Cerebellar hypoplasia, zonular cataract, and peripheral neuropathy in trisomy 17 mosaicism

Trisomy 17 mosaicism in liveborns is an extremely rare chromosomal abnormality, with only three cases reported in the literature. Here we describe a 7-year-old boy with trisomy 17 mosaicism. The chromosome abnormality was detected by amniocentesis and was confirmed postnatally in cultured skin fibroblasts. The main clinical features were mental retardation and growth reduction, peripheral motor and sensory neuropathy, hypoplastic cerebellar vermis, zonular cataract, and body asymmetry. In our patient, and in the three earlier described cases, the additional chromosome 17 was detected in skin fibroblasts, not in peripheral lymphocytes. Molecular investigations excluded uniparental disomy of chromosome 17 in our patient. The extra chromosome 17 probably originated from a postzygotic mitotic nondisjunction of the maternal chromosome 17. In most cases of trisomy 17 mosaicism detected in amniocytes the chromosome abnormality seems to be confined to extra-embryonic tissues and clinically normal children are born. If, however, there are also ultrasound abnormalities, the possibility of fetal trisomy 17 mosaicism should certainly be considered. If postnatal karyotyping is limited to blood the diagnosis of trisomy 17 mosaicism could easily be missed. Therefore, we recommend chromosome analysis to be based on cultured skin fibroblasts in all cases where mental retardation is accompanied by postnatal growth retardation, body asymmetry, peripheral neuropathy, and cerebellar hypoplasia or zonular cataract.     

Trisomy 7 mosaicism prenatally misdiagnosed and maternal uniparental disomy in a child with pigmentary mosaicism and Russell- Silver syndrome

Prenatal diagnosis of true mosaic trisomy 7 is rare in amniotic fluid and can be misinterpreted as pseudomosaic. The phenotype is highly variable and may be modified by a maternal uniparental disomy of chromosome 7 leading to mild Russell-Silver syndrome (RSS). We report here the third postnatal case of mosaic trisomy 7 with maternal uniparental disomy of chromosome 7 in a boy presenting a mild RSS. Fetal karyotype performed in amniocentesis for intrauterine growth retardation was considered normal. Mosaic trisomy 7 was diagnosed after birth, on fibroblasts karyotype performed for blaschkolinear pigmentary skin anomalies and failure to thrive. Maternal uniparental disomy of chromosome 7 was observed in blood sample. Retrospectively, trisomic 7 cells were identified in one prenatal long-term flask culture revealing a prenatal diagnosis failure. This report emphasizes the difficulty of assessing fetal mosaicism and distinguishing it from pseudomosaicism in cultured amniocytes. It is important to search for uniparental disomy as an indirect clue of trisomy 7 mosaicism and a major prognosis element. Although there are only few prenatal informative cases, detection of trisomy 7 in amniocentesis appears to be associated with a relatively good outcome when maternal uniparental disomy has been ruled out.     

Mosaic trisomy 17: variable clinical and cytogenetic presentation

Mosaic trisomy 17 is rare with only 28 cases reported and the clinical presentation is highly variable. The diagnosis is most commonly made by prenatal karyotype and in most cases is followed by a normal postnatal karyotype on blood lymphocytes.We present two cases of mosaic trisomy 17 diagnosed prenatally,with follow up in multiple tissues at birth. In the first case,trisomy 17 was identified in all amniocytes, and at birth standard results of chromosome analysis in peripheral blood were normal,but mosaic trisomy 17 was identified (50–75%) in skin fibroblasts by genome-wide SNP array analysis. This patient presented with congenital heart disease, asymmetry, intestinal malrotation, and other anomalies and died on day 9 of life. In the second patient amniocentesis after ultrasound finding of tetralogy of Fallot showed mosaic trisomy 17. Postnatally, results of a SNP array were normal in blood, buccal mucosa, and skin. It is possible that the cardiac defect is related to trisomy 17 in key tissues during heart development, although at birth the aneuploidy could not be identified in tissues that are routinely analyzed for diagnosis. These cases add to our understanding of mosaic trisomy 17, highlighting the failure to diagnose this aneuploidy in peripheral blood.     

