Genotype-phenotype dilemma in a case of sudden cardiac death with the E1053K mutation and a deletion in the SCN5A gene

Mutations in the cardiac sodium channel gene SCN5A may result in various arrhythmia syndromes such as long QT syndrome type 3 (LQTS), Brugada syndrome (BrS), sick sinus syndrome (SSS), cardiac conduction diseases (CCD) and possibly dilated cardiomyopathy (DCM). In most of these inherited cardiac arrhythmia syndromes the phenotypical expression may range from asymptomatic phenotypes to sudden cardiac death (SCD). A 16-year-old female died during sleep. Autopsy did not reveal any explanation for her death and a genetic analysis was performed. A variant in the SCN5A gene (E1053K) that was previously described as disease causing was detected. Family members are carriers of the same E1053K variant, some even in a homozygous state, but surprisingly did not exhibit any pathological cardiac phenotype. Due to the lack of genotype-phenotype correlation further genetic studies were performed. A novel deletion in the promoter region of SCN5A was identified in the sudden death victim but was absent in other family members. These findings demonstrate the difficulties in interpreting the results of a family-based genetic screening and underline the phenotypic variability of SCN5A mutations.

Exome sequencing identifies mutations in KIF14 as a novel cause of an autosomal recessive lethal fetal ciliopathy phenotype

Gene discovery using massively parallel sequencing has focused on phenotypes diagnosed postnatally such as well-characterized syndromes or intellectual disability, but is rarely reported for fetal disorders. We used family-based whole-exome sequencing in order to identify causal variants for a recurrent pattern of an undescribed lethal fetal congenital anomaly syndrome. The clinical signs included intrauterine growth restriction (IUGR), severe microcephaly, renal cystic dysplasia/agenesis and complex brain and genitourinary malformations. The phenotype was compatible with a ciliopathy, but not diagnostic of any known condition. We hypothesized biallelic disruption of a gene leading to a defect related to the primary cilium. We identified novel autosomal recessive truncating mutations in KIF14 that segregated with the phenotype. Mice with autosomal recessive mutations in the same gene have recently been shown to have a strikingly similar phenotype. Genotype-phenotype correlations indicate that the function of KIF14 in cell division and cytokinesis can be linked to a role in primary cilia, supported by previous cellular and model organism studies of proteins that interact with KIF14. We describe the first human phenotype, a novel lethal ciliary disorder, associated with biallelic inactivating mutations in KIF14. KIF14 may also be considered a candidate gene for allelic viable ciliary and/or microcephaly phenotypes.

Deletion in Xp22.11: PTCHD1 is a candidate gene for X-linked intellectual disability with or without autism

Submicroscopic chromosomal anomalies play an important role in the aetiology of intellectual disability (ID) and have been shown to account for up to 10% of non-syndromic forms. We present a family with two affected boys compatible with X-linked inheritance of a phenotype of severe neurodevelopmental disorder co-segregating with a deletion in Xp22.11 exclusively containing the PTCHD1 gene. Although the exact function of this gene is unknown to date, the structural overlap of its encoded patched domain-containing protein 1, the transmembrane protein involved in the sonic hedgehog pathway, and its expression in human cortex and cerebellum as well as in mice and drosophila brain suggests a causative role of its nullisomy in the developmental phenotype of our family. Our findings support the recent notions that PTCHD1 may play a role in X-linked intellectual disability (XLID) and autism disorders.

Dihydropyrimidine dehydrogenase deficiency caused by a novel genomic deletion c.505_513del of DPYD

Dihydropyrimidine dehydrogenase (DPD) deficiency is an autosomal recessive disorder of the pyrimidine degradation pathway. In a patient presenting with convulsions, psychomotor retardation and Reye like syndrome, strongly elevated levels of uracil and thymine were detected in urine. No DPD activity could be detected in peripheral blood mononuclear cells. Analysis of the gene encoding DPD (DPYD) showed that the patient was homozygous for a novel c.505_513del (p.169_171del) mutation in exon 6 of DPYD.

[New options in prenatal and preimplantation diagnosis of genetic disorders]

During recent years the progress with the most important practical impact in prenatal diagnosis has been the implementation of first trimester risk screening for common aneuploidies leading to a much improved identification of pregnancies at risk. Molecular methods for a rapid, cost-effective, but selective aneuploidy diagnosis such as interphase FISH or QF-PCR have been around for years, do have their specific indications, but will unlikely replace conventional cytogenetic tools in routine diagnosis. They apparently do also play a role as marketing instruments in the competition among cytogenetic laboratories. The most thrilling issue for all cytogeneticists in the years to come will be the introduction of array-based methods in the prenatal routine diagnosis of chromosomal abnormalities. Polar body diagnosis has been the only option available for preimplantation genetic diagnosis in german speaking countries. The overwhelming majority of all professionals involved and many families concerned share the hope that the legal situation will improve in these countries to allow the examination of early embryos in high risk situations.

