibodies to AChR. RESULTS: In anti-AChR antibody-associated AMC, fetal or neonatal death is common; other deformities or CNS abnormalities are common as well. The condition usually recurs in each pregnancy unless the mother is treated for MG, but some mothers are asymptomatic. The maternal antibodies cross the placenta and block the function of the fetal isoform of the AChR leading to fetal paralysis. Injection of maternal plasma into pregnant mice results in AMC in mouse fetuses. Some women with recurrent AMC in their babies have no detectable anti-AChR suggesting the presence of antibodies to other fetal muscle or neuronal proteins. CONCLUSIONS: Although rare, anti-AChR-associated AMC is potentially treatable and can be diagnosed by a routine antibody test. The mouse model can be used to investigate the role of these and other maternal antibodies in causing congenital conditions.

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.