Unbalanced translocation in a mother and her son in one of two 5;10 translocation families

Ring chromosome 10: report on two patients and review of the literature

Ring chromosome 10--r(10)--is a rare disorder, with 14 cases reported in the literature, but only two with breakpoint determination by high-resolution techniques. We report here on two patients presenting a ring chromosome 10, studied by G-banding, fluorescent in situ hybridization (FISH), multiplex ligation-dependent probe amplification (MLPA) and SNP-array techniques, in order to investigate ring instability and determine breakpoints. Patient 1 showed a r(10)(p15.3q26.2) with a 7.9 Mb deletion in 10q26.2-q26.2, while patient 2 showed a r(10)(p15.3q26.13) with a 1.0 Mb deletion in 10p15.3 and a 8.8 Mb deletion in 10q26.13-q26.3, both unstable. While patient 1 presented with clinical features usually found in patients with r(10) and terminal 10q deletion, patient 2 presented characteristics so far not described in other patients with r(10), such as Dandy-Walker variant, osteopenia, semi-flexed legs, and dermal pigmentation regions. Our data and the data from literature show that there are no specific clinical findings to define a r(10) syndrome.

Breakpoint mapping and haplotype analysis of three reciprocal translocations identify a novel recurrent translocation in two unrelated families: t(4;11)(p16.2;p15.4)

The majority of constitutional reciprocal translocations appear to be unique rearrangements arising from independent events. However, a small number of translocations are recurrent, most significantly the t(11;22)(q23;q11). Among large series of translocations there may be multiple independently ascertained cases with the same cytogenetic breakpoints. Some of these could represent additional recurrent rearrangements, alternatively they could be identical by descent (IBD) or have subtly different breakpoints when examined under higher resolution. We have used molecular breakpoint mapping and haplotyping to determine the origin of three pairs of reciprocal constitutional translocations, each with the same cytogenetic breakpoints. FISH mapping showed one pair to have different breakpoints and thus to be distinct rearrangements. Another pair of translocations were IBD with identical breakpoint intervals and highly conserved haplotypes on the derived chromosomes. The third pair, t(4;11)(p16.2;p15.4), had the same breakpoint intervals by aCGH and fosmid mapping but had very different haplotypes, therefore they represent a novel recurrent translocation. Unlike the t(11;22)(q23;q11), the formation of the t(4;11)(p16.2;p15.4) may have involved segmental duplications and sequence homology at the breakpoints. Additional examples of recurrent translocations could be identified if the resources were available to study more translocations using the approaches described here. However, like the t(4;11)(p16.2;p15.4), such translocations are likely to be rare with the t(11;22) remaining the only common recurrent constitutional reciprocal translocation.

Animal models for the molecular and mechanistic study of lymphatic biology and disease

The development of animal model systems for the study of the lymphatic system has resulted in an explosion of information regarding the mechanisms governing lymphatic development and the diseases associated with lymphatic dysfunction. Animal studies have led to a new molecular model of embryonic lymphatic vascular development, and have provided insight into the pathophysiology of both inherited and acquired lymphatic insufficiency. It has become apparent, however, that the importance of the lymphatic system to human disease extends, beyond its role in lymphedema, to many other diverse pathologic processes, including, very notably, inflammation and tumor lymphangiogenesis. Here, we have undertaken a systematic review of the models as they relate to molecular and functional characterization of the development, maturation, genetics, heritable and acquired diseases, and neoplastic implications of the lymphatic system. The translation of these advances into therapies for human diseases associated with lymphatic dysfunction will require the continued study of the lymphatic system through robust animal disease models that simulate their human counterparts.

Craniosynostosis associated with distal 5q-trisomy: further evidence that extra copy of MSX2 gene leads to craniosynostosis

Distal 5q-trisomy has been reported in less than 30 patients, with craniosynostosis present in five. We report two new patients with distal 5q-trisomy craniosynostosis. Patient 1 had mild Kleeblattschädel with synostosis of multiple sutures together with wide and medially deviated thumbs and halluces, indicative of Pfeiffer syndrome. Cytogenetic and CGH analyses showed a karyotype of 46,XY,der(10)t(5;10)(q33;q26.3). Patient 2 had a prominent forehead and ridging of the metopic suture. Craniosynostosis of the metopic suture was shown by CT scan. Cytogenetic and CGH analyses disclosed a karyotype of 46,XX,der(17)t(5;17)(q35.1;p13.3). Of the 22 previously reported patients, all had microcephaly and 14 had an abnormal skull shape. Our results support the previous finding that distal 5q-trisomy together with an extra copy of the MSX2 gene leads to abnormal closure of sutures and craniosynostosis.

