The significance of pericentric inversions of chromosome 2

A chromosome 10 variant with a 12 Mb inversion [inv(10)(q11.22q21.1)] identical by descent and frequent in the Swedish population

We identified a paracentric inversion of chromosome 10 [inv(10)(q11.22q21.1)] in 0.20% of Swedish individuals (15/7,439) referred for cytogenetic analysis. A retrospective analysis of 8,896 karyotypes from amniocenteses in Sweden revealed a carrier frequency of 0.079% (7/8,896) for the inversion. Cloning and detailed analysis of the inversion breakpoint regions show enrichment for interspersed repeat elements and AT-stretches. The centromeric breakpoint coincides with that of a predicted inversion from HapMap data, which suggests that this region is involved in several chromosome 10 variants. No known gene or predicted transcript are disrupted by the inversion which spans approximately 12 Mb. Carriers from four non-related Swedish families have identical inversion breakpoints and haplotype analysis confirmed that the rearrangement is identical by descent. Diagnosis was retrieved in 6 out of the 15 carriers referred for cytogenetic analysis. No consistent phenotype was found to be associated with the inversion. Our study demonstrates that the inv(10)(q11.22q21.1) is a rare and inherited chromosome variant with a broad geographical distribution in Sweden.

Evolution versus constitution: differences in chromosomal inversion

We compared the chromosomal breakpoints of evolutionary conserved and constitutional inversions. Multicolor banding and human-specific bacterial artificial chromosomes were applied to map the breakpoints of constitutional pericentric inversions on human chromosomes 2 and 9. For the first time, we present a high-resolution analysis of the breakpoint regions, which are characterized by gene destitution, co-localization with fragile sites, multitude repeats as well as pseudogenes and, remarkably, a large sequence homology to the opposite breakpoint. In contrast, evolutionary inversion breakpoints lack such extensive cross-hybridizing regions and are often associated with fragile sites of the genome and low-copy repeats. These molecular characteristics gave evidence for different types of inversion formation and indicate that evolutionary inversions cannot originate from constitutional inversions like those of chromosomes 2 and 9. Finally, the constitutional inversion breakpoints were investigated on three different great ape species and on four test persons each bearing the same cytogenetically determined inversion on chromosomes 2 and 9, respectively. Our data indicate the existence of different molecular breakpoints for the two variant chromosomes.

Unrelated patients with a rearrangement of chromosome 2 causing duplication of 2p23 and deletion of 2q37

We describe two unrelated patients who each have a similar chromosome 2 with duplication of 2p23 to pter, and deletion of 2q37 to qter. In one, the abnormality was derived from his mother with a pericentric inversion. Both individuals have frontal bossing; abnormally formed, low set and posteriorly rotated ears; redundant nuchal skin; inversion of the nipple(s); fleshy fingertips with prominent pads; a sacral dimple; significant developmental delay/mental retardation; and G-tube dependency. Most of these features are present in previously described individuals with either duplication of the 2p terminus or deletion of the 2q terminus. This report is the first that documents postnatal viability of individuals with concurrent duplication of 2p and deletion of 2q, and also generation of this imbalance through rearrangement of a maternally inherited pericentrically inverted 2. This report should be considered in the reproductive counseling of individuals with pericentric inversions of chromosome 2.

Pericentric inversion of chromosome 2 and echogenic vasculature in the basal ganglia: a new finding?

Linear branching echogenicities in the thalamus or basal ganglia have been reported in infants with several genetic and nongenetic disorders. In this article, we report 2 cases of newborns with a neurosonographic diagnosis of thalamic/basal ganglia vasculopathy and karyotype analysis showing pericentric inversion of chromosome 2. To our knowledge, there has been no previous mention of an association between these entities.

Case of partial duplication 2q3 with characteristic phenotype: rare occurrence of an unbalanced offspring resulting from a parental pericentric inversion

We report on a male infant with partial trisomy 2q (q34-->qter) resulting from a maternal pericentric inversion of chromosome 2 (p25. 2q34). The infant had clinical findings similar to the characteristic phenotype associated with a partial duplication of chromosome 2q3. Carriers of pericentric inversions of chromosome 2 have an increased risk of pregnancy loss but have only rarely been reported to have a liveborn offspring with an unbalanced chromosome constitution. This case further confirms the risks associated with a pericentric inversion of chromosome 2 and is the second report with manifestations of the trisomy 2q3 phenotype.

Characterization of the NPHP1 locus: mutational mechanism involved in deletions in familial juvenile nephronophthisis

