Partial trisomy 2q: Report of a patient with dup (2)(q33.1q35)

Complex genomic alterations and intellectual disability: an interpretative challenge

BACKGROUND

Complex chromosomal rearrangements (CCRs) are structural rearrangements involving more than three chromosomes or having more than two breaks; approximately 70% are not associated with any clinical phenotype. Here, we describe a CCR segregating in a two-generation family.

METHOD

A 4-year-old male was evaluated for developmental delay, mild intellectual disability and epicanthus. Karyotype, fluorescence in situ hybridisation (FISH) analysis and array comparative genomic hybridisation (aCGH) analysis were performed on the patient and of all family members.

RESULT

Array CGH analysis of the proband detected two non-contiguous genomic gains of chromosome 2 at bands q32.3q33.2 and bands q36.1q36.3. Both karyotype and FISH analysis revealed a recombinant chromosome 2 with a direct insertion of regions q32.3q33.2 and q36.1q36.3 into region q12. Both of these regions were also present in their original location. Karyotype and FISH analysis of the father revealed a de novo direct insertion of regions q32.3q33.2 and q36.1q36.3 into region q12. Moreover, a de novo balanced translocation involving the q arm of the same chromosome 2 and the p arm of chromosome 10 was observed in the father of the proband. The single nucleotide polymorphism (SNP) array analysis and haplotype reconstruction confirmed the paternal origin of the duplications. Karyotype, FISH analysis and array CGH analysis of other family members were all normal.

CONCLUSION

This report underlines the importance of using different methods to correctly evaluate the origin and the structure of CCRs in order to provide an appropriate management of the patients and a good estimation of the reproductive risk of the family.

The frequency of CNVs in a cohort population of consecutive fetuses with congenital anomalies after the termination of pregnancy

BACKGROUND

The implementation of molecular karyotyping has resulted in an improved diagnostic yield in the genetic diagnostics of congenital anomalies, detected prenatally or after the termination of pregnancy. However, the systematic epidemiologic ascertainment of copy number variations in the etiology of congenital anomalies has not yet been sufficiently explored.

METHODS

Consecutive fetuses, altogether 204, with major single or multiple congenital anomalies were ascertained by using the SLOCAT registry for the period from 2011 to 2015. After excluding aneuploidies by using conventional karyotyping or Quantitative Fluorescence-Polymerase Chain Reaction, array comparative genomic hybridization was performed for the detection of copy number variations.

RESULTS

We identified pathogenic or likely pathogenic copy number variations in 14 fetuses (6.8%); 2.9% in fetuses with isolated, and 3.9% in fetuses with multiple congenital anomalies. Additionally, aneuploidies and major structural chromosomal abnormalities were detected in 40.2%.

CONCLUSION

Our systematic approach of ascertaining congenital anomalies resulted in explaining the etiology of congenital anomalies in 47% of fetuses after the termination of pregnancy. By using array comparative genomic hybridization, we found that copy number variations represent an important part in the etiology of multiple, as well as isolated congenital anomalies, which indicates the importance of analyzing copy number variations in the diagnostic approach of fetuses with congenital anomalies after the termination of pregnancy.

Interstitial duplication of 2q32.1-q33.3 in a patient with epilepsy, developmental delay, and autistic behavior

Duplications of the 2q33 region are rare; to date, only 13 patients have been reported to have this chromosomal abnormality. The reported duplications are of varying size, and the patients shared developmental delay and minor dysmorphic findings. In this study, we identified a duplication of 2q32.1-q33.3 in a patient with psychomotor developmental delay, epilepsy, and autistic behavior. The duplicated region of this patient was reciprocal to the 2q32-q33 deletion syndrome. Chromosomal microarray testing confirmed the 19.5 Mb of duplication that includes over 100 genes, some of which could have functional relevance to the neurological features of this patient. The SATB homeobox 2 gene (SATB2)-the primary gene responsible for the 2q32-q33 deletion syndrome-may be one of them, because of its expression in the cortical projection neurons of the developing brain. The duplication of the potassium channel tetramerisation domain-containing 18 gene (KCTD18) and the ADAM metallopeptidase domain 23 gene (ADAM23) may also contribute to the phenotype. FISH analysis confirmed a tandem configuration of the duplicated segments. This result is in agreement with our previous study, in which we observed that duplicated segments as interstitial duplications are generally inserted in the tandem configuration.