Neue Möglichkeiten in der pränatalen Diagnostik

Mit den technischen Entwicklungen erweiterten sich in den letzten Jahren die Einsatzmöglichkeiten des pränatalen Ultraschalls. So konnten in den 80er und 90er-Jahren zunehmend fetale Fehlbildungen diagnostiziert und spezifiziert werden. Die Untersuchung mit der sonographischen Nackentransparenzmessung in der 11. bis 14. Schwangerschaftswoche findet nunmehr als wichtiges pränatales Screening zur individuellen Risikoabschätzung für Chromosomenstörungen Eingang in die pränatale Medizin. Neben der standardisierten Untersuchungstechnik sollte größter Wert auf die ausführliche Information und Beratung der Schwangeren sowie auf die Qualitätssicherung gelegt werden. Durch die Verbesserung der individuellen Risikospezifizierung mittels Sonographie, biochemischen Markern und dem mütterlichen Alter können unnötige invasive Untersuchungen vermieden und ihre Zahl insgesamt deutlich reduziert werden. Ein Trend, der sich auch anhand des nicht-invasiven Nachweises des fetalen Rhesus D Status und mit dem Einsatz der Dopplersonographie im Management fetaler Anämien verfolgen lässt.

First trimester maternal serum alpha-fetoprotein screening for Down syndrome and other aneuploidies

Low maternal serum AFP (MSAFP) values in the first trimester of pregnancy have been associated with an increased risk for chromosome disorders. In our own first trimester chorionic villus sampling (CVS) series, MSAFP determinations were carried out in 1,448 singleton pregnancies. Aneuploidies were detected in 26 of these. The pre-CVS MSAFP values in these pregnancies were compared to those in pregnancies with normal outcome. Statistical analysis did not show a diagnostically useful correlation between low first trimester MSAFP values and aneuploidy in our cohort.

[Genetic testing in pregnancy]

First trimester risk screening is probably the major methodological advance in identifying pregnancies at increased risk for genetic disease during recent years with an impact on all pregnancies. The high detection rate with moderate false positive rates will reduce the over-all number of invasive procedures as compared to the traditional approach based on maternal age exclusively, in particular considering the demographic shift towards higher mean maternal age. Non-invasive prenatal diagnosis from fetal cells or DNA in the maternal circulation remains an experimental approach, despite a growing number of reports on successful diagnoses of single gene disorders. In the lab molecular cytogenetic approaches have considerably broadened the diagnostic spectrum of conventional karyotyping and facilitated a rapid diagnosis of selected frequent aneuploidies. Molecular genetic testing, in particular on chorionic villi, allows an early and reliable diagnosis of a growing number of severe monogenic conditions. A restrictive legislation has hampered the development of preimplantation genetic diagnosis in German speaking countries, only a few groups work on polar body diagnosis, a legal but restricted alternative.

[Screening for aneuploidy by first trimester nuchal translucency measurement: results from a prospective trial including 1980 cases in a single center in Switzerland]

AIM

The purpose of this study was to evaluate the efficiency of first trimester screening for chromosomal abnormalities using the sonographically determined thickness of nuchal translucency (NT) combined with maternal age.

PATIENTS AND METHODS

Risk screening was offered to all patients with a fetal crown rump length (CRL) between 45 and 84 mm after extensive counselling. For the risk assessment the software provided by the Fetal Medicine Foundation was used. In accordance with the recommendation of the Swiss Working Group on First Trimester Screening a cut-off risk of 1 : 400 was chosen.

RESULTS

A total of 1980 consecutive pregnancies participating in the risk screening programme with due dates prior to May 1, 2001 were included. Mean maternal age was 30.1 yrs and 522 (26.4 %) patients were 35 yrs or older. A positive risk screening result was obtained in a total of 219 (11.1 %) pregnancies including 33 of the 37 (1.9 %) cases with unbalanced chromosomal abnormalities.

CONCLUSIONS

The detection rate for unbalanced chromosome abnormalities in general (89.2 %) as well as the one for trisomy 21 (93.3 %) in particular are very high with a moderate false-positive rate (9.6 %) in this series. As a comparison in the series presented here, traditional "maternal age screening" (cut-off age 35 yrs) would have yielded detection rates of 64.9 % for all unbalanced chromosome abnormalities and 73.3 % for trisomy 21 at a false-positive rate of 25.0 %. Reducing the false-positive rate by raising the cut-off age to 38 yrs would yield detection rates of 40.5 % for all unbalanced chromosome abnormalities and 46.7 % for trisomy 21 at a false-positive rate of 8.9 %. The number of invasive procedures performed to detect one unbalanced chromosome count may be calculated as 21.75 using the cut-off age of 35 yrs as compared to 6.4 using NT measurement and maternal age. The outcome of this ongoing study is in good accordance with the earlier observation that the main benefit of the addition of first trimester NT measurements to the risk screening protocol is a very high detection rate at a moderate false-positive rate.