Trisomy 20 mosaicism in two unrelated girls with skin hypopigmentation and normal intellectual development

The prenatal diagnosis of trisomy 20 mosaicism presents a challenge for practitioners and parents. The diagnosis implies an uncertain risk for an inconsistent set of physical and developmental findings, as well as a substantial chance for a child that is normal physically and developmentally. We report two girls (ages nine years one month and eight years one month) with normal intelligence and hypopigmented skin areas. Both girls were born after a prenatal diagnosis of trisomy 20 mosaicism in amniocytes. Case 1 had 83% and 57% trisomy 20 cells from two separate amniocenteses and Case 2 had 90% trisomy 20 cells from an amniocentesis. Trisomy 20 was confirmed after birth in urinary sediment (25%) and chorionic villus cells (15%) in Case 1, while cord blood lymphocytes (30 cells) and skin fibroblasts (50 cells) had only 46,XX cells. Trisomy 20 was confirmed after birth in urinary sediment (100%), placenta (100%), cord (10%), amniotic membrane (50%), and skin fibroblasts (30%) in Case 2, while cord blood lymphocytes (100 cells) had only 46,XX cells. This is the first report of a hypopigmented pigmentary dysplasia associated with isolated trisomy 20 mosaicism. Our patients are the oldest reported children with trisomy 20 mosaicism confirmed after birth.     

True trisomy 2 mosaicism in amniocytes and newborn liver associated with multiple system abnormalities

Among 58,000 amniocenteses completed, our laboratories found one case of true cytogenetic trisomy 2 mosaicism in a fetus with multiple abnormalities. In contrast, 11 fetuses phenotypically normal at birth were found to have true trisomy 2 mosaicism in their chorionic villus cells among the 10,500 fetuses tested by chorionic villus sampling (CVS). In our single abnormal case, amniocentesis performed at 19 weeks after finding an elevated maternal serum AFP found two independent cultures with trisomy 2 karyotypes in 8 of 25 and 7 of 31 amniocytes, respectively. Although oligohydramnios was noted by ultrasound, the mother elected to continue the pregnancy. At 26 weeks the fetus had intrauterine growth retardation (IUGR), hydronephrosis, and cardiac abnormalities. When delivered by Cesarean section at 30 weeks, the infant had multiple anomalies and developed necrotizing enterocolitis and severe cholestasis. At 5 months coronal magnetic resonance imaging (MRI) displayed delayed myelination and abnormal brain morphology. The patient also exhibited significant growth failure and developmental delay. Although chromosomes were normal in blood, skin fibroblasts, and ascites fluid cells, 4 of 100 hepatic biopsy fibroblasts were 47,XY,+2. Molecular analysis excluded uniparental disomy (UPD) of chromosome 2 in the 46,XY cell line. This and other reports of rare phenotypically abnormal trisomy 2 mosaic fetuses identified by karyotyping amniocytes emphasizes the substantially higher fetal risk of abnormal development than when trisomy 2 is found only in chorionic villus cells. Am. J. Med. Genet. 72:343–346, 1997. © 1997 Wiley-Liss, Inc.     

Non-mosaic trisomy 20 of paternal origin in chorionic villus and amniotic fluid also detected in fetal blood and other tissues

Trisomy 20 mosaicism is a common abnormality found in prenatal diagnosis. Its clinical significance remains unclear since approximately 90–93% of cases result in normal phenotype. Only 5 cases of non-mosaic trisomy 20 in amniotic fluid culture surviving beyond the first trimester have been reported. Moreover, trisomic cells are generally not detectable in blood and have only been reported in three cases. We present a case of non-mosaic trisomy 20 found in chorionic villi sample and amniotic fluid culture in a fetus with minor abnormalities not detected by ultrasound examination. Pathological examination of the fetus only revealed right pulmonary isomerism and camptodactily, and no major malformations were disclosed. Trisomic lineage was also detected in fetal blood, kidney, skin and brain tissue cultures. Molecular analysis revealed that the extra chromosome 20 was originated in paternal meiosis. To our knowledge, we report the first prenatal case of non-mosaic trisomy 20 of paternal origin that has been confirmed in several fetal tissues, including blood, in a fetus with minor malformations not detected prenatally.     

