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PubMed1997

Prenatal diagnosis of Prader-Willi syndrome using PW71 methylation analysis--uniparental disomy and the significance of residual trisomy 15.

Chorionic villus sampling (CVS) was performed on a 38-year-old woman at 10 weeks' gestation for advanced maternal age. Two long-term cultures showed true mosaicism of cells with a normal karyotype and cells with trisomy 15. Follow-up amniocentesis showed only cells with a normal karyotype. Methylation analysis of amniocyte DNA using the probe PW71B showed a result consistent with a diagnosis of Prader-Willi syndrome. This result was confirmed using dinucleotide microsatellite polymorphism analysis, which showed that the fetus had maternal uniparental heterodisomy for chromosome 15. This report describes the use of methylation analysis for prenatal diagnosis of uniparental disomy 15 but also indicates that there is some doubt regarding the methylation status of all amniocyte samples, as one of nine controls showed hypomethylation. Fetal skin was found to show low-level mosaicism for trisomy 15, indicating a prolonged persistence of mosaic trisomy 15, which raises questions regarding the management of pregnancies found to be mosaic for trisomy 15.

Adult↗
PubMed2000

Proportion of cells with paternal 11p15 uniparental disomy correlates with organ enlargement in Wiedemann-beckwith syndrome.

"Genetic mosaicism" describes the presence of two or more populations of cells within a single individual that differ in their genomic constitution. Although the occurrence of asymmetric overgrowth in Wiedemann-Beckwith syndrome (WBS) suggests that mosaicism has some role in the WBS phenotype, no direct evidence for this has been published. WBS is a congenital overgrowth syndrome with variable phenotype linked to the imprinted gene cluster on chromosome region 11p15. We have performed a molecular survey of multiple organs and tissues in a case of WBS with a high degree of mosaic paternal 11p15 uniparental disomy (UPD). The organs most severely affected were those with the highest percentage of cells with UPD. In particular there was a striking difference in the degree of mosaicism for 11p15 UPD between the extremely enlarged left adrenal and non-enlarged right adrenal gland. This result indicates that the proportion of paternal 11p15 UPD cells correlates with the tissue phenotype of WBS. Our results suggest that high proportions of abnormal cells result from a combination of stochastic events and cell selection. Mosaicism may explain the variable phenotypes including hemihyperplasia and predisposition to childhood cancers in WBS patients.

Adrenal Glands↗
PubMed1997

Maternal uniparental disomy for chromosome 22 in a child with generalized mosaicism for trisomy 22.

We report on a case of generalized mosaicism for trisomy 22. At chorionic villus sampling (CVS) in the 37th week of pregnancy, a 47,XX,+22 karyotype was detected in all cells. The indication for CVS was severe unexplained symmetrical intrauterine growth retardation (IUGR) and a ventricular septal defect (VSD) was noted. In cultured cells from amniotic fluid taken simultaneously, only two out of ten clones were trisomic. At term, a growth-retarded girl with mild dysmorphic features was born. Lymphocytes showed a normal 46,XX[50] karyotype; both chromosomes 22 were maternal in origin (maternal uniparental disomy). Investigation of the placenta post-delivery using fluorescence in situ hybridization showed a low presence of trisomy 22 cells in only one out of 14 biopsies. In cultured fibroblasts of skin tissue, a mosaic 47,XX,+22[7]/46,XX[25] was observed. Clinical follow-up is given up to 19 months.

Abnormalities, Multiple↗
PubMed2000

Maternal uniparental disomy (UPD) for chromosome 2 discovered by exclusion of paternity.