Myomectomy during the first trimester associated with fetal limb anomalies and hydrocephalus in a twin pregnancy

OBJECTIVES

To present the complications of a twin pregnancy after first trimester myomectomy and to discuss the possible etiologic relationship.

CASE REPORT

A 44-year-old primigravida with a dichorionic-diamniotic twin pregnancy underwent myomectomy in another hospital at 12 weeks' gestational age. At 28 weeks the patient was referred to our unit because of ventriculomegaly and limb anomalies in the second twin. The patient underwent a Caesarean section at 37 weeks of gestation delivering twin A, a healthy female weighing 3235 g and twin B, a female weighing 2810 g with hydrocephalus and limb anomalies (clubfeet and hypoplasia of the nails and terminal phalanges). The placenta from twin A was normal, but in the placenta of twin B haemorrhage, thrombosis and infarction were noted.

CONCLUSIONS

Despite several reports of myomectomy in pregnancy without any problems for mother and fetus, the authors believe that myomectomy - especially in the first trimester - may be associated with the type of problems observed in the present case. The pathophysiological relationship between placental trauma and haemodynamic alterations as a possible cause of the malformations in twin B is discussed.

Duplication dup(1)(q32q44) detected by comparative genomic hybridization (CGH): further delineation of trisomies 1q

Partial trisomy 1q is rare and mostly the result of an abnormal segregation of parental translocation chromosomes and their homologues. Only 31 cases have been described with pure partial trisomy 1q. In the fetus presented, chromosome analysis after amniocentesis had shown an unbalanced male karyotype with an aberrant chromosome 1. A de novo terminal duplication of the long arm was suspected but could not be verified by FISH in 1994. Five years after fetal death, retrospective identification of the additional material in 1q could finally be achieved by comparative genomic hybridization (CGH) using DNA extracted from formalin-fixed and paraffin-embedded fetal tissues. A direct duplication dir dup (1)(pter-->q44::q32.1-->qter) was found. Only 6 other individuals with duplication of this segment have been described so far. Comparative delineation of a dup1q phenotype with regard to size and origin of the dup (1q) segment evidenced that large duplications as well as proximal and interstitial duplications coincide with more severe visceral malformations, severe mental retar- dation and a short life span. Terminal duplications (1q32-->qter) concur with less severe malformations and longer periods of survival, but marked mental retardation. With small terminal duplications (1q42-->qter) dysmorphisms are usually mild and intellectual performance is mostly in the normal range.

The long-term effect of external quality assessment on performance in service cytogenetics

In 1993 a nationwide cytogenetic external quality assessment program (EQA) was initiated in the Federal Republic of Germany. Presently, some 70 laboratories, representing approximately 90% of all cytogenetic diagnostic tests, are participating in the study. Based on the quality assessment scheme of the Association of Clinical Cytogeneticists (1988) in the United Kingdom, quality of chromosome preparation and speed of routine diagnostic services are being evaluated. As a result of continuous external quality assessment, the mean banding level of participating laboratories rose from below 400 bands per haploid set (bphs) in 1994 to approximately 450 bphs in 1999 in prenatal tests and from about 400 to approximately 500 bphs in postnatal tests over the same 5-yr period. The percentage of participants achieving a banding level of 400 bphs or higher rose from approximately 50% to 93% in prenatal tests and from 60% to 96% in postnatal tests. No significant differences were observed in banding scores achieved by private laboratories compared to university institutes. The impact of the assessment of interpretation, reporting, and documentation remains difficult to evaluate. Preliminary data point to a more stringent adherence to ISCN nomenclature in karyotype designation by participants.

Fanconi anemia associated with increased nuchal translucency detected by first-trimester ultrasound

Increased nuchal translucency between 10 and 14 weeks of gestation has now been established as a marker for chromosomal defects in several large-scale studies. In addition, a growing number of structural defects and some rare genetic syndromes have been identified in association with this marker. We describe a case of a fetus with increased nuchal translucency at 12 weeks of gestation, in which second-trimester evaluation by ultrasound showed an enlarged cisterna magna, a ventricular septal defect and moderate signs of dysmorphia. Karyotyping by chorionic villus sampling revealed a high rate of chromosomal breaks. The diagnosis of Fanconi anemia with early onset was confirmed following the development of severe postnatal anemia 2 months after birth.

