TRISOMY 22 MOSAICISM
Trisomy 22 is the second most common autosomal trisomy found among spontaneous abortions, accounting for 3-5% of all spontaneous abortions. Full (non-mosaic) trisomy 22 may in very rare cases survive to term. Some common clinical findings in full trisomy 22 include intrauterine growth restriction, microcephaly, hypertelorism, epicanthal folds, hypoplastic or low set ears, midface hypoplasia, hypoplastic distal phalanges, genitalia anomalies in males (Bacino et al.1995). Other findings seen may include Cleft palate, cardiac and/or renal anomalies and anal atresis/stenosis.
Mosiac trisomy 22 diagnosed through prenatal diagnosis can be either confined to the placental tissues or present in the fetus as well. When confined to the placenta, the outcome can be normal, although there is a risk of low birth weight. When present in the fetus, the outcome is variable.
Trisomy 22 detected on CVS
It is difficult at this point to say how often trisomy 22 present at CVS will be confirmed at amniocenetesis. However there are at least multiple cases where 100% trisomy was observed in a CVS culture, no evidence of the trisomy was found in amniotic fluid and the baby appeared normally grown and developed at birth. The behaviour of trisomy 22 confined to the placenta appears similar to that involving trisomy 16: The origin of the trisomy has been maternal meiotic in all 7(?) cases studied to date; the outcome can be normal, but there is a risk of poor intrauterine growth which is generally attributed to the trisomic placenta; and it is possible for trisomy to persist in selected fetal tissues even if absent from most other tissues.
We are aware of 7 cases of trisomy 22 detected on CVS which showed low or absent levels of trisomy in follow-up amniocentesis (Robinson et al. 1997, de Pater et al. 1997, Phillips et al. 1996, Balmer et al. 1999). Of these, 5 showed no trisomy on AF: 3 had a normal outcome and 2 exhibited IUGR. One case which showed 8.5% trisomic cells detected in AF was IUGR at birth and was positive for the trisomy in blood . Another with 20% trisomic cells in AF showed IUGR plus some anomalies (VSD etc) and followup showed the trisomic cells in skin but not in blood cultures.
Maternal uniparental disomy for chromosome 22 has been found in normal individuals and not believed to have a phenotype. A prenatal effect on growth has not been formally excluded, however, and all 5 cases of maternal UPD22 associated with trisomy detected prenatally or at birth did have a low birthweight.
Trisomy 22 detected on amniocentesis
Of 6 cases of trisomy 22 mosaicism present in AF (Schinzel 1981, Robinson et al. 1997, de Pater 1997; Berghella 1998, Hsu et al. 1997, Stoui et al. 1989) blood cultures were negative for the trisomy in all but two cases. Unfortunately little follow-up data is available in these cases. While IUGR was common, 4 of these 6 were not noted to have any obvious anomalies at birth.
Trisomy 22 detected postnatally
Crowe (1997) reviews 10 cases with generalized trisomy 22 mosaicism. Some features found included failure to thrive, mental delay, ptosis, dental anomaly, hearing loss, low posterior hair line, ovarian failure, syndactyly, hemiatrophy, streaked pigmentation. Most of these were however detected in blood or fibroblasts from children ascertained through abnormalitites. They thus likely over-estimate poor outcomes.
Uniparental Disomy (UPD 22)
UPD22 is not known to have a phenotype associated with imprinting. Prenatal testing for UPD is not currently indicated
Link to What is UPD?
Link to Maternal UPD 22 page
Link to Paternal UPD 22 page
- HUGO Chromosome 22 - Chromosome 22 specific sites
Human Chromosome 22 - Provides links to gene maps, sequences, associated genetic disorders, nonhuman genetic models, identified genes, research efforts and laboratories, and other information as available. Links are very scientific.
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