Maternal uniparental disomy of chromosome 13 in a phenotypically normal child

Genomic study via chromosomal microarray analysis in a group of Romanian patients with obesity and developmental disability/intellectual disability

Background Obesity with developmental disability/intellectual disability (DD/ID) is the most common association in syndromic obesity. Genomic analysis studies have allowed the decipherment of disease aetiology, both in cases of syndromic obesity as well as in cases of isolated or syndromic DD/ID. However, more data are needed to further elucidate the link between the two. The aim of this pangenomic study was to use single nucleotide polymorphism (SNP) array technology to determine the copy number variant (CNV) type and frequency associated with both obesity and DD/ID. Methods Thirty-six patients were recruited from the Clinical Emergency Hospital for Children, in Cluj-Napoca, Romania during the period 2015-2017. The main inclusion criterion was a diagnosis that included both obesity and DD/ID. Genomic analysis via SNP array technology was performed. Results Out of the 36 patients, 12 (33%) presented CNVs with a higher degree of pathogenicity (A group) and 24 (66%) presented benign CNVs (B group). The SNP array results for the A group were as follows: pathogenic CNVs in 8/12 patients (67%); variants of unknown significance (VOUS) in 2/12 patients (16%); and uniparental disomy (UPD) in 2/12 patients (16%). Conclusions Some of these CNVs have already been observed in patients with both obesity and DD/ID, but the others were noticed only in DD/ID patients and have not been described until now in association with obesity.

Monozygotic Twins Discordant for Trisomy 13: A Case of Trisomic Rescue Supporting the Continued Need for First-Trimester Ultrasound

Monozygotic twins with discordant karyotypes for trisomy 13 are rare. We report a case of a spontaneously conceived pregnancy who presented with first-trimester ultrasound finding of umbilical cord cyst and increased nuchal translucency in Twin A and no abnormalities in Twin B. Amniocentesis revealed 47,XY,+13 karyotype in Twin A and 46,XY karyotype in Twin B. Selective fetal reduction was performed for Twin A. Twin B was delivered at 32 weeks gestation with normal phenotype. Peripheral blood karyotype revealed 15% mosaicism for trisomy 13 and skin fibroblast revealed 46,XY karyotype. The surviving twin will be monitored for potential complication of uniparental disomy 13 and mosaic trisomy 13. This case reinforces the need for early ultrasound and nuchal translucency measurements, especially in twin gestations.

Monozygotic twins discordant for trisomy 13

Monozygotic twins with discordant karyotypes are rare. We report a case of monozygotic twins discordant for trisomy 13 by amniocyte karyotypes. Ultrasound revealed multiple congenital anomalies in Twin A (47,XY,+13), none in Twin B (46,XY), and monochorionic-diamniotic placentation. Zygosity testing performed both prenatally and after birth supported monozygosity. Twin A died in the neontal period. Twin B survived and had normal physical examination, but peripheral blood karyotype revealed 20% mosaicism for trisomy 13. Monochorionic-diamniontic placentation with vascular anastomoses was confirmed by pathological examination. In this paper, we discuss the various mechanisms by which monozygotic twins may have discordant karyotypes. The surviving twin, structurally and developmentally normal at 6 months of age, will be monitored for potential complications of uniparental disomy of chromosome 13 and trisomy 13 mosaicism.

Isochromosome 13 in a patient with childhood-onset schizophrenia, ADHD, and motor tic disorder

BACKGROUND

A small percentage of all cases of schizophrenia have a childhood onset. The impact on the individual and family can be devastating. We report the results of genetic analyses from a patient with onset of visual hallucinations at 5 years, and a subsequent diagnosis at 9 years of schizophrenia, attention deficit hyperactivity disorder (ADHD) with hyperactivity and impulsivity, and chronic motor tic disorder.

