Barbara Fritz

Deficiency of PORCN, a regulator of Wnt signaling, is associated with focal dermal hypoplasia

Focal dermal hypoplasia (FDH) is an X-linked dominant multisystem birth defect affecting tissues of ectodermal and mesodermal origin. Using a stepwise approach of (i) genetic mapping of FDH, (ii) high-resolution comparative genome hybridization to seek deletions in candidate chromosome areas and (iii) point mutation analysis in candidate genes, we identified PORCN, encoding a putative O-acyltransferase and potentially crucial for cellular export of Wnt signaling proteins, as the gene mutated in FDH. The findings implicate FDH as a developmental disorder caused by a deficiency in PORCN.

Cytogenetic analyses of culture failures by comparative genomic hybridisation (CGH)-Re-evaluation of chromosome aberration rates in early spontaneous abortions.

Comparative genomic hybridisation (CGH) represents an alternative molecular-cytogenetic technique capable of detecting chromosomal imbalances by reverse fluorescence in situ hybridisation. As the technique uses genomic DNA for assessment it does not rely on metaphase chromosomes in the test material and thus circumvents technical problems associated with tissue culturing. In the present study, we applied CGH to identify chromosome anomalies in 60 spontaneous abortions of the first trimester, that had failed to grow in culture. In 57 out of 60 cases CGH analyses were successful. The overall aneuploidy rate detected was 72%. Trisomy was the predominant chromosome anomaly accounting for 68.0% of abnormal abortions, followed by triploidy (17.1%) and monosomy X (9.8%). An unbalanced structural rearrangement was found in one (2.4%) abortion. Most frequently involved in trisomies were chromosomes 16 (32.1%), 7 and 22 (10.7% each), 4, 13, 15, and 21 (7.2 % each). Three triploid cases and one complete mole were detected by microsatellite analysis as supplementary method. CGH data on culture failures were compared with data derived from 4693 successfully karyotyped first trimester spontaneous abortions, resulting in a chromosome aberration rate of 64.8%. The distribution of the different chromosome anomalies was similar with the exception of a higher rate of trisomies 7 and of XYY-triploidies in the culture failures. Based on our data we suggest that the genetic contribution to pregnancy loss is still underestimated. Investigating abortion tissues hitherto unassessed by conventional methods, we suggest that the contribution of chromosome aberrations to first trimester pregnancy loss is nearly 70%.

Microdeletion 22q11 in complex cardiovascular malformations

Abstract Besides DiGeorge, velocardiofacial and conotruncal anomaly face syndromes, some of the isolated congenital heart diseases have also been associated with a chromosomal deletion in 22q11. These disease entities, which had originally been considered to have a different genetic background, are now included in the CATCH-22 microdeletion complex. CATCH 22 is an acronym for cardiac defect, abnormal facies, thymic hypoplasia or aplasia and T-cell deficiency, cleft palate, hypoparathyroidism, and hypocalcemia. In the present study, we focused on the complex cardiovascular defects (CCVD) and screened 40 patients for a microdeletion of 22q11 by fluorescence in situ hybridization using the D22S75 DNA probe and for associated CATCH features. The patients were from genetic counseling (n = 15) or fetopathology (n = 3) of the Clinical Genetics Department in Marburg and from the Pediatric Cardiology Department (n = 22) in Mainz. Monosomy 22q11 was detected in 9 cases (= 22.5%). Familial transmission with one mildly affected parent and one affected sib each was proven in two cases. The CCVDs comprised complex conotruncal defects such as tetralogy of Fallot, double outlet right ventricle, transposition of great arteries and truncus arteriosus communis, or anomalies of the derivatives of the branchial arch arteries in association with a ventricular septal defect, including one case of atresia of the ductus arteriosus with pulmonary artery aneurysm and resulting in fetal hydrops. All 13 patients with a deletion of 22q11 showed at least one additional CATCH symptom. Most consistently, facial dysmorphy was apparent (92%), while hypocalcemia, mostly at threshold values, was present in 62% and thymic hypoplasia including borderline low T-lymphocyte numbers was observed in 41%. None of the patients presented with a cleft palate. A high intrafamilial variability in expression was also evident with respect to the CCVD. Our findings indicate that seemingly isolated complex cardiovascular defects associated with a 22q11 microdeletion most probably do not represent a distinct subgroup within the CATCH-22 complex but are syndromal in nature with extracardiac features that are often overlooked.

