Genetic study of sample of 70 patients with myasthenia gravis

Dysfunctional chemosensation in myasthenia gravis: a systematic review

OBJECTIVES

Myasthenia gravis has traditionally been viewed as a disorder that solely affects the neuromuscular junction within the peripheral nervous system. However, there is now evidence that the cholinergic dysfunction of this disorder may be more widespread than previously believed. This article provides a systematic review of the studies that examined smell and taste function in myasthenia gravis.

METHODS

We analyzed studies that reported chemosensory function alterations in patients with myasthenia gravis. PubMed, MEDLINE, Web of Science, EMBASE, and SciELO, searched to identify articles published from January 1950 through December 2012, were supplemented by relevant articles. The following information was identified from each article: the number of patients, number of controls (if any), clinical stage of patients, neurological involvement, serological state, taste or smell involvement, chemosensory test used, and country of publication.

RESULTS

Ten studies reporting smell and taste function and dysfunction in patients with myasthenia gravis were identified, most of which were case reports commenting on apparent abnormalities in the taste system. The sole empirical study that investigated taste function, however, was negative, suggesting that some reports of taste loss may reflect olfactory loss. One study clearly documented olfactory dysfunction in patients with myasthenia gravis, dysfunction most likely attributable to altered central nervous system cholinergic function.

CONCLUSIONS

Chemosensory dysfunction has been reported in a number of patients with myasthenia gravis. Given the close association between complaints of taste dysfunction and loss of flavor sensations secondary to olfactory system damage, quantitative testing should be used to accurately assess the nature and degree of the dysfunction present in this debilitating disorder.

Profound olfactory dysfunction in myasthenia gravis

In this study we demonstrate that myasthenia gravis, an autoimmune disease strongly identified with deficient acetylcholine receptor transmission at the post-synaptic neuromuscular junction, is accompanied by a profound loss of olfactory function. Twenty-seven MG patients, 27 matched healthy controls, and 11 patients with polymiositis, a disease with peripheral neuromuscular symptoms analogous to myasthenia gravis with no known central nervous system involvement, were tested. All were administered the University of Pennsylvania Smell Identification Test (UPSIT) and the Picture Identification Test (PIT), a test analogous in content and form to the UPSIT designed to control for non-olfactory cognitive confounds. The UPSIT scores of the myasthenia gravis patients were markedly lower than those of the age- and sex-matched normal controls [respective means (SDs) = 20.15 (6.40) & 35.67 (4.95); p<0.0001], as well as those of the polymiositis patients who scored slightly below the normal range [33.30 (1.42); p<0.0001]. The latter finding, along with direct monitoring of the inhalation of the patients during testing, implies that the MG-related olfactory deficit is unlikely due to difficulties sniffing, per se. All PIT scores were within or near the normal range, although subtle deficits were apparent in both the MG and PM patients, conceivably reflecting influences of mild cognitive impairment. No relationships between performance on the UPSIT and thymectomy, time since diagnosis, type of treatment regimen, or the presence or absence of serum anti-nicotinic or muscarinic antibodies were apparent. Our findings suggest that MG influences olfactory function to the same degree as observed in a number of neurodegenerative diseases in which central nervous system cholinergic dysfunction has been documented.

