CCMG guidelines: prenatal and postnatal diagnostic testing for uniparental disomy

Chromosomal microarray analysis for prenatal diagnosis of uniparental disomy: a retrospective study

BACKGROUND

Chromosomal microarray analysis (CMA) is a valuable tool in prenatal diagnosis for the detection of chromosome uniparental disomy (UPD). This retrospective study examines fetuses undergoing invasive prenatal diagnosis through Affymetrix CytoScan 750 K array analysis. We evaluated both chromosome G-banding karyotyping data and CMA results from 2007 cases subjected to amniocentesis.

RESULTS

The detection rate of regions of homozygosity (ROH) ≥ 10 Mb was 1.8% (33/2007), with chromosome 11 being the most frequently implicated (17.1%, 6/33). There were three cases where UPD predicted an abnormal phenotype based on imprinted gene expression.

CONCLUSION

The integration of UPD detection by CMA offers a more precise approach to prenatal genetic diagnosis. CMA proves effective in identifying ROH and preventing the birth of children affected by imprinting diseases.

Prenatal diagnosis and genetic etiology analysis of talipes equinovarus by chromosomal microarray analysis

BACKGROUND

With the advancement of molecular technology, fetal talipes equinovarus (TE) is believed to be not only associated with chromosome aneuploidy, but also related to chromosomal microdeletion and microduplication. The study aimed to explore the molecular etiology of fetal TE and provide more information for the clinical screening and genetic counseling of TE by Chromosomal Microarray Analysis (CMA).

METHODS

This retrospectively study included 131 fetuses with TE identified by ultrasonography. Conventional karyotyping and SNP array analysis were performed for all the subjects. They were divided into isolated TE group (n = 55) and complex group (n = 76) according to structural anomalies.

RESULTS

Among the total of 131 fetuses, karyotype analysis found 12(9.2%) abnormal results, while SNP array found 27 (20.6%) cases. Trisomy 18 was detected most frequently among abnormal karyotypes. The detection rate of SNP array was significantly higher than that of traditional chromosome karyotype analysis (P < 0.05). SNP array detected 15 (11.5%) cases of submicroscopic abnormalities that karyotype analysis did not find. The most common CNV was the 22q11.2 microdeletion. For both analyses, the overall detection rates were significantly higher in the complex TE group than in the isolated TE group (karyotype: P < 0.05; SNP array: P < 0.05). The incremental yield of chromosomal abnormalities in fetuses with unilateral TE (22.0%) was higher than in fetuses with bilateral TE (19.8%), but this difference was not statistically significant (P > 0.05). Abnormal chromosomes were most frequently detected in fetuses with TE plus cardiovascular system abnormalities.

CONCLUSION

Fetal TE is related to chromosomal microdeletion or microduplication. Prenatal diagnosis is recommended for fetuses with TE, and CMA testing is preferred. CMA can improve the detection rate of chromosomal abnormalities associated with fetal TE, especially in pregnancies with complex TE.

Prenatal diagnosis of genetic aberrations in fetuses with short femur detected by ultrasound: A prospective cohort study

OBJECTIVES

To investigate the genetic aberrations in fetuses with short femur and explore the relationships with respect to degree of femoral shortening and the initial diagnostic gestational age GA.

METHODS

Singleton pregnancies with fetal short femur who consented to amniocentesis and to single nucleotide polymorphism (SNP) array and Sanger sequencing for G380R mutations in FGFR3 gene were enrolled in this 5-year period prospective study. Clinical follow-up assessments were performed after birth.

RESULTS

Of a total of 161 fetuses, the prevalence of genetic aberrations was 16.2% (26/161), comprised of 65.4% (17/26) with chromosomal abnormalities and 34.6% (9/26) with G380R mutations. All fetuses with chromosomal abnormalities had FL 2-4SDs below GA. Fewer chromosomal abnormalities were detected in fetuses with short femurs presenting in the third trimester. Significantly more FGFR3 mutations were detected in fetuses with FL below -4SDs. All fetuses with FL 2-4SDs below GA diagnosed as achondroplasia were between 22 and 24 gestational weeks, and all of those diagnosed in third trimester had FL below -4SDs.