Low incidence of UPD in spontaneous abortions beyond the 5th gestational week.

Approximately 15–20% of all clinically recognised pregnancies abort, most commonly between 8–12 gestational weeks. While the majority of early pregnancy losses is attributed to cytogenetic abnormalities, the aetiology of approximately 40% of early abortions remains unclear. To determine additional factors causing spontaneous abortions we retrospectively searched for uniparental disomies (UPD) in 77 cytogenetically normal diploid spontaneous abortions. In all cases an unbalanced chromosome anomaly was ruled out by cytogenetic investigation of chorionic/amniotic membranes and/or chorionic villi. For UPD screening microsatellite analyses were performed on DNA of abortion specimens and parental blood using highly polymorphic markers showing UPD in two cases. The distribution of markers analysed indicated maternal heterodisomy for chromosome 9 (UPhD(9)mat) in case 1 and paternal isodisomy for chromosome 21 (UPiD(21)pat) in case 2. The originating mechanism suggested was monosomy complementation in UPiD(21)pat and trisomy rescue in UPhD(9)mat. In the case of UPhD(9)mat purulent chorioamnionitis was noted and a distinctly growth retarded embryo of 3 cm crown-rump length showing no gross external malformations. Histological analysis in the case of UPiD(21)pat suggested a primary anlage defect. Our results indicate that less than 3% of genetically unexplained pregnancy wastage is associated with total chromosome UPD. UPD may contribute to anlage defects of human conception. Chromosome aneuploidy correction can occur in very early cleavage stages. More research, however, ought to be performed into placental mosaicism to further clarify timing and mechanisms involved in foetal UPD.

Molecular cytogenetic studies in three patients with partial trisomy 2p, including CGH from paraffin-embedded tissue.

We report on three cases of partial trisomy 2p in which the identification and exact localization of the duplicated chromosome segment was possible only by application of molecular cytogenetic techniques. These included fluorescence in situ hybridization by use of wcp2, N-myc, and subtelomeric 2p probes and comparative genomic hybridization with DNA isolated from blood samples, frozen fetal tendon, and formalin fixed, paraffin-embedded fetal lung tissue. Two of the cases concerned fetuses of gestational week 20 and 24 with duplication of nonoverlapping terminal (2pter-->p24) and more proximal (2p25-->p23) segments and with distinctly different phenotypes. The third case was due to a de novo inverted duplication of 2p25-->p23, with loss of the subtelomeric region of 2p. This 53-month-old girl was a Bloom syndrome carrier. The patient had prenatal growth failure, borderline microcephaly, dilated lateral horns of the cerebral ventricles, transient cortical blindness, myopia, muscle hypotonia, and dilatation of the left renal collecting system. Dermal cysts were found on the glabella, the soles of both feet, and the vocal cord, causing respiratory embarrassment. Previously reported cases of pure trisomy 2p are reviewed, in an attempt to correlate clinical findings to overlapping regions in 2p. These cases illustrate the effectiveness of molecular cytogenetic methods in resolving subtle chromosomal aberrations in order to coordinate more accurately a chromosome regionspecific phenotype.

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.

Pigmentary mosaicism in hypomelanosis of Ito. Further evidence for functional disomy of Xp.

