Severe ACTA1-related nemaline myopathy: intranuclear rods, cytoplasmic bodies, and enlarged perinuclear space as characteristic pathological features on muscle biopsies.

Nemaline myopathy (NM) is a muscle disorder with broad clinical and genetic heterogeneity. The clinical presentation of affected individuals ranges from severe perinatal muscle weakness to milder childhood-onset forms, and the disease course and prognosis depends on the gene and mutation type. To date, 14 causative genes have been identified, and ACTA1 accounts for more than half of the severe NM cases. ACTA1 encodes α-actin, one of the principal components of the contractile units in skeletal muscle. We established a homogenous cohort of ten unreported families with severe NM, and we provide clinical, genetic, histological, and ultrastructural data. The patients manifested antenatal or neonatal muscle weakness requiring permanent respiratory assistance, and most deceased within the first months of life. DNA sequencing identified known or novel ACTA1 mutations in all. Morphological analyses of the muscle biopsy specimens showed characteristic features of NM histopathology including cytoplasmic and intranuclear rods, cytoplasmic bodies, and major myofibrillar disorganization. We also detected structural anomalies of the perinuclear space, emphasizing a physiological contribution of skeletal muscle α-actin to nuclear shape. In-depth investigations of the nuclei confirmed an abnormal localization of lamin A/C, Nesprin-1, and Nesprin-2, forming the main constituents of the nuclear lamina and the LINC complex and ensuring nuclear envelope integrity. To validate the relevance of our findings, we examined muscle samples from three previously reported ACTA1 cases, and we identified the same set of structural aberrations. Moreover, we measured an increased expression of cardiac α-actin in the muscle samples from the patients with longer lifespan, indicating a potential compensatory effect. Overall, this study expands the genetic and morphological spectrum of severe ACTA1-related nemaline myopathy, improves molecular diagnosis, highlights the enlargement of the perinuclear space as an ultrastructural hallmark, and indicates a potential genotype/phenotype correlation.

Acute Flaccid Myelitis Associated with Enterovirus D68 in Children, Argentina, 2016.

After a 2014 outbreak of severe respiratory illness caused by enterovirus D68 in the United States, sporadic cases of acute flaccid myelitis have been reported worldwide. We describe a cluster of acute flaccid myelitis cases in Argentina in 2016, adding data to the evidence of association between enterovirus D68 and this polio-like illness.

Choline Acetyltransferase Mutations Causing Congenital Myasthenic Syndrome: Molecular Findings and Genotype-Phenotype Correlations.

Choline acetyltransferase catalyzes the synthesis of acetylcholine at cholinergic nerves. Mutations in human CHAT cause a congenital myasthenic syndrome due to impaired synthesis of ACh; this severe variant of the disease is frequently associated with unexpected episodes of potentially fatal apnea. The severity of this condition varies remarkably, and the molecular factors determining this variability are poorly understood. Furthermore, genotype-phenotype correlations have been difficult to establish in patients with biallelic mutations. We analyzed the protein expression of phosphorylated ChAT of seven CHAT mutations, p.Val136Met, p.Arg207His, p.Arg186Trp, p.Val194Leu, p.Pro211Ala, p.Arg566Cys, and p.Ser694Cys, in HEK-293 cells to phosphorylated ChAT, determined their enzyme kinetics and thermal stability, and examined their structural changes. Three mutations, p.Arg207His, p.Arg186Trp, and p.Arg566Cys, are novel, and p.Val136Met and p.Arg207His are homozygous in three families and associated with severe disease. The characterization of mutants showed a decrease in the overall catalytic efficiency of ChAT; in particular, those located near the active-site tunnel produced the most seriously disruptive phenotypic effects. On the other hand, p.Val136Met, which is located far from both active and substrate-binding sites, produced the most drastic reduction of ChAT expression. Overall, CHAT mutations producing low enzyme expression and severe kinetic effects are associated with the most severe phenotypes.

Clinical, histological and genetic characterization of reducing body myopathy caused by mutations in FHL1.