RESULTS

Karyotypic analysis found 45,XX,i(13)(q10) in all cells examined. Alpha satellite FISH of isochromosome 13 revealed a large unsplit centromeric region, interpreted as two centromeres separated by minimal or undetectable short-arm material or as a single monocentric centromere, indicating that the isochromosome likely formed post-zygotically by a short arm U-type or centromeric exchange. Characterization of chromosome 13 simple tandem repeats and Affymetrix whole-genome 6.0 SNP array hybridization found homozygosity for all markers, and the presence of only a single paternal allele in informative markers, consistent with an isodisomic isochromosome of paternal origin. Analysis of two chromosome 13 schizophrenia candidate genes, D-amino acid oxidase activator (DAOA) and 5-hydroxytryptamine (serotonin) receptor 2A (5-HTR2A), failed to identify non-synonymous coding mutations but did identify homozygous risk polymorphisms.

CONCLUSIONS

We report a female patient with childhood-onset schizophrenia, ADHD, and motor tic disorder associated with an isodisomic isochromosome 13 of paternal origin and a 45,XX,i(13)(q10q10) karyotype. We examined two potential mechanisms to explain chromosome 13 involvement in the patient's pathology, including reduction to homozygosity of a paternal mutation and reduction to homozygosity of a paternal copy number variation, but were unable to identify any overtly pathogenic abnormality. Future studies may consider whether epigenetic mechanisms resulting from uniparental disomy (UPD) and the lack of chromosome 13 maternal alleles lead to the patient's features.

Identification of a novel chromosome region, 13q21.33-q22.2, for susceptibility genes in familial chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is the most prevalent form of leukemia in adults in western countries. A genome scan of CLL-prone families revealed a lod score of one in band 13q22.1. To investigate this finding, we selected 6 CLL families consisting of 63 individuals (CLL affected, n = 19; unaffected, n = 44) for fine mapping of a 23-megabase region in 13q14.2-q22.2. Interphase fluorescence in situ hybridization (FISH) revealed 13q14 deletion in 85% (11/13) of CLL patients. Four CLL families shared a 3.68-Mb minimal region in 13q21.33-q22.2. Two asymptomatic siblings who shared the 13q21.33-q22.2 at-risk haplotype exhibited CD5+ monoclonal B-cell lymphocytosis (MBL) on flow cytometry. One of these individuals also had a 13q14 deletion by FISH. These 2 individuals with MBL shared the at-risk haplotype with their CLL-affected relatives, providing further evidence of the relationship between CLL and MBL, as well as of the biologic significance of this novel region. Using direct DNA sequencing analysis, we screened 13 genes for mutations, but no frameshift or nonsense mutations were detected. Our studies revealed that 11 of the 13 genes in the candidate region were expressed in immune tissues, supporting their functional relevance in investigations of familial CLL. In conclusion, we identified a novel candidate region that may predispose to familial CLL.

A fascination with chromosome rescue in uniparental disomy: Mendelian recessive outlaws and imprinting copyrights infringements

With uniparental disomy (UPD), the presence in a diploid genome of a chromosome pair derived from one genitor carries two main types of developmental risk: the inheritance of a recessive trait or the occurrence of an imprinting disorder. When the uniparentally derived pair carries two homozygous sequences (isodisomy) with a duplicated mutant, this 'reduction to homozygosity' determines a recessive phenotype solely inherited from one heterozygote. Thus far, some 40 examples of such recessive trait transmission have been reported in the medical literature and, among the current 32 known types of UPDs, UPD of chromosomes 1, 2, and 7 have contributed to the larger contingent of these conditions. Being at variance with the traditional mode of transmission, they constitute a group of 'Mendelian outlaws'. Several imprinted chromosome domains and loci have been, for a large part, identified through different UPDs. Thus, disomies for paternal 6, maternal 7, paternal 11, paternal and maternal 14 and 15, maternal 20 (and paternal 20q) and possibly maternal 16 cause as many syndromes, as at the biological level the loss or duplication of monoparentally expressed allele sequences constitutes 'imprinting rights infringements'. The above pitfalls represent the price to pay when, instead of a Mendelian even segregation and independent assortment of the chromosomes, the fertilized product with a nondisjunctional meiotic error undergoes correction (for unknown or fortuitous reasons) through a mitotic adjustment as a means to restore euploidy, thereby resulting in UPD. Happily enough, UPDs leading to the healthy rescue from some chromosomal mishaps also exist.

