TRISOMY 9 MOSAICISM
Trisomy 9 is an uncommon chromosome abnormality which can occur in a mosaic or non-mosaic state and presents with a distinct clinical picture.
The finding of mosaic trisomy 9 on chorionic villus sampling presents a difficult counselling situation. Diagnosis of trisomy 9 on CVS should be followed up with amniocentesis and serial ultrasound to exclude trisomy in the fetus (Saura et al, 1995). In most cases where trisomy is found on CVS but not on amniocentesis, the outcome is normal. However, an abnormal outcome can also occur. Despite that a number of cases of prenatally detected trisomy 9 mosaicism have been identified, outcome ranges from normal to neonatal death.
Trisomy 9 detected on CVS
9 cases of trisomy 9 were reported in a large study of chromosomal mosaicism detected on CVS (Hahneman & Vejerslev, 1997) and two others were reported in Robinson et al. 1997. None of the 8 cases with mosaic (<100%) trisomy detected on CVS were confirmed in the fetus. However, trisomy 9 was confirmed in one of the 3 fetuses with non-mosaic trisomy on both direct and long term culture.
Of other unpublished cases we are aware: 2 were mosaic on CVS and had no trisomy in amniotic fluid and had a normal outcome; While of three with 100% trisomy on cultured CVS, trisomy was confirmed in fetal tissues in two cases.
Trisomy 9 detected on amniocentesis.
The risk of abnormal outcome is significant when trisomy 9 is detected in amniotic fluid. Hsu et al (1997) summarized the outcome of 25 cases of trisomy 9 mosaicism detected in amniotic fluid. Of these, 14 resulted in abnormal offspring; 8 had multiple congenital anomalies, 7 had facial dysmorphism, 4 had congenital heart disease, 3 had urogenital abnormalities, 3 had skeletal problems, 3 had intra-uterine growth restriction (IUGR).
Trisomy 9 detected postnatally
Over 40 cases of trisomy 9, mosaic or non-mosaic, have been diagnosed postnatally. The features of trisomy 9 syndrome are growth retardation, mental retardation, characteristic facial features, congenital heart defects, kidney anomalies, skeletal abnormalities. The facial features include bulbous nose, small, deep set eyes, ear anomalies, small jaw and large fontanels (Arnold et al, 1995).
In a review of 42 cases of mosaic and non-mosaic trisomy 9 the degree of mosaicism in blood lymphocytes or skin fibroblasts did not relate to survival or severity of anomalies. It seems that infants who are more severely affected in the neonatal period may have more involvement of vital organ and thus have a more severe prognosis.
It is possible that those that appear to be complete trisomy 9 may in fact be mosaic trisomy 9.
Uniparental Disomy (UPD 9)
Based on the information reported to date on UPD9, chromosome 9 is unlikely to be associated with imprinting effects.
The first case of maternal uniparental disomy (UPD) of chromosome 9 in a fetus who was shown to have mosaic trisomy 9 on CVS. Karyotyping and molecular studies following termination of the pregnancy confirmed mosaicism in the placenta and maternal UPD(9) in the fetal tissues. This case demonstrates that the mechanism of trisomy correction may result in a fetus with UPD(9). (Wilkinson et al, 1996). Further cases are referenced in the links below:
Link to What is UPD?
Link to Maternal UPD 9 page
Link to Paternal UPD 9 page
Human Chromosome 9 - 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.
Arnold GL, Kirby RS, Stern TP, Sawyer JR. (1995) Trisomy 9: review and report of two new cases. American Journal Medical Genetics. 56:252-257 PubMed
Hahnemann JM, Vejerslev LO. ( 1997) European collaborative research on mosaicism in CVS (EUCROMIC)--fetal and extrafetal cell lineages in 192 gestations with CVS mosaicism involving single autosomal trisomy. American Journal of Medical Genetics 70(2):179-87. PubMed
Hsu LY, Yu MT, Neu RL, Van Dyke DL, Benn PA, Bradshaw CL, Shaffer LG, Higgins RR, Khodr GS, Morton CC, Wang H, Brothman AR, Chadwick D, Disteche CM, Jenkins LS, Kalousek DK, Pantzar TJ, Wyatt P. (1997) Rare trisomy mosaicism diagnosed in amniocytes, involving an autosome other than chromosomes 13, 18, 20, and 21: karyotype/phenotype correlations. Prenatal Diagnosis 17(3):201-242. PubMed
Ledbetter DH, Engel E. (1995) Uniparental disomy in humans: development of an imprinting map and its implications for prenatal diagnosis. Human Molecular Genetics 4:1757-1764 PubMed
Wilkinson TA, James RS, Crolla JA, Cockwell AE, Campbell PL, Temple IK. (1996) A case of maternal uniparental disomy of chromosome 9 in association with confined placental mosaicism for trisomy 9. Prenatal Diagnosis. 16(4):371-374. PubMed
Willatt LR, Clare Davison BC, Goudie D, Alexander J, Dyson HM, Jenks PE, Ferguson-Smith ME. (1992) A male with trisomy 9 mosaicism and maternal uniparental disomy for chromosome 9 in the euploid cell line. Journal of Medical Genetics. 29:742-744 PubMed
Wolstenholme J. (1996) Confined placental mosaicism for trisomies 2, 3, 7, 8, 9, 16, and 22: their incidence, likely origins, and mechanisms for cell lineage compartmentalization. Prenatal Diagnosis.16(6):511-524. PubMed