High-Throughput Genomics Identify Novel FBN1/2 Variants in Severe Neonatal Marfan Syndrome and Congenital Heart Defects.

Fibrillin-1 and fibrillin-2, encoded by FBN1 and FBN2, respectively, play significant roles in elastic fiber assembly, with pathogenic variants causing a diverse group of connective tissue disorders such as Marfan syndrome (MFS) and congenital contractural arachnodactyly (CCD). Different genomic variations may lead to heterogeneous phenotypic features and functional consequences. Recent high-throughput sequencing modalities have allowed detection of novel variants that may guide the care for patients and inform the genetic counseling for their families. We performed clinical phenotyping for two newborn infants with complex congenital heart defects. For genetic investigations, we employed next-generation sequencing strategies including whole-genome Single-Nucleotide Polymorphism (SNP) microarray for infant A with valvular insufficiency, aortic sinus dilatation, hydronephrosis, and dysmorphic features, and Trio whole-exome sequencing (WES) for infant B with dextro-transposition of the great arteries (D-TGA) and both parents. Infant A is a term male with neonatal marfanoid features, left-sided hydronephrosis, and complex congenital heart defects including tricuspid regurgitation, aortic sinus dilatation, patent foramen ovale, patent ductus arteriosus, mitral regurgitation, tricuspid regurgitation, aortic regurgitation, and pulmonary sinus dilatation. He developed severe persistent pulmonary hypertension and worsening acute hypercapnic hypoxemic respiratory failure, and subsequently expired on day of life (DOL) 10 after compassionate extubation. Cytogenomic whole-genome SNP microarray analysis revealed a deletion within the FBN1 gene spanning exons 7-30, which overlapped with the exon deletion hotspot region associated with neonatal Marfan syndrome. Infant B is a term male prenatally diagnosed with isolated D-TGA. He required balloon atrial septostomy on DOL 0 and subsequent atrial switch operation, atrial septal defect repair, and patent ductus arteriosus ligation on DOL 5. Trio-WES revealed compound heterozygous c.518C>T and c.8230T>G variants in the FBN2 gene. Zygosity analysis confirmed each of the variants was inherited from one of the parents who were healthy heterozygous carriers. Since his cardiac repair at birth, he has been growing and developing well without any further hospitalization. Our study highlights novel FBN1/FBN2 variants and signifies the phenotype-genotype association in two infants affected with complex congenital heart defects with and without dysmorphic features. These findings speak to the importance of next-generation high-throughput genomics for novel variant detection and the phenotypic variability associated with FBN1/FBN2 variants, particularly in the neonatal period, which may significantly impact clinical care and family counseling.

Impact of male age on paternal aneuploidy: single-nucleotide polymorphism microarray outcomes following blastocyst biopsy.

RESEARCH QUESTION: Does advanced paternal age (APA; ≥40 years) contribute to a higher incidence of paternal origin aneuploidy in preimplantation embryos? DESIGN: This was a multicentre retrospective study of single-nucleotide polymorphism (SNP) microarray (Natera and Karyomapping) preimplantation genetic testing (PGT) outcomes of blastocyst-stage embryos. Whole-chromosome aneuploidy analysis was performed on 2409 embryos from 389 male patients undertaking 681 assisted reproductive technology (ART) cycles between 2012-2021. Segmental aneuploidy analysis was performed on 867 embryos from 140 men undertaking 242 ART cycles between 2016-2021. Embryos were grouped based on paternal age at sperm collection: <35, 35-39 and ≥40 years. Paternal and maternal origin aneuploidy rates were compared between groups using chi-squared and/or Fisher's exact tests. RESULTS: There was no significant difference across groups in paternal origin whole-chromosome aneuploidy rate, overall (P=0.7561) or when segregated by type (trisomy and monosomy: P=0.2235 and 0.8156) or complexity (single versus 2, 3 or ≥4 aneuploidies: P=0.9733, 0.7517, 0.669 and 0.1481). Conversely, maternal origin whole-chromosome aneuploidy rate differed across groups (P<0.0001) in alignment with differing mean maternal age (P<0.001). Paternal origin deletions were 2.9-fold higher than maternal origin deletions (P=0.0084), independent of age stratification. No significant difference in paternal origin deletions was observed with APA ≥40 compared with the younger age groups (4.8% versus 2.5% and 2.8%, P=0.5292). Individual chromosome aneuploidy rates were too low to perform statistical comparisons. CONCLUSIONS: No significant association was found between APA and the incidence of paternal origin aneuploidy in preimplantation embryos, irrespective of type or complexity. Thus, APA may not be an indication for PGT.

