Recombinant DNA strategies in genetic neurological diseases

The first decade of molecular genetics in neurology: changing clinical thought and practice

Molecular genetics has had a powerful impact on clinical neurology. Definitions of disease are changing from clinical criteria to DNA analysis, resolving questions about the nature of clinically similar but not identical diseases. Genetic counseling is more reliable. Concepts of mendelian inheritance are being tested and new forms of mutation have been discovered to explain anticipation. Nonmendelian forms of inheritance have emerged; concepts of pathogenesis are on a more secure footing; and novel treatments are being explored.

Molecular genetics in basic myology: a rapidly evolving perspective

Myology has greatly benefited from the recent unification of concepts in molecular, cellular, and developmental biology. The interplay between intrinsic and extrinsic factors in determining the physiologic characteristics of individual myofibers has emerged as an important theme. Of special note is the manner in which the study of contractile protein gene structure and expression has contributed to our understanding of the development and ultimate plasticity of the contractile apparatus. As mechanistic models of normal myogenesis achieve increasing sophistication, the opportunities for understanding the pathogenesis of progressive muscle disfunction improve. In this article we review recent progress in basic myology which will be of interest to clinicians studying the heritable neuromuscular disorders.

Molecular genetics in muscular dystrophy research: revolutionary progress

The contribution of "reverse genetic" strategies to neuromuscular disease research is evident in the progression of breakthroughs that have recently culminated in the cloning of the Duchenne muscular dystrophy (DMD) cDNA. The resultant improvements in our understanding of the genetic basis of Becker muscular dystrophy (BMD) and DMD serve as models for similar investigation of other heritable disorders. These genetic advances have outpaced concurrent work on the molecular pathogenesis of the dystrophic process, with the curious result that inferences about the DMD protein's amino acid sequence have preceded any information about its function or intracellular localization. In recognition that this foundation sets the stage for the rapid elucidation of the disease's pathogenesis, we review the experimental basis of such advances, with reference to relevant progress in basic myology, pathology, and molecular biology. We conclude with a view towards the ultimate clinical implications of these experimental breakthroughs.

AAEE minimonograph #27: differential diagnosis of myotonic syndromes

Recent advances in neuromuscular diseases have also widened the diagnostic spectrum of myotonic disorders. Treatment, prognosis, and genetic aspects are different in the various syndromes and mandate a correct diagnosis. The combination of neurologic examination, standard EMG, exercise test, cold exposure, potassium loading, eye examination, and pedigree analysis allows correct classification of nearly all patients with myotonic disorders. In this review emphasis is placed on clinical features and electrophysiologic evaluation.

Genetic considerations in childhood epilepsy

This report reviews various lines of evidence demonstrating important genetic influences in the epilepsies, with special emphasis on childhood epilepsy. Five pertinent topics are discussed: (a) examples of dominant, recessive, and X-linked single-gene disorders known to be associated with epilepsy, (b) examples of gross chromosomal aberrations associated with epilepsy, (c) discussion of multifactorial and polygenic inheritance and issues of genetic heterogeneity with specific reference to idiopathic generalized epilepsy, febrile seizures, and infantile spasms, (d) brief review of experimental clues to possible pathogenetic mechanisms underlying genetic forms of epilepsy, and (e) an overview of strategies for applying genetic linkage analysis to hereditary epileptic disorders.

Molecular analysis of human muscular dystrophies

The ability to map disease loci using restriction fragment length polymorphisms (RFLPs) identified by DNA probes has revolutionized molecular genetics. Duchenne and Becker muscular dystrophies have been shown to be localized within the same very small region of Xp21 on the human X chromosome. The mutation itself should soon be identified at the DNA level, which will permit a detailed analysis of the molecular defect at the biochemical level. Rapid progress has also been made in the study of myotonic dystrophy on chromosome 19. DNA markers closely linked to the mutant locus have been identified, making antenatal diagnosis possible in informative families. Autosomal recessive muscular dystrophies are more difficult to study, but the means to localize even these mutations is being developed. The next decade should prove to be an exciting one for those involved in the molecular analysis and clinical management of human muscular dystrophies.

Localization of cloned unique DNA to three different regions of chromosome 19: screen for linkage probes for myotonic dystrophy

Screening polymorphic DNA probes for linkage to myotonic dystrophy (DM) and to other reported chromosome 19 (CH19) genes will develop a linkage map for human CH19. We report here the assignment of 3 cloned unique DNA sequences to 3 distinct regions of CH19. The novel use of 35S-labeled probes facilitated the rapid localization of the gene for the third complement factor (C3) to 19p13.2 by in situ hybridization. Metaphase chromosomes were from normal peripheral lymphocytes as well as from a fibroblast line containing a 15;19 translocation which permitted clear identification of CH19 regions of localization. Two random clones isolated from a plasmid library of human F-group enriched chromosomal DNA (D19S5 and D19S6) were in like manner assigned to 19p1.2 and 19q13.2 to 19qter, respectively.

Familial syringomyelia

A woman with syringobulbia and syringomyelia and her sister with syringomyelia are described. The diagnosis was confirmed radiologically and surgically in the first sister and no other definite abnormalities of her craniocervical junction were found.

Recombinant DNA approach to X-linked mental retardation

Currently, approximately 115 X-linked diseases have been documented. Many of these defects are neurological in nature and about 25% result in a broad spectrum of mental impairments which can be distinguished by biochemical or clinical means. It is not known how many of the retarded population carry an X-linked defect due to lack of a distinct marker. By constructing a molecular linkage map of the X chromosome using DNA polymorphisms, it will be possible to identify these individuals, classify their disorder by the chromosomal region in which their polymorphism is detected, offer genetic counseling and prenatal diagnosis to their family members and try to determine which gene the polymorphism is linked to in order to identify the defect and devise therapy.

Structural gene for beta-nerve growth factor not defective in familial dysautonomia

The developmental loss of neurons in sympathetic, sensory, and some parasympathetic ganglia in familial dysautonomia suggests an inherited defect in the action of beta-nerve growth factor (beta-NGF). The role of this growth factor in dysautonomia has been difficult to resolve as there is no known source of authentic human beta-NGF. The availability of a cloned DNA probe for the human beta-NGF gene has allowed identification of some copies of the gene (alleles) in six affected families. Alleles differ in the length of restriction endonuclease fragments that hybridize to DNA probes for the gene. In two families, affected children did not inherit the same two alleles at the beta-NGF locus. Since this disease is transmitted in an autosomal recessive manner, affected children must share the same alleles at the locus causing the disease. This analysis excludes the beta-NGF gene region as the cause of this neurologic disease but does not eliminate other genes involved in beta-NGF action, such as those coding for processing enzymes, receptors, or other subunits of the NGF complex.