In 70-75% of fetuses, increased nuchal translucency can be seen on first-trimester ultrasonography. We can also mention the exceptional Aymé-Gripp syndrome. Differential diagnosisĭifferential diagnosis includes Zellweger syndrome, 9qter deletion or other chromosomal abnormalities. In the remaining 5%, the supernumerary chromosome 21 or portion of chromosome 21 is translocated to another chromosome (Robertsonian translocation in most cases). 2-3% of those cases are in a mosaic state. In 95% of the cases, trisomy 21 is an additional independent chromosome 21 (47,+21): the extra chromosome is due to an accidental non-disjunction during meiosis. The main potential malformations and complications include: short stature, congenital cataract, conductive hearing loss, heart defects (atrio-ventricular canal), digestive malformations (duodenal atresia), Hirschsprung disease, seizures, sleep apnea, sensory deficiencies, leukemia, auto-immune and endocrine pathologies (hypothyroidism, celiac disease, diabetes mellitus type 1, alopecia areata, earlier aging and early-onset Alzheimer disease. Morphological features (upslanting palpebral fissures, epicanthus, flat neck, round face, small nose, bilateral single palmar crease) can be mild and are not pathognomonic of the condition. Clinical descriptionĬlinical features include variable (often mild) intellectual disability, almost constant muscular hypotonia and joint laxity, associated with morphological signs, malformations (half of cases) and increased risks of some medical complications all-life-long. The risk of having a baby with Down syndrome (DS) increases with maternal age, identically in every population. In brief, it varies from 1/400 to 1/3000 live births. public policies regarding prenatal diagnosis and care for disabled people, and view of the population for DS and for abortion. Prevalence at birth of Down syndrome (DS) in a country depends largely on non-medical factors, i.e.
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