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Ebook Oxford textbook of neuromuscular disorders: Part 2

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Part 2 book “Oxford textbook of neuromuscular disorders” has contents: Inherited myasthenic syndromes, myasthenia gravis, the dystrophinopathies, skeletal muscle channelopathies, endocrine myopathies, metabolic myopathies , and other contents. | SECTION 5 Neuromuscular Junction: Inherited and Acquired CHAPTER 19 Inherited myasthenic syndromes Jacqueline Palace and Sarah Finlayson Introduction Congenital myasthenic syndromes (CMS) are a heterogeneous group of inherited disorders of neuromuscular junction (NMJ) transmission. In contrast to transient neonatal myasthenia (TNM), these syndromes are caused by mutations in genes that encode proteins of the NMJ, and have no immunological basis. The advent of molecular genetic techniques in the late twentieth century allowed significant advances in our understanding of the underlying mechanisms of NMJ pathophysiology to be made, including clear identification of genetic subtypes. No fewer than 17 genes have so far been identified (Table 19.1) as causing CMS, many of which involve private mutations. Accurate prevalence data are difficult to ascertain. An analysis of genetically confirmed cases found an overall UK prevalence of 3.8 per million. However, this varied considerably between regions, ranging from 1.6 to 6.7 per million in different UK strategic health authorities (SHAs) or devolved nations. Furthermore, within SHAs there is clustering, with some areas demonstrating prevalence as high as 13 per million [1] (and authors’ unpublished observations). Although this variability may be partially explained by differences in the racial composition of populations and familial clustering it is likely that many patients are undiagnosed. Fatigable muscle weakness presenting early in life is the hallmark of this group of disorders as a whole, but each genetic subtype of CMS has typical phenotypic characteristics which will be discussed in detail in this chapter. Eye signs can often be of considerable help in directing genetic testing (Table 19.2). Importantly there are a number of effective treatments in routine use for CMS and the genetic subtype determines the treatment choice (Table 19.3). Congenital myasthenia has a variable impact on patients’ lives, with the