Blaschkolinear malformation syndrome in complex trisomy-7 mosaicism

Genome-Wide, Non-Invasive Prenatal Testing for rare chromosomal abnormalities: A systematic review and meta-analysis of diagnostic test accuracy

Genome-Wide Non-Invasive Prenatal Testing (GW-NIPT) can provide positive results not only for common autosomal aneuploidies but also for rare autosomal trisomies (RATs) and structural chromosomal abnormalities (StrCAs). Due to their rarity, there is currently insufficient information on positive predictive value PPV of RAT and StrCA-positive cases in the literature. In this study, the screening accuracy and pregnancy outcomes of cases positive for rare chromosomal abnormalities were examined based on publications in which GW-NIPT testing was performed. True positive cases were determined using two different methodologies. One was a confirmed methodology, where only cases validated by genetic testing were considered true positives with a definite diagnosis, and the other was an extended methodology, where, in addition to cases confirmed by genetic testing, intrauterine fetal death and termination of pregnancy due to an abnormality confirmed by ultrasound examination were also considered true positives, where no diagnosis had been made but the fetus was probably affected. Seventeen studies were analyzed, with a total GW-NIPT population of 740,076. Of these, 1,738 were RAT positive. Using the confirmed method, we found the highest rates of true positives in T16, followed by T22, and T2, using the extended method, the highest rate of true positives in T15, T16 and T22. This is the first meta-analysis to determine the frequency of rare chromosomal abnormalities, test-positive rates, and the PPV of each chromosomal abnormality with high precision. Our results could aid pre- and post-test genetic counselling and help patients and clinicians in their decision-making.

Low-level mosaic trisomy 7 at amniocentesis in a pregnancy associated with cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes, perinatal progressive decrease of the trisomy 7 cell line and a favorable fetal outcome

OBJECTIVE

We present low-level mosaic trisomy at amniocentesis in a pregnancy associated with cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes, perinatal progressive decrease of the trisomy 7 cell line and a favorable fetal outcome.

CASE REPORT

A 40-year-old, primigravid woman underwent amniocentesis at 16 weeks of gestation because of advanced maternal age. Amniocentesis revealed a karyotype of 46,XY in cultured amniocytes. Simultaneous array comparative genomic hybridization (aCGH) analysis on the DNA extracted from uncultured amniocytes revealed the result of arr (7) × 2-3, (X,Y) × 1, consistent with 24% mosaicism for trisomy 7. Polymorphic DNA marker analysis on the DNA extracted from the uncultured amniocytes and parental bloods excluded uniparental disomy (UPD) 7. Prenatal ultrasound findings were normal. She was referred for genetic counseling at 19 weeks of gestation. No repeat amniocentesis was suggested, and continuing the pregnancy was advised. At 22 weeks of gestation, the result of soluble fms-like tyrosine kinase-1 (sFlt-1)/placental growth factor (PlGF) = 6.1 (normal < 38). She did not have preeclampsia. At 39 weeks of gestation, a 3346-g male baby was delivered without any phenotypic abnormality. aCGH analysis on the DNA extracted from cord blood and placenta revealed the result of arr (1-22) × 2, (X,Y) × 1 with no genomic imbalance in all tissues. When follow-up at age three months, the baby was normal in development and phenotype. The peripheral blood had a karyotype of 46,XY, and interphase fluorescence in situ hybridization (FISH) analysis using the bacterial artificial chromosome (BAC) probes of chromosome 7 showed disomy 7 cells in all 102/102 cells.

CONCLUSION

Low-level mosaic trisomy 7 at amniocentesis can be associated with cytogenetic discrepancy between cultured amniocytes and uncultured amniocytes, perinatal progressive decrease of the trisomy 7 cell line and a favorable fetal outcome.

Prenatal diagnosis of a trisomy 7 mosaic case: CMA, CNV-seq, karyotyping, interphase FISH, and MS-MLPA, which technique to choose?

OBJECTIVE

This study aims to perform a prenatal genetic diagnosis of a high-risk fetus with trisomy 7 identified by noninvasive prenatal testing (NIPT) and to evaluate the efficacy of different genetic testing techniques for prenatal diagnosis of trisomy mosaicism.

