A complex chromosomal rearrangement with formation of a ring 4

Clinical, cytogenetic, and molecular findings in a patient with ring chromosome 4: case report and literature review

Background

Since 1969, 49 cases have been presented on ring chromosome 4. All of these cases have been characterized for the loss of genetic material. The genes located in these chromosomal regions are related to the phenotype.

Case presentation

A 10-year-old Ecuadorian Mestizo girl with ring chromosome 4 was clinically, cytogenetically and molecularly analysed. Clinical examination revealed congenital anomalies, including microcephaly, prominent nose, micrognathia, low set ears, bilateral clinodactyly of the fifth finger, small sacrococcygeal dimple, short stature and mental retardation. Cytogenetic studies showed a mosaic karyotype, mos 46,XX,r(4)(p16.3q35.2)/46,XX, with a ring chromosome 4 from 75 to 79% in three studies conducted over ten years. These results were confirmed by fluorescence in situ hybridization (FISH). Loss of 1.7 Mb and gain of 342 kb in 4p16.3 and loss of 3 Mb in 4q35.2 were identified by high-resolution mapping array.

Conclusion

Most cases with ring chromosome 4 have deletion of genetic material in terminal regions; however, our case has inv dup del rearrangement in the ring chromosome formation. Heterogeneous clinical features in all cases reviewed are related to the amount of genetic material lost or gained. The application of several techniques can increase our knowledge of ring chromosome 4 and its deviations from typical “ring syndrome.”

Ring Chromosome 4 in a Child with Multiple Congenital Abnormalities: A Case Report and Review of the Literature

A female child born preterm with intrauterine growth retardation and presenting with facial dysmorphism with clefts, microcephaly, limb deformities, and congenital abnormalities involving cardiovascular and urinary systems is described. Chromosomal analysis showed a de novo 46,XX,r(4)(p15.3q35) karyotype. The clinical features of the patient were compared with the phenotypic characteristics of 17 previously reported cases with ring chromosome 4 and those with Wolf-Hirschhorn syndrome (4p-). Clinical features observed in this case are consistent with the consensus phenotype in ring chromosome 4. Patent ductus arteriosus and bilateral talipes equinovarus observed in this baby widen the phenotypic spectrum associated with ring chromosome 4.

Mammalian chromosomes contain cis-acting elements that control replication timing, mitotic condensation, and stability of entire chromosomes

Recent studies indicate that mammalian chromosomes contain discrete cis-acting loci that control replication timing, mitotic condensation, and stability of entire chromosomes. Disruption of the large non-coding RNA gene ASAR6 results in late replication, an under-condensed appearance during mitosis, and structural instability of human chromosome 6. Similarly, disruption of the mouse Xist gene in adult somatic cells results in a late replication and instability phenotype on the X chromosome. ASAR6 shares many characteristics with Xist, including random mono-allelic expression and asynchronous replication timing. Additional "chromosome engineering" studies indicate that certain chromosome rearrangements affecting many different chromosomes display this abnormal replication and instability phenotype. These observations suggest that all mammalian chromosomes contain "inactivation/stability centers" that control proper replication, condensation, and stability of individual chromosomes. Therefore, mammalian chromosomes contain four types of cis-acting elements, origins, telomeres, centromeres, and "inactivation/stability centers", all functioning to ensure proper replication, condensation, segregation, and stability of individual chromosomes.

Genetic predisposition in degenerative lumbar scoliosis due to the copy number variation

STUDY DESIGN

Comparative genomic hybridization (CGH) microarrays.

OBJECTIVE

To identify genomic copy number variations (CNVs) in degenerative lumbar scoliosis (DLS) patients, and investigate the possibility of genetic predisposition in DLS.

SUMMARY OF BACKGROUND DATA

Genome scanning technology enables search for presence of CNVs. CGH microarray is a useful procedure in a genome-wide study.

METHODS

Among 45 consecutive patients who were diagnosed as DLS, 15 patients who manifested greatest Cobb's angle were selected for the array-CGH based CNV analysis. Control group was blood samples from 58 individuals without DLS. Oligonucleotide CGH microarray was utilized to analyze the CNV. Gene searches were performed for CNV DNA with significant gene-dosage difference. Validation qualitative PCR(qPCR) was performed at 3 genetic loci: at chromosome 2--TMEM163 gene, at chromosome 16--ANKRD 11 gene, and at chromosome 18--NFATC1 gene.

