Trisomy 18q. A case report and review of karyotype-phenotype correlations

Transcriptomic analysis of cell-free fetal RNA suggests a specific molecular phenotype in trisomy 18

Trisomy 18 is a common human aneuploidy that is associated with significant perinatal mortality. Unlike the well-characterized "critical region" in trisomy 21 (21q22), there is no corresponding region on chromosome 18 associated with its pathogenesis. The high morbidity and mortality of affected individuals has limited extensive investigations. In order to better understand the molecular mechanisms underlying the congenital anomalies observed in this condition, we investigated the in utero gene expression profile of second trimester fetuses affected with trisomy 18. Total RNA was extracted from cell-free amniotic fluid supernatant from aneuploid fetuses and euploid controls matched for gestational age and hybridized to Affymetrix U133 Plus 2.0 arrays. Individual differentially expressed transcripts were obtained by two-tailed t tests. Over-represented functional pathways among these genes were identified with DAVID and Ingenuity(®) Pathways Analysis. Results show that three hundred and fifty-two probe sets representing 251 annotated genes were statistically significantly differentially expressed between trisomy 18 and controls. Only 7 genes (2.8% of the annotated total) were located on chromosome 18, including ROCK1, an up-regulated gene involved in valvuloseptal and endocardial cushion formation. Pathway analysis indicated disrupted function in ion transport, MHCII/T cell mediated immunity, DNA repair, G-protein mediated signaling, kinases, and glycosylation. Significant down-regulation of genes involved in adrenal development was identified, which may explain both the abnormal maternal serum estriols and the pre and postnatal growth restriction in trisomy 18. Comparison of this gene set to one previously generated for trisomy 21 fetuses revealed only six overlapping differentially regulated genes. This study contributes novel information regarding functional developmental gene expression differences in fetuses with trisomy 18.

Identification and characterization of a new type of asymmetrical dicentric chromosome derived from a single maternal chromosome 18

Molecular cytogenetic analysis identified a new type of dicentric chromosome involving different breakpoints at 18q in a female fetus. The chromosome anomaly was designated as an asymmetrical pseudoisodicentric chromosome 18, 46,XX,psu dic(18)(pter-->q11.2::q21.3-->pter)mat. A series of BAC clones for 18q11.2 and q21.3 regions were used to identify one breakpoint within the region q11.2 between 19.8 and 21.6 Mb from the telomere of 18p and another breakpoint within q21.3 between 55.4 and 56.9 Mb from the telomere of 18p by FISH analysis. Real-time quantitative PCR and microsatellite analysis further verified that the dicentric chromosome was maternal in origin and resulted from a break-reunion between sister chromatids of a single maternal chromosome. We propose that a loop-type configuration of sister chromatids took place and that the break-reunion occurred at cross sites of the loop to form an asymmetrical isodicentric chromosome during either mitosis or meiosis. In this case, the asymmetrical pseudoisodicentric resulted in an 18pter--> q11.2 duplication and an 18q21.3-->qter deletion, which could have led to certain dysmorphic features of 18q- syndrome in this fetus.

Bilateral semilunar valve dysplasia in a patient with inverted duplication 2p25-22

Here we report a patient with partial trisomy 2p and congenital dysplasia of the semilunar valves. To our knowledge, this is the first case of 2p duplication with developmental defects of both semilunar valves and suggests that genes on this region contribute to the formation of the semilunar valves.

Duplication 18q21.31-q22.2

We report on three siblings with mild mental retardation and minor dysmorphic features carrying an interstitial duplication of the long arm of chromosome 18 inherited from a healthy mosaic carrier mother. The duplicated region spanned between 18q21.31 and 18q22.2 for about 12 Mb. The distal duplications of 18q are rare and only a small number of subjects, manifesting quite different clinical outcomes, have been described. However, in most of these cases, molecular characterization was not available. We have reviewed nine patients, including three familial cases, displaying overlapping duplicated regions, and compared them with the present individuals in an attempt to delineate karyotype-phenotype correlation.