Uniparental disomy (UPD) other than 15: Phenotypes and bibliography updated

Uniparental disomy (UPD) describes the inheritance of a pair of chromosomes from only one parent. The concept was introduced in Medical Genetics by Engel (1980); Am J Med Genet 6:137-143. Aside UPD 15, which is the most frequent one, up to now (February 2005) 197 cases with whole chromosome maternal UPD other than 15 (124 X heterodisomy, 59 X isodisomy, and 14 cases without information of the mode of UPD) and 68 cases with whole chromosome paternal UPD other than 15 (13 X heterdisomy, 53 X isodisomy, and 2 cases without information of the mode of UPD) have been reported. In this review we discuss briefly the problems associated with UPD and provide a comprehensive clinical summary with a bibliography for each UPD other than 15 as a guide for genetic counseling.

Array comparative genomic hybridization analysis of a familial duplication of chromosome 13q: A recognizable syndrome

We report on a family with six persons in three generations who have mild mental retardation, behavioral problems, seizures, hearing loss, strabismus, dental anomalies, hypermobility, juvenile hallux valgus, and mild dysmorphic features. Classical cytogenetic analysis showed a partial duplication of chromosome 13q, array comparative genomic hybridization showed the duplication to span approximately 21 Mb, ranging from chromosome band 13q21.31 to 13q31.1. The relatively mild presentation of this large duplication may be explained by the relative paucity of genes in the chromosome region involved. Genotype-phenotype correlations in patients with similar partial 13q duplications are inconsistent. Emerging cytogenetic techniques will allow more reliable genotype-phenotype correlations.

A child with Angelman syndrome and trisomy 13 findings due to associated paternal UPD 15 and segmental UPD 13

A child with Angelman syndrome, cutis aplasia, cleft palate, and congenital microform cleft lip, born to a father with a Robertsonian translocation 13;15 is described. Molecular studies using polymorphic markers on chromosomes 15 and 13 showed paternal uniparental disomy (UPD) 15 and segmental UPD 13.

Under-ascertainment of mosaic carriers of balanced homologous acrocentric translocations and isochromosomes

Acrocentric rearrangements are the most common chromosome abnormalities in humans. Carriers of homologous acrocentric rearrangements (Robertsonian translocations (ROBs) between homologous chromosomes and isochromosomes) are at very high risk of having multiple spontaneous abortions and chromosomally abnormal offspring. Parents of fetuses and children with unbalanced homologous acrocentric rearrangements are rarely found to be carriers or mosaic for the same rearrangement. Even though recurrent miscarriages may indicate a carrier parent, carriers are rarely identified. Comparison of non-chromosome 21 homologous rearrangements to rea(21q21q) culled from the literature revealed a 7-fold decrease in the number of mosaic cases among the parents of non-rea(21q21q) offspring. This under-ascertainment in parents may be due to low level mosaicism confined to the gonads, a true biological difference between chromosome 21 rearrangements and other homologous acrocentric rearrangements, or simply to the lack of rigorous clinical investigation of the parental karyotypes to uncover mosaicism. We recommend that polymorphic marker analysis be applied to apparently de novo acrocentric rearrangements to distinguish those resulting from biparental postzygotic formation from those resulting from meiotic formation; the latter of which may indicate a potential carrier parent. Parental chromosomal constitutions could then be screened in a large number of cells and in more than one tissue type to identify mosaicism. Identification of mosaicism allows for accurate genetic counseling and discussion of reproductive options. However, given that mosaicism may be restricted to the gonads, prenatal testing is likely to be desired by the family whether or not mosaicism is found.

Complex and segmental uniparental disomy (UPD): review and lessons from rare chromosomal complements

OBJECTIVE

To review all cases with segmental and/or complex uniparental disomy (UPD), to study aetiology and mechanisms of formation, and to draw conclusions.

DESIGN

Searching published reports in Medline.

