염색체 이상의 유전병이 의심되는 환자의 karyotype을 확인했다.
위와 같을 때 이 병의 흔한 발생기전은?
Pathophysiology: Three cytogenetic variants cause Down syndrome: trisomy 21, chromosomal translocation, and mosaicism.
Trisomy 21 accounts for nearly 95% of all patients with Down syndrome. Most of the remaining patients have 46 chromosomes with translation of the long arm of an extra number 21 either to a D group or to another G group chromosome. As a woman ages, her risk of giving birth to a child with Down syndrome increases. This is of particular concern for women older than 35 years.
Less commonly, patients with Down syndrome may have 46 chromosomes with either 21/22 translocation or 21/21 translocation.
A few patients have mosaicism with a normal cell line, usually milder physical stigmata, and impaired intelligence.
Two different hypotheses have been proposed to explain the mechanism of gene action in Down syndrome: developmental instability (loss of chromosomal balance) and "gene dosage effect" (Reeves, 2001). According to the gene dosage effect hypothesis, the genes located on chromosome 21 have been overexpressed in cells and tissues of Down syndrome patients, and this contributes to the phenotypic abnormalities (Cheon, 2003