Patient with Mosaic Turner Syndrome and a Derivative X Chromosome with a Variant Triple X Diagnosis in Fetus: A Case Report.

Although Turner syndrome is most often sporadic, multigenerational recurrence has been reported more often in the offspring of women with mosaic or variant forms of Turner syndrome. We present a case in which natural conception in a woman with identified 45,X/46,XX mosaicism resulted in a fetus with a gain of a derivative X chromosome. The unexpected fetal finding prompted further cytogenetic evaluation of the patient and subsequent identification of an additional cell line with the same derivative X chromosome, not observed in the initial study. To our knowledge, this is the first case in which further investigation of an abnormal noninvasive prenatal screen resulted in the identification of both maternal and fetal sex chromosome abnormality. We discuss the discordant finding, similar cases, and potential phenotype with respect to skewed X inactivation. We also highlight the use of multiple testing methodologies to characterize the serendipitous identification of a derivative X chromosome.

Diagnosis and discovery: Insights from the NIH Undiagnosed Diseases Program.

Living with an undiagnosed medical condition places a tremendous burden on patients, their families, and their healthcare providers. The Undiagnosed Diseases Program (UDP) was established at the National Institutes of Health (NIH) in 2008 with the primary goals of providing a diagnosis for patients with mysterious conditions and advancing medical knowledge about rare and common diseases. The program reviews applications from referring clinicians for cases that are considered undiagnosed despite a thorough evaluation. Those that are accepted receive clinical evaluations involving deep phenotyping and genetic testing that includes exome and genomic sequencing. Selected candidate gene variants are evaluated by collaborators using functional assays. Since its inception, the UDP has received more than 4500 applications and has completed evaluations on nearly 1300 individuals. Here we present six cases that exemplify the discovery of novel disease mechanisms, the importance of deep phenotyping for rare diseases, and how genetic diagnoses have led to appropriate treatment. The creation of the Undiagnosed Diseases Network (UDN) in 2014 has substantially increased the number of patients evaluated and allowed for greater opportunities for data sharing. Expansion to the Undiagnosed Diseases Network International (UDNI) has the possibility to extend this reach even farther. Together, networks of undiagnosed diseases programs are powerful tools to advance our knowledge of pathophysiology, accelerate accurate diagnoses, and improve patient care for patients with rare conditions.

An Anomaly with Potential as a New Prognostic Marker in CLL with del(13q): Gain of 16p13.3.

Deletion 13q [del(13q)] is a favorable prognostic marker if it is detected as a sole abnormality in chronic lymphocytic leukemia (CLL). However the clinical courses of cases with isolated del(13q) are quite heterogeneous. In our study, we investigated copy number variations (CNVs), loss of heterozygosity (LOH), and the size of del(13q) in 30 CLL patients with isolated del(13q). We used CGH+SNP microarrays in order to understand the cause of this clinical heterogeneity. We detected del(13q) in 28/30 CLL cases. The size of the deletion varied from 0.34 to 28.81 Mb, and there was no clinical effect of the deletion size. We found new prognostic markers, especially the gain of 16p13.3. These markers have statistically significant associations with short time to first treatment and advanced disease stage. Detecting both CNVs and LOH at the same time is an advantageous feature of aCGH+SNP. However, it is very challenging for the array analysis to detect mosaic anomalies. Therefore, it is very important to confirm the results by FISH. In our study, we detected approximately 9% mosaic del(13q) by microarray. In addition, the gain of 16p13.3 may affect the disease prognosis in CLL. However, additional studies with more patients are needed to confirm these results.

A rare case of postnatal mosaic trisomy 12 with severe congenital heart disease and literature review.

