Isochromosome (18q) in siblings

A report is presented on a familial occurrence of isochromosome (18q) in a newborn infant and in a fetus in the 24th week of gestation after amniocentesis.     

Trisomy 18 and 18p- features in a case of isochromosome 18q [46,XY,i(18q)]: prenatal diagnosis and autopsy report

This paper reports the prenatal diagnosis and autopsy findings of a case of true isochromosome 18q [46,XY,i(18q)] with severe cephalic malformations. Comparison is made with other cases of i(18q).     

Isochromosome 18q with karyotype 46, XX, i(18q). Cytogenetics and pathology

Cytogenetic and morphological findings of a 20-gestational-week-old female fetus with karyotype 46,XX,i(18q) are reported. The fetus displayed clinical features resembling Edward's syndrome. No characteristic symptoms of monosomy 18p could be observed.     

Novel isodicentric chromosome 18 in an abnormal infant with a mosaic karyotype [46, XY/46,XY, –18,+ dic(18)(q12.2)]

A previously unreported isodicentric chromosome 18 was discovered in an abnormal infant boy whose mosaic karyotype was 46, XY/46,XY,–18, + idic(18)(q12.2). His constellation of congenital anomalies was typical of the 18q-syndrome. The clinical and cytogentic characteristics of this patient are reported, and the literature concerning isochromosomes of 18 is reviewed.     

Gonadoblastoma in a patient with an isodicentric X chromosome

Although gonadoblastoma is known to be associated with the presence of a Y chromosome, this case report of a 15-year-old patient with gonadal dysgenesis, gonadoblastoma, and an idic(Xq-) chromosome provides evidence for the occurrence of gonadoblastoma even in the absence of a Y chromosome. A review of previous cases reported to have gonadoblastoma in the absence of a Y chromosome revealed that the presence of some breast development was the common denominator among those patients. Therefore, a patient who presents with gonadal dysgenesis with some breast development, but lacks a Y chromosome may observe as close scrutiny as the patient with gonadal dysgenesis in the presence of a Y chromosome.     

Trisomy (18q) and tetrasomy (18p) resulting from isochromosome formation

In this paper we report two clinically recognizable chromosomal syndromes, both resulting from isochromosome 18 formation, i.e. trisomy 18q and tetrasomy 18p. The possible mechanisms of the isochromosome formation are discussed and the literature on subject is reviewed.     

Isodicentric chromosome 18 in an abnormal infant using chromosome specific DNA probe

A report is made on a rare isodicentric chromosome 18 in an abnormal male infant whose karyotype was 46,XY,idic(18)(p11.31----qter), confirmed by in situ hybridization using non-radioactive biotin-labelled 18 probe. His clinical features were similar to 18 trisomy syndrome. The literature concerning isochromosome 18 is reviewed.     

Replication patterns of three isodicentric X chromosomes and an X isochromosome in human lymphocytes

Chromosomes from four patients with variants of the Turner syndrome were investigated by G- and C- banding and DNA replication techniques. Their karyotypes were: 1) 46,X,idic(X)(q28), 2) 45,X/46,X,idic(X)(q24), 3)45,X/ 46,X,idic(X)(p11), and 4) 46,X,i(Xq). In Patients 1, 2, and 3, the abnormal X was isodicentric, with different break-and-fusion points in each case. In each, the G-band pattern on one side of the breakpoint was a mirror image of that on the other side. Each had two distinct C-bands, only one of which was associated with a primary constriction. The fourth patient had an isochromosome of the long arm of an X in which only one C-band could be discerned. Replication studies were done on lymphocyte cultures by incorporating a thymidine analogue and staining with acridine orange. In addition, replication patterns of normal early- and late-replicating X chromosomes were studied in two normal females. In the four patients, all the normal X chromosomes had normal early-replication patterns. The two idic(X) chromosomes with break-and-fusion points on their long arms almost always had symmetric replication patterns, which demonstrates that the corresponding bands replicated synchronously. In contrast, many of the idic(X)(p11) and i(Xq) chromosomes showed asymmetric or asynchronous replication. In each, the replication pattern of the abnormal X was similar to the equivalent portions of a normal late-replicating X.     

Syndromes associated with deletion of the long arm of chromosome 18[del(18q)]

We studied eight persons whose karyotypes demonstrated deletion of a portion of the long arm of chromosome 18. Seven of these persons who showed the typical del(18q) syndrome had a common deletion in band 18q21, most likely band q21.3, and in at least two persons the deletion was interstitial. Another mentally retarded child, dissimilar in appearance, had a more proximal deletion within band 18q12. Two different clinical syndromes resulted from deletions of these different segments of the long arm of chromosome 18.     

Thymus deficiency in an infant with a chromosome t(18;22)(q12.2;p11.2)pat rearrangement

The finding of an unbalanced t(18;22)pat chromosome rearrangement in a boy with multiple anomalies including apparent absence of the thymus is described. The observation is of interest because of the reported association of chromosome 22 rearrangements with the DiGeorge sequence. In contrast to previous reports of this association, the deletion involving chromosome 22 is confined to the short arm.     

Features of trisomy 18 and 18p-syndromes in an infant with 46, XY, i(18q)

An isochromosome for the long arm of chromosome number 18 - 46,XY,i(18q) - was found in an infant who had features of both trisomy 18 and 18p- syndromes. Findings compatible with trisomy 18 included postmature delivery, prominent occiput, severe congenital heart disease, overlapping fingers, and rocker-bottom feet. Those of 18p- syndrome, which frequently resembles Turner syndrome, were downward obliquity to the palpebral fissures, short, webbed neck, low posterior hairline, and widely-spaced nipples. The infant died of heart failure at 3.5 months of age. Parental karyotypes were normal.     