CONCLUSION

In this small cohort study, we demonstrated that different degrees of femur shortness may be attributed to different genetic aberrations. SNP array should be regarded as the first-tier test for fetuses with FL 2-4SDs below GA. The prognoses for fetuses with FL 2-4SDs below GA was significantly better than those with FL below 4SDs.

Prenatal diagnosis of mosaic trisomy 2 and literature review

Background

We presented two cases of mosaic trisomy 2 with high risk of maternal serum screening and non-invasive prenatal testing (NIPT). The invasive amniocentesis was performed and genetic tests including karyotype, single nucleotide polymorphism array(SNP-array), interphase fluorescence in situ hybridization (FISH) were employed to detect the chromosomal abnormality.

Results

Cytogentic analysis of the case 1 and 2 showed a mosaic karyotype consisting of two cell lines (mos 47,XY,+2[8]/46,XY[19] and mos 47,XX,+2[7]/46,XX[28], respectively). SNP-array using DNA extracted from uncultured amniotic fluid cells revealed a result of arr[GRCh38](2)x2~3, which indicated that chromosome 2 may be trisomy of mosaicism in both two cases. The results of interphases FISH confirmation test showed that three red signals of the CEP 2 specific probe in 14%(14/100) and 12%(12/100) of the two cases’ cells, respectively, which indicated a mosaicism for trisomy 2 in the uncultured amniocytes. Fetal ultrasound of case 1 suggested that the long bone is smaller than the gestational age, while the case 2 showed that the biparietal diameter (BPD), head circumference (HC) and femur length (FL) were smaller than gestational age along with abnormal cardiac structure.

Conclusions

We presented two cases with mosaic trisomy 2 and performed confirmatory genetic testing using cultured and uncultured amniocytes. When maternal serum screening and NIPT suggesting high risk, genetic counselor should be alert for increasing possibility of chromosomal anomalies if combined with abnormal ultrasound findings.

Impact of preimplantation genetic testing for aneuploidy on obstetrical practice

PURPOSE OF REVIEW

To provide updated information on preimplantation genetic testing for aneuploidy (PGT-A), focusing on its implications on prenatal diagnostic approaches after transferal of mosaic aneuploid embryos.

RECENT FINDINGS

PGT-A is a technology to screen for chromosome aneuploidy or major chromosome structural rearrangement in embryos before implantation using different cytogenetic analyses. PGT-A has been shown to reduce the negative effect of increasing maternal age on in-vitro fertilization (IVF) outcomes. PGT-A also encourages clinicians and patients to accept single embryo transfer after IVF-PGT-A to reduce the chance of multiple pregnancies. However, mosaic aneuploid embryo may be encountered following PGT-A. Recent discussions have focused on the consideration of transferal of mosaic aneuploid embryos in couples with no euploid embryo following multiple trials of IVF-PGT-A. A risk score for each chromosome has been developed to prioritize which mosaic embryos should be considered for transfer. However, there is a lack of long-term outcome data following mosaic aneuploid embryo transfer.

SUMMARY

Recent advances in PGT-A increase the detection of embryos with mosaicism, which is associated with an increased risk of miscarriage, fetal mosaic aneuploidy, and uniparental disomy. Strategy in prenatal diagnostic testing after mosaic aneuploid embryo transfer is discussed in this review.