Pseudo dicentric chromosome (5;21): a rare example of maternal germline mosaicism

Karyotyping of a malformed male newborn revealed the unbalanced karyotype of 46,XY, psudic(5;21)(q12;p13), +5 resulting in trisomy for the short arm of chromosome 5 and partial trisomy for 5q. Both parents had normal karyotypes in their peripheral blood lymphocytes. A second pregnancy ended in a miscarriage at 16 weeks gestation, sonographically 12 weeks. Karyotyping of chorionic villi from the abortus revealed the same unbalanced karyotype that had been identified in the first child. Fluorescence in-situ hybridization analysis confirmed a trisomy 5p. Microsatellite marker analysis ruled out illegitimacy and proved the maternal origin of the trisomic section of chromosome 5. Extended chromosome analysis of 60 metaphase cells from maternal skin fibroblasts and 40 metaphase cells from lymphocytes did not reveal mosaicism for psudic(5;21). These findings suggest the presence of a maternal germline mosaicism.     

Trisomy 7 mosaicism, maternal uniparental heterodisomy 7 and Hirschsprung's disease in a child with Silver-Russell syndrome

Prenatal trisomy 7 is usually a cell culture artifact in amniocytes with normal diploid karyotype at birth and normal fetal outcome. In the same way, true prenatal trisomy 7 mosaicism usually results in a normal child except when trisomic cells persist after birth or when trisomy rescue leads to maternal uniparental disomy, which is responsible for 5.5-7% of patients with Silver-Russell syndrome (SRS). We report here on the unusual association of SRS and Hirschsprung's disease (HSCR) in a patient with maternal uniparental heterodisomy 7 and trisomy 7 mosaicism in intestine and skin fibroblasts. HSCR may be fortuitous given its frequency, multifactorial inheritance and genetic heterogeneity. However, the presence of the trisomy 7 mosaicism in intestine as well as in skin fibroblasts suggests that SRS and HSCR might possibly be related. Such an association might result from either an increased dosage of a nonimprinted gene due to trisomy 7 mosaicism in skin fibroblasts (leading to SRS) and in intestine (leading to HSCR), or from an overexpression, through genomic imprinting, of maternally expressed imprinted allele(s) in skin fibroblasts and intestine or from a combination of trisomy 7 mosaicism and genomic imprinting. This report suggests that the SRS phenotype observed in maternal uniparental disomy 7 (mUPD(7)) patients might also result from an undetected low level of trisomy 7 mosaicism. In order to validate this hypothesis, we propose to perform a conventional and molecular cytogenetic analysis in different tissues every time mUPD7 is displayed.     

Trisomy/tetrasomy 21 mosaicism in CVS: interpretation of cytogenetic discrepancies between placental and fetal chromosome complements

Trisomy/tetrasomy 21 mosaicism was found in chorionic villi (semidirect preparation) obtained from a 40 year old pregnant woman. Since both cell lines were abnormal, the couple elected for pregnancy termination. Placenta and fetal tissue samples were obtained for cytogenetic study. Long term cultured villi showed a non-mosaic trisomy 21 karyotype, while other tissues showed either a normal karyotype or normal/trisomy21 mosaicism. These discrepancies could be explained by a modified "bottle neck" embryogenic model with a trisomic zygote and a non-disjunction event taking place in one of the first divisions. Our case emphasises the need for confirmatory studies in other tissues when mosaicism is encountered in chorionic villi, even if all cell lines are abnormal.     

Patient with trisomy 6 mosaicism

Trisomy 6 and trisomy 6 mosaicism were found in chorionic villi cell culture and short term incubation in a prenatal diagnosis at 12 weeks of gestation in a pregnancy with a growth retarded fetus showing nuchal translucency. The child was born in the 25th gestational week with a number of malformations including heart defects, deep-set ears, cleft right hand, cutaneous syndactylies, and overlapping toes of irregular shape and length. Trisomy 6 was not found in peripheral blood lymphocytes but was confirmed in umbilical cord fibroblasts. Currently, at the age of 2-3/4 years, the development of the child is relatively normal despite considerable growth delay. At the age of two years, she developed a papular erythema clinically suggestive of epidermal nevi. Cytogenetic analysis of fibroblast cultures derived from skin from a right hand finger and the inguinal area confirmed the presence of a trisomy 6 mosaicism. This is the first observation of a liveborn with trisomy 6 mosaicism.     