Serological and molecular (DNA-STR) analysis of a paternity case demonstrated exclusion of paternity of the presumptive father in two markers (ACP and Apo B, both localized on chromosome 2, region 2p25.2 and 2p23/24, respectively) in a phenotypically normal girl with a normal karyotype 46,XX (by GT-banding). The index of paternity calculated for other serological (seven erythrocyte antigens, six serum protein systems, and seven isozymes, as well as the A- and B-HLA loci) and nine DNA markers, excluding ACP and Apo B, gives a very high (virtually certain) degree of paternity for the presumptive father. Maternal uniparental disomy (UPD) for chromosome 2 was suspected. Evaluation of polymorphic DNA markers (STRs) spanning chromosome 2 of the child, mother, and presumptive father demonstrated that the girl had inherited two maternal chromosome 2 homologues, whereas alleles for markers from other chromosomes were inherited from the father in a Mendelian fashion. The girl was homoallelic for informative markers mapping to the chromosomal regions 2p23-25, but she was heteroallelic for informative markers on the long arm of chromosome 2, establishing that the maternal UPD with partial isodisomy of the short arm was caused by a meiosis I nondisjunction event with genetic recombination (chiasmata in this region 2p23-25) during oogenesis.

Blood Group Antigens↗
PubMed2001

Detailed characterization of 12 supernumerary ring chromosomes using micro-FISH and search for uniparental disomy.

Twelve patients with varying degrees of mosaicism for a supernumerary ring chromosome were studied. The ring chromosomes were characterized using microdissection in combination with degenerate nucleotide-primed polymerase chain reaction (PCR) and reverse painting (micro-FISH). This method made it possible to determine the chromosomal origin of the ring chromosomes in detail, and thus to compare the phenotypes of similar cases. Eleven of the marker chromosomes were derived from the most proximal part of 1p, 3p, 3q, 5p, 7q, 8p, 8q, 9p, 10p and 20p. One marker chromosome had a complex origin, including the proximal and the most distal part of 20q. Eight of the families were also investigated for uniparental disomy (UPD) using microsatellite analysis. One case with maternal UPD 9 was found in a child with a ring chromosome derived from chromosome 9, r(9)(p10p12).

Adolescent↗
PubMed1999

Prenatal diagnosis of supernumerary marker 15 chromosomes and exclusion of uniparental disomy for chromosome 15.

Supernumerary marker chromosomes (SMC) were identified in amniocytes from two unrelated fetuses. Fluorescence in situ hybridization (FISH) characterization of the SMC showed they were derived from chromosome 15; SMC(15). Parental karyotyping demonstrated the SMC(15) to be de novo in one fetus and paternally derived in the other. Previous reports showed that the presence or absence of the Prader-Willi/Angelman syndrome (PWS/AS) critical region, loci D15S11 and distal, in a SMC(15) was associated with an abnormal or normal phenotype, respectively. FISH analysis demonstrated both SMC(15) lacked the D15S11 locus. Because SMC(15) were found at an increased incidence in patients with PWS/AS, we performed methylation analysis at the SNRPN locus to exclude a deletion or uniparental disomy (UPD) of chromosome 15. Both probands showed biparental inheritance at this locus. Based on the FISH and molecular analyses, both fetuses were predicted to have a normal phenotype. The pregnancies were continued and both probands are phenotypically and developmentally normal. These cases illustrate the importance of a combination of family studies, FISH characterization and molecular analyses in SMC(15) identified prenatally. In particular, any chromosome 15 rearrangement identified at prenatal diagnosis should be considered a candidate for UPD15 studies.

Adult↗
PubMedDate not supplied

Uniparental disomy in cartilage-hair hypoplasia.

Cartilage-hair hypoplasia (CHH) is an autosomal recessive disorder that presents with pleiotropic manifestations including impaired skeletal growth and cellular immunity. It is most prevalent among two founder populations, the Old Order Amish in the USA and the Finns. The gene has been localized to 9p13 by linkage analysis and linkage disequilibrium mapping. A statistically significant deficiency of affected members resulting in a lower than expected segregation ratio has been reported in the Amish, but was not found in a previous study in Finnish CHH families. Reduced penetrance was the mechanism suggested in the Amish, but could not be verified by haplotype analyses performed after the assignment of the CHH gene. Here we have carried out segregation analysis of 101 Finnish CHH families, but again, evidence of a significant deficiency of affected members was not found. Nevertheless, among 54 uniplex families, 2 patients with CHH and uniparental disomy (UPD) for chromosome 9 were discovered. UPD might contribute to low segregation ratios by increasing the number of families with only 1 affected individual. These observations show that UPD may occur in an unexpectedly high number of the patients and should be taken into account in the genetic counselling and prenatal diagnostics of CHH families.