Genetic syndromes associated with isolated fetal growth restriction

Early onset fetal growth restriction (FGR) may be due to impaired placentation, environmental or toxic exposure, congenital infections or genetic abnormalities. Remarkable research, mainly based on retrospective series, has been published on the diverse genetic causes. Those have become more and more relevant with the improvement in the accuracy of the analysis techniques and the rising of breakthrough genomewide methods such as the whole genome sequencing. However, no publication has presented an integrated view of management of those fetuses with an early and severe affection. In this review, we explored to which extent genetic syndromes can cause FGR fetuses without structural defects. The most common chromosomal abnormalities (Triploidies and Trisomy 18), submicroscopic chromosomal anomalies (22q11.2 microduplication syndrome) and single gene disorders (often associated with mild ultrasound findings) related to early and severe FGR had been analysed. Finally, we addressed the impact of epigenetic marks on fetal growth, a matter of growing importance. At the end of this review, we should be able to provide an adequate counseling to parents in terms of diagnosis, prognosis and management of those pregnancies.

Paternal uniparental disomy for chromosome 14: prenatal management

We present a case of a 34-year-old multiparous woman who had been diagnosed with a 14 weeks' gestation showing an abdominal wall bulge possibly representing an omphalocele, containing liver and intestinal loops, at her first-trimester ultrasound scan. At 16 weeks' gestation, an amniocentesis was performed and karyotype analysis revealed a balanced Robertsonian translocation between chromosomes 13 and 14 in a female fetus (45,XX,der(13;14)(q10;q10)). Given this result and ultrasound findings, karyotype and molecular study of the couple were suggested. The results pointed out the absence of maternal contribution to the analysed regions by paternal uniparental disomy for chromosome 14 (isodisomy), which is associated with a severe phenotype. The correlation between ultrasound findings and the genetic study is primordial to guide the diagnostic assessment and to establish the prognosis of the fetal pathology.

The mechanisms and clinical application of mosaicism in preimplantation embryos

Embryos containing distinct cell lines are referred to as mosaic embryos, which are considered to be caused by mitotic errors in chromosome segregation during preimplantation development. As the accuracy and resolution of detection techniques improve, more and more mosaic embryos were identified recently. The impacts of mosaic embryos on survival and potential pregnancy outcome have been reported to be diverse in different studies. Because of the universality and clinical significance of mosaicism, it is essential to unravel the mechanisms and consequences with regard to this phenomenon in human pre- and post-implantation embryos. The purpose of this review is to explore the mechanisms, causes of mosaicism, and the development of pre- and post-implantation mosaic embryos in the light of recent emerging data, with the aim of providing new references for clinical applications.

Segmental uniparental disomy of chromosome 4 in a patient with methylmalonic acidemia

BACKGROUND

Methylmalonic acidemia (MMA) is an autosomal recessive genetic disorder involving the metabolism of organic acids.

METHODS

Here, we report the case of a patient who developed acute metabolic crisis after vaccination and was diagnosed with cblA type MMA after hospitalization.

RESULTS

Further examination revealed a homozygous pathogenic variant in the MMAA gene that caused the disease in the patient but did not conform to Mendelian inheritance. Using chromosomal microarray analysis, maternal uniparental disomy (UPD) was found on chromosome 4q26-q35.2 of the patient. The MMAA gene of the patient was inherited only from the mother and carried the same pathogenic variant on both alleles of chromosome 4. MMAA gene expression levels in whole blood were detected by real-time PCR.

CONCLUSION

The nonsense pathogenic variant, NM_172250.2:c.742C>T (p.Gln248*), carried by the patient leads to a premature termination of transcription of the gene, thereby resulting in partial loss of protein function while retaining some others. Segmental UPD 4 is rare, and to our knowledge, has not been reported previously.

