Book contents
- Frontmatter
- Contents
- Preface
- Glossary of genetic and molecular terms
- Part I Approach to the child with special needs
- Part II The management of selected single congenital anomalies and associations
- Part III Chromosomal syndromes
- 7 Autosomal aneuploidy syndromes
- 8 Sex chromosome aneuploidy and X-linked mental retardation syndromes
- 9 Chromosome microdeletion syndromes
- Part IV Syndromes remarkable for altered growth
- Part V Management of craniofacial syndromes
- Part VI Management of connective tissue and integumentary syndromes
- Part VII The management of neurologic and neurodegenerative syndromes
- Part VIII Management of neurodegenerative metabolic disorders
- References
- Index
9 - Chromosome microdeletion syndromes
Published online by Cambridge University Press: 29 January 2010
- Frontmatter
- Contents
- Preface
- Glossary of genetic and molecular terms
- Part I Approach to the child with special needs
- Part II The management of selected single congenital anomalies and associations
- Part III Chromosomal syndromes
- 7 Autosomal aneuploidy syndromes
- 8 Sex chromosome aneuploidy and X-linked mental retardation syndromes
- 9 Chromosome microdeletion syndromes
- Part IV Syndromes remarkable for altered growth
- Part V Management of craniofacial syndromes
- Part VI Management of connective tissue and integumentary syndromes
- Part VII The management of neurologic and neurodegenerative syndromes
- Part VIII Management of neurodegenerative metabolic disorders
- References
- Index
Summary
Improvements in chromosome banding allowed detection of small deletions and duplications, beginning with missing small bands on chromosome 13 in certain children with retinoblastoma and on chromosome 15 in certain children with Prader–Willi syndrome. These subtle deletions, called microdeletions, were sometimes not reproducible because banding techniques could vary according to the specimen and laboratory conditions. Fluorescent in situ hybridization (FISH) and chromosome painting technologies, using fluorescent DNA probes to highlight specific chromosome regions, improved the characterization of microdeletions and complex rearrangements, revealing a new class of submicroscopic deletions that were not visible by the best-banding techniques. If targeted DNA segment is deleted, then the probe will not yield a fluorescent signal on that chromosome. Chromosome microscopic and submicroscopic deletions cause half (haploid) dosage of autosomal genes within the deleted area, or complete deficiency of genes within deleted regions of the X chromosome in males. The phenotypes of submicroscopic deletions are more easily explained by their haploid or missing genes than are aneuploidies of larger chromosome segments described in Chapters 7 and 8.
Schmickel (1986) coined the term “contiguous gene deletion” to denote composite phenotypes that result when neighboring deleted genes are associated with standard Mendelian diseases. Several examples of these aggregate phenotypes are found with small X chromosome deletions like that causing Duchenne muscular dystrophy, glycerol kinase, and adrenal hypoplasia. Each of these disorders had been described as a separate X-linked-recessive disease, so their concurrence in one patient is caused by deletion of the contiguous genes.
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- Information
- Preventive Health Care for Children with Genetic ConditionsProviding a Primary Care Medical Home, pp. 230 - 262Publisher: Cambridge University PressPrint publication year: 2006