CONGENITAL MYASTHENIA IN SIBLINGS

Something in the Blood? A history of the autoimmune hypothesis regarding myasthenia gravis

From the first descriptions of myasthenia gravis (MG) in the late nineteenth century, speculation about the cause of MG has centered on the possibility of some curare-like factor circulating in the blood. The transfer of transient myasthenic symptoms from a myasthenic mother to her newborn reinforced this speculation. However, it was not until 1960, when William Nastuk and coworkers noted that serum complement correlated with the clinical course in MG, and Arthur Strauss and colleagues described antiskeletal muscle antibodies in the sera of some MG patients, that a paradigm shift occurred from prior exclusive focus on the neuromuscular junction to a broader consideration of the relevance of immunological mechanisms in myasthenia. These findings coincided with an even greater scientific revolution pioneered by Macfarlane Burnet towards cell-mediated and away from chemical immunology. The dominant immunological question of the decade 1955-1965, however, was whether human autoimmune diseases actually existed. During the next decade, 1965-1975, various diseases were accepted as being autoimmune in character, and although comparatively rare, MG became prominent among them because of a known antigen, the acetylcholine receptor, and an excellent experimental model.

Congenital myasthenic syndrome: a rare, potentially treatable cause of respiratory failure in a "floppy" infant

A four-month-old infant, thought to suffer from cerebral palsy, presented with respiratory failure on the background of a gradually deteriorating general level of function. Whilst being ventilated in intensive care he was noted to have severe muscle weakness. A disorder of the neuromuscular junction was suspected and he was subsequently demonstrated to have a congenital myasthenic syndrome. Anticholinesterase therapy produced a dramatic recovery. The congenital myasthenic syndromes and the diagnosis of a "floppy baby" are briefly reviewed.

Congenital myasthenic syndromes

The Congenital Myasthenic Syndromes (CMS) constitute a group of rare genetic disorders affecting neuromuscular transmission. They differ from myasthenia gravis and the Lambert-Eaton myasthenic syndrome, which are autoimmune antibody-mediated conditions. CMS can present at any time from birth to adulthood, though usually within the first 2 yr of life, and result in a spectrum of diseases ranging from mild weakness to severe disability with life-threatening episodes. Several of these syndromes have been well documented, and in recent years fully investigated using a variety of electrophysiological, histochemical, and morphological techniques. In this review we describe the main results of these investigations, and attempt to classify the disorders into groups that can be recognized by the clinician. They include defects in acetylcholine release, absence of the endplate-specific form of acetylcholinesterase, and alterations in the number or function of postsynaptic acetylcholine receptors. Clinical features are described in detail, and treatment reviewed. These disorders involve a potentially large number of candidate genes. Further elucidation of the underlying abnormalities will not only lead to improved treatment, but should contribute to our understanding of the molecular biology of the neuromuscular junction.

Single fiber EMG in a congenital myasthenic syndrome associated with facial malformations

Six patients with a newly described genetic syndrome in Iraqi and Iranian Jews of congenital myasthenia associated with facial malformations were studied with voluntary and stimulation single fiber EMG (SFEMG). Voluntary SFEMG revealed abnormal jitter in all patients in both extensor digitorum communis (EDC) and orbicularis oculi (OOC) muscles, though much smaller in the clinically unaffected EDC. SFEMG study of OOC muscle by axonal stimulation at rates from 1 to 48 Hz showed the most increased jitter at the highest stimulation frequencies in the majority of end-plates, one-third of which showed maximal jitter at intermediate rates. These results may suggest a postsynaptic abnormality as the underlying cause for the neuromuscular transmission defect, and demonstrate the usefulness of SFEMG in the diagnosis of congenital myasthenia.

A congenital myasthenic syndrome refractory to acetylcholinesterase inhibitors

We studied 4 siblings (3 men and 1 woman), ages 22 to 43 years, with congenital ptosis, external ophthalmoplegia, proximal muscle weakness and fatigability unresponsive to acetylcholinesterase (AChE) inhibitors. Repetitive nerve stimulation showed a significant compound muscle action potential (CMAP) area decrement at 2 or 3 Hz. Nerve conduction studies and concentric needle electromyography were normal, and repetitive CMAPs to single nerve stimulation were not observed. Voluntary single fiber electromyography (SFEMG) showed increased jitter and blocking. Assessment of individual end-plates using SFEMG with intramuscular axonal microstimulation showed no uniform relationship between jitter and the rate of stimulation, consistent with a postsynaptic defect of neuromuscular transmission. Edrophonium eliminated the decremental response to repetitive nerve stimulation, but caused no significant clinical improvement, suggesting an additional mechanism for weakness in these patients.