A novel syndrome involving primary skeletal growth and retardation in siblings

An identical pattern of malformations was found in two brothers both having microcephaly and severe developmental delay. Additionally, they had hypotelorism, epicanthic folds, and convergent strabismus. There was shortening of either the radius or the tibia and shortening of the first metacarpals. Persistently dorsally flexed fingers and toes were noted, all of which are unusually long. Both boys had a high-pitched voice and were unable to communicate verbally at the age of 4.5 years. They both developed short stature. One brother has anal atresia; the other had a pulmonary artery atresia, VSD, ASD, and an over-riding aorta. This apparently new syndrome is possibly an autosomal, or a X-linked recessive trait.

Assessing the chromosome copy number in metaphase II oocytes by sequential fluorescence in situ hybridization

PURPOSE

Aneuploidy in oocytes is the main cause of failed embryo implantation and of miscarriage. At present, only limited data on the prevalence of aneuploidy in freshly collected human oocytes are available and all studies have been performed with conventional methods for karyotyping. In this feasibility study, multiple-hybridization fluorescence in situ hybridization (FISH) was evaluated as an alternative method to determine the number of chromosomes in oocytes.

METHODS

Fifty-two spare oocytes were collected from 23 patients treated with gonadotropins for intrauterine insemination or intracytoplasmic sperm injection. A conventional dual color FISH approach using mixtures of chromosome-specific standard alpha-satellite probes was applied consecutively to the chromosomes of the same metaphase II oocyte. Mixtures of three to six probes were designed in order to allow chromosome identification based on signal color and centromeric index.

RESULTS

One hybridization cycle was possible in 52 uninseminated metaphase II oocytes, two hybridizations in 43 oocytes (82.7%), three hybridizations in 30 oocytes (57.6%), four hybridizations in 27 oocytes (51.9%), and five hybridizations in 15 oocytes (28.8%). Altogether, 591 chromosomes could be marked (47.4% of the entire chromosome complement, 11.4 chromosomes per oocyte). The most important single factor contributing to technical failure was loss of the oocyte from the slide.

CONCLUSION

This feasibility study demonstrates that multiple-hybridization FISH can be used for the assessment of a larger proportion of the chromosome complement in oocyte as compared to previous studies based on FISH.

Parental origin and mechanisms of formation of cytogenetically recognisable de novo direct and inverted duplications

Cytogenetic, FISH, and molecular results of 20 cases with de novo tandem duplications of 18 different autosomal chromosome segments are reported. There were 12 cases with direct duplications, three cases with inverted duplications, and five in whom determination of direction was not possible. In seven cases a rearrangement between non-sister chromatids (N-SCR) was found, whereas in the remaining 13 cases sister chromatids (SCR) were involved. Paternal and maternal origin (7:7) was found almost equally in cases with SCR (3:4) and N-SCR (4:3). In the cases with proven inversion, there was maternal and paternal origin in one case each. Twenty three out of 43 cytogenetically determined breakpoints correlated with common or rare fragile sites. In five cases, including all those with proven inverse orientation, all breakpoints corresponded to common or rare fragile sites. In at least two cases, one with an interstitial duplication (dup(19)(q11q13)) and one with a terminal duplication (dup(8) (p10p23)), concomitant deletions (del(8) (p23p23.3) and del(19)(q13q13)) were found.

Characterization of an immortalized human granulosa cell line (COV434)

We have investigated the biological characteristics of an immortalized granulosa cell line (COV434), which may be used to study follicular and oocyte maturation in vitro. Granulosa cell function was defined as consisting of three distinct properties: (i) production of 17beta-oestradiol in response to follicle stimulating hormone (FSH); (ii) presence of specific molecular markers of apoptosis enabling the induction of follicular atresia; and (iii) capacity to form intercellular connections with cells surrounding an oocyte. The addition of FSH to the culture medium supplemented with 10% fetal calf serum and 4-androstene-3,17-dione resulted in proliferation of the COV434 granulosa cells and in an increased synthesis of 17beta-oestradiol, indicating the presence of the FSH receptor and cytochrome P450 aromatase in these cells. The receptor for luteinizing hormone (LH) was undetectable. Similar expression of various apoptosis-associated genes was found in COV434 granulosa cells and in granulosa cells of patients stimulated with gonadotrophins for in-vitro fertilization, thus indicating that the immortalized COV434 granulosa cells were able to sustain apoptosis. Multiple intercellular connections were formed during co-culture of COV434 granulosa cells with cumulus cells containing an immature oocyte but not with cumulus cells devoid of an oocyte. Detailed morphological analysis of the intercellular connections with scanning electron microscopy and confocal light microscopy demonstrated the presence of long slender structures. It is concluded that the immortalized human granulosa cell line COV434 may be useful for experimental studies on follicular development.