Methodological quality of clinical practice guidelines for genetic testing in children: A systematic assessment using the appraisal of guidelines for research and evaluation II instrument

Genetic testing of children is faced with numerous problems. High-quality clinical practice guidelines (CPGs) are needed to ensure its safe, and appropriate use. This study aimed to systematically identify the current CPGs for genetic testing in children, and to assess the methodological quality of these CPGs.We searched 6 databases, 3 guideline clearinghouses, and 9 web sites of relevant academic agencies from inception to February 2019. CPGs focused on genetic testing in children were included. Four reviewers independently appraised the quality of the eligible CPGs using the appraisal of guidelines for research, and evaluation (AGREE) II instrument.Seventeen CPGs meeting our inclusion criteria were included. Among them, 16 CPGs were focused on the genetic diagnosis/evaluation of diseases, while only 1 CPG was focused on pharmacogenetics. The median domain scores from highest to lowest were: scope and purpose 80.56% (range: 56.95%-87.50%), clarity of presentation 72.22% (range: 45.83%-88.89%), stakeholder involvement 45.83% (range: 27.78%-55.56%), applicability 31.25% (range: 19.79%-54.17%), rigor of development 21.88%, (range: 13.02%-71.88%), and editorial independence 18.75% (range: 0%-83.33%). According to the overall quality, 6 (35%) CPGs were "not recommended," 8 (47%) CPGs were "recommended with modifications," and only 3 (18%) CPGs were "recommended." The clinical topics of the "recommended" CPGs were warfarin, familial Mediterranean fever, and pediatric pulmonary arterial hypertension.The quality of CPGs for genetic testing in children was generally low, and variable across different CPGs and different AGREE II domains. In future guideline development, more attention should be paid to the aspects of stakeholder involvement, rigor of development, applicability, and editorial independence. Not only will guideline users benefit from our results when determining whether to adopt related CPGs to guide genetic testing in children, but guideline developers could also take into account our results to improve the quality of future CPGs.

Rare autosomal trisomies: comparison of detection through cell-free DNA analysis and direct chromosome preparation of chorionic villus samples

OBJECTIVE

Direct chromosome preparations of chorionic villus samples (CVS) and cell-free DNA (cfDNA) testing both involve analysis of the trophoblastic cell lineage. The aim of this study was to compare the spectrum of rare autosomal trisomies (RATs) detected by these two approaches and assess the available information on their clinical significance.

METHODS

Data from 10 reports on genome-wide cfDNA testing were pooled to determine which chromosomes were most frequently involved in RAT-positive cases, and pregnancy outcome information was reviewed. CVS information was obtained from an updated database of 76 102 consecutive CVS analyses performed over a period of 18 years at TOMA laboratory, in which trophoblastic and mesenchymal layers were analyzed and amniotic fluid cell analysis was recommended for RAT-positive cases. Chromosomes involved and presence of confined placental mosaicism, true fetal mosaicism and uniparental disomy (UPD) for imprinted chromosomes were assessed. Also evaluated were the frequency and types of RATs in products of conception.

RESULTS

RATs were present in 634 of 196 662 (0.32%) cfDNA samples and 237 of 57 539 (0.41%) CVS trophoblast samples (P < 0.01). The frequency of RATs varied over 8-fold between the cfDNA reports. Confirmation of abnormality through amniocentesis was more likely when RATs were ascertained through cfDNA (14 of 151; 9.3%) than through CVS trophoblasts (seven of 237; 3.0%) (P < 0.01). In cfDNA-ascertained cases, trisomies 15, 16 and 22, which are associated with fetal loss, were identified proportionately more often. Of 151 cases with RAT identified by cfDNA and outcome information available, 41.1% resulted in normal live birth; 27.2% in fetal loss; 7.3% had phenotypic abnormality detected through ultrasound or other follow-up evaluation; 2.0% had a clinically significant UPD; and 14.6% had fetal growth restriction or low birth weight. All autosomes were involved in trisomies in products of conception; the most common RATs detected were trisomies 16, 22 and 15 with a frequency of > 9% each.

CONCLUSIONS

Although there are strong parallels between RATs ascertained through cfDNA analysis and direct chromosome preparation of CVS, caution is needed in applying conclusions from CVS analysis to cfDNA testing, and vice versa. RATs identified through genome-wide cfDNA tests have uncertain risks for fetal loss, growth restriction or fetal abnormality. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.

