Review Question - QID 106508

This patient demonstrated a flattened nasal bridge, epicanthal folds, gap between the first and second toes, and single palmar crease, indicative of Down syndrome, or trisomy 21.

Down syndrome is the most common chromosomal disorder and most common genetic cause of mental retardation. Down syndrome occurs as a result of trisomy 21. Trisomy 21 can be due to nondisjunction (most common cause), Robertsonian translocation, or mosaicism (least common cause). Presentation is variable, but common features are reviewed below.

Saenz reviews the presentation of Down syndrome. Frequently affected patients present with oblique palpebral fissure, wide space between first and second toes, ear abnormalities, flat nasal bridge, hypotonia, epicanthal folds, and abnormalities of the fifth finger. Patients are significantly more likely to have congenital cardiac defects and congenital gastrointestinal defects, as well as leukemias and early onset Alzheimer's.

Witters et al. review the presentation of trisomy 21, including associated abnormalities. Many additional malformations occur with increased frequency in these patients, including hypogonadism, cryptorchidism, atrial and ventricular septal defects, duodenal atresia, imperforate anus, and in later life acute myeloid leukemia.

Figure A shows the classic facial features seen in Down syndrome, including a flattened nasal bridge and epicanthal folds. Figure B demonstrates increased gap between the first and second toes, frequently seen in Down. Figure C demonstrates a single palmar crease. Illustration A shows classic features of trisomy 18, for comparison. Note the low set ears and clenched fists.

Incorrect answers:
Answer 1: Hypothyroidism can lead to cretinism.
Answer 2: Microdeletion on chromosome 22 is the mechanism behind DiGeorge syndrome.
Answer 3: Maternal alcohol consumption during pregnancy can lead to fetal alcohol syndrome.
Answer 4: Trisomy 18 is the mechanism behind Edward's syndrome, with some features shown in illustration A.