Diseases and disorders of muscle

Muscle may suffer from a number of diseases or disorders, some being fatal to humans and animals. Their management or treatment depends on correct diagnosis. Although no single method may be used to identify all diseases, recognition depends on the following diagnostic procedures: (1) history and clinical examination, (2) blood biochemistry, (3) electromyography, (4) muscle biopsy, (5) nuclear magnetic resonance, (6) measurement of muscle cross-sectional area, (7) tests of muscle function, (8) provocation tests, and (9) studies on protein turnover. One or all of these procedures may prove helpful in diagnosis, but even then identification of the disorder may not be possible. Nevertheless, each of these procedures can provide useful information. Among the most common diseases in muscle are the muscular dystrophies, in which the newly identified muscle protein dystrophin is either absent or present at less than normal amounts in both Duchenne and Becker's muscular dystrophy. Although the identification of dystrophin represents a major breakthrough, treatment has not progressed to the experimental stage. Other major diseases of muscle include the inflammatory myopathies and neuropathies. Atrophy and hypertrophy of muscle and the relationship of aging, exercise, and fatigue all add to our understanding of the behavior of normal and abnormal muscle. Some other interesting related diseases and disorders of muscle include myasthenia gravis, muscular dysgenesis, and myclonus. Disorders of energy metabolism include those caused by abnormal glycolysis (Von Gierke's, Pompe's, Cori-Forbes, Andersen's, McArdle's, Hers', and Tauri's diseases) and by the acquired diseases of glycolysis (disorders of mitochondrial oxidation). Still other diseases associated with abnormal energy metabolism include lipid-related disorders (carnitine and carnitine palmitoyl-transferase deficiencies) and myotonic syndromes (myotonia congenita, paramyotonia congenita, hypokalemic and hyperkalemic periodic paralysis, and malignant hyperexia). Diseases of the connective tissues discussed include those of nutritional origin (scurvy, lathyrism, starvation, and protein deficiency), the genetic diseases (dermatosparaxis, Ehlers-Danlos syndrome, osteogenesis imperfecta, Marfan syndrome, homocystinuria, alcaptonuria, epidermolysis bullosa, rheumatoid arthritis in humans, polyarthritis in swine, Aleutian disease of mink, and the several types of systemic lupus erythematosus) and the acquired diseases of connective tissues (abnormal calcification, systemic sclerosis, interstitial lung disease, hepatic fibrosis, and carcinomas of the connective tissues). Several of the diseases of connective tissues may prove to be useful models for determining the relationship of collagen to meat tenderness and its other physical properties. Several other promising models for studying the nutrition-related disorders and the quality-related characteristics of meat are also reviewed.

Familial myasthenia gravis

A family is reported in which myasthenia gravis and thyroid disease occur over three generations. The grandmother and granddaughter have ocular myasthenia and an aunt in the second generation had generalised myasthenia gravis with a thymoma. The pattern of histocompatibility antigens (HLA) haplotypes, anti-AChR antibodies, anti-striate muscle antibodies and thyroid disease is described. The haplotype HLA-A1, B8 was found in affected members of the first and third generation but the family study showed that this was not the same haplotype because the HLA-A1, B8 haplotype in the third generation was contributed by an unaffected person marrying into the family in the second generation.

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.

Evaluation of the jitter phenomenon in myasthenic patients and their relatives

Single fiber electromyography with jitter measurements and blocking evaluation was used for investigating 23 myasthenic patients, their 29 healthy relatives, coming from 10 families, and a control group of 10 subjects. Blocking was never seen in the healthy controls, and the jitter averaged some 30 microsec. Blocking was present in the myasthenic patients in 25.4% of the recorded potential pairs and there was a pathological jitter, which often extended over a few hundred microsec. The records of ten healthy relatives of patients were suggestive of slight but unquestionable abnormalities of neuromuscular transmission, viz. blocking and a jitter of over 60 microsec or more. The results demonstrate subclinical derangements of neuromuscular transmission in families of myasthenic patients, which points to a familial factor as involved in the pathomechanism of the disease.

Myasthenia gravis: a personal view of pathogenesis and mechanism, part 1

A review of our current knowledge of the etiology and pathogenesis of myasthenia gravis is presented, with particular emphasis on the immunological aspects of the disease. Part 1, published in this issue, deals with the clinical and genetic features of myasthenia gravis which led to the autoimmune theory of the etiology of this disease. Various theories in this field are reviewed, and recent advances in our knowledge of the acetylcholine receptor protein, and its immunology, are examined. Part 2, which will appear in the March/April issue, provides a review of the dysfunction of physiology, pharmacology, and structure of the neuromuscular junction in myasthenia gravis, and the part played by the autoimmune process.

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.