Abnormalities, Multiple↗
PubMed2000

Recurrent trisomy 21 in a couple with a child presenting trisomy 21 mosaicism and maternal uniparental disomy for chromosome 21 in the euploid cell line.

Recurrence of trisomy 21 was observed in a family in which both parents had a normal chromosome complement. Mosaic trisomy 21 was found in a blood karyotype of the first child, a second pregnancy ended in spontaneous abortion, and a full trisomy 21 was found at prenatal diagnosis of the third pregnancy of this same couple. Although recurrent trisomy 21 may be due to chance, the possibility of germline mosaicism for trisomy 21 in one of the parents has important implications for recurrence risk. Molecular analysis was therefore undertaken in this family to determine the parental origin and the stage of nondisjunction of the extra chromosome 21 in both cases. Although a maternal origin of both instances of trisomy 21 was observed, the mosaic case showed homozygosity for all markers along the duplicated maternal chromosome. Such a finding would normally suggest a postzygotic origin of the trisomy 21. However, the diploid cell line in this same case showed maternal uniparental disomy 21, implying that it was the result of a trisomic conception. We suggest that a somatic nondisjunction in the maternal germ cells is the most likely explanation for these findings. The apparent meiotic II stage of nondisjunction of the nonmosaic trisomy 21 fetus was consistent with maternal mosaicism. A review of the literature for recurrent trisomy 21 cases studied by molecular means, suggests that mosaicism in germ cells may account for more cases than is detected cytogenetically. These results also show that DNA marker analysis does not provide a valuable tool for patient counseling in case of recurrent trisomy 21.

Child↗
PubMed1992

A male with trisomy 9 mosaicism and maternal uniparental disomy for chromosome 9 in the euploid cell line.

We describe a 17 year old male with a low level of trisomy 9 mosaicism. Maternal uniparental chromosome 9 disomy in the euploid cell line was shown to have arisen after postzygotic loss of the paternal chromosome 9 from the trisomic cell line by cytogenetic and molecular analysis. This is believed to be the first report of uniparental disomy for chromosome 9. In four of the 11 reported cases of mosaic trisomy 9 syndrome, including our patient, a maternally derived pericentric inversion of the heterochromatic area of chromosome 9 has been present in duplicate in the trisomic cell line. This may have implications for the counselling of patients with this common chromosomal variant.

Abnormalities, Multiple↗
PubMed1997

Maternal uniparental disomy of chromosome 1 with reduction to homozygosity of the LAMB3 locus in a patient with Herlitz junctional epidermolysis bullosa.

Junctional epidermolysis bullosa (JEB) is an autosomal recessive disorder characterized by blister formation at the level of the lamina lucida within the cutaneous basement-membrane zone. Classic lethal JEB (Herlitz type [H-JEB]; OMIM 226700) is frequently associated with premature-termination-codon mutations in both alleles of one of the three genes (LAMA3, LAMC2, or LAMB3) encoding the subunit polypeptides (alpha3, beta3, and gamma2) of laminin 5. In this study, we describe a unique patient with H-JEB, who was homozygous for a nonsense mutation, Q243X, in the LAMB3 gene on chromosome 1 and who had normal karyotype 46,XY. The mother was found to be a carrier of the Q243X mutation, whereas the father had two normal LAMB3 alleles. Nonpaternity was excluded by use of 11 microsatellite markers from six different chromosomes. The use of 17 partly or fully informative microsatellite markers spanning the entire chromosome 1 revealed that the patient had both maternal uniparental meroisodisomy of a 35-cM region on 1q containing the maternal LAMB3 mutation and maternal uniparental heterodisomy of other regions of chromosome 1. Thus, the results suggested that reduction to homozygosity of the 1q region containing the maternal LAMB3 mutation caused the H-JEB phenotype. The patient was normally developed at term and did not show overt dysmorphisms or malformations. This is the first description of uniparental disomy of human chromosome 1.

Alleles↗
PubMed1998

Uniparental disomy for chromosome 6 results in steroid 21-hydroxylase deficiency: evidence of different genetic mechanisms involved in the production of the disease.