METHODS

For prenatal diagnosis of a pregnant woman with a high risk of trisomy 7 suggested by NIPT, karyotyping and chromosomal microarray analysis (CMA) were performed on an amniotic fluid sample. Low-depth whole-genome copy number variation sequencing (CNV-seq) and fluorescence in situ hybridization (FISH) were used to clarify the results further. In addition, methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) was performed to analyze the possibility of uniparental disomy(UPD).

RESULTS

Amniotic fluid karyotype analysis revealed a 46, XX result. Approximately 20% mosaic trisomy 7 was detected according to the CMA result. About 16% and 4% of mosaicism was detected by CNV-seq and FISH, respectively. MS-MLPA showed no methylation abnormalities. The fetal ultrasound did not show any detectable abnormalities except for mild intrauterine growth retardation seen at 39 weeks of gestation. After receiving genetic counseling, the expectant mother decided to continue the pregnancy, and follow-up within three months of delivery was normal.

CONCLUSION

In high-risk NIPT diagnosis, a combination of cytogenetic and molecular genetic techniques proves fruitful in detecting low-level mosaicism. Furthermore, the exclusion of UPD on chromosome 7 remains crucial when NIPT indicates a positive prenatal diagnosis of trisomy 7.

Prenatal Diagnosis of Chromosomal Mosaicism in 18,369 Cases of Amniocentesis

OBJECTIVE

The prenatal diagnosis of chromosomal mosaicism is fraught with uncertainty. Karyotyping, chromosomal microarray analysis (CMA), and fluorescence in situ hybridization (FISH) are three commonly used techniques. In this study, we evaluated these techniques for the prenatal diagnosis of chromosomal mosaicism and its clinical outcome.

STUDY DESIGN

A retrospective review of mosaicism was conducted in 18,369 pregnant women from January 2016 to November 2021. The subjects underwent amniocentesis to obtain amniotic fluid for G-band karyotyping with or without CMA/FISH. Cases diagnosed with chromosomal mosaicism were selected for further analysis.

RESULTS

In total, 101 cases of chromosomal mosaicism were detected in 100 pregnant women (0.54%, 100/18,369). Four were lost during follow-up, 61 opted to terminate their pregnancy, and 35 gave birth to a healthy singleton or twins. Among these 35 cases, postnatal cytogenetic testing was performed on eight and two exhibited mosaicism; however, nothing abnormal was observed in the postnatal phenotype follow-up. Karyotyping identified 96 incidents of chromosomal mosaicism including 13 with level II mosaicism and 83 with level III mosaicism, FISH identified 37 cases of mosaicism, and CMA identified 17. The most common form of chromosomal mosaicism involved monosomy X, of which the mosaic fraction in cultured karyotyping appeared higher or comparable to uncultured FISH/CMA (p < 0.05). Discordant mosaic results were observed in 34 of 101 cases (33.7%), most of which resulted from the detection limit of different techniques and/or the dominant growth of a certain cell line.

CONCLUSION

Based on the postnatal follow-up results from the babies born, we obtained a more hopeful result for the prognosis of chromosomal mosaicism. Although karyotyping was the most sensitive method for detecting chromosomal mosaicism, artifacts and bias resulting from culture should be considered, particularly for sex chromosomal abnormalities involving X monosomy, in which the combination with uncultured FISH was necessary.

KEY POINTS

· Karyotyping combined with uncultured FISH or CMA is beneficial for prenatal diagnosis of chromosomal mosaicism.. · Fetuses without ultrasound structural anomalies with chromosomal mosaicism often have optimistic prognosis..

Pigmentary mosaicism: a review of original literature and recommendations for future handling

Background

Pigmentary mosaicism is a term that describes varied patterns of pigmentation in the skin caused by genetic heterogeneity of the skin cells. In a substantial number of cases, pigmentary mosaicism is observed alongside extracutaneous abnormalities typically involving the central nervous system and the musculoskeletal system. We have compiled information on previous cases of pigmentary mosaicism aiming to optimize the handling of patients with this condition. Our study is based on a database search in PubMed containing papers written in English, published between January 1985 and April 2017. The search yielded 174 relevant and original articles, detailing a total number of 651 patients.