RESULTS

Genomic gains and losses were observed using the oligonucleotide CGH microarray. Identified CNVs were 446 ± 129 per individual. Gain- and loss-CNVs were identified as 196 ± 24 and 250 ± 110, respectively. The length of total CNV per individual was 30,946,730 ± 31,658,175 bp, and mean CNV-length was 61,017 ± 40,620 (median length 6411 ± 1994). Comparison with control group revealed 260 CNVs, which were significant (P < 10(-3)). Validation qPCR for gene-dosage comparison of DLS group DNA versus control group DNA in TMEM163 (P < 0.001); ANKRD 11 (P = 0.000); and NFATC1 (P = 0.000) gene showed significant difference.

CONCLUSION

Various whole-genome CNVs specific to DLS patients were observed. Validation qPCR confirmed significantly different gene-dosages for TMEM163, ANKRD 11, and NFATC1 genes. We consider that the expression of DLS is supported by various typical CNV-associated structural variants of the genome.

Structural variation in the human genome

The first wave of information from the analysis of the human genome revealed SNPs to be the main source of genetic and phenotypic human variation. However, the advent of genome-scanning technologies has now uncovered an unexpectedly large extent of what we term 'structural variation' in the human genome. This comprises microscopic and, more commonly, submicroscopic variants, which include deletions, duplications and large-scale copy-number variants - collectively termed copy-number variants or copy-number polymorphisms - as well as insertions, inversions and translocations. Rapidly accumulating evidence indicates that structural variants can comprise millions of nucleotides of heterogeneity within every genome, and are likely to make an important contribution to human diversity and disease susceptibility.

Ring chromosome 4 and Wolf–Hirschhorn syndrome (WHS) in a child with multiple anomalies

We report on a 16-month-old male patient with ring chromosome 4 and deletion of Wolf-Hirschhorn syndrome (WHS) region with multiple congenital anomalies including unilateral cleft lip and palate, iris coloboma, microcephaly, midgut malrotation, hypospadias, and double urethral orifices. Peripheral chromosome analysis of the patient showed 46,XY,r(4)(p16.3q35) de novo. Multicolor fluorescence in situ hybridization (FISH) study was also performed and according to multicolor banding (MCB) a r(4)(::p16.3 --> q34.3 approximately 35.1::) was found in all metaphases. Subtelomeric 4p region, subtelomeric 4q region, as well as, Wolf-Hirschhorn critical region were deleted in ring chromosome 4. Genomic microarray analysis was also performed to delineate the size of deletion. Cranial magnetic resonance imaging (MRI) showed hypoplastic corpus callosum, delayed myelinization, and frontal and occipital lobe atrophies. Both maternal and paternal chromosomal analyses were normal. We compare the phenotypic appearance of our patient with the previously reported 16 cases of ring chromosome 4 in the medical literature.

Ring chromosome 4 in a child with duodenal atresia

We report on a 19-month-old girl with ring chromosome 4 and a multiple congenital anomaly syndrome. The clinical and cytogenetic findings are compared with those of previous cases in whom the breakpoints in ring chromosome 4 are known.

The human homeobox gene HOX7 maps to chromosome 4p16.1 and may be implicated in Wolf-Hirschhorn syndrome

A cosmid containing the human sequence (HOX7) homologous to the mouse homeogene Hox-7 was isolated from a genomic cosmid library. There is only one highly conserved homologous gene in the human genome. The C-terminal two-thirds of the HOX7 homeobox DNA sequence has been determined; there are no predicted amino acid changes from the mouse sequence. Data from mouse/human hybrid cell lines show that HOX7 maps to human chromosome 4p16.1, a region that is syntenic with part of mouse chromosome 5, the site of the murine Hox-7 gene. Analysis of chromosomes from two patients with Wolf-Hirschhorn syndrome, which is characterised by profound dysmorphologies, indicates that the HOX7 locus is deleted. Although not all Wolf-Hirschhorn syndrome patients analysed were deleted for HOX7, the combination of positional data and functional correlation with mouse expression implicates HOX7 as a candidate gene for this syndrome.

Complex chromosome rearrangements involving chromosomes 1;3 and 2;3 in two abnormal children

Complex chromosome rearrangements (CCR) involving multiple breaks in two chromosomes are rare. The detection of a four-break apparently balanced rearrangement involving chromosomes 1 and 3 in a child with developmental delay led us to reanalyse, using prometaphase banding, another complex two-chromosome rearrangement in a previously reported case (Fitzgerald 1974). The relationship between clinical abnormalities and apparently balanced rearrangements is discussed.

Decreased cell viability of fibroblasts from two patients with a ring chromosome: an in vitro reflection of growth failure?

