Molecular cytogenetic characterisation of a mosaic add(12)(p13.3) with an inv dup(3)(q26.31 --> qter) detected in an autistic boy

Multicolor FISH methods in current clinical diagnostics

Multicolor FISH (mFISH) assays are currently indispensable for a precise description of derivative chromosomes. Routine application of such techniques on human chromosomes started in 1996 with the simultaneous use of all 24 human whole-chromosome painting probes in multiplex-FISH and spectral karyotyping. Since then, multiple approaches for chromosomal differentiation based on multicolor-FISH (MFISH) assays have been developed. Predominantly, they are applied to characterize marker or derivative chromosomes identified in conventional banding analysis. Since the introduction of array-based comparative genomic hybridization (aCGH), mFISH is also applied to verify and further delineate aCGH-detected aberrations. For the latter, it is important to consider the fact that aCGH cannot detect or characterize balanced rearrangements, which are important to be resolved in detail in infertility diagnostics. In addition, mFISH is necessary to distinguish different imbalanced situations detectable in aCGH; small supernumerary marker chromosomes have to be differentiated from insertions or unbalanced translocations. This review presents an overview on the available mFISH methods and their applications in pre- and post-natal clinical genetics.

Somatic genome variations in health and disease

It is hard to imagine that all the cells of the human organism (about 10(14)) share identical genome. Moreover, the number of mitoses (about 10(16)) required for the organism's development and maturation during ontogeny suggests that at least a proportion of them could be abnormal leading, thereby, to large-scale genomic alterations in somatic cells. Experimental data do demonstrate such genomic variations to exist and to be involved in human development and interindividual genetic variability in health and disease. However, since current genomic technologies are mainly based on methods, which analyze genomes from a large pool of cells, intercellular or somatic genome variations are significantly less appreciated in modern bioscience. Here, a review of somatic genome variations occurring at all levels of genome organization (i.e. DNA sequence, subchromosomal and chromosomal) in health and disease is presented. Looking through the available literature, it was possible to show that the somatic cell genome is extremely variable. Additionally, being mainly associated with chromosome or genome instability (most commonly manifesting as aneuploidy), somatic genome variations are involved in pathogenesis of numerous human diseases. The latter mainly concerns diseases of the brain (i.e. autism, schizophrenia, Alzheimer's disease) and immune system (autoimmune diseases), chromosomal and some monogenic syndromes, cancers, infertility and prenatal mortality. Taking into account data on somatic genome variations and chromosome instability, it becomes possible to show that related processes can underlie non-malignant pathology such as (neuro)degeneration or other local tissue dysfunctions. Together, we suggest that detection and characterization of somatic genome behavior and variations can provide new opportunities for human genome research and genetics.

Prenatally diagnosed partial trisomy 3q case with an omphalocele and less severe phenotype

Trisomy 3q is a very rarely reported chromosomal disorder. Duplication of part of the long arm of human chromosome 3 causes a distinct and severe syndrome that leads to multiple congenital abnormalities. A 27 year-old pregnant woman was admitted to our clinic at 17 weeks of gestation. Prenatal sonography identified a fetus with an omphalocele that contained the liver and bowel, mild ventriculomegaly and polyhydramnios. Amniocentesis revealed the karyotype of 46, XY, der (3) (3qter→3q21: : 3pter→3qter). The pregnancy was subsequently terminated. Postnatally, the proband showed midfacial hypoplasia, micrognathia, hypoplastic 12th ribs, omphalocele and prominent heels. We reported this partial trisomy 3q case because he had less marked malformations compared to other reported cases and also different features such as an omphalocele and hypoplastic 12th rib which have not been described previously in an isolated Trisomy 3q case with this karyotype.