Familial juvenile nephronophthisis is an autosomal recessive, genetically heterogeneous kidney disorder representing the most frequent inherited cause of chronic renal failure in children. A gene, NPHP1, responsible for approximately 85% of the purely renal form of nephronophthisis, has been mapped to 2q13 and characterized. The major NPHP1 gene defect is a large homozygous deletion found in approximately 80% of the patients. In this study, by large-scale genomic sequencing and pulsed-field gel electrophoresis analysis, we characterized the complex organization of the NPHP1 locus and determined the mutational mechanism that results in the large deletion observed in most patients. We showed that the deletion is 290 kb in size and that NPHP1 is flanked by two large inverted repeats of approximately 330 kb. In addition, a second sequence of 45 kb located adjacent to the proximal 330-kb repeat was shown to be directly repeated 250 kb away within the distal 330-kb repeat deleting the sequence tag site (STS) 804H10R present in the proximal copy. The patients' deletion breakpoints appear to be located within the 45-kb repeat, suggesting an unequal recombination between the two homologous copies of this smaller repeat. Moreover, we demonstrated a nonpathologic rearrangement involving the two 330-kb inverted repeats found in 11 patients and, in the homozygous state, in 2 (1.3%) control individuals. This could be explained by interchromosomal mispairing of the 330-kb inverted repeat, followed by double recombination or by a prior intrachromosomal mispairing of these repeats, leading to an inversion of the NPHP1 region, followed by an interchromosomal unequal crossover event. This complex rearrangement, as well as the common deletion found in most patients, illustrates the high level of rearrangements occurring in the centromeric region of chromosome 2.

De novo direct duplication 2 (p12-->p21) with paternally inherited pericentric inversion 2p11.2 2q12.2

We report a 4-year-old girl with a previously undescribed de novo duplication of 2p12->2p21 on the same homologue as a paternally inherited pericentric inversion of region 2p11.2-->2q12.2, resulting in dysmorphic features, cardiac abnormality, cleft palate, respiratory problems, severe growth retardation and developmental delay. This case raises an important question--did the paternal pericentric inversion influence the occurrence of the de novo duplication?

Prenatal detection of de novo inversion of chromosome (2) (p13q11.2) and postnatal follow-up

We report the first case of an apparent de novo pericentric inversion of chromosome 2 at the breakpoints p13q11.2 that was detected prenatally. Follow-up performed over 4 years showed phenotypic abnormalities including minor craniofacial dysmorphism, hypotonia, hearing loss, gustatory flushing syndrome, and severe developmental delays. The literature on chromosome 2 inversion is reviewed.

The origin of human chromosome 2 analyzed by comparative chromosome mapping with a DNA microlibrary

Fluorescence in situ hybridization (FISH) of microlibraries established from distinct chromosome subregions can test the evolutionary conservation of chromosome bands as well as chromosomal rearrangements that occurred during primate evolution and will help to clarify phylogenetic relationships. We used a DNA library established by microdissection and microcloning from the entire long arm of human chromosome 2 for fluorescence in situ hybridization and comparative mapping of the chromosomes of human, great apes (Pan troglodytes, Pan paniscus, Gorilla gorilla, Pongo pygmaeus) and Old World monkeys (Macaca fuscata and Cercopithecus aethiops). Inversions were found in the pericentric region of the primate chromosome 2p homologs in great apes, and the hybridization pattern demonstrates the known phylogenetically derived telomere fusion in the line that leads to human chromosome 2. The hybridization of the 2q microlibrary to chromosomes of Old World monkeys gave a different pattern from that in the gorilla and the orang-utan, but a pattern similar to that of chimpanzees. This suggests convergence of chromosomal rearrangements in different phylogenetic lines.

De novo inv(2)(p21q31) associated with isolated bilateral microphthalmia and cataracts

We report on a patient with bilateral microphthalmia and unusual cataracts with a de novo pericentric inversion of chromosome (2)(p21q31). A literature review of previous associations of eye abnormalities and anomalies of chromosome 2 suggests probable gene locations for eye development.

A human immunoglobulin kappa orphon without sequence defects may be the product of a pericentric inversion

The VK gene segments that have been transposed from the kappa locus on the short arm of chromosome 2 at 2p11-12 to other chromosomal sites are called orphons. The 18 VK orphons sequenced up to now carry defects and are to be considered pseudogenes. We now describe the VKI gene segment V108 whose sequence is without any defects and which was localized to the long arm of chromosome 2 at 2q12-14 by in situ hybridization. The V108 region may have been transposed from the short to the long arm of chromosome 2 by a pericentric inversion. Possible reasons for the conservation of its sequence are discussed. In spite of its bona fide sequence V108 is considered to be an unlikely candidate for a VK-JK rearrangement and subsequent functional expression.

Abnormal chromosome complement resulting from a familial inversion of chromosome 2

It has been suggested that pericentric inversions of chromosome 2 increase the risk for spontaneous abortion but do not increase the risk for unbalanced recombinant offspring. We report our experience of a familial pericentric inversion of chromosome 2 resulting in two unbalanced recombinant offspring. Both subjects have 46,XX,rec(2),dup q,inv(2)(p25q35).

Familial pericentric inversion of chromosome 12

A pericentric inversion in one of the chromosomes 12, found in two families living in the same region, is described. This inversion was detected during routine chromosomal analysis in two separate laboratories. The breakpoints were at 12p112 and 12q13. The inverted segment represented approximately 20% of the length of chromosome 12. Twenty nine descendants of carriers of the inversion were investigated, and the inversion was present in 23 of them. The other six descendants showed a normal karyotype. After correction for sample bias with the single selection scheme, a segregation ratio of 3:1 was estimated, indicating that the inverted chromosome 12 was preferentially transmitted. All the carriers of the inversion were phenotypically normal, without noticeable fertility disturbances.