We found decreased cell viability in fibroblast cultures from two patients, one with ring chromosome 4, the other with ring chromosome 15, who had severe somatic retardation. Cell viability was studied with the trypan blue exclusion assay, and in comparison with matched control cells was found to be 72.0 vs. 93.1%, and 79.8 vs 90.2%, respectively. Cloning efficiency of fibroblasts from the patient with ring chromosome 15 was also decreased (12.3 vs. 25.7%). It is suggested that the decreased cell viability is due to a continuous production of hypomodal cells, a process related to the ring structure per se, and perhaps responsible for the severe somatic retardation frequently observed in patients with a ring chromosome.

De novo translocation heterozygote with three reciprocal translocations

An extremely rare case of a child with three balanced reciprocal translocations involving six different autosomes is described. These abnormalities have apparently arisen de novo and seem to have only relatively minor phenotypic effects. The meiotic possibilities are discussed and cytogenetic markers suggest that the damage may have occurred in a paternal gamete.

Neurological and neuropathological findings in ring chromosome 4

Despite the fact that mental retardation, microcephaly, seizures, and hyperactivity are common in patients with ring chromosome 4, little has been written about the underlying neuropathology. We describe a 6-year-old girl whose neuropathological findings included low brain weight, abnormal gyral development, and heterotopic neurons. The significance of these findings in regard to other retardation syndromes is discussed.

The Wolf-Hirschhorn syndrome. I. Genetics

Four new cases of the Wolf-Hirschhorn syndrome are presented, two of which were due to t(4;22)mat. Review of the literature (more than 100 cases of the Wolf-Hirschhorn syndrome) showed that 13 % of all the reported cases were not mutations but segregations of parental chromosomal aberrations, primarily translocations. Similar data were obtained previously for other deletions (5p--, 18p--, 18q--). Analysis of data on some "new" deletion syndromes (4q--, 8p--, 9p--, 10p--, 11p--, 11q--) revealed that 14.5 % were inherited cases. Thus, all human autosomal deletions have virtually the same genetic pattern.

Partial monosomy of long arm of chromosome 4 due to interstitial deletion

A child with congenital malformations and a de novo interstitial deletion of the long arm of chromosome 4 is described. Detailed analysis by G banding revealed the loss of the whole of band q21 and part of bands q13 and q22. The clinical abnormalities are quite dissimilar from those features described in other cases of partial 4q monosomy, which generally appear to result from the deletion of more distally placed segments of the chromosome.

Translocation of chromosome 4 and 9 with ring formation of chromosome 4 short arm

Cytogenetic investigation of a 3-year-old mentally retarded boy revealed a translocation of the long arm of chromosome 4 onto the short arm of chromosome 9, with ring formation of the remaining short arm of chromosome 4. The clinical features are described and correlated with the cytogenetic findings. The behaviour of the ring derived from a deleted chromosome 4 is discussed.

Partial trisomy 11,46,XX,-3,-20, + der3, + der20,t(3:11:20), resulting from a complex maternal rearrangement of chromosomes 3, 11, 20

Clinical findings of partial trisomy 11p are described in a patient bearing t(3;11;20) (p13;p11;q13). The translocation was present in balanced form in her mother (46, XX)t(3;11;20) (p13;p11;q13).

Derivative chromosomal structures from a ring chromsome 4

This report describes the results from cultured lymphocytes studied at metaphase, anaphase, and interphase from an individual with a ring chromosome 4. A ring was present in 90.1% of metaphases. Special attention was directed towards the occurrence of derivative chromosomal structures, such as partially duplicated and triplicated rings, tricentric rings, chains of 3 interlocked rings, rod-shaped chromosomes, "pulverized" rings, and others. The clinical features of the individual (small stature and impaired mental development, hypoplastic thumbs, ptosis palpebrae hypoplastic external male genitalia, abnormal dermatoglphic pattern) did not conform to a specific phenotype.

A child with multiple congenital malformations and a 46,XX,t(Bq+;Dq-)-45,XX,-B,-D,+der(B),t(Bq+;Dq-) karyotype

A case of a female infant with malformations of upper extremities and mental and growth retardation is reported.

The karyotype showed a 46,XX,t(Bq+;Dq−)/45,XX,−B,−D,+der(B),t(Bq+;Dq−) mosaicism. The clinical findings in relation to the long arm deletion of a B-group chromosome are discussed.

An inherited small extra chromosome: a mother with 46,XX,t(17;22)(pl;ql) and a son with 47,XY,+der(22)mat

A boy with multiple congenital anomalies was found to have a small extra chromosome. This small chromosome was interpreted as a der(22)mat because his mother was a balanced carrier with 46,XX,t(17;22) (p1;q1) chromosomes. It is hoped that with the use of the banding techniques many karyotypes will be revaluated and reinterpreted. The mother's karyotype was erroneously interpreted earlier as a 21/22 translocation.