Prognosis for pregnancies with trisomy 16 confined to the placenta: A Danish cohort study

OBJECTIVE

To evaluate the risk of adverse pregnancy outcome when trisomy 16 confined to the placenta is diagnosed and to identify possible prognostic markers for adverse outcomes in these pregnancies.

METHOD

Registered cases (n = 49) of trisomy 16 diagnosed prenatally in Denmark from 1990 to 2013 were included.

RESULTS

Twenty-five of the pregnancies intended to be continued had confined placental trisomy 16 mosaicism (CPM16). Adverse pregnancy outcome was seen in 17 CPM16 pregnancies (68%), ranging from mild small for gestational age (SGA) to fetal malformations and intrauterine demise. For cases ascertained by combined first trimester screening, the median concentration of pregnancy associated plasma protein A (PAPP-A) was 0.17 MoM (IQR: 0.11 MoM). Adverse pregnancy outcome showed a trend toward an association with a high frequency of trisomic cells. Eight children (32%) were born at term with a normal birth weight and no malformations.

CONCLUSION

The risk of adverse pregnancy outcome in case of CPM16 is correlated to ascertainment by combined first trimester screening and tends to be associated with a high frequency of trisomic cells in the placenta. We recommend that variables including ascertainment, the frequency of trisomic cells, and the maternal serum concentration of PAPP-A are taken into consideration when evaluating the prognosis in CPM16 while acknowledging that these factors are strongly correlated.

Uniparental disomy as a cause of pediatric endocrine disorders

Uniparental disomy (UPD) refers to a condition in which two homologous chromosomes or chromosomal regions are inherited from one parent. Recent studies have shown that UPD is not rare among the general population, arising from trisomy rescue, gamete complementation, and other mechanisms. Although UPD is not necessarily pathogenic, it can lead to various disease phenotypes by causing imprinting disorders or by unmasking autosomal recessive mutations. Notably, known UPD-mediated autosomal recessive disorders include congenital adrenal hyperplasia due to 21-hydroxylase deficiency, 11β-hydroxylase deficiency, and 3β-hydroxysteroid dehydrogenase deficiency. In addition, UPD can occur in combination with additional cytogenetic abnormalities that may affect growth and development. Therefore, UPD represents a clinically important condition that accounts for a certain percentage of the etiology of growth failure and endocrine abnormalities. Although UPD is barely detectable by standard karyotyping or sequence analyses, it can be screened by single nucleotide polymorphism- and microsatellite-genotyping of patients and their parents, or by DNA methylation analysis of the patients. This mini-review introduces the underlying mechanisms and phenotypic consequences of UPD in association with pediatric endocrine disorders.

Predicting fetoplacental chromosomal mosaicism during non-invasive prenatal testing

OBJECTIVE

Non-invasive prenatal detection of aneuploidies can be achieved with high accuracy through sequencing of cell-free maternal plasma DNA in the maternal blood plasma. However, false positive and negative non-invasive prenatal testing (NIPT) results remain. Fetoplacental mosaicism is the main cause for false positive and false negative NIPT. We set out to develop a method to detect placental chromosomal mosaicism via genome-wide circulating cell-free maternal plasma DNA screening.

METHOD

Aneuploidy detection was combined with fetal fraction determination to enable the detection of placental mosaicism. This pipeline was applied to whole genome sequencing data derived from 19 735 plasma samples. Following an abnormal NIPT, test results were validated by conventional invasive prenatal or postnatal genetic testing.

RESULTS

Respectively 3.2% (5/154), 12.8% (5/39), and 13.3% (2/15) of trisomies 21, 18, and 13 were predicted and confirmed to be mosaic. The incidence of other, rare autosomal trisomies was ~0.3% (58/19,735), 45 of which were predicted to be mosaic. Twin pregnancies with discordant fetal genotypes were predicted and confirmed.