Unbalanced 18q/21q translocation in a patient previously reported as monosomy 21

We describe a patient in whom full monosomy 21 was initially assumed from routine GTG-banded karyotyping. Re-examination with chromosome painting demonstrated an unbalanced translocation between the long arms of chromosomes 18 and 21. Fluorescence in situ hybridisation (FISH) and microsatellite marker analysis revealed partial monosomy of chromosome 21 (pter-q21) and 18(q22-qter). The patient, 18 years old at the second examination, revealed multiple dysmorphic features, genital hypoplasia, dilated cerebral ventricles, muscular hypotonia and severe mental retardation. In not one out of all patients investigated postnatally in whom an initial examination had revealed monosomy 21, this could be confirmed by FISH; in all of them, re-examination detected an unbalanced rearrangement leading to only partial monosomy 21 plus partial monosomy of another chromosome to which the distal 21q segment was attached. Thus, it is still highly likely that full monosomy 21 is incompatible with intra-uterine survival.     

Congenital anomalies and anthropometry of 42 individuals with deletions of chromosome 18q

Deletions of chromosome 18q are among the most common segmental aneusomies compatible with life. The estimated frequency is approximately 1/40,000 live births [Cody JD, Pierce JF, Brkanac Z, Plaetke R, Ghidoni PD, Kaye CI, Leach RJ. 1997. Am. J. Med. Genet. 69:280–286]. Most deletions are terminal encompassing as much as 36 Mb, but interstitial deletions have also been reported. We have evaluated 42 subjects with deletions of 18q at our institution. This is the largest number of individuals with this chromosome abnormality studied by one group of investigators. Here we report the physical findings in these individuals. We have compared our findings with those of previously reported cases and have found a significantly different incidence of several minor anomalies in our subjects. We also describe here several anomalies not previously reported in individuals with deletions of 18q, including short frenulum, short palpebral fissures, disproportionate short stature, overlap of second and third toes, and a prominent abdominal venous pattern. Characteristics found in subjects were analyzed for correlation with cytogenetic breakpoints. Several traits were found to correlate with the extent of the deletion. Large deletions were associated with significantly decreased head circumference and ear length as well as the presence of proximally placed and/or anomalous thumbs. Individuals with the smallest deletions were more likely to have metatarsus adductus. Although relatively few genotype/phenotype correlations were apparent, these data demonstrate that correlations with breakpoint are possible. This implies that more correlations will become evident when the more precise molecularly based genotyping is completed. These correlations will identify critical regions on the chromosome in which genes responsible for specific abnormal phenotypes are located. Am. J. Med. Genet. 85:455–462, 1999. © 1999 Wiley-Liss, Inc.     

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.     

Autistic symptoms among children and young adults with isodicentric chromosome 15

A standardized assessment of autistic symptomatology was completed for 29 children and young adults with a supernumerary isodicentric chromosome 15 (formerly known as inverted duplication 15). Although there was variability in severity, 20 individuals with an isodicentric chromosome 15 [idic(15)] had a high probability of being autistic. Eight of the 9 remaining children were under age 5 years and were more sociable than the rest of the cohort. Group characteristics such as gender and seizure presence could not explain the observed difference between older and younger individuals in our study. The natural history of isodicentric 15 syndrome remains to be shown through longitudinal work and may include an age-related risk for developing autism. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 81:428–433, 1998. © 1998 Wiley-Liss, Inc.     

Monosomy 18q 12.1→21.1: A recognizable aneuploidy syndrome? Report of a patient and review of the literature

This report of a patient with an interstitial deletion 18q and review of previously described cases suggest a clinically recognizable syndrome. The phenotype appears to result from a microdeletion of part of 18q12.2 or q12.3, or a deletion of parts of both bands. © 1992 Wiley-Liss, Inc.     

Mental retardation/shortness of stature/multiple minor anomalies syndrome associated with insertion of 3q material into 18p

This is a case report of a 16-year-old Arab girl with mental subnormality, shortness of stature and multiple minor phenotypic anomalies. She is obese with normal secondary sexual characteristics, and has a speech deficit. Cytogenetic studies showed a 46,XX,dir ins (18;3)(p11.1;q13.2→q25). The chromosome arrangement appeared balanced. Her condition is not a recognizable specific syndrome; thus, it remained unclear as to whether her condition is attributable to disruption of 3q or 18p or both. Further cytogenetic analysis by molecular biologists is required to solve this problem. © 1995 Wiley-Liss, Inc.     

De novo balanced translocation (6;18)(q21;q21.3) in a patient with heterotaxia

We report on a sporadic case of heterotaxia with a de novo chromosome structural abnormality. The patient had inversely located heart (dextrocardia), stomach, duodenum, and cecum. In addition, she had cerebral atrophy, hypertelorism with telecanthus, infraorbital skin furrows, ear-lobe grooves, prominent maxilla and teeth, large carp mouth, short fifth fingers with limited flexion, generalized hypotonicity, and severe psychomotor retardation. High-resolution chromosome banding analysis demonstrated an apparently balanced translocation: 46,XX,t(6;18)(q21;q21.3). It is hypothesized that both heterotaxia and the chromosomal abnormality in the patient are causally related and a putative situs determining gene has been disrupted by the chromosome break, i.e., a position effect or a cryptic deletion at around the breakpoints. The translocation in our patient may be a good source for positional cloning of the gene. © 1996 Wiley-Liss, Inc.