Hypothalamic hypothyroidism and XXY/XY sex chromosome mosaicism. Report of a case

An 18-year-old boy with clinical features of Klinefelter's syndrome in whose case the buccal smear was chromatin-negative and chromosomal analysis of peripheral blood revealed 46 XY karyotype is described. Diagnosis was confirmed by demonstration of an XXY cell line in cultured skin fibroblasts. Low circulating thyroxine levels were found despite absence of clinical hypothyroidism, and TSH was barely detectable. The studies are consistent with an isolated deficiency of thyrotropin-releasing hormone in a patient with XY/XXY mosaicism.     

Mosaic trisomy 17 in amniocytes: phenotypic outcome, tissue distribution, and uniparental disomy studies.

Mosaicism for trisomy 17 in amniocyte cultures is a rare finding, whilst postnatal cases are exceptional. In order to gain insight into the possible effects of the distribution of the trisomic line and of uniparental disomy (UPD) on embryofoetal development, we have performed follow-up clinical, cytogenetic and molecular investigations into three newly detected prenatal cases of trisomy 17 mosaicism identified in cultured amniotic fluid. In the first case, the pregnancy ended normally with the birth of a healthy girl, and analysis of newborn lymphocytes and of multiple extra-embryonic tissues was indicative of confined placental mosaicism. The second case was also associated with a normal pregnancy outcome and postnatal development, and only euploid cells were found in peripheral blood after birth. However, maternal isodisomy 17 consequent to a meiosis II error and loss of a chromosome 17 homologue was detected in peripheral lymphocytes postnatally. In the third case, pathological examination after termination of pregnancy showed growth retardation and minor dysmorphisms, and the trisomic line was detected in foetal skin fibroblasts. In addition, biparental derivation of chromosome 17 was demonstrated in the euploid lineage. These results, together with previously reported data, indicate that true amniotic trisomy 17 mosaicism is more commonly of extra-embryonic origin and associated with normal foetal development. Phenotypic consequences may arise when the trisomic line is present in foetal tissues. Case 2 also represents the first observation of maternal UPD involving chromosome 17; the absence of phenotypic anomalies in the child suggests that chromosome 17 is not likely to be subject to imprinting in maternal gametes.     

Variable clinical expression of mosaic trisomy 16 in the newborn infant

Trisomy 16 is common in embryos and fetuses aborted early during development. Mosaicism for trisomy 16 is sometimes encountered during prenatal diagnosis, particularly with chorionic villi biopsy specimens, and, until recently, was thought to be confined to the placenta. However, recently, several liveborn infants with trisomy 16 mosaicism have been described. We report on an additional liveborn infant with trisomy 16 mosaicism and compare the clinical findings with those of the previously reported cases in an attempt to delineate a mosaic trisomy 16 syndrome. Cytogenetic analysis from our patient showed that there was a different proportion of abnormal cells in different tissues and that the anomaly was undetectable in blood lymphocyte cultures. This observation was consistent with some of the previous reports. DNA analysis of parents and child was carried out using a polymorphic dinucleotide marker that maps to the long arm of chromosome 16. This analysis showed that the extra chromosome 16 in the infant was maternal in origin and suggested that the nondisjunction was probably a first meiotic division error. Our results suggest that an investigation of multiple tissues is required before concluding that mosaicism is confined to the placenta. We conclude that a finding of trisomy 16 mosaicism at prenatal diagnosis should be regarded with extreme caution. This diagnosis may be associated with a highly variable phenotype that may occasionally be compatible with extrauterine life. © 1993 Wiley-Liss, Inc.     