We recently identified the X-chromosomal four and a half LIM domain gene FHL1 as the causative gene for reducing body myopathy, a disorder characterized by progressive weakness and intracytoplasmic aggregates in muscle that exert reducing activity on menadione nitro-blue-tetrazolium (NBT). The mutations detected in FHL1 affected highly conserved zinc coordinating residues within the second LIM domain and lead to the formation of aggregates when transfected into cells. Our aim was to define the clinical and morphological phenotype of this myopathy and to assess the mutational spectrum of FHL1 mutations in reducing body myopathy in a larger cohort of patients. Patients were ascertained via the detection of reducing bodies in muscle biopsy sections stained with menadione-NBT followed by clinical, histological, ultrastructural and molecular genetic analysis. A total of 11 patients from nine families were included in this study, including seven sporadic patients with early childhood onset disease and four familial cases with later onset. Weakness in all patients was progressive, sometimes rapidly so. Respiratory failure was common and scoliosis and spinal rigidity were significant in some of the patients. Analysis of muscle biopsies confirmed the presence of aggregates of FHL1 positive material in all biopsies. In two patients in whom sequential biopsies were available the aggregate load in muscle sections appeared to increase over time. Ultrastructural analysis revealed that cytoplasmic bodies were regularly seen in conjunction with the reducing bodies. The mutations detected were exclusive to the second LIM domain of FHL1 and were found in both sporadic as well as familial cases of reducing body myopathy. Six of the nine mutations affected the crucial zinc coordinating residue histidine 123. All mutations in this residue were de novo and were associated with a severe clinical course, in particular in one male patient (H123Q). Mutations in the zinc coordinating residue cysteine 153 were associated with a milder phenotype and were seen in the familial cases in which the boys were still more severely affected compared to their mothers. We expect the mild end of the spectrum to significantly expand in the future. On the severe end of the spectrum we define reducing body myopathy as a progressive disease with early, but not necessarily congenital onset, distinguishing this condition from the classic essentially non-progressive congenital myopathies.

Myasthenia gravis in childhood.

INTRODUCTION: Pathologic alterations in neuromuscular transmission, known as Myasthenia Gravis (MG), comprise combinations (forms) of pre- and post-synaptic changes whose age at onset and clinical manifestations are dissimilar. Some forms have autoimmune features, while others have a defect due to functional or structural plaque alternations. The purpose of this work is to describe the clinical forms of MG seen in childhood, to facilitate proper diagnosis and treatment. MATERIAL AND METHODS: Retrospective data from 87 patients studied at the Ricardo Gutierrez Children's Hospital from 1990 to 2002 are presented. They were evaluated by clinical, pharmacological, electrophysiological, laboratory and radiological exams. RESULTS: Three distinct groups of patients were found: Group 1, Transient Neonatal Myasthenia Gravis (TNMG) represented 6.8% 9 (n=6) of the total number of patients. None of these six patients had ocular involvement. Group 2, Congenital Myasthenia (CMG) represented 17.2% of cases 9 (n=15). These patients had an onset of symptoms from 1 to 12 months of age. Eight cases were sporadic and the remainder familial. The most frequent symptom in this group was bilateral blepharoptosis in 13 patients. Group 3, Juvenile Myasthenia (JMG) comprised 76% of the patients (n=66). The onset of symptoms in this group ranged from 13 months to 14 years (mean 3.6 years). Thirty-nine of these children presented purely with ocular symptoms. CONCLUSIONS: Children with myasthenia gravis may present to the ophthalmologist first, with symptoms such as unilateral or bilateral blepharoptosis, diplopia, strabismus or ophthalmoplegia. Therefore, it is essential that the ophthalmologist be aware of the varied features of this disorder in children in order to diagnosis it correctly and make appropriate treatment referrals.

Paralytic poliomyelitis caused by a vaccine-derived polio virus in an antibody-deficient Argentinean child.

We describe a case of poliomyelitis in a 3-year-old Argentinean boy with X-linked hypogammaglobulinemia. The child had no history of polio vaccination, but a poliovirus isolated from a stool sample had 97.2% genetic similarity to the Sabin 1 vaccine strain. According to the WHO definition, this is the first case reported of a vaccine-derived poliovirus infection recorded in continental Latin America.

Deficiencia cronica de hexosaminidasa A asociada a neuropatia periferica sensitiva pura / Chronic hexosaminidase A deficiency associated to pure sensory peripheral neuropathy

Se presenta a un paciente con deficiencia de hexosaminidasa A (Hx A), que conduce a la gangliosidosis GM2, que desarrolla un cuadro neurológico progresivo cuyo comienzo pudo fijarse a los 10 años y que se caracterizó por deterioro intelectual, compromiso cerebeloso, alteración de neuromas motoras superior e inferior y neuropatía sensitiva sin aparente compromiso de las fibras motoras que integran el nervio mixto. La biopsia del nervio safeno externo mostró pérdida de fibras mielínicas, en especial de aquellas de mayor y menor diámetro, agrupamiento axonal, axones con cubiertas mielínicas anormalmente finas en relación con su diámetro, degeneración axonal, desmielinización segmentaria y paranodal y remielinización. La microscopia electrónica reveló cuerpos de inclusión electrodensos no específicos e incusiones laminares concéntricas dentro del citoplasma de las células de Schwann. Los hallazgos hechos señalan que la neuropatía sensitiva pura puede formar parte del espectroclínico de la deficiencia de HxA

Peripheral motor nerve conduction studies in patients with chronic Chagas' disease