Psychiatric disorder in a familial 15;18 translocation and sublocalization of myelin basic protein of 18q22.3

Two related patients with similar clinical features consisting of a few dysmorphic signs and psychiatric disturbance were reported to have a partial trisomy of chromosomes 15(pter-q13.3) and 18(q23-qter) deriving from a familial translocation t(15;18). One patient is affected by bipolar disorder and the other by schizoaffective disorder. Both cases have a predominantly affective course; nevertheless, a clear diagnosis is difficult in the first patient, who is 15 years of age, and only a longitudinal course will allow us to establish a definite diagnosis. The possibility that these two pathologies belong to a single category is discussed, and the presence of a susceptibility locus on chromosome 18 is hypothesized. Cytogenetic data, FISH, and DNA studies indicate that the myelin basic protein (MPB) gene is not involved in the translocation, and localize it centromeric to the breakpoint on chromosome 18(q22.3). Thus, it is unlikely to be involved in the disease.

Congenital polyvalvular cardiac disease without chromosomal abnormalities

Congenital polyvalvular cardiac disease has been reported in association with trisomies 18, 13, and 15. Ninety-three percent of trisomy 18 patients have polyvalvular disease, and 34% have all four valves involved. Four cases of polyvalvular disease without chromosomal abnormalities were studied and compared to polyvalvular disease with trisomy. In these four cases, all four valves were markedly abnormal with nodularity and reductant tissue; one aortic and two pulmonary valves were bicuspid; and one aortic, two tricuspid, and three mitral valves were unicuspid. The chordae tendineae were generally abbreviated and papillary muscles were hypoplastic. Microscopically, the valves had spongiosis, vacuolar degeneration, and a decrease in elastic fibers. Multiple other cardiac anomalies were present in each case. Three of the four cases also had significant extracardiac anomalies, which were lethal in two cases. The fourth case with no other anomalies had a history of maternal tobacco, alcohol, and cocaine abuse, with the latter being detected in fetal urine after birth. There does not appear to be a significant difference between polyvalvular disease with and without trisomy. Polyvalvular disease is usually not an isolated disorder but is associated with other intra- and extracardiac anomalies.

Molecular cytogenetic determination of a deletion/duplication of 1q that results in a trisomy 18 syndrome-like phenotype

We report on an infant who presented at birth with some characteristics of trisomy 18 syndrome, including low birth weight, facial abnormalities, overlapping fingers, and congenital heart defects. On chromosome analysis, no additional chromosome 18 was observed and both chromosome 18 homologues appeared normal. However, a small piece of chromosomal material of unknown origin was detected at the tip of the long arm of chromosome 1. Fluorescence in situ hybridization (FISH) using whole chromosome 18 painting probes disclosed no additional hybridization at the telomere of 1q, suggesting that the material was derived from another chromosome. Further chromosome painting experiments suggested that the telomeric addition was of chromosome 1 origin. To identify subchromosomal regions involved in the rearrangement, additional FISH analyses were performed using single copy and repetitive DNA probes mapping to different portions of chromosome 1. The analyses showed that probes mapping to 1q34-43 were duplicated in the derivative chromosome 1. In addition, a DNA probe mapping to 1q44 was found to be deleted from the derivative chromosome 1. Our composite analysis suggests that a deletion and a duplication of chromosome 1q can result in some of the clinical findings usually associated with trisomy 18 syndrome. These results demonstrate the usefulness of FISH analysis when karyotype analysis is not consistent with the clinical description.

Precise mapping of a de novo duplication 18(q21-->q22) utilizing cytogenetic, biochemical, and molecular techniques

We describe the first de novo inverted duplication of 18q. Due to the difficulty of identifying de novo chromosome abnormalities based solely on cytologic studies, precise definition of the 18q duplication was attempted by integrating cytogenetic and clinical findings with biochemical and molecular dosage studies. The combined results demonstrated that the proposita had a duplication of 18q21-->q22 with a karyotype of 46,XX,-18, + inv dup(18) (pter-->q12.1::q22-->q21::q12.1-->qter). The duplication of this specific chromosome region does not result in the typical 18 phenotype, supporting the hypothesis that various loci on chromosome 18 may interact to produce the manifestations of this syndrome.