Autosomal recessive disorder otospondylomegaepiphyseal dysplasia is associated with loss-of-function mutations in the COL11A2 gene

Otospondylomegaepiphyseal dysplasia (OSMED) is an autosomal recessive skeletal dysplasia accompanied by severe hearing loss. The phenotype overlaps that of the autosomal dominant disorders-Stickler and Marshall syndromes-but can be distinguished by disproportionately short limbs, severe hearing loss, and lack of ocular involvement. In one family with OSMED, a homozygous Gly-->Arg substitution has been described in COL11A2, which codes for the alpha2 chain of type XI collagen. We report seven further families with OSMED. All affected individuals had a remarkably similar phenotype: profound sensorineural hearing loss, skeletal dysplasia with limb shortening and large epiphyses, cleft palate, an extremely flat face, hypoplasia of the mandible, a short nose with anteverted nares, and a flat nasal bridge. We screened affected individuals for mutations in COL11A2 and found different mutations in each family. Individuals from four families, including three with consanguineous parents, were homozygous for mutations. Individuals from three other families, in whom parents were nonconsanguineous, were compound heterozygous. Of the 10 identified mutations, 9 are predicted to cause premature termination of translation, and 1 is predicted to cause an in-frame deletion. We conclude that the OSMED phenotype is highly homogenous and results from homozygosity or compound heterozygosity for COL11A2 mutations, most of which are predicted to cause complete absence of alpha2(XI) chains.

International, collaborative assessment of 146,000 prenatal karyotypes: expected limitations if only chromosome-specific probes and fluorescent in-situ hybridization are used

The development of chromosome-specific probes (CSP) and fluorescent in-situ hybridization (FISH) has allowed for very rapid identification of selected numerical abnormalities. We attempt here to determine, in principle, what percentage of abnormalities would be detectable if only CSP-FISH were performed without karyotype for prenatal diagnosis. A total of 146 128 consecutive karyotypes for prenatal diagnosis from eight centres in four countries for 5 years were compared with predicted detection if probes for chromosomes 13, 18, 21, X and Y were used, and assuming 100% detection efficiency. A total of 4163 abnormalities (2.85%) were found including 2889 (69. 4%) (trisomy 21, trisomy 18, trisomy 13, numerical sex chromosome abnormalities, and triploidies) which were considered detectable by FISH. Of these, 1274 were mosaics, translocations, deletions, inversions, rings, and markers which would not be considered detectable. CSP-FISH is a useful adjunct to karyotype for high risk situations, and may be appropriate in low risk screening, but should not be seen as a replacement for karyotype as too many structural chromosome abnormalities will be missed.

[Is sterility a genetic burden?]

Genetic causes of infertility are probably not rare. Today only a fraction of genes directly or indirectly involved in reproduction including sex determination and differentiation are known. Nevertheless, the list of well-defined genetic disorders impairing fertility is impressing already today and growing rapidly. Gonosomal aneuploidy and structural rearrangements represent a significant portion of the genetic causes of infertility in both sexes. Other chromosomal conditions include autosomal balanced structural changes (e.g. translocations), probably due to pairing disturbances of the affected chromosomes during meiosis. Some fundamental mechanisms in sex determination and differentiation have been characterized in recent years. Mutations in some of the genes involved in this process may lead to familial infertility. Genetic defects in gametogenesis of both sexes are currently being investigated using mouse models. Male specific causes of infertility include microdeletion within the AZF region of the euchromatic part of the long arm of the Y chromosome and obstructive azoospermia due congenital aplasia of the vas deferens in the presence of mutations in the CFTR gene.

Low rates of pregnancy termination for prenatally diagnosed Klinefelter syndrome and other sex chromosome polysomies

Over the past 9 years we counseled 55 couples whose unborn child was found to carry a sex chromosome polysomy. We performed a survey of postcounseling parental decisions about continuation or termination of these pregnancies. Of the 55 embryos or fetuses, 23 had the karyotype 47,XXY, 10 had 47,XYY, and 12 had 47,XXX. In addition, there were 10 instances of true mosaicism, i.e. 47,XXY/46,XY (n = 5), 47,XYY/46,XY (n = 2), or 47,XXX/46,XX (n = 3). Mean gestational age (+/-standard deviation) at diagnosis was 18.3+/-3.0 weeks. After comprehensive genetic counseling 48 (87.3%) of these pregnancies were carried to term. In seven cases (12.7%) the parents elected a pregnancy termination. Two of 31 pregnancies (6.5%) primarily ascertained at our center were aborted, whereas amongst the 24 referred cases, 5 couples (20.8%) opted for a termination. The mean gestational age of the terminated pregnancies was 19.7 weeks. The overall termination rate of 12.7% appears low in comparison with literature data. Most reports from other institutions present termination rates between 32 and 66%. The reason for the low rate of induced abortions in our study cohort is not clear. Cultural differences in parental perception of sex chromosomal polysomies may be of importance, and peculiarities of genetic counseling at our institution could also play a role. Although counseling was nondirective, we did put emphasis on providing prospective parents with information from unbiased follow-up studies of children with Klinefelter syndrome and other sex chromosome polysomies.