RESULTS

The survey found at least nine cases with segmental UPD and a normal karyotype, 22 cases with UPD of a whole chromosome and a simple or a non-homologous Robertsonian translocation, eight cases with UPD and two isochromosomes, one of the short arm and one of the long arm of a non-acrocentric chromosome, 39 cases with UPD and an isochromosome of the long arm of two homologous acrocentric chromosomes, one case of UPD and an isochromosome 8 associated with a homozygous del(8)(p23.3pter), and 21 cases with UPD of a whole or parts of a chromosome associated with a complex karyotype. Segmental UPD is formed by somatic recombination (isodisomy) or by trisomy rescue. In the latter mechanism, a meiosis I error is associated with meiotic recombination and an additional somatic exchange between two non-uniparental chromatids. Subsequently, the chromatid that originated from the disomic gamete is lost (iso- and heterodisomy). In cases of UPD associated with one isochromosome of the short arm and one isochromosome of the long arm of a non-acrocentric chromosome and in cases of UPD associated with a true isochromosome of an acrocentric chromosome, mitotic complementation is assumed. This term describes the formation by misdivision at the centromere during an early mitosis of a monosomic zygote. In cases of UPD associated with an additional marker chromosome, either mitotic formation of the marker chromosome in a trisomic zygote or fertilisation of a gamete with a marker chromosome formed in meiosis by a disomic gamete or by a normal gamete and subsequent duplication are possible.

CONCLUSIONS

Research in the field of segmental and/or complex UPD may help to explain undiagnosed non-Mendelian disorders, to recognise hotspots for meiotic and mitotic recombinations, and to show that chromosomal segregation is more complex than previously thought. It may also be helpful to map autosomal recessively inherited genes, genes/regions of genomic imprinting, and dysmorphic phenotypes. Last but not least it would improve genetic counselling.

Investigation of two cases of paternal disomy 13 suggests timing of isochromosome formation and mechanisms leading to uniparental disomy

Uniparental disomy (UPD) is the abnormal inheritance of two copies of a chromosome from the same parent. Possible mechanisms for UPD include trisomy rescue, monosomy rescue, gametic complementation, and somatic recombination. Most of these mechanisms can involve rearranged chromosomes, particularly isochromosomes and Robertsonian translocations. Both maternal and paternal UPD have been reported for most of the acrocentric chromosomes. However, only UPD for chromosomes 14 and 15 show an apparent imprinting effect. Herein, we present two cases of paternal UPD 13 involving isochromosomes. Both cases were referred for UPD studies due to the formation of a de novo rea(13q13q). Case 2 was complicated by the segregation of a familial rob(13q14q) of maternal origin. Both propositi were phenotypically normal at the time of examination. Polymorphic marker analysis in Case 1 showed the distribution of alleles of markers along chromosome 13 to be complete isodisomy, consistent with an isochromosome. This rearrangement could have occurred either meiotically, without recombination, or mitotically. A likely mechanism for UPD in this case is monosomy rescue, through postzygotic formation of the isochromosome. In Case 2 the distribution of proximal alleles indicated an isochromosome, but recombination was evident. Thus, this isochromosome must have formed prior to or during meiosis I. A likely mechanism for UPD in this case is gametic complementation, since the mother carries a rob(13q14q) and is at risk of producing aneuploid gametes. However, trisomy rescue of a trisomy 13 conceptus cannot be completely excluded. Given that both cases were phenotypically normal, these data further support that paternal UPD 13 does not have an adverse phenotypic outcome and, thus, does not show an apparent imprinting effect.

Trisomy 13 mosaicism at prenatal diagnosis: dilemmas in interpretation

We describe six cases of trisomy 13 mosaicism detected at prenatal diagnosis. Most level I and level II trisomy 13 mosaicism detected at prenatal diagnosis is pseudomosaicism or confined placental mosaicism. Rarely, low-level mosaicism at chorionic villus sampling or amniocentesis reflects a true fetal mosaicism. In this case, a normal phenotype is a possible, but not a certain, outcome. Genetic counselling is not straightforward.