CONCLUSION

This approach permits the non-invasive detection of fetal autosomal aneuploidies and identifies pregnancies with a high risk of fetoplacental mosaicism. Knowledge about the presence of chromosomal mosaicism in the placenta influences risk estimation, genetic counseling, and improves prenatal management.

Uniparental disomy and prenatal phenotype: Two case reports and review

RATIONALE

Uniparental disomy (UPD) gives a description of the inheritance of both homologues of a chromosome pair from the same parent. The consequences of UPD depend on the specific chromosome/segment involved and its parental origin.

PATIENT CONCERNS

We report prenatal phenotypes of 2 rare cases of UPD.

DIAGNOSES

The prenatal phenotype of case 1 included sonographic markers such as enlarged nuchal translucency (NT), absent nasal bone, short femur and humerus length, and several structural malformations involving Dandy-Walker malformation and congenital heart defects. The prenatal phenotype of Case 2 are sonographic markers, including enlarged NT, thickened nuchal fold, ascites, and polyhydramnios without apparent structural malformations.

INTERVENTIONS

Conventional G-band karyotype appears normal in case 1, while it shows normal chromosomes with a small supernumerary marker chromosome (sSMC) in case 2. Genetic etiology was left unknown until single-nucleotide polymorphism-based array (SNP-array) was performed, and segmental paternal UPD 22 was identified in case 1 and segmental paternal UPD 14 was found in case 2.

OUTCOMES

The parents of case 1 chose termination of pregnancy. The neonate of case 2 was born prematurely with a bellshaped small thorax and died within a day.

LESSONS

UPD cases are rare and the phenotypes are different, which depend on the origin and affected chromosomal part. If a fetus shows multiple anomalies that cannot be attributed to a common aneuploidy or a genetic syndrome, or manifests some features possibly related to an UPD syndrome, such as detection of sSMC, SNP-array should be considered.

Mosaic partial pericentromeric trisomy 8 and maternal uniparental disomy in a male patient with autism spectrum disorder

Various chromosomal anomalies including small supernumerary marker chromosome (sSMC) and Uniparental disomy (UPD) have been described in association with intellectual disability and autism spectrum disorder. Based on our reported findings, we recommend that patients with sSMC(8) be evaluated for autism spectrum disorder (ASD) for early institution of therapy. In the presence of an identifiable sSMC, exploration of UPD is also recommended to further investigate the role of chromosome 8 UPD in ASD.

Prenatal diagnosis of complete maternal uniparental isodisomy of chromosome 4 in a fetus without congenital abnormality or inherited disease-associated variations

Background

The prenatal diagnosis of subjects with complete uniparental isodisomy of chromosome 4 (iUPD4) has rarely been reported and poses a great challenge for genetic counseling. In this study, a prenatal case with a high (1 in 58) risk of Down syndrome was diagnosed with iUPD4 by combined chromosomal microarray analysis (CMA), whole exome sequencing (WES) and ultrasound morphology scan.

Results

By CMA, a pathogenic copy number variant was not detected; however, a complete maternal iUPD4 was identified in this fetus after analyzing the parental genotype results. To detect potentially autosomal recessive variants, WES was performed. Two missense and two frameshift variants were identified but were predicted with uncertain significance; none of the mutations were definitively associated with congenital abnormality or inherited disease. In addition, a detailed ultrasound morphology scan did not identify any structural abnormalities, facial dysmorphisms or intrauterine growth restriction. The family history was unremarkable. The couple was counseled with the prenatal diagnostic results, and they opted to give birth to the child. No phenotypic abnormalities were observed in this child after the first year of life.

Conclusion

This study provides further evidence that iUPD4 can result in a healthy live birth and demonstrates that the combined use of CMA, WES and ultrasound technology provides additional information for the prenatal diagnosis and clinical management of rare UPD events.

