Down syndrome

Down syndrome is a genetic condition caused by extra genetic material from chromosome 21. It is associated with characteristic physical features and variable effects on development and health.

Trisomy 21: A chromosomal condition in which cells have three copies of chromosome 21 instead of two. This is the most common chromosomal pattern underlying Down syndrome.
Human karyotype: The complete set of chromosomes in a human cell, arranged by number, size, and shape. A karyotype can reveal the extra chromosome material associated with Down syndrome.
Congenital heart defect: A structural abnormality of the heart or major blood vessels present at birth. Heart defects are more common in Down syndrome and are assessed early in care.
Jérôme Lejeune: A French physician and geneticist who reported the chromosome abnormality associated with Down syndrome in 1959. His work helped establish the chromosomal basis of the condition.
Robertsonian translocation: A chromosome rearrangement in which two acrocentric chromosomes join near their centromeres. A translocation involving chromosome 21 can cause Down syndrome and may be inherited.
Meiosis: Cell division that produces eggs and sperm with one copy of each chromosome. Errors during meiosis can create a reproductive cell with extra chromosome 21.
Hearing loss: Reduced ability to detect or understand sound, ranging from mild to profound. Regular hearing assessment can identify a frequent, treatable concern.
Edouard Séguin: A French physician and educator who developed methods for educating children with intellectual disabilities in the nineteenth century. His educational work influenced early approaches to supporting children with Down syndrome.
Mosaicism: The presence of two or more genetically distinct cell populations in one individual. Mosaic Down syndrome occurs when only some cells carry extra chromosome 21 material.
Gene dosage: The number of copies of a gene and the resulting influence on its expression or product abundance. Extra chromosome 21 material changes dosage for many genes, with downstream effects.

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