The Principles of Clinical Cytogenetics - Extra Materials - Springer

146 Jin-Chen Wang
joints, bone dysplasia, narrow chest, 13 ribs), overlapping fingers, hypoplastic external genitalia, and
cryptorchidism. Cardiac anomalies are seen in more than 60% of cases, most frequently VSD. Renal
malformations are present in 40% of patients. The majority of patients die in the early postnatal
period. With rare exceptions, all survivors have severe mental deficiency. Mosaic patients tend to
survive longer, but the proportion of trisomy 9 cells does not predict the severity of the condition or
the length of survival. It is possible that a normal cell line could be present in some tissues in apparently
nonmosaic patients.
A recent study showed that the mean maternal age of women bearing trisomy 9 offspring is significantly
increased over that of the general population (103). This suggests that the occurrence of
trisomy 9 might also be associated with advanced maternal age. The risk for recurrence is not known.
Trisomy 16
Trisomy 16 is the most frequently observed autosomal aneuploidy in spontaneous abortuses (see
Chapter 13). Full trisomy 16 is almost always lethal during early embryonic or fetal development,
although a single case of a stillborn at 35 weeks gestation has been recorded (107).
Mosaic trisomy 16 fetuses, however, can occasionally survive to term. At least ten such cases have
been reported (108–114). Intrauterine growth retardation is invariable. An elevated maternal serum
human chorionic gonadotropin (hCG) or α-fetoprotein level during pregnancy was noted in more
than 50% of cases. Congenital cardiac defects (mainly VSD or ASD) were present in 60% of patients.
Other clinical findings included postnatal growth retardation, mild developmental/speech delay, craniofacial
asymmetry, ptosis, flat broad nasal bridge, low-set dysplastic ears, hypoplastic nipples,
umbilical hernia, deep sacral dimple, scoliosis, nail hypoplasia, and single transverse palmar crease.
Approximately 50% of the patients died within the first year of life. Long-term follow-up is not
available; however, survival to more than 5 years to date has been observed (Hajianpour and Wang,
personal observation).
The risk for recurrence is probably negligible.
Trisomy 20
Although mosaic trisomy 20 is one of the most frequent autosomal aneuploidies detected prenatally, its
occurrence in liveborns is very rare (115). The majority of prenatally diagnosed cases are not cytogenetically
confirmed in postnatal life. It appears that in conceptuses capable of surviving to the second trimester,
trisomy 20 cells are largely confined to extraembryonic tissues. Very few liveborns with documented
mosaic trisomy 20 have been reported and all were phenotypically normal at birth (116–121). In cases
with long-term follow-up, hypopigmentation was reported in three, but no major malformation or intellectual
impairment was observed. No case of liveborn nonmosaic trisomy 20 has been recorded.
Phenotypic abnormalities in abortuses with cytogenetically confirmed mosaic trisomy 20 include
microcephaly, facial dysmorphism, cardiac defects, and urinary tract anomalies (megapelvis, kinky
ureters, double fused kidney) (122).
Trisomy 20 cells have been found in various fetal tissues, including kidney, lung, esophagus,
small bowel, rectum, thigh, rib, fascia, and skin (115,122,123). Postnatally, they have been detected
in cultured foreskin fibroblasts and urine sediments (116–121). The detection of trisomy 20 cells in
newborn cord blood has been reported in one case, but subsequent study of peripheral blood at
4 months of age produced only cytogenetically normal cells (118). There are no other reports of
trisomy 20 cells in postnatal blood cultures.
The risk for recurrence is probably negligible.
Trisomy 22
Trisomy 22 was first reported in 1971 (124). Since then, more than 20 liveborns have been reported
in the literature (reviewed in ref. 125,126–129). Although most cases were apparently nonmosaic full