We report on a female with mental and motor retardation, facial dysmorphism, abnormal pigmentation reminiscent to hypomelanosis of Ito (HI), and karyotypic mosaicism involving a small supernumerary marker chromosome. The marker chromosome was defined by fluorescence in situ hybridisation (FISH) as a ring X chromosome with breakpoints in the juxtacentromeric region. FISH analysis showed that the ring does not include the XIST locus at the X-inactivation centre and, therefore, may not be subject to X inactivation. X-inactivation studies with the HUMARA (human androgen receptor) and FMR1 assay showed a skewed X-inactivation pattern (85:15) with preferential inactivation of the paternal X chromosome. These results are discussed with respect to the role of functional disomy of Xp in the pathogenesis of HI.

Variability in the phenotypic expression of Fryns syndrome: A report of two sibships

We report on two sibships with four fetuses of 12, 15, 17, and 20 weeks of gestation, respectively, and 1 preterm baby of 31 weeks of gestation affected by a multiple congenital disorder with manifestation suggestive of Fryns syndrome. In addition to the characteristic malformation pattern in Fryns syndrome, they presented with fetal hydrops, cystic hygroma, and multiple pterygias, allowing prenatal ultrasound diagnosis as early as in the 11th week of gestation. The two affected fetuses of family 1 showed severe craniofacial anomalies with bilateral cleft lip and palate, acral hypoplasia, postaxial oligodactyly, persistent truncus arteriosus, and interrupted aortic arch, asplenia sequence, and complex central nervous system midline malformations. In family 2 with three affected sibs, ear anomalies with atresia of the auditory canals, postaxial hexadactyly, intestinal atresias, callosal defects, and eye colobomas were the most outstanding features. On the basis of the present findings and former reports, the inter- and intrafamiliar phenotypic variability in Fryns syndrome, possible pathogenetic mechanisms, and the value of prenatal diagnosis are discussed. In the pathogenetic discussion, a special emphasis is put on the neural crest cell developmental field.

Trisomy 2q35-q37 due to insertion of 2q material into 17q25: clinical, cytogenetic, and molecular cytogenetic characterization.

We present a 7-year-old boy with growth retardation, developmental and mental delay, and minor physical abnormalities. The patient had a male karyotype with duplicated material of unknown origin in the long arm of chromosome 17. The origin of the duplicated material was clarified by fluorescence in situ hybridization. Forward chromosome painting showed that the extra material originated from chromosome 2, which was inserted into 17q25. Further characterization of the aberrant chromosome 17 by microdissection and reverse chromosome painting revealed a duplication of bands 2q35 to q37.1. To our knowledge, no other individual with a duplication of this small segment has been described so far. The clinical findings of 13 cases with isolated trisomy 2q are reviewed in relation to the size of the duplicated region. Functional analysis of the duplicated 2q region suggests that critical loci for visceral and central nervous system development in distal trisomy 2q are proximal to 2q33.

Clinical, Cytogenetic and Molecular Investigation in a Fetus with Wolf-Hirschhorn Syndrome with Paternally Derived 4p Deletion

Wolf-Hirschhorn (4p-) syndrome (WHS), caused by partial deletion of the short arm of chromosome 4, has been extensively described in children and young adults. Knowledge on fetuses with WHS is still limited due to the small number of published cases. We report on a fetus with prenatally diagnosed severe intrauterine growth retardation, reduced thoracal diameter, clubfeet deformity and midface hypoplasia including slight microretrognathia indicative for fetal karyotyping. Chromosome analysis after amniocentesis revealed a de novo terminal deletion of chromosome 4p [karyotype: 46,XX,del(4) (p16)] which was confirmed by FISH. Analyses of a set of polymorphic markers mapping in 4pter->4p15.3 showed absence of paternal haplotypes. These observations corroborate the preferential paternal origin of the de novo 4p deletion in WHS patients. Furthermore, the distal breakpoint could be narrowed to band 4p16.1. At autopsy, the fetus showed typical craniofacial dysmorphic signs of WHS, severe IUGR and delayed bone age. This report suggests the possibility of recognising the particular phenotype of WHS in utero by prenatal ultrasound and emphasises the importance of karyotyping fetuses with severe IUGR, especially when the amount of amniotic fluid is normal.