Phenotypic and molecular characterization of partial trisomy 2q resulting from insertion-duplication in chromosome 18q: a case report and review of literature

Trisomy 2q is a well-documented chromosomal anomaly with considerable variation in the phenotype depending upon the breakpoints and the co-existing chromosomal aberrations. The case of a dysmorphic male infant found to have trisomy of the 2q31.1-q37.3 segment, resulting from insertion-duplication of this segment in chromosome 18q23 is reported here. The rearrangement was resolved in detail by cytogenetic microarray and whole chromosome paint-based fluorescence in situ hybridization studies. There is some overlap of the phenotypic features in the reported patient with those described in previously reported cases with partial trisomy 2q. A detailed review of the available literature on 2q trisomy has also been presented and delineation of the phenotypic characteristics common to all patients with 2q trisomy has been attempted.

Molecular characterization of a new patient with a non-recurrent inv dup del 2q and review of the mechanisms for this rearrangement

We report on newborn baby with microcephaly, facial anomalies, congenital heart defects, hypotonia, wrist contractures, long fingers, adducted thumbs, and club feet. Cytogenetic studies revealed an inverted duplication with terminal deletion (inv dup del) of 2q in the patient and a paternal 2qter deletion polymorphism. Microsatellite markers demonstrated that the inv dup del was maternal in origin and intrachromosomal. Intra or interchromosomal rearrangements may cause this aberration either by a U-type exchange (end-to-end fusion), an unequal crossover between inverted repeats (non-allelic homologous recombination: NAHR), or through breakage-fusion-bridge (BFB) cycles leading to a sister chromatid fusion by non-homologous end joining (NHEJ). A high-resolution oligo array-CGH (244 K) defined the breakpoints and did not detect a single copy region with a size exceeding 12.93 Kb in the fusion site. The size of the duplicated segment was 38.75 Mb, extending from 2q33.1 to 2q37.3 and the size of the terminal deletion was 2.85 Mb in 2q37.3. Our results indicate that the inv dup del (2q) is likely a non-recurrent chromosomal rearrangement generated by a NHEJ mechanism. The major clinical characteristics associated with this 2q rearrangement overlap with those commonly found in patients with 2q duplication reported in the literature.

Cryptic chromosomal abnormalities identified in children with congenital heart disease

Congenital heart disease (CHD) is the most common type of birth defect, and the etiology of most cases is unknown. CHD often occurs in association with other birth malformations, and only in a minority are disease-causing chromosomal abnormalities identified. We hypothesized that children with CHD and additional birth malformations have cryptic chromosomal abnormalities that might be uncovered using recently developed DNA microarray-based methodologies. We recruited 20 children with diverse forms of CHD and additional birth defects who had no chromosomal abnormality identified by conventional cytogenetic testing. Using whole-genome array comparative genomic hybridization, we screened this population, along with a matched control population with isolated heart defects, for chromosomal copy number variations. We discovered disease-causing cryptic chromosomal abnormalities in five children with CHD and additional birth defects versus none with isolated CHD. The chromosomal abnormalities included three unbalanced translocations, one interstitial duplication, and one interstitial deletion. The genetic abnormalities were predominantly identified in children with CHD and a neurologic abnormality. Our results suggest that a significant percentage of children with CHD and neurologic abnormalities harbor subtle chromosomal abnormalities. We propose that children who meet these two criteria should receive more extensive genetic testing to detect potential cryptic chromosomal abnormalities.

A familial inverted duplication 2q33–q34 identified and delineated by multiple cytogenetic techniques

We describe a unique family with two children having a delay in psychomotor development. In both children we identified an interstitial duplication dup(2)(q34q33) using multiple, complementary molecular cytogenetic techniques. Comparative genomic hybridisation (CGH) and array-CGH were used to determine the size and the location of the duplicated region, the orientation of the duplicated region was identified with fluorescence in situ hybridisation (FISH). Both parents demonstrated a normal karyotype and normal CGH and array-CGH-profiles. However, FISH on peripheral blood cells from the mother showed the inv dup(2) in 9% of metaphases and 19% of interphase nuclei. To our knowledge this is the first report of a mosaic carrier of duplication in the long arm of chromosome 2. The finding of chromosomal mosaicism of at least 19% in the mother increases the recurrence risk. The exact characterisation of the inv dup(2) with FISH probes enabled us to offer a reliable prenatal FISH test. Comparison of the clinical features of the two children with those of previously described cases supports the hypothesis that the characteristic facial phenotype is linked to the distal part of the 2q33-q37 region. This report illustrates that in case of two sibs with an identical structural chromosomal abnormality the possibility of parental chromosomal mosaicism must be thoroughly investigated.