Congenital myasthenia: end-plate acetylcholine receptors and electrophysiology in five cases

The nature of the defect in congenital myasthenia was investigated in biopsy specimens of intercostal muscle from 5 male patients whose symptoms presented between birth and 2 years of age. Miniature end-plate potentials were reduced in amplitude in all 5 patients. The number of acetylcholine receptors as determined by alpha-bungarotoxin binding was normal in case 1 and reduced in cases, 2, 4, and 5. The shape of the end-plates as shown by autoradiography and cholinesterase staining was normal in case 1 and elongated in cases 2, 4, and 5. In cases 3, alpha-bungarotoxin binding was slowly reversible, and there were some muscle fibers with multiple end-plate regions. The acetylcholine content of the muscle was normal in all 5 cases. None of the patients had serum antibody to human acetylcholine receptor as measured by immunoprecipitation or inhibition of alpha-bungarotoxin binding. We conclude that congenital myasthenia is a heterogeneous condition of nonimmune etiology in which both presynaptic and postsynaptic defects can be found.

Disorders of neuromuscular transmission other than myasthenia gravis

Disorders of neuromuscular transmission in humans are caused by a wide variety of agents including systemic diseases, drugs, environmental toxins, animal envenomation, cations, and hormones. Some are genetically determined. Many are of known etiology. All such disorders interfere with one or more events in the sequence whereby a nerve impulse excites a muscle action potential. In many disorders of neuromuscular transmission, abnormal fatigue occurs, and some cases respond dramatically to treatment. Investigation of the microphysiology, microanatomy, and pharmacology of both normal and diseased neuromuscular junctions has increased our knowledge of these disorders.

Immune disease and HLA associations with myasthenia gravis

In the late 1950's laboratory and clinical evidence suggested that myasthenia gravis was an autoimmune disorder. Since then a voluminous literature has developed documenting the many immunological abnormalities that occur in this condition. Recent findings point to a central disorder of immunoregulation. It is postulated that the disease occurs as a result of host genetic and environmental influences-the latter being, as yet unidentified and possibly a virus.

Familial myasthenia gravis. Report of four cases

Two pairs of siblings with myasthenia gravis, belonging to two different families, are reported. This is the only record of familial myasthenia during the past twenty years, in a total of 145 patients seen at the Neurological Clinic of the São Paulo Medical School. In spite of the fact that myasthenia gravis does not show hereditary characteristics, the peculiar features of the four cases justify the present report. The two pairs of siblings were born from non myasthenic nor consanguineous parents. The disease started at birth showing bilateral partial eyelid ptosis in all patients. The course of the illness has been favorable. There was no thymoma.

A genetic study of infantile and juvenile myasthenia gravis

From the present study, and from reports in the literature, two forms of childhood myasthenia emerge. There is an early-onset form (with onset of symptoms under 2 years of age) where the illness is milder but more persistent, and where there is frequent occurrence of myasthenia in sibs. Such cases are likely to be inherited as an autosomal recessive, although it is possible that they represent the extreme edge of a multifactorial distribution of combined genetic and environmental aetiology. The second group (with onset of symptoms between the age of 2 and 20 years) clinically resembles adult myasthenia, which is associated with autoimmunity and an increased incidence of thyroid dysfunction. Some genetic contribution occurs in this form but it is less marked than with the early-onset cases and there is no recognizable pattern of inheritance. As secondary cases are even less common among the families of adult myasthenics, it is likely that individuals with most genetic predisposition to myasthenia tend to develop symptoms early, and that non-genetic factors are relatively more important for the development of myasthenia in adults.

Myasthenia gravis occurring in twins

Myasthenia gravis in one member each of two sets of twins is described. A 17 year old girl developed generalized myasthenia gravis at the age of 14 years, while her monozygotic twin sister has remained in good health during a three year period of observation. Another patient was a 19 year old woman with the onset of generalized myasthenia gravis at the age of 11 years, and her dizygotic twin sister has been in good health.Myasthenia gravis has been described in 13 sets of monozygotic twins, seven sets of dizygotic twins, and one set of twins with undetermined zygosity. Both members of twins were affected in five sets of monozygotic twins and one set of twins with undetermined zygosity, and only one twin was affected in the remaining sets of twins. Occurrence of myasthenia gravis in both members of monozygotic twins and in none of dizygotic twins, and frequent familial occurrence of the disease suggest the role of a genetic factor in the pathogenesis of this disease.

Myasthenia gravis in identical twins

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Neonatal myasthenia gravis; report of a case

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Myasthenia gravis in children:

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