[A rare combination of partial trisomy 9 with pulmonary atresia]

We report of an previously unpublished combination of partial trisomy 9 and a membranous pulmonary atresia with a large conotruncal ventricular septal defect. The dystrophic female, term newborn presented after delivery with microcephaly, prominent nose and several other facial and skeletal deformities. The echocardiography and angiography showed a membranous pulmonary atresia with ventricular septal defect. Chromosomal analysis revealed a partial trisomy of the short arm with parts of the long arm of chromosome 9 and a small part of the long arm of chromosome 4. A surgical repair of the heart defect was not performed by the known high risk of severe mental retardation of partial trisomy 9. The child died at the age of six months.

[Prenatal diagnosis]

A growing number of methods for the in-utero diagnosis of fetal disease became available during recent decades, mainly due to rapid advances in ultrasound technology and laboratory methods. Exclusion of fetal aneuploidy in pregnancies of women beyond 34 years is still by far the most common reason for an invasive procedure event at a time when the number of diagnosable inborn errors of metabolism and monogenetic disorders is increasing rapidly. Great efforts have been made to improve the poor predictive value of maternal age as an indicator for an increased risk for fetal aneuploidy. Maternal serum screening using various parameters [e.g. AFP, hCG, uE3] has been found effective in identifying the majority of pregnancies with Down syndrome in the second trimester. Current research goals are the optimal choice of markers and the introduction of maternal serum screening in the first trimester of pregnancy. Ultrasound is another suitable tool to identify pregnancies at high risk for aneuploidy at least in the hands of experienced operators. The diagnostic use of fetal cells in the maternal circulation is presently investigated in a large collaborative trial. Second trimester amniocentesis still is the most widely applied invasive technique in pregnancies with maternal age related risks for fetal aneuploidy. Safety and diagnostic accuracy are well established and amniotic fluid can easily be shipped. Without major changes in conventional sampling and laboratory techniques the procedure can be performed at 13 weeks of gestation and later. The safety and efficacy of first-trimester amniocentesis has still to be established in larger series. First-trimester chorionic villus sampling is a well-established alternative to amniocentesis with comparable procedure-related risks. It is the method of first choice in pregnancies at high risk for aneuploidy, inborn errors of metabolism and monogenic disorders, since uncultured villi can be used for a rapid diagnosis. Placental biopsy should also be considered in the second and third trimester of pregnancy for these indications whenever time is a critical issue. Fetal blood obtained by ultrasound-guided cordocentesis has successfully been used for the diagnosis of fetal infection and is at the same time another good source of cells for rapid karyotyping. Other invasive procedures such as fetal skin or liver biopsies for electron microscopy or specific metabolic tests are restricted to the relatively rare instances of diseases where DNA diagnosis is currently not available or uninformative. Providing information on the different alternatives in an individual situation is one of the critical issues in pregnancy care today.

Congenital heart disease in the 48,XXYY syndrome

We report on an infant with severe tetralogy of Fallot, bilateral preauricular pits, and a 48,XXYY chromosomal complement. This case and evidence collected from the literature suggest that congenital heart disease may occur in the 48,XXYY syndrome more frequently than currently appreciated.

Parental origin of the extra haploid chromosome set in triploidies diagnosed prenatally

The parental origin of the additional chromosome complement in a total of 17 cases of triploidy was determined mainly using highly polymorphic microsatellites. Maternal origin of the triploidy was demonstrated in most cases. To the best of our knowledge, this is the first systematic evaluation of the parental origin of chromosome sets in fetuses who survived until a cytogenetic diagnosis was established. In contrast to previous investigations this study documented a predominance of maternal origin of the extra haploid set mainly due to longer survival time for digynic triploidies. The concept of 2 distinct fetal phenotypes in triploidy is clearly supported by this study.