Discordant phenotype in monozygotic twins with mosaic trisomy 12p in lymphocytes

We report on monochorionic diamniotic male twins discordant for the trisomy 12p syndrome. Trisomy 12p mosaicism with a supernumerary der(12)(pter > q12) was detected in approximately 50% of lymphocytes in both children. Fluorescence in situ hybridisation (FISH) revealed a high grade mosaicism of approximately 77% trisomy 12p cells in buccal smear and 85% in hair follicles in the affected twin, while in the normal developing brother an additional 12p chromosome fragment could not be detected in those tissues. Instead, in 3% of buccal smear and hair follicle cells a minute supernumerary marker chromosome comprising central portions of chromosome 12 was observed. Trisomy 12p mosaicism, confined to the lymphocytes of the unaffected twin, may be due to prenatal twin-to-twin transfusion, explaining the conspicuously discordant clinical phenotype. We discuss the possible sequence of events leading to the cytogenetic findings and compare the clinical phenotype presented in the affected twin with other cases of trisomy 12p and tetrasomy 12p (Pallister-Killian syndrome).     

Prenatal detection of double aneuploidy trisomy 10/monosomy X in a liveborn twin with exclusively monosomy X in blood

Both double aneuploidy and trisomy 10 are rare chromosome findings. All five published cases of trisomy 10 in liveborns were found to be mosaic with an euploid cell line. In a liveborn female twin, double aneuploidy mosaicism 47,XX, + 10/45,X was detected prenatally by amniocentesis performed because of severe intrauterine growth retardation and malformations. Chromosome analysis from neonatal lymphocyte cultures revealed exclusively the 45,X cell line. Double aneuploidy mosaicism trisomy 10/monosomy X was confirmed from skin fibroblasts. The child died at the age of 7 weeks. This is the first reported case of double aneuploidy involving trisomy 10, and the first case of trisomy 10 without a normal cell line in a liveborn. Prenatal diagnosis of trisomy 10 in a liveborn has not been published so far. The case illustrates that in specific cases amniotic fluid cells may reflect the karyotype of the fetus better than blood.     

Case of 45,X/46,XY mosaicism with non-mosaic discordance between short-term villi (45,X) and cultured villi (46,XY)

We report on a prenatally detected case of discordant non-mosaic karyotypes following chorionic villus sampling. A 45,X karyotype was found in cytotrophoblast cells and a 46,XY karyotype in mesenchymal core cells. A subsequent amniocentesis showed a true 45,X/46,XY mosaicism. Confirmatory studies, including fluorescence in situ hybridization (FISH) in various fetal and placental tissues as well as in the original villi preparations changed the presumed condition of generalized mosaicism with culture confined normality to that of generalized mosaicism with absolute concordance. This case underscores the importance of the investigation of both short-term and cultured villi preparations, the implementation of prenatal FISH studies, and the need for thorough follow-up investigation in cases of discrepant results.     

Trisomy 16 and trisomy 16 mosaicism: A review

A review of all prenatal and postnatal diagnoses of trisomy 16 and trisomy 16 mosaicism was carried out in the context of the current understanding of confined placental mosaicism and uniparental disomy (UPD). The prenatal detection of trisomy 16 cells is associated with a high probability of fetal death, preterm delivery, intrauterine growth retardation, and fetal anomalies. Birth defects were typical of those seen in nonmosaic partial duplications of chromosome 16. Surprisingly, anomalies were sometimes limited to a single organ and included some relatively common isolated defects such as a ventricular septal defect, hypospadias, imperforate anus, inguinal hernia, and clubfoot. The risk for abnormality appeared to be higher in those pregnancies in which trisomy 16 cells were identified in amniotic fluid compared to the detection in chorionic villi samples. Contrary to nonmosaic trisomy 16 with an excess of males, mosaic trisomy 16 shows an excess of female karyotypes. Following the prenatal detection of trisomy 16 cells, aneuploid cells are almost never found in fetal or neonatal lymphocytes. Studies on fibroblasts also often fail to confirm the presence of the abnormal cell line even in cases in which multiple anomalies are present. It is likely that trisomy 16 cells are sometimes present in the early developing embryo even though subsequent cytogenetic studies on fetal or neonatal tissues may not detect any aneuploid cells. UPD can be excluded as a mechanism for those anomalies that are common to mosaic trisomy 16 and nonmosaic partial duplications. The term “occult mosaicism” is suggested to describe the situation in which the presence of an abnormal cell line is suspected on the basis of clinical data but unproven by laboratory analysis. Am. J. Med. Genet. 79:121–133, 1998. © 1998 Wiley-Liss, Inc.     