Trisomy 12 is a rare autosomal aneuploidy. All postnatally diagnosed individuals with trisomy 12 have been mosaic for this chromosome abnormality. We herein report an infant girl presented at 2 weeks of age with severe congenital heart defect, tracheobronchomalacia, and dysmorphic features. All of the dysmorphic features of this patient fit into the known phenotype spectrum of mosaic trisomy 12, although this patient uniquely presented with macrocephaly. Tracheo-bronchomalacia has been described once previously but had a significant impact on this patient's clinical course. The patient passed away at 2-month-old due to cardiac and respiratory complications. Chromosomal single nucleotide polymorphism (SNP) microarray analysis on a peripheral blood sample from the patient revealed trisomy 12 in approximately 50% of cells. Concurrent fluorescence in situ hybridization analysis of uncultured blood cells detected a comparable level of trisomy 12 mosaicism. Compared to conventional cytogenetics, SNP microarray examines all nucleated cells without sampling bias, has an increased power to estimate mosaicism level, and can provide a quick assessment of the underlying mechanism. Here we demonstrate the utilization of SNP microarray in the clinical diagnosis of those once considered rare disorders but might have been missed by conventional cytogenetic techniques.

Temple syndrome resulting from uniparental disomy is undiagnosed by a methylation assay due to low-level mosaicism for trisomy 14.

We describe a patient with Temple syndrome resulting from maternal uniparental disomy of chromosome 14 who also has low-level mosaicism for trisomy 14. UPD was initially suspected when SNP microarray analysis detected a large region of homozygosity on chromosome 14 and the patient's clinical features were consistent with the phenotype of upd(14)mat. However, SNP arrays cannot prove UPD, as homozygosity may also result from identity by descent. Methylation assays diagnose imprinting disorders such as Prader-Willi, Angelman and Temple syndromes; they detect methylation defects that occur in imprinted loci, which have parent-of-origin-specific expression and have the advantage of making a diagnosis without parental samples. However, in this patient methylation analysis using endpoint PCR detected biparental inheritance. Therefore, sequencing analysis was performed and diagnosed upd(14)mat. Re-examination of the microarray suggested that the explanation for the discrepancy between the array and methylation testing was low-level mosaicism for trisomy 14 and fluorescence in situ hybridization testing detected a trisomic cell line. Thus, this patient's Temple syndrome is a result of a maternal M1 error, which gave a trisomic zygote, followed by loss of the paternal chromosome 14 in an early mitotic division to give maternal UPD with low-level mosaicism for trisomy 14. The methylation assay detected the paternal allele in the trisomic line. The diagnostic failure of the methylation assay in this patient highlights a significant shortcoming of methylation endpoint analysis, especially for Temple syndrome, and underscores the need to use other methods in cases with mosaicism.

Genetic counseling and screening of consanguineous couples and their offspring practice resource: Focused Revision.

There are no evidence-based guidelines to inform genetic counseling for consanguineous couples and their offspring. This focused revision builds on the expert opinions from the original publication of "Genetic Counseling and Screening of Consanguineous Couples and Their Offspring," based on a review of literature published since 2002.

Analysis of the Origin of Double Mosaic Aneuploidy in Two Cases.

We present 2 cases of double mosaic aneuploidy harboring 2 or more different aneuploid cell lines, but no line with a normal chromosome constitution. One of these cases presented mosaicism of sex chromosome aneuploid cell lines (47,XXX/45,X) along with another line containing an autosomal trisomy (47,XX,+8), while the other case showed mosaicism of 2 different autosomal trisomy cell lines (47,XY,+5 and 47,XY,+8). To elucidate the mechanisms underlying these mosaicisms, we conducted molecular cytogenetic analyses. Genotyping data from the SNP microarray indicated that 2 sequential meiotic or early postzygotic segregation errors likely had occurred followed by natural selection. These cases suggest that frequent segregation errors and selection events in the meiotic and early postzygotic stages lead to this condition.

Comprehensive Genomic Analysis of Noonan Syndrome and Acute Myeloid Leukemia in Adults: A Review and Future Directions.

Acute myeloid leukemia (AML) in the setting of Noonan syndrome (NS) has been reported before without clear guidelines for treatment or prognosis in these subgroups of patients, most likely due to its rarity and incomplete understanding of the pathogenesis of both diseases. In the current era of next-generation sequencing-based genomic analysis, we can better identify patients with NS with more accurate AML-related prognostic markers. Germline mutations in PTPN11 are the most common cause of NS. Somatic mutations in NPM1 occur frequently in AML. Here, we describe a young adult patient with a novel combined germline PTPN11 and somatic NPM1, IDH1,and BCL6 mutations who presented with fatal AML. In addition, a 50.5-Mb interstitial deletion of 7q21.11-q33 in tumor DNA was detected by chromosomal microarray analysis. While mutations in the transcriptional repressor BCL6 are known to contribute to the pathogenesis of diffuse large B cell lymphoma (DLBCL) and chronic lymphocytic leukemia (CLL), its novel identification in this patient suggests an expanded role in aggressive AML. The identification of key molecular aberrations including the overexpression of SHP2, which drives leukemogenesis and tumorigenesis, has led to the development of novel investigational targeted SHP2 inhibitors.