Electronic supplementary material

The online version of this article (doi:10.1186/s13039-015-0190-z) 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).

Uniparental disomy in Robertsonian translocations: strategies for uniparental disomy testing

Robertsonian translocations (ROBs) are whole arm rearrangements involving the acrocentric chromosomes 13-15 and 21-22 and carriers are at increased risk for aneuploidy and thus uniparental disomy (UPD). Chromosomes 14 and 15 are imprinted with expression of genes dependent on the parental origin of the chromosome. Correction of a trisomic or monosomic conceptus for chromosomes 14 or 15 would lead to one of the established UPD 14mat/pat or UPD 15 (Prader-Willi/Angelman) syndromes (PWS/AS). In view of this, prenatal UPD testing should be considered for balanced carriers of a ROB, fetuses with a familial or de novo balanced ROB that contains chromosome 14 or 15 or with a normal karyotype when a parent is a carrier of a balanced ROB with a 14 or 15. Individuals with congenital anomalies and an abnormal phenotype and carry a ROB involving the two imprinted chromosomes should also be UPD tested.

Phenotypic spectrum in uniparental disomy: Low incidence or lack of study?

CONTEXT

Alterations in the human chromosomal complement are expressed phenotypically ranging from (i) normal, via (ii) frequent fetal loss in otherwise normal person, to (iii) sub-clinical to severe mental retardation and dysmorphism in live births. A subtle and microscopically undetectable chromosomal alteration is uniparental disomy (UPD), which is known to be associated with distinct birth defects as per the chromosome involved and parental origin. UPD can be evident due to imprinted genes and/or activation of recessive mutations.

AIMS

The present study comprises of data mining of published UPD cases with a focus on associated phenotypes. The goal was to identify non-random and recurrent associations between UPD and various genetic conditions, which can possibly indicate the presence of new imprinted genes.

SETTINGS AND DESIGN

Data mining was carried out using the homepage "http://www.fish.uniklinikum-jena.de/UPD.html.", an online catalog of published cases with UPD.

MATERIALS AND METHODS

The UPD cases having normal karyotype and with or without clinical findings were selected to analyze the associated phenotypes for each chromosome, maternal or paternal involved in UPD.

RESULTS

Our results revealed many genetic conditions (other than the known UPD syndromes) to be associated with UPD. Even in cases of bad obstetric history as well as normal individuals chance detection of UPD has been reported.

CONCLUSIONS

The role of UPD in human genetic disorders needs to be studied by involving larger cohorts of individuals with birth defects as well as normal population. The genetic conditions were scrutinized in terms of inheritance patterns; majority of these were autosomal recessive indicating the role of UPD as an underlying mechanism.

Genetic basis of single-suture synostoses: genes, chromosomes and clinical implications

BACKGROUND

Non syndromic craniosynostoses are the most frequent craniofacial malformations worldwide. They represent a wide and heterogeneous group of entities, in which the dysmorphism may occur in a single (simple forms) or in multiple sutures (complex forms). Simple forms present a higher birth prevalence and are classified according to the involved suture and to the corresponding abnormal cranial shape: scaphocephaly (SC; sagittal suture), trigonocephaly (TC; metopic suture), anterior plagiocephaly (unilateral coronal suture), posterior plagiocephaly (unilateral lambdoid suture). They occur commonly as sporadic forms, although a familiar recurrence is sometimes observed, suggesting a mendelian inheritance. The genetic causes of simple craniosynostosis are still largely unknown, as mutations in common craniosynostosis-associated genes and structural chromosomal aberrations have been rarely found in these cases.

AIMS

This review is intended to dissect comprehensively the state-of-the art on the genetic etiology of single suture craniosynostoses, in the attempt to categorize all known disease-associated genes and chromosomal aberrations. Possible genotype/phenotype correlations are discussed as useful clues towards the definition of optimized clinical management flowcharts.