Pallister-Killian syndrome: normal karyotype in prenatal chorionic villi, in postnatal lymphocytes, and in slowly growing epidermal cells, but mosaic tetrasomy 12p in skin fibroblasts.

We report on two patients with Pallister-Killian syndrome: an 18 month old male infant followed since the neonatal period and a 4 year old boy. Prenatal diagnosis by chorionic villi sampling (CVS) in the first case showed a normal karyotype without mosaicism. Chromosome analysis on peripheral lymphocytes of the newborn also showed a normal karyotype. The clinical diagnosis of Pallister-Killian syndrome was made after the first year of life because of the typical facial dysmorphism and other characteristic clinical features, such as frontotemporal alopecia, depigmented area of the skin, sensorineural hearing loss, and severe psychomotor retardation. Chromosome analysis from skin fibroblasts now showed an isochromosome 12p mosaicism. The origin of the extra chromosome was confirmed by in situ hybridisation using a chromosome 12 specific library. In the second case chromosomal analysis from peripheral lymphocytes at the age of 19 months showed a normal karyotype 46,XY. Following the clinical diagnosis of Pallister-Killian syndrome a superficial skin biopsy was performed which showed very poor and slow growth of cells and a normal karyotype. Because of the typical symptoms a larger and deeper skin biopsy was performed from which there was rapid growth of fibroblasts. Now the diagnosis was established on the basis of the presence of an i(12p) extra chromosome in 69% of the metaphases.     

Trisomy 9 confined to the placenta: prenatal diagnosis and neonatal follow-up.

Chorionic villus sampling (CVS), performed on a woman in the 23rd menstrual week because of bilateral fetal hydronephrosis and suspected intrauterine growth retardation (IUGR), documented trisomy 9 in all cells examined. Chromosomes of amniocytes and fetal blood lymphocytes were normal. The ongoing pregnancy was monitored closely, and at 37 weeks, a phenotypic normal male infant was delivered. Multiple placental biopsies showed 47,XY,+9, while a repeat chromosome analysis of the infant and biopsies from the amniotic membrane were normal (46,XY). This case further emphasizes the association between placental aneuploidy and IUGR. To our knowledge, nonmosaic trisomy 9 in CVS confined to the chorionic villi and later confirmed in the placenta has not been reported previously.     

Dilemma of trisomy 20 mosaicism detected prenatally: Is it an innocent finding?

The clinical significance of mosaicism trisomy 20 detected prenatally following amniocentesis remains uncertain, due to the rarity of liveborn cases with inconsistent clinical findings, the short postnatal follow-up, and failure in evaluating other fetal tissues for the presence of the trisomy. We report on a 15 month-old 46,XX chromosome constitution in white blood cells, while skin fibroblasts demonstrated trisomy 20 mosaicism (54%) by fluorescence in situ hybridization (FISH) analysis. Clinical examination of the baby showed only minor phenotypic signs (bilateral epicanthal folds, delayed closure of fontanel with no other gross anomalies), but demonstrated a considerable developmental delay in gross and fine motor skills along with hypotonicity. This is the second oldest described liveborn with trisomy 20 mosaicism confirmed in skin fibroblasts. This cytogenetic aberration along with her developmental delay suggests that the two findings are related and that aberration affects various fetal tissues and is not confined to extra-embryonic tissue as suggested previously. Yet, an undiagnosed condition may be the cause of the child's developmental delay. Based on this case and following a review of the literature we suggest that when mosaic trisomy 20 is identified in amniocytes, further evaluation is required. Cord blood should be analyzed preferably by FISH. During counseling the parents should be advised of an additional risk, such as developmental delay, even when fetal cord karyotype and detailed ultrasonic scan are normal. Am. J. Med. Genet. 77:72–75, 1998. © 1998 Wiley-Liss, Inc.