Genomic disorders: An overview
- Carlos A Bacino, MD, FACMG
Carlos A Bacino, MD, FACMG
- Professor of Molecular and Human Genetics
- Baylor College of Medicine
- Section Editors
- Helen V Firth, DM, FRCP, DCH
Helen V Firth, DM, FRCP, DCH
- Section Editor — Genetics
- Consultant Clinical Geneticist
- Addenbrooke's Hospital, Cambridge, UK
- Benjamin A Raby, MD, MPH
Benjamin A Raby, MD, MPH
- Section Editor — Genetics
- Associate Professor of Medicine
- Harvard Medical School
Genomic disorders are diseases that result from the loss or gain of chromosomal/DNA material. The most common and better-delineated genomic disorders are divided in two main categories: those resulting from copy number losses (deletion syndromes) and copy number gains (duplication syndromes).
An overview of genomic disorders is presented here. Specific syndromic disorders are reviewed separately.
COPY NUMBER VARIATIONS
Structural genetic variation refers to a class of sequence alterations spanning typically more than 1000 base pairs (one kilobase or kb) . However, studies have indicated that these genetic variations can be smaller (eg, in the 450 base pair and up range) and that most individuals have at least 1,000 such variations .
These sequence variations include quantitative variations such as copy number variations (CNVs), sequence rearrangements (such as those observed among immunoglobulins), and other less common variations, including chromosomal rearrangements that may or may not alter the genome contents and in some cases result in disease.
CNVs, the most prevalent type of structural variation, are DNA segments spanning thousands to millions of bases whose copy number varies between different individuals [3,4]. These submicroscopic genomic differences in the number of copies of one or more sections of DNA are the result of DNA gains or losses. Copy number gains can be the result of duplications, triplications, or even multiple copy number gains. Most deletions are one copy loss (heterozygous), but in some instances the loss can affect both copies (homozygous deletions).
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