Confirmation of a cryptic unbalanced translocation using whole chromosome fluorescence in situ hybridization

We report on a 7-year-old boy with minor anomalies, growth retardation, and developmental delay with an initial 46,XY,der(18)t(18;?)(q23;?) chromosome constitution. To determine the origin of the additional chromosome segment, several candidate regions were identified including 4q and 18q. Clinical comparison showed more similarities to individuals with partial dup(4q) than to those with a dup(18q). Whole chromosome fluorescence in situ hybridization (FISH) was used to demonstrate the correct origin of the translocated region, clarifying the karyotype as 46,XY,der(18)t(4;18)(q28.2;q22.2), thus generating information of clinical importance. This illustrates the use of whole chromosome FISH to identify chromosome regions that cannot be determined conclusively using standard cytogenetic banding techniques.

Somatic cell hybrid deletion map of human chromosome 18

The creation of a physical map of chromosome 18 will be useful for the eventual identification of specific chromosomal regions that are critical in the occurrence of Edwards syndrome, the 18q- syndrome, and the 18p- syndrome. To begin the investigation of these syndromes, a physical map has been constructed to order random DNA fragments to specific portions of chromosome 18. A set of somatic cell hybrids that retain deletions or translocations involving chromosome 18 has been isolated and characterized. Over 200 lambda phage from a chromosome 18-specific library have been localized to 11 distinct regions of chromosome 18 using the chromosomal breakpoints present in the somatic cell hybrids.

Partial 18q trisomy and 18p monosomy resulting from a maternal pericentric inversion, inv(18)(p11.2q21.3)

A 7-year-old boy with dysmorphic features was found to have a recombinant chromosome 18, rec(18), resulting from meiotic recombination of a maternal pericentric inversion, inv(18) (p11.2q21.3), as defined by high-resolution banding. He was trisomic for the long arm (q21.3-qter) and monosomic for the short arm (p11.2-pter) of chromosome 18. His clinical features were compared with those in other rec(18) cases, and also those in monosomy 18p, trisomy 18qter and full trisomy 18 syndromes. The risk of recombinant formation for inv(18) carriers was also discussed.

Hypothesis: association of the critical region of trisomy 18 and 18q2--syndrome with dermatoglyphic findings and a growth suppressor (deleted in colon cancer) locus

Evidence from the literature is reviewed to suggest that when fingertip dermal ridge patterns in chromosomal deletion syndromes are characteristic of the opposite spectrum of the developmental scale from patterns found in cases trisomic for the same chromosomal region, the association may be a consequence of loci with growth regulatory functions. Evidence is presented that DNA markers at 18q21 should be the first candidate sequences to be used to test this hypothesis in families with fingertip arches segregating in an apparent autosomal dominant fashion.

Partial trisomy 18 with minimal anomalies: lack of correspondence between phenotypic manifestations and triplicated loci along chromosome 18

A 2-year-old boy with microcephaly, developmental delay, and minimal anomalies was found to have an extra submetacentric chromosome equivalent to 18pter----q12. Review of the phenotypes produced by various triplicated 18 regions supports the hypothesis that no one chromosome 18 region is sufficient to produce the phenotype of trisomy 18. The mild phenotype of trisomy 18p, the variable phenotype of trisomy 18pter----q12, and the discontinuous phenotype of triplication for band 18q12 alone emphasizes that the contribution of triplicated loci to the phenotype is neither additive nor invariant.

Tetrasomy 18p in a child with trisomy 18 phenotype

We report on a patient with trisomy 18 syndrome and tetrasomy 18p. The case indicates that the presence of an isochromosome i(18p) can mimic complete trisomy 18 syndrome.

The pathologist's perspective of genetic disease. Malformations and dysmorphology

The pathologic approach to the study of malformations and congenital abnormalities emphasizes the importance of careful dissection and pathologic studies. Concepts and terms of morphogenesis as defined by the International Working Group are presented. The developmental field is the central concept of a malformation. Malformation syndromes, disruptions, sequences, deformations, dysplasias, and associations are presented. The significance of fetal hydrops and short umbilical cord is discussed. Pathologic studies in chromosome defects suggest pathologic markers for some chromosome abnormalities.

Prenatal diagnosis of a case of 46,XY,18p-/46,XY,18p+ mosaicism

A case of mosaicism involving structural abnormality of chromosome 18 found in cultured amniotic fluid is reported.