Congenital adrenal hyperplasia (CAH) is an inherited recessive disorder of adrenal steroidogenesis caused by mutations in the steroid 21-hydroxylase gene (CYP21) in more than 90% of affected patients. The CYP21 gene is located within the HLA complex locus on chromosome 6 (6p21.3). During a molecular characterisation study of a group of 47 Mexican families with 21-hydroxylase deficiency, we identified nine in which the mutation or mutations found in the patient did not appear to originate from one of the parents. Through DNA fingerprinting, paternity was established in all nine families with a probability of non-paternity in the range of 10(-19) to 10(-23). Among these families, we identified one patient with exclusive paternal inheritance of all eight markers tested on chromosome 6p, despite normal maternal and paternal contributions for eight additional markers on three different chromosomes. We did not identify duplication of paternal information for markers in the 6q region, consistent with lack of expression of transient neonatal diabetes owing to genomic imprinting in this patient. Our results substantiate evidence for the existence of different genetic mechanisms involved in the expression of this recessive condition in a substantial portion (approximately 19%) of affected Mexican families. In addition to the identification of a patient with paternal uniparental disomy, the occurrence of germline mutations may explain the unusual pattern of segregation in the majority of the remaining eight families.

Adrenal Hyperplasia, Congenital↗
PubMed2006

Prenatal diagnostic indicators of paternal uniparental disomy 14.

OBJECTIVES: To present clinical findings of a child with paternal uniparental isodisomy 14 (pat UPD14) focusing on relevant prenatal characteristics. METHODS/RESULTS: Ultrasonography at 23 weeks of gestation of a 37-year-old multigravid woman revealed a fetus with polyhydramnios, small thorax, and short, distinctively angled ribs. Fetal karyotype was 46,XY. The child was born spontaneously at 35 weeks with poor neonatal adaptation. From birth, he presented with severe respiratory insufficiency due to severe thoracic malformation. Clinical examination revealed a small, bell-shaped thorax, redundant lax skin, mild contractures of the fingers and dysmorphic facial features. Chest X rays showed short, abnormally curved ribs that suggested the possibility of pat UPD14, which was confirmed by molecular analysis. CONCLUSION: Pat UPD14 is associated with a distinct clinical phenotype. Prognosis is poor because of severe respiratory insufficiency and neurodevelopmental retardation. Our report confirms salient postnatal signs of previous descriptions, especially the characteristic radiological abnormalities with ribs showing a 'coat-hanger' configuration. Retrospective fetal ultrasound of our case allowed the identification of this pathognomonic feature prenatally, which makes it possible to consider pat UPD14 at routine prenatal sonography, in particular in combination with a small bell-shaped thorax and polyhydramnios.

Abnormalities, Multiple↗
PubMedDate not supplied

Uniparental disomy.

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Chromosome Disorders↗
PubMed2005

Trisomy 10 mosaicism and maternal uniparental disomy 10 in a liveborn infant with severe congenital malformations.

We report on a liveborn infant with trisomy 10 mosaicism combined with maternal uniparental heterodisomy for chromosome 10. The mosaicism 47,XY,+10/46,XY was found in five different tissues, including one blood sample, while cultured lymphocytes from two other blood samples showed a normal karyotype, 46,XY. DNA analysis with six PCR-based microsatellite markers demonstrated the trisomic cell line to be a result of maternal meiotic nondisjunction, and revealed maternal uniparental heterodisomy in the diploid cell line, suggesting that the formation of the diploid cell line was due to trisomy rescue. The boy had severe growth retardation, major dysmorphism, and malformations, and died at 37 days. We reviewed the previous nine reports of infants and fetuses with trisomy 10 mosaicism reported in the literature. We suggest that a common clinical syndrome can be defined comprising skull, jaw and ear abnormalities, cleft lip/palate, malformations of eyes, heart and kidneys, deformity of hands and feet, and most often death neonatally or in early infancy. The cytogenetic findings in the present patient demonstrate the importance of karyotyping more than one tissue, and not only lymphocytes, when a chromosomal aberration is strongly suspected.

Abnormalities, Multiple↗