Foi feita investigaçäo da velocidade de conduçäo motora no nervo ulnar de 70 pacientes em fase crônica da doença de Chagas. Foi verificado que 2,6% deles apresentavam lentificaçäo em grandes axônios motores em segmentos distais e 14% em segmentos proximais: 27% deles apresentavam também conduçäo lentificada em pequenas fibras motoras. Essas observaçöes indicam que alguns pacientes na fase crônica da doença podem desenvolver uma neuropatia motora

Cerebral evoked potentials in human chronic Chagas' disease

Setenta y cinco pacientes con el diagnóstico de enfermedad de Chagas crónica fueron estudiados con el empleo de los potenciales evocados cerebrales. Tres de ellos tuvieron retardo del arribo de la senal al punto de Erb ó al ingreso medular en los potenciales evocados somatosensitivos (PESS). Dos pacientes presentaron incremento del intervalo entre las ondas I y III en los potenciales evocados auditivos de tronco (PEAT). Estos hallazgos fueron interpretados como debidos al dano en la fibra nerviosa ériférica, un hecho descripto en trabajos previos. El hallazgo mas sorprendente fue la prolongación del intervalo de tiempo entre las ondas N13-N20 en los PESS, hallandose en dos pacientes y entre las ondas III y V en los PEAT en 7 sujetos. Estas observaciones sugieren de algun modo, el compromiso de sistema nervioso central, quizás relacinado al dano de la mielina, en pacientes en estadio crónico de la infección

Neuromuscular transmission studies in human chronic Chagas' disease

Cincuenta y ocho pacientes con edades entre los 1 y 58 años, con diagnóstico de enfermedad de Chagas crónica fueron estudiados para evaluar la transmisión neuromuscular. Se estimuló en forma supramáxima el nervio cubital a nivel de muñeca, con registro de electrodos de superficie en hipotenar. Dicha estimulación se realizó a 3 Hz durante 2 segundos y 10 Hz durante 1 segundo en condiciones basales, trás 4 minutos de ejercicio mecánico, luego de 4 minutos de ejercicio mecánico mas isquemia y trás 2 minutos de liberada la isquemia. Se procedió a medir la amplitud del 3, 5, 6 y 10 potencial, que fueron expresados como variación porcentual con respecto al primero al que se le asignó un valor de 100%. Treinta pacientes no evidenciaron diferencias con respecto a la curva obtenida en 20 sujetos controles, 4 mostraron una caida del potencial evocado muscular, 6 una caida del mismo cuando el estímulo se realizó frecuencias y un incremento cuanto el estímulo fue a altas frecuencias. En los restantes 18 pacientes se observó un incremento del pem. Estos hallazgos susgieren una posible alteración de la transmisión neuromuscular en algunos pacientes que han alcanzado el estadio crónico de la efemedad de Chagas de probable localización pré y/o post-sináptica

Conducción nerviosa periférica proximal y distal en la insuficiencia renal crónica / Proximal and distal peripheral nerve conduction in chronic renal failure

Veintidós pacientes con IRC terminal, en plan de hemodiálisis periódica trisemanal, fueron estudiados para evaluar la función total de la unidad motora en el segmento proximal y distal de los miembros superiores. Se estimuló el nervio cubital a nivel de muñeca y axila con registro con electrodo de superficie en hipotenar, determinándose amplitud de la onda M y sus respectivas latencias, obteniéndose la velocidad de conducción en el segmento axila-muñeca. Con el estímulo en el mismo nervio se obtuvieron 10 respuestas F en muñeca analizando latencia y amplitud de cada una de ellas y la velocidad de conducción de la onda F total (VCMFT) según fórmula de Kimura y la velocidad de conducción de dicha onda en el segmento proximal (C7-axila) (VCMFP). Asimismo se determinó en el nervio medicano la latencia residual motora y las velocidades de conducción motora (VCM) y sensitiva (VCS) y en el nervio ciático poplíteo externo la latencia distal y la VCM. Se dosaron valores sanguíneos de urea, creatinina y K++. Los resultados fueron comparados con un grupo de sujetos controles. En el grupo de probandos se halló una disminución significativa de la amplitud de la onda M en hipotenar (p<0,0005). A medida que se producía la lentificación de la conducción en el segmento axila-muñeca se evidenciaba una paralela reducción de la amplitud de la onda M (r = 0,44, p<0,05). La VCS del nervio mediano estuvo reducida significativamente con respecto a los controles (p<0,0005). La VCMFT fue en los probandos significativamente inferior a los controles (p<0,0005), mientras que en la VCMFP hubo diferencia de menor significación entre ambos (p<0,050). No se halló relación entre los valores de amplitud y latencia de la onda M en el nervio cubital, tampoco entre VCM y VCS en el nervio mediano ni entre los valores de urea, creatinina y K+ y los parámetros electrofisiológicos estudiados. Los resultados obtenidos señalan que en este grupo de pacientes la neuropatía es de tipo axonal y a predominio distal (ASU)