Growth effects of uniparental disomies and the conflict theory of genomic imprinting

While numerous theories have been proposed for the evolution of genomic imprinting, few have been tested. The conflict theory proposes that imprinting is an intra-individual manifestation of classical parent-offspring conflict. This theory is unique in predicting that imprinted genes expressed from the paternally derived genome should be enhancers of pre- and post-natal growth, while those expressed from the maternally derived genome should be growth suppressors. We examine this prediction by reviewing the literature on growth of human and mouse progeny that have inherited both copies (or part thereof) of a particular chromosome from only one parent. Perhaps surprisingly, we find that much of the data do not support the hypothesis.

Maternal uniparental heterodisomy for chromosome 16: case report

A patient with uniparental heterodisomy for chromosome 16 presented initially at prenatal diagnosis with a karyotype of 47, XX + 16 on chorionic villus sampling at 11 weeks gestation. The pregnancy was proceeding normally and follow up amniocentesis showed a normal female karyotype. At birth, the child was healthy, but had intrauterine growth retardation. She had unilateral talipes equinovarus and unilateral renal agenesis. Her growth had improved to within the normal range by age three years. On examination, she has epicanthic folds, a flat midface and almond shaped eyes. While these characteristics are not frankly abnormal, they are significantly different from other relatives in her family.

Short-limb dwarfism and hypertrophic cardiomyopathy in a patient with paternal isodisomy 14: 45,XY,idic(14)(p11)

Uniparental disomy (UPD) has been shown to result in specific disorders either due to imprinting and/or homozygosity of mutant alleles. Here we present the findings in a child with paternal UPD14. Ultrasound evaluation was performed at 30 weeks of gestation because of abnormally large uterine size. Pertinent ultrasound findings included polyhydramnios, short limbs, abnormal position of hands, small thorax, and nonvisualization of the fetal stomach. Post-natally the infant was found to have a low birth weight, short birth length, contractures, short limbs, and a small thorax with upslanting ribs. Assisted ventilation and gastrostomy were required. At age 6 months, the infant required hospitalization for hypertrophic cardiomyopathy which responded to Atenolol. Initial cytogenetic studies demonstrated an apparently balanced de novo Robertsonian translocation involving chromosomes 14 and a karyotype designation of 45,XY,t(14q14q). No indication of mosaicism for trisomy 14 was observed in metaphase spreads prepared from peripheral blood lymphocytes or skin-derived fibroblasts. C-band and fluorescence in situ hybridization results demonstrated that the chromosome was dicentric. DNA analyses showed paternal uniparental isodisomy for chromosome 14. Based on the cytogenetic and DNA results a final karyotype designation of 45,XY,idic(14)(p11) was assigned to this infant with paternal isodisomy of chromosome 14.

Uniparental disomy and genome imprinting: an overview

The following paper is concerned with potential changes in the normal epigenetic process in a diploid individual, when a chromosome pair or segment is inherited from one parent only, instead of the expected biparental contribution. This aberrant mode of transmission arises from the high rate of gamete aneuploidy in humans. It has received the name uniparental disomy (UPD), and has emerged as an important factor in the new field of nontraditional inheritance, depicted in Table 1.

The following definitions may foster a better understanding of this discussion.

UPDis the inheritance ofbothcopies of a chromosome [or chromosomal segment(s)] from asingleparent, instead of the normal biparental transmission of the pair. Inisodisomy,the two uniparental copies areidentical, being derived from the same parental chromosome. Inheterodisomy, the two uniparental chromosomes aredifferent, being derived from the homologues of a pair.

Why is there no diploid overdose effect in Prader-Willi syndrome due to uniparental disomy?

