Neurogenetic analysis and cognitive functions in trisomy 21

Abstract

Trisomy 21 (TRS21) is also known as Down's syndrome and for a long time was called mongolism. At the beginning of the third millennium, TRS21 remains the most frequent genetic cause of mental deficiency in Western society. According to estimates in recent studies by Roizen and Patterson (2003), TRS21 occurs once in every 800 or 1,000 births. TRS21 is a syndrome, defined by a complex set of cardiac, immune, bone, brain, and cognitive disorders, most being highly variable in expression. Not all persons with TRS21 have leukemia, although it is more prevalent in the TRS21 population compared to the general population. Cardiac disorders are responsible for approximately 60% of perinatal mortality in neonates with TRS21. Immune disorders are more common in TRS21 (30% of TRS21 persons have abnormal levels of T-lymphocytes - Ugazio, Maccario, Notarangelo, & Burgio, 1990); bone anomalies are also more common. The characteristic morphology is short and stocky with virtually no neck because of skeletal abnormalities. Facial features of persons with TRS21 typically include oblique eye fissures, epicanthic eye-folds, a flat nasal bridge, the mouth permanently open and the tongue protruding. The limbs are malformed, and hands are short and broad with a single transverse palmar crease and shortened, incurved fifth finger. Mental deficiency, while of variable severity, is the most constant feature of persons with TRS21 (Antonarakis, Lyle, Dermitzakis, Reymond, & Deutsch, 2004; Patterson & Costa, 2005).