Prenatal diagnosis and management of fetal hydrocephaly and lissencephaly

Two cases of prenatal diagnosis of lissencephaly are presented in the context of a series of 118 cases of prenatally diagnosed hydrocephalus. Within this series there was one case of Walker-Warburg syndrome and another of Miller-Dieker syndrome. It is stressed that the cases reported here of ventriculomegaly diagnosed in utero show a very different outcome from those in published studies of fetal hydrocephalus which only deal with patients in whom the diagnosis was determined after birth. In those postnatal series there is a considerable selection bias, and the fate of the fetuses reported here was much worse than in postnatal series. Of the 118 fetuses 6 had fetal infections, 6 had chromosomal abnormalities, 26 had associated spina bifida, 64 fetuses had associated other anomalies, and only 28 had isolated hydrocephalus. Although it is difficult to determine the prognosis individually after prenatal diagnosis of ventriculomegaly, the data presented here may be helpful in counseling parents prenatally. The counseling should be performed with the collaboration of obstetricians, pediatricians, surgeons, and geneticists.

Genetic factors in lissencephaly syndromes: a review

Lissencephaly is a sign of various genetic and non-genetic conditions and a constant feature in the so-called lissencephaly syndromes. Type I lissencephaly in the Miller-Dieker syndrome (MDS) and the isolated lissencephaly sequence (ILS) is differentiated from type II lissencephaly in the Walker-Warburg (hydrocephalus, agyria, retinal dysplasia with or without encephalocele, HARD +/- E) syndrome and related conditions (e.g. muscle-eye-brain syndrome). In about 90% of patients with MDS structural defects have been confirmed in the short arm of chromosome 17 (p13.3), detectable by classical cytogenetic methods, fluorescence in situ hybridisation (FISH), or molecular genetic techniques. The identification of unbalanced inversions and translocations is of particular importance because of the risk of their recurrence, while deletions and ring chromosomes are mainly sporadic. Recently, submicroscopic deletions have also been reported in ILS, providing evidence that lissencephaly in MDS and ILS is caused by deletions of the same gene(s) in 17p13.3 and that MDS may be considered to be a "contiguous gene syndrome." Syndromes featuring lissencephaly type II (HARD +/- E and related conditions) are most probably autosomal-recessively inherited. Neither the location of the genes involved nor the nature of the mutations are known at present. It is also unknown whether HARD +/- E and muscle-eye-brain syndrome are allelic.

Detection of fetal trisomies 21 and 18 from maternal blood using triple gradient and magnetic cell sorting

PROBLEM

The need for an inexpensive and reproducible technique for noninvasive prenatal diagnosis by fetal cell isolation from maternal blood.

METHOD

For enrichment of fetal cells we used a combination of triple density gradient and magnetic sorting (MACS) of (anti-CD71) transferrin receptor antibody labeled cells followed by fluorescence in situ hybridization (FISH) with chromosome-specific DNA probes for detection of fetal aneuploidies. We identified 15 cases of fetal trisomy (five cases with a trisomy 18 and ten cases with a trisomy 21) with subsequent chromosome-specific FISH.

RESULTS

We found in all of the aneuploid pregnancies that the percentage of cells with three hybridization signals did not overlap with those of normal controls independent from gestational ages and previous invasive procedures.

CONCLUSIONS

Our new approach for noninvasive prenatal diagnosis has proven to be reliable in this first series.

First-trimester alpha-fetoprotein screening for Down syndrome

Screening for Down syndrome and other chromosomal aneuploidies by biochemical parameters in maternal serum is well established for the second trimester. With screening as late as 16 weeks of gestation, the option of chorionic villus sampling (CVS) unfortunately is lost. In our study population, the maternal serum alpha-fetoprotein (MSAFP) concentration was determined in 2471 women in the first trimester immediately prior to CVS. Although in this sample MSAFP tended to be lower in Down syndrome (DS) pregnancies than in pregnancies with a chromosomally normal fetus, at this early gestational age neither a fixed cut-off level of 0.5 multiples of the normal median (MOM) nor one of 0.6 MOM was suitable for identifying pregnancies at higher risk for DS. This also applied to trisomy 18, although on average MSAFP in trisomy 18 pregnancies was lower than in normal and DS pregnancies.

Magnetic cell sorting and the transferrin receptor as potential means of prenatal diagnosis from maternal blood

OBJECTIVE

We wanted to test whether the recently described method of using the transferrin receptor system for fluorescence-activated cell-sorter enrichment of nucleated red blood cells can be used for prenatal diagnosis from maternal blood.

STUDY DESIGN

Instead of the laborious, expensive fluorescence-activated cell-sorter system, we used the newly described magnetic-activated cell sorter.

RESULTS

An effective enrichment could be achieved with separation of lymphocyte subsets. With the transferrin receptor, however, the enrichment was very inefficient because of the poor specificity of the antibody itself. Even in umbilical cord blood only 25% of nucleated red blood cells were labeled as demonstrated by immunogold silver enhancement of transferrin receptor-labeled cells.