Due to DNA technology, it is now apparent that the mechanisms of genetic disease are more complex than the model of a gene with biallelic expression in the diploid state. If a gene is imprinted, monoallelic expression is the norm when the chromosomes of a pair are inherited normally from each parent. Uniparental disomy (UPD) is the abnormal situation where both chromosomes of a pair come from the same parent. When the chromosome contains an imprinted gene, UPD may result in nullisomy or disomy for a functional copy of that gene. If there are two imprinted loci on the same chromosome, UPD for that chromosome results in nullisomy for one imprinted gene but functional disomy for the other a "diploid overdose" (DO). This situation has been well demonstrated in the Prader-Willi syndrome (PWS) which is the nullisomic phenotype for the PWS gene(s) on chromosome 15q11-13. Chromosome 15q11-13 also contains the gene for Angelman syndrome (AS) which has a phenotype distinct from PWS. Both loci are subject to imprinting--in PWS, the imprint is on the maternal chromosome 15, in AS it is on the paternal chromosome 15. All individuals with PWS due to maternal UPD, while functionally nullisomic for the PWS locus, are functionally disomic for the AS locus--a DO situation. Assuming that biallelic expression of an imprinted gene is harmful, one would expect DO for an imprinted gene to produce a phenotypic effect. Cases of PWS due to UPD do not appear to differ from those due to deletion (hypopigmentation in deletional cases can be explained by loss of D15S12 downstream from the critical region). There is no good evidence of DO for the AS locus in PWS due to UPD. Why then was it 'necessary' in evolutionary terms to imprint the AS locus and maintain the imprint faithfully for life. A similar situation of two imprinted genes on the same chromosome occurs with IGF2 and H19 on chromosome 11p15. Maternal imprinting for IGF2 and paternal imprinting for H19 is the norm. Paternal UPD in this situation does lead to a DO effect, namely Beckwith-Wiedemann syndrome. The possibility of a DO effect needs to be considered when assessing the phenotypic spectrum of UPD for other chromosomes currently under investigation.

Prenatal and postnatal growth failure associated with maternal heterodisomy for chromosome 7

The association of maternal uniparental disomy for chromosome 7 and postnatal growth failure has been reported in four cases and suggests the presence of genomic imprinting of one or more growth related genes on chromosome 7. However, in the reported cases, the possibility of homozygosity for a recessive mutation could not be excluded as the cause of the growth failure as in all cases isodisomy rather than heterodisomy for chromosome 7 was present. We report a case of prenatal and postnatal growth retardation associated with a prenatal diagnosis of mosaicism for trisomy 7 confined to the placenta. DNA typing of polymorphic markers on chromosome 7 has established that the zygote originated as a trisomy 7 with two maternal and one paternal chromosomes 7 with subsequent loss of the paternal chromosome resulting in a disomic child with maternal heterodisomy for chromosome 7. The growth failure seen in this child with heterodisomy 7 lends strong support to the hypothesis of imprinted gene(s) on chromosome 7.

The 13q- syndrome: the molecular definition of a critical deletion region in band 13q32

Patients with interstitial deletions of the long arm of chromosome 13 may have widely varying phenotypes. From cytogenetic analysis, we have postulated that there is a discrete region in 13q32 where deletion leads to a syndrome of severe malformations, including digital and brain anomalies. To test this hypothesis at the molecular level, we have studied the deletions in 17 patients; 5 had severe malformations, while the remaining 12 had only minor malformations. Our results indicate that the deletions in the severely affected patients all involve an overlapping region in q32, while the deletions in the mildly affected patients include some, but not all, of this overlapping region. Our findings are consistent with the hypothesis that the severely malformed 13q- phenotype results from the deletion of a critical region in 13q32. This region is presently defined as lying between D13S136 and D13S147 and is on the order of 1 Mb in size.

Possible genetic heterogeneity in hypochondroplasia

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UPD 13: no indication of maternal or paternal imprinting of genes on chromosome 13

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Kabuki syndrome-like features in monozygotic twin boys with a pseudodicentric chromosome 13

We present monozygotic twin boys with features of Kabuki syndrome. The twins were discordant for cleft palate and coarctation of the aorta. The occurrence of Kabuki syndrome in monozygotic twins has not been previously reported and reinforces the belief that this condition has a genetic basis. Chromosomal analysis on the boys showed a pseudodicentric chromosome 13 with an inactive centromere and satellite stalks at 13q12.11: 46,XY,psu dic(13)(13pter-->13q12.11::13p12-->13q11.00:: 13q12.11-->13qter). Their phenotypically normal mother appears to carry the same pseudodicentric chromosome 13.