Results

Forty-three percent of the patients exhibited hyperpigmentation, 50% exhibited hypopigmentation, and 7% exhibited a combination of hyperpigmentation and hypopigmentation. Fifty-six percent exhibited extracutaneous manifestations. The presence of extracutaneous manifestations in each subgroup varied: 32% in patients with hyperpigmentation, 73% in patients with hypopigmentation, and 83% in patients with combined hyperpigmentation and hypopigmentation. Cytogenetic analyses were performed in 40% of the patients: peripheral blood lymphocytes were analysed in 48%, skin fibroblasts in 5%, and both analyses were performed in 40%. In the remaining 7% the analysed cell type was not specified. Forty-two percent of the tested patients exhibited an abnormal karyotype; 84% of those presented a mosaic state and 16% presented a non-mosaic structural or numerical abnormality. In patients with extracutaneous manifestations, 43% of the cytogenetically tested patients exhibited an abnormal karyotype. In patients without extracutaneous manifestations, 32% of the cytogenetically tested patients exhibited an abnormal karyotype.

Conclusion

We recommend a uniform parlance when describing the clinical picture of pigmentary mosaicism. Based on the results found in this review, we recommend that patients with pigmentary mosaicism undergo physical examination, highlighting with Wood’s light, and karyotyping from peripheral blood lymphocytes and skin fibroblasts. It is important that both patients with and without extracutaneous manifestations are tested cytogenetically, as the frequency of abnormal karyotype in the two groups seems comparable. According to the results only a minor part of patients, especially those without extracutaneous manifestations, are tested today reflecting a need for change in clinical practice.

Electronic supplementary material

The online version of this article (10.1186/s13023-018-0778-6) contains supplementary material, which is available to authorized users.

Chromosomal Mosaicism in Human Feto-Placental Development: Implications for Prenatal Diagnosis

Chromosomal mosaicism is one of the primary interpretative issues in prenatal diagnosis. In this review, the mechanisms underlying feto-placental chromosomal mosaicism are presented. Based on the substantial retrospective diagnostic experience with chorionic villi samples (CVS) of a prenatal diagnosis laboratory the following items are discussed: (i) The frequency of the different types of mosaicism (confined placental, CPM, and true fetal mosaicisms, TFM); (ii) The risk of fetal confirmation after the detection of a mosaic in CVS stratified by chromosome abnormality and placental tissue involvement; (iii) The frequency of uniparental disomy for imprinted chromosomes associated with CPM; (iv) The incidence of false-positive and false-negative results in CVS samples analyzed by only (semi-)direct preparation or long term culture; and (v) The implications of the presence of a feto-placental mosaicism for microarray analysis of CVS and non-invasive prenatal screening (NIPS).

Structural genetic variation in the context of somatic mosaicism

Somatic mosaicism is the result of postzygotic de novo mutation occurring in a portion of the cells making up an organism. Structural genetic variation is a very heterogeneous group of changes, in terms of numerous types of aberrations that are included in this category, involvement of many mechanisms behind the generation of structural variants, and because structural variation can encompass genomic regions highly variable in size. Structural variation rapidly evolved as the dominating type of changes behind human genetic diversity, and the importance of this variation in biology and medicine is continuously increasing. In this review, we combine the evidence of structural variation in the context of somatic cells. We discuss the normal and disease-related somatic structural variation. We review the recent advances in the field of monozygotic twins and other models that have been studied for somatic mutations, including other vertebrates. We also discuss chromosomal mosaicism in a few prime examples of disease genes that contributed to understanding of the importance of somatic heterogeneity. We further highlight challenges and opportunities related to this field, including methodological and practical aspects of detection of somatic mosaicism. The literature devoted to interindividual variation versus papers reporting on somatic variation suggests that the latter is understudied and underestimated. It is important to increase our awareness about somatic mosaicism, in particular, related to structural variation. We believe that further research of somatic mosaicism will prove beneficial for better understanding of common sporadic disorders.