CONCLUSION

In spite of the availability of a fast and effective separation method (magnetic-activated cell sorter) the use of the transferrin receptor antigen alone is not likely to enable a reliable identification of fetal cells in maternal circulation.

Distal limb deficiency following chorionic villus sampling?

We have reviewed the follow-up of almost 3000 completed pregnancies in the Münster CVS Program and identified 4 children with distal limb deficiencies. Two cases involved only minor anomalies of distal digital phalanges. One child had a Hanhart anomaly (hypoglossia hypodactylia). We also reviewed 24 cases of limb defects following CVS reported previously. With the exception of a single series, neither the overall incidence of affected children nor cases reported from larger series provide unambiguous evidence of an increased risk of distal limb deficiency caused by CVS.

[Prenatal diagnosis with chorionic villi and placenta puncture biopsy in the 1st to 3d trimester of pregnancy: diagnostic value of chromosome studies]

Chorionic villus sampling and placental biopsies became established diagnostic alternatives to amniocentesis worldwide during the 80's. Safety and accuracy are the most important criteria for the evaluation of these newer techniques as compared to amniocentesis. We report on our experience with more than 3400 chromosome analyses between 1985 and 1990 from first to third trimester of pregnancy in a single centre. Most obvious is the higher frequency of mosaicism, which is often, but not always confined to the placenta. Mosaicism accounts for the overwhelming majority of all discrepant (so-called false negative or false positive) cytogenetic findings. The most important prerequisites for diagnostic accuracy of chromosome analyses are meticulous separation of villi immediately after the sampling procedure as well as simultaneous use of direct preparation and cell culture. If mosaicism is not taken as sound evidence for foetal aneuploidy, the accuracy of cytogenetic diagnoses after chorionic villus sampling and placental biopsies is in the same range as the one after amniocentesis.

Mosaicism and accuracy of prenatal cytogenetic diagnoses after chorionic villus sampling and placental biopsies

Discrepant chromosome findings in placenta and fetus (false negative and false positive) after chorionic villus sampling (CVS) are mainly due to confined mosaicism. Non-mosaic normal or abnormal chromosome counts after direct preparation and culture nearly always correctly reflect the fetal chromosome constitution. False-negative results have almost exclusively been restricted to cytotrophoblast cells not representing a fetal chromosome abnormality. Diagnosis of placental mosaicism definitely requires an adequate follow-up by amniocentesis, fetal blood sampling, or sonography before a pregnancy is terminated. When direct preparations and cultured cells are used for cytogenetic diagnoses and placental mosaicism is not taken as proof for a chromosomal abnormality in the fetus, CVS is an accurate diagnostic tool.

[Prenatal chromosome findings in sonographically conspicuous fetuses]

A retrospective evaluation of 463 prenatal chromosome analyses in a total of 375 patients with suspicious ultrasound findings, revealed a high rate of severe chromosomal abnormalities (16%). The highest risk for an abnormal karyotype was found after sonographic detection of hygroma colli. Abnormal chromosome counts were also frequently found in fetuses with omphaloceles, duodenal atresia and hydrops fetalis, as well as in presence of intrauterine growth retardation and/or anomalies of the amniotic fluid volume. The anomalies mentioned above are, therefore, an urgent indication for a prenatal chromosome analysis. The technical improvements of ultrasound machines and growing experience of operators will lead to an increasing importance of sonography as a method for the identification of pregnancies, that are at high risk for chromosomal abnormalities.

'False-negative' and 'false-positive' prenatal cytogenetic results due to 'true' mosaicism

A 37-year-old gravida was referred for CVS because of advanced maternal age. A trisomy 21 was present in all cells after short-term incubation (direct processing (DP)) and long-term culture. According to our policy, a retap was offered for confirmation of the result during the legally required 3-day waiting period between communication of the result and termination of pregnancy. Unexpectedly all cells after DP showed a normal male chromosome complement. Further investigations revealed mosaicism in trophoblast tissue and a normal karyotype in amniotic fluid cells and fetal blood (50 mitoses each). The parents elected to continue the pregnancy after extensive ultrasound examinations did not show suspicious findings. After the birth of a healthy child, cell cultures from ten different placental sites confirmed mosaicism. Four out of 100 mitoses from a lymphocyte culture showed an additional chromosome 21. The child had no dysmorphic features and the development was normal at the age of 10 weeks. This case demonstrates the restricted validity of prenatal cytogenetic analysis in the presence of true fetal mosaicism. It also stresses the benefit of our policy to offer a retap in cases with abnormal cytogenetic results prior to termination of pregnancy which is considered unnecessary by many cytogeneticists.