Physical examination of an infant delivered to a 42 year old, gravida 3, para 2, woman, is remarkable for slight hypotonia and a poor Moro reflex. Fuher examination reveals upslanting palpebral fissures, epicanthal folds, excess nuchal skin, an enlarged tongue, clinodactyly of the fifth fingers, and a single transverse palmar crease. Which of the following is the most likely diagnosis?

Down syndrome, or trisomy 21, is the most common autosomal chromosome abnormality. The incidence increases as maternal age increases. The classic features are hypotonia, upslanting palpebral fissures, epicanthal folds, excess nuchal skin, an enlarged tongue, clinodactyly of the fifth fingers, and a single transverse palmar crease. Edwards syndrome or trisomy 18, has features of small palpebral fissures, low-set ears, low bih weight, microcephaly, rocker-bottom feet, cleft lip, hypotonia, and clenched hands. Fetal alcohol syndrome is characterized by growth retardation, small palpebral fissures, smooth philtrum, a thin upper lip, microcephaly, and a sho nose. Features often go unnoticed in the newborn period, although sometimes tremulousness and irritability occur. Marfan syndrome is associated with increased stature, thin limbs, scoliosis, joint hypermobility, and ocular manifestations. Features often go unnoticed in the newborn period. Ref: Hauk P.J., Johnston, Jr. R.B., Liu A.H. (2012). Chapter 33. Immunodeficiency. In W.W. Hay, Jr., M.J. Levin, R.R. Deterding, J.J. Ross, J.M. Sondheimer (Eds),CURRENT Diagnosis & Treatment: Pediatrics, 21e.