Infantile spasms and pigmentary mosaicism

We present a 3-year-old boy with pigmentary mosaicism and persistent intractable infantile spasms due to mosaicism of chromosome 7. Getting the diagnosis of pigmentary mosaicism in a child with infantile spasms may not be easy, as most diagnostic work-up is done in infancy, at a time when skin manifestations can be subtle. We stress the need for a meticulous search for an etiology in cases of infantile spasms. Diagnostic work-up should include a dermatologic evaluation with skin biopsies for fibroblast culture (and karyotyping) from abnormal pigmented skin areas.

aCGH detects partial tetrasomy of 12p in blood from Pallister-Killian syndrome cases without invasive skin biopsy

Pallister-Killian syndrome (PKS) is a genetic disorder characterized by mental retardation, seizures, streaks of hypo- or hyperpigmentation and dysmorphic features. PKS is associated with tissue-limited mosaic partial tetrasomy of 12p, usually caused by an isochromosome 12p. The mosaicism is usually detected in cultured skin fibroblasts or amniotic cells and rarely in phytohemagluttinin-stimulated lymphocytes, which suggests stimulation of T-lymphocytes may distort the percentage of abnormal cells. We recently reported on the identification by microarray-based comparative genomic hybridization (aCGH) of a previously unsuspected case of partial tetrasomy of 12p caused by an isochromosome 12p. Here we report on seven additional individuals with partial tetrasomy of 12p characterized by our laboratory. All individuals were referred for mental retardation/developmental delay and/or dysmorphic features. In each case, aCGH using genomic DNA extracted from whole peripheral blood detected copy-number gain for all clones for the short arm of chromosome 12. In all but one case, FISH on metaphases from cultured lymphocytes did not detect the copy-number gain; in the remaining case, metaphase FISH on cultured lymphocytes showed an isochromosome in 10% of cells. However, interphase FISH using probes to 12p on peripheral blood smears showed additional hybridization signals in 18-70% of cells. Microarray and FISH analysis on cultured skin biopsies from four individuals confirmed the presence of an isochromosome 12p. Our results demonstrate the usefulness of aCGH with genomic DNA from whole peripheral blood to detect chromosome abnormalities that are not present in stimulated blood cultures and would otherwise require invasive skin biopsies for identification.

Microarray-based CGH detects chromosomal mosaicism not revealed by conventional cytogenetics

Somatic chromosomal mosaicism is a well-established cause for birth defects, mental retardation, and, in some instances, specific genetic syndromes. We have developed a clinically validated, targeted BAC clone array as a platform for comparative genomic hybridization (aCGH) to enable detection of a wide range of pathologic copy number changes in DNA. It is designed to provide high sensitivity to detect well-characterized submicroscopic micro-deletion and duplication disorders while at the same time minimizing detection of variation of uncertain clinical significance. In the course of studying 2,585 samples submitted to our clinical laboratory, chromosomal mosaicism was detected in 12 patient samples; 10 of these cases were reported to have had a normal blood chromosome analysis. This enhanced ability of aCGH to detect mosaicism missed by routine chromosome analysis may be due to some combination of testing multiple cell lineages and/or failure of cytogenetically abnormal T lymphocytes to respond to mitogens. This suggests that aCGH may detect somatic chromosomal mosaicism that would be missed by conventional cytogenetics.

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.

Pigmentary mosaicism following the lines of Blaschko in a girl with a double aneuploidy mosaicism: (47,XX,+7/45,X)

We report on a 6-year-old girl with linear streaks of apparent hypopigmentation and hyperpigmentation following the Blaschko lines, growth retardation, bupthalmos of the left eye, and mild mental retardation. She had a 45,X karyotype in lymphocytes. In cultured fibroblasts a double aneuploidy mosaicism was detected, consisting of a cell line with trisomy for chromosome 7 and a cell line with monosomy for the X-chromosome and no cell line with a normal karyotype. Cutis tricolor or three levels of pigmentation in different skin areas suggested presence of a third, probably normal cell line. Double aneuploidy mosaicism of a cell line with monosomy X and a cell line with trisomy of an autosome is a rare finding. The combination of monosomy X with trisomy of chromosomes 8, 10, 13, 18, and 21 has been reported, but not the combination with trisomy 7. In the 45,X cell line, microsatellite analysis showed loss of the maternal X-chromosome, and presence of a maternal and paternal chromosome 7. The 47,XX,+7 cell line showed a paternal and a maternal X-chromosome, and a paternal and two identical maternal chromosomes 7. Mechanisms that might explain this double aneuploidy mosaicism are discussed.