A homozygous nonsense variant in DYM underlies Dyggve-Melchior-Clausen syndrome associated with ectodermal features.

Dyggve melchior clausen syndrome (DMC, MIM 223800) is a very rare autosomal recessive form of skeletal dysplasia associated with various degrees of mental retardation. It is characterized by a progressive spondyloepimetaphyseal dysplasia (SEMD) with disproportionate short stature, generalized platyspondyly and lacy iliac crest. Here, we report characterization of large consanguineous family segregating DMC in autosomal recessive manner. Scanning SNP-based human genome identified a 5.3 Mb homozygous region on chromosome 18q21.1-q21.2. Sanger sequencing of the DYM gene, located in the homozygous region, revealed a novel homozygous nonsense variant [c.59 T > A; p.(Leu20*)] in affected members of the family. Analysis of the mRNA, extracted from hair follicles of an affected individual, suggested non-sense mediated decay (NMD) of the truncated transcript. This is the first nonsense and fourth loss of function variant in the DYM gene, causing DMC, reported in the Pakistani population. This study not only extended spectrum of the mutations in the DYM gene but will also facilitate diagnosis of similar other cases in Pakistani population.

Prenatal diagnosis of Desbuquois dysplasia Type 1: Utilization of high-density SNP array to map homozygosity and identify the gene.

Desbuquois dysplasia (DBQD1 [MIM 251450]) is an autosomal recessive chondrodysplasia with micromelia, severe joint laxity and dislocations, and a characteristic radiographic "monkey wrench" appearance at the proximal femur. Type 1 Desbuquois dysplasia is caused by mutations in CANT1 and is distinct from Type 2, caused by mutations in XYLT1, in that the former has unique hand anomalies including accessory phalangeal ossification centers, advanced carpal bone maturation, and/or axial phalangeal deviation. Severe prenatal presentations have been rarely reported. We report a Pakistani female in a consanguineous relationship with a diagnosis of Type 1 Desbuquois dysplasia in three consecutive pregnancies. Multiple similar severe fetal limb anomalies were detected by ultrasound in Pregnancy 1 and 2. Regions of homozygosity within the single nucleotide polymorphism (SNP)-microarray from both terminated fetuses were compared, revealing CANT1 as a likely disease-causing candidate gene. Insufficient fetal DNA precluded confirmatory testing, therefore parents were tested; both had a previously reported heterozygous CANT1 mutation (c.643G>T; Glu215Term). The patient presented with a third pregnancy revealing similarly abnormal limb position and probable polysyndactyly by ultrasound. Targeted testing of CANT1 revealed homozygous c.643G>T CANT1 mutations and this pregnancy was terminated. In clinical situations in which ample DNA is not available or more expensive testing (e.g., whole exome sequencing) with a longer turnaround time is not feasible, utilization of SNP-microarray in consanguineous families at risk for rare autosomal recessive disorders may dramatically narrow the list of candidate genes.

Insight into the mechanisms and consequences of recurrent telomere capture associated with a sub-telomeric deletion.

A complex mosaicism of the short arm of chromosome 1 detected by SNP microarray analysis is described in a patient presenting a 4-Mb 1p36 terminal deletion and associated phenotypic features. The array pattern of chromosome 1p displayed an intriguing increase in divergence of the SNP heterozygote frequency from the expected 50% from the centromere towards the 1p36 breakpoint. This suggests that various overlapping segments of UPD were derived by somatic recombination between the 1p homologues. The most likely explanation was the occurrence of a series of events initiated in either a gamete or an early embryonic cell division involving a 1pter deletion rapidly followed by multiple telomere captures, resulting in additive, stepped increases in frequency of homozygosity towards the telomere. The largest segment involved the entire 1p, and at least four other capture events were observed, indicating that at least five independent telomere captures occurred in separate cell lineages. The determination of breakpoint position by detection of abrupt changes in B-allele frequency using a moving window analysis demonstrated that they were identical in blood and saliva, the tissues available for analysis. We developed a model to explain the interaction of parameters determining the mosaic clones and concluded that, while number, size, and position of telomere captures were important initiating determinants, variation in individual clone frequencies was the main contributor to mosaic differences between tissues. All previous reports of telomere capture have been restricted to single events. Other cases involving multiple telomere capture probably exist but require investigation by SNP microarrays for their detection.

