The lower extremity with foot shown here is from a premature newborn with multiple congenital anomalies. The foot has a "rocker bottom" appearance that is most characteristic for trisomy 18 (Edwards syndrome), but which may also be seen with other syndromes, including Patau syndrome (trisomy 13). There is a wide range of anomalies seen with trisomy 18, including small face with micrognathia, digits 2 and 5 overlapping 3 and 4 on the hands, short thin ribs, cardiac defects, diaphragmatic hernia, and renal anomalies including horseshoe kidney. There is an association with advanced maternal age, but not to the degree seen with trisomy 21, because of chromosomal nondysjunction, which is the cause for the extra chromosome 18 in most cases, with a karyotype such as 47, XX, +18. Other possibilities include a translocation type, with a karyotype such as 46,XX-14,+t(14q 13q), or a mosaic with sex chromosome aneuploidy such as 46,XXX/47,XX,+18. Most cases are not liveborn, and those that are liveborn (as in this case--note the heelsticks to obtain specimens for laboratory testing) rarely survive beyond a few months.