Directly transmitted unbalanced chromosome abnormalities and euchromatic variants

In total, 200 families were reviewed with directly transmitted, cytogenetically visible unbalanced chromosome abnormalities (UBCAs) or euchromatic variants (EVs). Both the 130 UBCA and 70 EV families were divided into three groups depending on the presence or absence of an abnormal phenotype in parents and offspring. No detectable phenotypic effect was evident in 23/130 (18%) UBCA families ascertained mostly through prenatal diagnosis (group 1). In 30/130 (23%) families, the affected proband had the same UBCA as other phenotypically normal family members (group 2). In the remaining 77/130 (59%) families, UBCAs had consistently mild consequences (group 3). In the 70 families with established EVs of 8p23.1, 9p12, 9q12, 15q11.2, and 16p11.2, no phenotypic effect was apparent in 38/70 (54%). The same EV was found in affected probands and phenotypically normal family members in 30/70 families (43%) (group 2), and an EV co-segregated with mild phenotypic anomalies in only 2/70 (3%) families (group 3). Recent evidence indicates that EVs involve copy number variation of common paralogous gene and pseudogene sequences that are polymorphic in the normal population and only become visible at the cytogenetic level when copy number is high. The average size of the deletions and duplications in all three groups of UBCAs was close to 10 Mb, and these UBCAs and EVs form the "Chromosome Anomaly Collection" at http://www.ngrl.org.uk/Wessex/collection. The continuum of severity associated with UBCAs and the variability of the genome at the sub-cytogenetic level make further close collaboration between medical and laboratory staff essential to distinguish clinically silent variation from pathogenic rearrangement.

Duplication 4p and deletion 4p (Wolf-Hirschhorn syndrome) due to complementary gametes from a 3:1 segregation of a maternal balanced t(4;13)(p16;q11) translocation

We present clinical and cytogenetic data on a family with a t(4;13)(p16;q11) translocation present in four generations. The balanced translocation resulted in one individual with monosomy 4p and one individual with trisomy 4p, due to 3:1 segregation. The male patient with trisomy 4p was fertile and transmitted the extra chromosome to his daughter.

Characterization of terminal chromosome anomalies using multisubtelomere FISH

Telomeric repeat sequences (TTAGGG) are known to cap the termini of every human chromosome. Proximal to these repeat sequences are chromosome-specific repeat sequences, which in turn are distal to gene-rich regions. Submicroscopic, subtle, or cryptic abnormalities in these regions can now be investigated using commercial probe sets for all of the chromosome-specific subtelomeric regions of the human genome. Using this technology, previously unidentified genomic imbalance has been found in a proportion of patients with idiopathic developmental delay and learning difficulties. We have used these probe sets to investigate cases with apparently terminal anomalies detected on G-banded chromosome analysis. As a result of such investigations, we have found that 3 (19%) of 16 apparently terminal deletion cases were the result of more complex rearrangements involving other chromosome subtelomeres. The remaining 13 cases contained no chromosome-specific subtelomere repeats on the deleted arm, but in all 16 cases, the TTAGGG telomere repeat cap was present. A further case was investigated where extra material was found in the terminal region of the chromosome 12 short arm, found to represent a complex inversion/duplication/deletion rearrangement. Investigation of all cases with terminal anomalies, including apparently terminal deletions, is likely to uncover further cases involving complex rearrangements and should lead to a greater understanding of the mechanisms by which these abnormalities arise.

Research perspectives in inherited lymphatic disease

The hereditary lymphedemas provide an opportunity to identify genes involved in normal and deranged lymphatic development. Genetic analysis of families with Milroy's disease identified mutations in VEGFR3 as a cause of congenital lymphedema, confirming the importance of VEGFC/VEGFR3 signaling in lymphatic development. These observations led to the identification of a mouse model for primary lymphedema, and subsequent analysis of this mouse model, using transgenic and gene transfer techniques, has provided initial clues to the development of a biologically based therapy for primary lymphedema. Of more importance from a public health perspective is the fact that manipulation of this pathway may lead to effective therapies for the more prevalent forms of secondary lymphedema. Identification of FOXC2 as the gene mutated in the lymphedema-distichiasis syndrome has revealed new molecular insight into lymphatic development. Molecular analysis of the FOXC2 pathway may provide clues to developmental pathways shared by the lymphatic system and the other developmental abnormalities associated with this complex syndrome. With improving knowledge of the human genome, genetic analysis of families with lymphedema continues to offer one of the most promising approaches to identifying genes influencing lymphatic development.