Biparental/androgenetic mosaicism in a male with features of overgrowth and placental mesenchymal dysplasia.

Biparental/androgenetic mosaicism is a rarely diagnosed condition in humans. It is typically ascertained prenatally on the basis of placental mesenchymal dysplasia. Fetal outcome can range from demise due to intrauterine growth retardation to term delivery. Most of the published cases of liveborns represent females that are either completely normal or have features of Beckwith-Wiedemann syndrome. Only two healthy liveborn males with mosaicism detected in the placenta have been described to date. Here, we report another liveborn male with hepatic mesenchymal hamartoma, soft tissue overgrowth on his right fifth toe, hemangiomas over his chest, right buttock and foot, anemia, thrombocytopenia and congenital hypothyroidism with biparental/androgenetic mosaicism detected in the toe mass in addition to the placenta. This new case adds to the existing literature of individuals with biparental/androgenetic mosaicism and expands the range of clinical presentations that may be seen in male patients with this condition. This study also illustrates the important use of single-nucleotide polymorphism microarray in conjunction with short-tandem repeat analysis on affected tissue to provide a diagnosis for patients with features of overgrowth and prior, non-diagnostic, genetic analyses of their peripheral blood.

Features of Feingold syndrome 1 dominate in subjects with 2p deletions including MYCN.

Interstitial deletions of the distal short arm of chromosome 2 including MYCN have only been reported for a small number of individuals. Germline deletions and mutations of MYCN cause Feingold syndrome 1 (FS1), a rare disorder characterized by microcephaly, digit anomalies, gastrointestinal atresias, short stature, dysmorphic features, and intellectual disability. We present a series of six individuals referred for SNP microarray with overlapping deletions of 2p ranging from 3.4 to 16.8 Mb in size, with a common overlapping region of 1.53 Mb spanning (14,614,477-16,148,021) [hg19] and including five genes: NBAS, DDX1, MYCNUT, MYCNOS, and MYCN. Clinical information was available for five individuals. Clinical features included core features of FS1 such as microcephaly, digit anomalies, and gastrointestinal atresias as well as structural cardiac defects, hearing loss, and renal anomalies, which are features less consistently associated with FS1. Other features observed in several individuals, that have not specifically been associated with FS1 were motor delay, structural brain abnormalities, genital abnormalities, and radioulnar synostosis. These results indicate that while individuals with deletions of 2p spanning several megabases and including MYCN can present with features not typically associated with FS1, the common core features are usually present.

Delineation of the 9q31 deletion syndrome: Genomic microarray characterization of two patients with overlapping deletions.

Interstitial deletions of chromosome 9q31 are very rare. The deletions in most reported patients have been detected by conventional cytogenetics, with reported breakpoints ranging between 9q21 and 9q34. Therefore, an accurate description of a "9q31 deletion syndrome" could not be established. However, based on microarray studies, a small region of overlap has recently been proposed. We report clinical features of two unrelated individuals with overlapping 9q deletions identified by SNP microarray analysis. Patient 1 has a 9 Mb deletion, while Patient 2's deletion was 21.6 Mb. The clinical features common to our patients and those in the literature include developmental delay and short stature. Patient 2 shows additional features not reported in other 9q31 deletions, such as hearing loss, ventriculomegaly, cleft lip and palate, and small kidneys, which could be due to the larger size of the deletion, hence the influence of the genes in the region beyond the smallest region of overlap. Based on the comparison of these patients with the previously reported patients, we redefine the smallest region of overlap and characterize the clinical features of the 9q31 deletion syndrome.

Investigation of Yersinia pestis and Yersinia pseudotuberculosis strains from Georgia and neighboring countries in the Caucasus by high-density SNP microarray.

