children s health issues
Overview of Chromosome and Gene Disorders
Chromosome Abnormalities
(See also Chromosomal abnormalities .) Chromosome abnormalities can affect any chromosome, including the Sex chromosomes . Chromosome abnormalities affect the Number of chromosomes Structure of chromosomes Larger abnormalities may be visible with a microscope in a test called chromosome analysis or karyotyping. Smaller chromosome abnormalities can be identified using specialized genetic tests that scan a person's chromosomes for extra or missing parts. These tests include chromosomal microarray analysis (CMA) and fluorescent in situ hybridization (FISH). (See also Next-generation sequencing technologies .) occur when a person has one or more extra copies of a chromosome (for example, one extra is trisomy, and two extra is tetrasomy) or is missing an entire chromosome (monosomy) or part of a chromosome. Trisomy can affect any of the 23 paired chromosomes, but the most common are trisomy 21 ( Down Syndrome (Trisomy 21) ), The older a pregnant woman is, the greater the chance that her fetus will have a whole extra chromosome or will be missing a chromosome (see table). The same is not true of a man. As a man gets older, the chance of conceiving a baby with a chromosome abnormality is only slightly increased. occur when part of a chromosome is abnormal. Sometimes part or all of a chromosome incorrectly joins with another chromosome (called translocation). Sometimes parts of chromosomes are missing (called deletion―see Overview of Chromosomal Deletion Syndromes ) or have been duplicated. Some chromosome abnormalities cause the death of the embryo or fetus before birth. Other abnormalities cause problems such as Intellectual Disability , 