Deletion 9p, duplication 18q in two sisters resulting from a maternal (9;18) (p22;q21.3) translocation

We have studied two sisters with partial deletion 9p and partial duplication 18q resulting from adjacent 1 segregation of a maternal translocation (9;18) (p22;q21.3). The clinical manifestations identified in our patients were compared with those reported in the literature for 9p- and 18q+ patients involving approximately the same amount of genetic material. There was relatively greater similarity with the 9p- syndrome than with dup (18q) syndrome, but typical characteristics of both conditions were lacking.

Prenatal detection of monosomy 18p and trisomy 18q mosaicism with unexpected fetal phenotype

A mosaic karyotype 46,XX,del(18)(p11)/46,XX,-18,+?i(18q) was found in cultured amniotic cells. Fetal blood sampling confirmed the presence of both cell lines. The pregnancy was terminated and the two cell lines were demonstrated in varying proportions in the fetal tissues. The few abnormal features seen in the fetus may represent a mild expression of the 18p-- phenotype inhibiting the effects of the trisomy 18q.

Segregation patterns and phenotypes of unbalanced offspring in a large family with (10;18) chromosome translocation

We describe a large family in whom a balanced 10;18 chromosome translocation is segregating through five generations. Six severely mentally retarded relatives and an abnormal fetus further define the phenotypic expression of dup (18q21----qter). Other segregants detected prenatally included a fetus with deletion 18q21----qter and two fetuses with dup(18pter----q21) owing to tertiary trisomy. One of the latter also had an extra X chromosome; this might be another example of possible nonhomologous pairing in man.

Phenotype-karyotype correlations in dup(18q): report of a case and review

We report on a case of dup(18q) due to de novo translocation 46,XX,-21,t(18;21)(18qter----cen----21qter). The patient had many characteristic signs of full trisomy 18 except for internal organ malformations and early death. We review the phenotype-karyotype correlations between full trisomy 18 and dup(18q) and discuss the possibility of the existence of "critical zone(s)" at the proximal or/and distal region of 18q responsible for most signs of trisomy 18, such as congenital heart defect and early death.

Chromosomal abnormalities associated with congenital contractures (arthrogryposis)

In a study of 350 patients with multiple congenital contractures (arthrogryposis), 80 (23%) patients had mental retardation or were developmentally delayed. Out of that group of 80 patients, 13 (16%) were found to have abnormal karyotypes. Two of the thirteen had a family history of chromosomal abnormalities without congenital contractures, therefore, 11 patients had chromosomal anomalies which appeared to be associated with the congenital contractures. Five of the eleven (45%) had chromosome mosaicism, three of those had tissue mosaicism. Two had abnormal skin fibroblast cell lines and normal peripheral leukocyte chromosome studies and one had a normal bone marrow karyotype with abnormal peripheral leukocyte chromosome studies. Chromosome studies were done in these patients with congenital contractures because of developmental delay and multisystem involvement, or recognition of clinical features typical of a chromosomal syndrome. We recommend first lymphocyte; and if those are normal, then fibroblast studies be done on all patients with multiple joint contractures and developmental delay, particularly if unusual facial features or multisystem abnormalities are present.

Congenital heart anomalies in the trisomy 18 syndrome, with reference to congenital polyvalvular disease

Congenital polyvalvular disease (CPVD) is seen in trisomy 18 and other aneuploidy syndromes. However, its extent and nature have not been studied. Gross pathologic and histologic aspects of the heart were studied in 15 autopsied cases of trisomy 18. All had CPVD; other congenital defects included membranous ventricular septal defect (87%), patent ductus arteriosus (73%), and high takeoff of the right coronary ostium (80%). With a scoring system, histologic findings of the valves of all trisomy 18 cases were compared with those of 30 normal hearts of comparable age in order to determine the degree of morphologic abnormality. This included the presence of blood cysts, derangement of the spongiosa and fibrosa, vascular degeneration of the spongiosa, and defective elastic fibers. There were distinct differences between the changes seen in CPVD with trisomy 18 syndrome and those seen in the normal individuals. The most severe changes were present in the tricuspid and mitral valves with derangement of the spongiosa and fibrosa and defective elastic fibers. The valve tissue had a similar histologic appearance and structure to that of low birth weight infants (gestational age, 25 weeks). The valvular changes observed therefore are of fetal type and represent errors in tissue differentiation occurring as last as the third trimester.