Molecular diagnosis of neurologic disorders

K K Jain MD (Dr. Jain is a consultant in neurology and has no relevant financial relationships to disclose.)
Originally released July 17, 2000; last updated July 13, 2017; expires July 13, 2020

Overview

Molecular diagnosis can be defined as the clinical application of molecular technologies to elucidate, diagnose, and monitor human diseases. This article gives an introduction to basic technologies and new developments in application for clinical diagnostics. These technologies are important for precise and rapid diagnosis of diseases of the nervous system such as infections, brain tumors, genetic disorders, and neurodegenerative diseases. Introduction of nanotechnology in diagnostics has further refined these procedures.

Key points

 

• Molecular diagnosis is the clinical application of molecular technologies to refine diagnosis.

 

• Many new biotechnologies have been incorporated in molecular diagnostics including biochips and nanobiotechnology.

 

• Next-generation sequencing is having an increasing impact on molecular diagnostics as sequencing of the human genome becomes more affordable.

 

• Molecular diagnostics has important applications in neurology including genetic disorders, infections, and cancer of the nervous system.

 

• Besides diagnosis of disease, molecular diagnostic technologies are also useful for drug discovery, monitoring of therapy by using biomarkers, and the development of personalized neurology.

Historical note and terminology

Molecular diagnosis can be defined as the clinical application of molecular technologies to elucidate, diagnose, and monitor human diseases. Basic technologies have been described in detail elsewhere (Jain 2017b). Molecular technologies incorporate the use of nucleic acids (DNA and RNA) as well as recombinant antibodies. Proteomic technologies are also applied to molecular diagnosis, justifying the term "proteodiagnostics." More than 500 molecular diagnostic systems have been developed to date. This article describes the basic principles of these technologies and their application to the diagnosis of neurologic disorders. The College of American Pathologists has used the term “molecular pathology” for molecular diagnostics, and as an extension of this, the application for neurologic disorders can be considered as “molecular neuropathology." Imaging technologies have been refined to the molecular level and the term "molecular brain imaging" is suggested.

Landmarks in the historical development of molecular diagnostics appear in Table 1. DNA was shown to carry genetic code in pneumococci (Avery 1944) even before the discovery of the double-stranded structure of the DNA (Watson and Crick 1953). DNA probes (segments of DNA labeled with radioactive markers) were used for diagnostic purposes in the 1980s, but the most important landmark in molecular diagnostics was the discovery of polymerase chain reaction (PCR) in 1985 (Mullis et al 1986). In the pre-PCR era, molecular biologists needed cumbersome and slow laboratory methods to study a few copies of a DNA sequence of interest in a clinical sample. Polymerase chain reaction, by providing unlimited copies of DNA, facilitated the applications in clinical diagnostics. Although several other technologies for amplification and detection of nucleic acids have been developed since then, PCR, with its modifications, remains the mainstay of current molecular diagnosis.

Availability of the human genome sequence will provide many opportunities for the development of molecular diagnostics. This will lead to the development of novel diagnostics as well as therapeutics for neurologic disorders and facilitate the development of personalized neurology.

Table 1. Historical Development of Molecular Diagnostics

Year

Discovery and development

1944

DNA shown to carry genetic code in pneumococci (Avery 1944)

1953

Identification of the double-stranded structure of DNA (Watson and Crick 1953)

1950s

Discovery of the enzyme DNA polymerase (Kornberg 1959)

1969

Discovery of in situ hybridization for gene location by labeled RNA probes (Gall and Pardue 1969)

1970

Discovery of restriction enzymes that cut DNA at the site of specific sequences

1970

Discovery of reverse transcriptase and copying of RNA into DNA (Baltimore 1970)

1972

First recombinant DNA molecule is produced with use of ligase. The genomic age begins (Jackson et al 1972).

1975

Southern blot test (Southern 1975)

1975

Monoclonal antibody technology (Kohler and Milstein 1975)

1977

Invention of the technology for DNA sequencing (Sanger 1977)

1980

Creation of the first recombinant DNA molecule

1981

Gene mapping by in situ hybridization becomes a standard method

1980s

DNA probes: segments of DNA labeled with radioactive markers

1983

Demonstration of Huntington disease gene (Gusella et al 1983)

1985

Discovery of polymerase chain reaction at Cetus Corporation (Mullis et al 1986)

1987 and 1988

Discovery of dystrophin, the protein product of the human Duchenne muscular dystrophy locus, and its characterization in muscle biopsies by immunoblotting (Hoffman et al 1988)

1986

Development of fluorescent in situ hybridization technique (Pinkel et al 1986)

1989

Start of Human Genome Project, National Institutes of Health, USA

1991

Ligase chain reaction (Barany 1991)

1991

Wedding of molecular biology and cytogenetics to create molecular cytogenetics (Lichter et al 1991)

1991

Peptide nucleic acid, a mimic of DNA, is invented. Peptide nucleic acid arrays are useful for detection of DNA and RNA (Nielsen et al 1991).

1992

Branched DNA technology used to quantify HIV levels

1998

Invention of locked nucleic acid, a DNA analogue with a high affinity for complementary DNA or RNA and the ability to discriminate between correct and incorrect target sequences (Kumar et al 1998)

1998

Antisense oligonucleotides labeled to detect RNA and tracked in their sojourn through the body by PET (Tavitian et al 1998)

2000

Sequencing of human genome is completed. The postgenomic era begins.

2001

Application of proteomic technologies in diagnosis: proteodiagnostics

2002

Application of nanotechnologies in diagnosis: nanodiagnostics

This article describes the new technologies for molecular diagnostics based mostly on nucleic acids, but proteomics-based diagnostic technologies are also developing rapidly. Most of these technologies have potential applications in neurologic disorders.

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