Clinical outcome and follow-up of the first reported case of Russell-Silver syndrome with the unique combination of maternal uniparental heterodisomy 7 and mosaic trisomy 7

BACKGROUND

Russell-Silver syndrome (RSS) has been associated with maternal uniparental disomy (UPD) for chromosome 7 although the etiology of the syndrome is still unknown. Cases of RSS associated with maternal UPD7 have involved isodisomies, heterodisomies, and mixed isodisomy with heterodisomy simultaneously. This publication is a follow-up report of the postnatal clinical outcome of the first prenatally suspected case of combined mosaic trisomy 7 with maternal uniparental disomy of chromosome 7 (UPD7).

CASE

The diagnosis of RSS in the proband was suspected prenatally because trisomy 7 mosaicism (47,XX,+7[13]/46,XX[19]) and maternal uniparental heterodisomy 7 were both found in amniotic fluid cells. Cord blood karyotype analysis showed only disomic cells (46,XX[50]), whereas postpartum chorionic villus analysis was completely trisomic for chromosome 7 (47,XX,+7[19]). Postnatally, the diagnosis of RSS was confirmed by physical findings, her trisomy 7 mosaicism was confirmed by cytogenetic analysis of her skin biopsy (47,XX,+7[9]/46,XX[20]) and her UPD7 was confirmed on both peripheral blood and skin biopsy using microsatellite markers. During infancy, the proband experienced growth deficiency, persistent hypoglycemia, and psychomotor developmental delay.

CONCLUSIONS

Trisomic rescue as a life-saving mechanism, with subsequent chromosomal mosaicism in combination with UPD may occur more frequently in RSS than has been reported. Systematic testing of cases suspected prenatally or postnatally would be informative regarding the individual contribution of each factor. Imprinting, loss of heterozygosity for recessive genes, and mosaicism may explain the short stature, asymmetry, and the variable expression of the phenotype. The contribution of these mechanisms to the syndrome should be evaluated in these cases.

Mosaic trisomy 15 in a short girl with hemihypotrophy and mental retardation

We describe a girl with short stature, mild mental retardation, hemihypotrophy, atrial septal defect I, bilateral branchial cleft fistulas and abnormal skin pigmentation. Growth hormone deficiency and other frequent causes of short stature were excluded. Blood karyotype was investigated twice. In one sample an additional marker chromosome was found in one of 53 analysed metaphases, which could not be further characterized, whereas a second investigation showed a normal female karyotype. Cytogenetic studies in skin fibroblasts revealed a mosaic trisomy 15. Although mosaic trisomy 15 is a rare finding the diagnosis must be considered in the presence of pigmentary changes, body asymmetry, short stature and other minor dysmorphic signs even if blood karyotype is normal.

Mosaic trisomy 15 and hemihypertrophy

We report a case of mosaic trisomy 15 with mental retardation, facial dysmorphism, and hemihypertrophy, but no manifestations of Prader-Willi or Angelman syndromes. Mosaic trisomy 15 (11%) was discovered at the amniocentesis. Uniparental disomy for chromosome 15 was excluded by molecular analysis. Post-natal blood karyotype and examination were normal. Mosaic was confirmed on skin fibroblasts, placenta and cord. Evolution was marked by progressive right hemi-hypertrophy, and developmental delay. Our case is the first patient reported with hemihypertrophy associated with mosaic trisomy 15. The relevant literature is reviewed.

Hypomelanosis of ito and a 'mirror image' whole chromosome duplication resulting in trisomy 14 mosaicism

We describe a female infant with multiple congenital anomalies including unusual hyperpigmentation, tetralogy of Fallot, absent corpus callosum and wide prominent nasal bridge. The infant was initially seen for genetic consultation on day one after birth. Chromosome analysis from cultured lymphocytes showed a normal 46,XX karyotype. However, cultured skin fibroblasts showed mosaicism with 46,XX,add(14)(q32).ish psu dic dup(14)(q32p13)(wcp14+)/46,XX complements. A review of the published report with chromosome mosaicism and hypomelanosis of Ito (HMI) is included. We suggest that the trisomy 14 mosaicism seen in fibroblast cultures has importance in the expression of pigmentation dysplasias in this patient. Pigmentary anomaly may be due to loss or gain of specific genes that influence pigmentation located on the long arm of chromosome 14 in this patient.