Yersinia pestis, the causative agent of plague, is a recently evolved clone of the enteropathogenic bacterium Yersinia pseudotuberculosis. Y. pestis has been extensively studied for decades; however, there are insufficient data about the intra-species diversity of this microorganism in certain parts of the world, including the Caucasus region. Using a high-density single-nucleotide polymorphism (SNP) microarray, we genotyped a total of 46 Y. pestis isolates from two plague foci in Georgia and neighboring Caucasus countries together with 12 Y. pseudotuberculosis isolates from Georgia. The genotyping microarray captured a total of 13,525 SNP positions across the Y. pestis and Y. pseudotuberculosis genomes and plasmids with high-throughput capability and superior reproducibility. From this analysis, we confirmed the presence of two independent and relatively distant phylogenetic groups of Y. pestis in the Caucasus region. The signature SNP patterns identified from this study will allow assay development for plague surveillance and pseudotuberculosis diagnostics.

Whole Genome Sequencing instead of Whole Exome Sequencing is required to identify the Genetic Causes of Polycystic Ovary Syndrome in Pakistani families.

BACKGROUND & OBJECTIVE: Polycystic Ovary Syndrome (PCOS) is the major cause of infertility in females. PCOS is a complex and multifactorial disease, genetic and environmental factors being important predisposing factors. Diagnosis of PCOS is difficult due to the complexity of this disease; hence, better diagnostic tests are required to improve its management. Aim of the study was to elucidate the genetic causes of PCOS in three Pakistani families. METHODS: Three Pakistani families segregating PCOS in an apparently autosomal recessive mode were recruited. Whole genome Single Nucleotide Polymorphism (SNP) genotyping and Whole Exome Sequencing (WES) were carried out to identify the candidate genes. RESULTS: SNP genotypes data analyses identified multiple regions of homozygosity on different chromosomes. WES was performed in affected members of the family. Screening for pathogenic mutations in homozygous regions failed to detect any mutation/variant of interest. CONCLUSION: PCOS is multifactorial and complex disease so variants in the coding as well as in non-coding regions may be the genetic causes of the disease. To elucidate the genetic cause(s) of the PCOS, Whole Genome Sequencing (WGS) is recommended to cover both coding and non-coding regions of the genome.

Assessing the Clinical Utility of SNP Microarray for Prader-Willi Syndrome due to Uniparental Disomy.

Maternal uniparental disomy (UPD) 15 is one of the molecular causes of Prader-Willi syndrome (PWS), a multisystem disorder which presents with neonatal hypotonia and feeding difficulty. Current diagnostic algorithms differ regarding the use of SNP microarray to detect PWS. We retrospectively examined the frequency with which SNP microarray could identify regions of homozygosity (ROH) in patients with PWS. We determined that 7/12 (58%) patients with previously confirmed PWS by methylation analysis and microsatellite-positive UPD studies had ROH (>10 Mb) by SNP microarray. Additional assessment of 5,000 clinical microarrays, performed from 2013 to present, determined that only a single case of ROH for chromosome 15 was not caused by an imprinting disorder or identity by descent. We observed that ROH for chromosome 15 is rarely incidental and strongly associated with hypotonic infants having features of PWS. Although UPD microsatellite studies remain essential to definitively establish the presence of UPD, SNP microarray has important utility in the timely diagnostic algorithm for PWS.

Detection of mutually exclusive mosaicism in a girl with genotype-phenotype discrepancies.

Discordance between clinical phenotype and genotype has multiple causes, including mosaicism. Phenotypes can be modified due to tissue distribution, or the presence of multiple abnormal cell lines with different genomic contributions. We have studied a 20-month-old female whose main phenotypes were failure to thrive, developmental delay, and patchy skin pigmentation. Initial chromosome and SNP microarray analysis of her blood revealed a non-mosaic ∼24 Mb duplication of 15q25.1q26.3 resulting from the unbalanced translocation of terminal 15q to the short arm of chromosome 15. The most common feature associated with distal trisomy 15q is prenatal and postnatal overgrowth, which was not consistent with this patient's phenotype. The phenotypic discordance, in combination with the patchy skin pigmentation, suggested the presence of mosaicism. Further analysis of skin biopsies from both hyper- and hypopigmented regions confirmed the presence of an additional cell line with the short arm of chromosome X deleted and replaced by the entire long arm of chromosome 15. The Xp deletion, consistent with a variant Turner Syndrome diagnosis, better explained the patient's phenotype. Parental studies revealed that the alterations in both cell lines were de novo and the duplicated distal 15q and the deleted Xp were from different parental origins, suggesting a mitotic event. The possible mechanism for the occurrence of two mutually exclusive structural rearrangements with both involving the long arm of chromosome 15 is discussed.