Molecular regulation of lymphangiogenesis and targets for tissue oedema

New insight has recently been obtained into the molecular mechanisms regulating the function of lymphatic endothelial cells. Vascular endothelial growth factors-C and -D have been shown to stimulate lymphangiogenesis, and their receptor VEGFR-3 has been linked to human hereditary lymphoedema, although there is evidence that other genes are also involved. These data suggest that it may become possible to stimulate lymphatic growth and function and to treat tissue oedema involved in many diseases.

Genetic evidence for a novel gene(s) involved in urogenital development on 10q26

BACKGROUND

Although the frequent association between distal 10q monosomy and urogenital anomalies suggests the presence of a gene(s) for urogenital development on distal 10q, molecular deletion mapping has not been performed for the putative gene(s). In this study, we examined genotype-phenotype correlations in patients with distal 10q monosomy.

METHODS

This study consisted of six karyotypic males (cases 1 through 6) and four karyotypic females (cases 7 through 10) with 10q26 monosomy. Cases 3 through 5 and 7 through 10 had urinary anomalies such as vesicoureteral reflux and hypoplastic kidney, and cases 1 through 6, 8, and 9 exhibited genital anomalies such as micropenis, hypospadias, cryptorchidism, and hypoplastic labia majora. Fluorescence in situ hybridization (FISH) for 10q telomere, whole chromosome 10 painting, and microsatellite analysis for 35 loci on distal 10q were performed in cases 1 through 8.

RESULTS

FISH and whole chromosome painting confirmed distal 10q monosomy in cases 1 through 8. Microsatellite analysis revealed that hemizygosity for the region distal to D10S186 was shared by cases with urinary anomalies and that for the region distal to D10S1248 was common to cases with genital anomalies. Furthermore, it was indicated that PAX2, GFRA1, and EMX2 on distal 10q, in which the deletions could affect urinary and/or genital development, were present in two copies in cases 1 through 8.

CONCLUSIONS

The results suggest that a novel gene(s) for urinary development and that for genital development reside in the approximately 20 cM region distal to D10S186 and in the approximately 10 cM region distal to D10S1248, respectively, although it remains to be determined whether the two types of genes are identical or different.

Missense mutations interfere with VEGFR-3 signalling in primary lymphoedema

Primary lymphoedema is a rare, autosomal dominant disorder that leads to a disabling and disfiguring swelling of the extremities and, when untreated, tends to worsen with time. Here we link primary human lymphoedema to the FLT4 locus, encoding vascular endothelial growth factor receptor-3 (VEGFR-3), in several families. All disease-associated alleles analysed had missense mutations and encoded proteins with an inactive tyrosine kinase, preventing downstream gene activation. Our study establishes that VEGFR-3 is important for normal lymphatic vascular function and that mutations interfering with VEGFR-3 signal transduction are a cause of primary lymphoedema.

Repeated unbalanced offspring due to a familial translocation involving chromosomes 5 and 6

We identified 10 members of a single family with mental retardation and microcephaly, one member having macrocephaly instead. The pedigree was best compatible with the segregation of a small translocation, despite results of previous cytogenetic studies in several relatives being apparently normal. Eventually high resolution and fluorescence in situ hybridization studies in the parents allowed the detection of a balanced translocation between 5qter and 6qter, and of its unbalanced products in the offspring. The pertinent findings from the family are briefly compared with the clinical findings in patients from the literature with either a duplication or deletion of 5q35-ter, or a duplication or deletion of 6q27-ter.

Trisomy 2q11.2-->q21.1 resulting from an unbalanced insertion in two generations

In this communication, we describe two cases of proximal 2q trisomy (2q11.2--> q21.1) resulting from an interchromosomal insertion. The chromosomal origin of the insertion was confirmed by fluorescence in situ hybridisation. An unbalanced karyotype, 46,XX,der(8) ,ins(8;2) (p21.3; q21.1q11.2), was found in the proband and her mother, who both have mild mental retardation, short stature, dysmorphic features, insulin dependent diabetes mellitus, and a psychotic illness. This family is a rare example of direct transmission of a partial autosomal trisomy.