As shown in Table 1, some chromosomal diseases have a relatively high incidence, so they are the object of prenatal diagnosis, especially in conditions of high risk (advanced age of the pregnant woman, familiarity with the disease, suggestive fetal ultrasound signs). Until a few years ago, prenatal diagnosis of chromosomal diseases was performed exclusively in cells collected by amniocentesis (usually in the fifth month of pregnancy) through the classic analysis of the karyogram. The amniocytes are placed in culture; after a few days, cell growth in metaphase is stopped, and the chromosomes are studied under the microscope after staining, evaluating numerical or structural abnormalities. In addition to classic chromosome staining, more sophisticated techniques can be used, such as banding, which allows better resolution of the image of individual chromosomes and major defects (deletions, translocations), or gene probes associated with fluorescence detection systems that bind specific regions of individual chromosomes and allow their specific recognition (fluorescent in situ hybridization, FISH). Subsequently, chromosome analysis by karyogram was extended to chorionic villi, allowing prenatal diagnosis by chorionic villus sampling (in the first trimester of pregnancy). Amniocentesis and chorionic villus sampling, even in experienced hands, maintain a minimal risk of causing irreversible damage to the fetus or mother (around 1% overall), so they are currently defined as invasive prenatal diagnoses.

Table1. Incidence of some chromosomopathies

Alternatively, non-invasive diagnostic approaches are available. The first group of methods involves the analysis, at a specific time of pregnancy, of some markers in the maternal serum whose concentrations, assessed together with other parameters (age of the pregnant woman, family history of chromosomal diseases, etc.), allow an estimation of the risk of Down’s syndrome for the fetus. When the risk exceeds a threshold, it is suggested to perform an invasive prenatal diagnosis.

More recently, non-invasive screening molecular tests have become available, defined by the acronym NIPT (non- invasive prenatal testing) based on the analysis of fetal DNA in maternal blood (which begins to appear from the fifth week of pregnancy). These tests are based on massive sequencing analysis of the entire fetal genome or comparative genomic hybridization techniques (see section “Pre- implantation Diagnosis”), followed by analyzing the results using sophisticated bioinformatics programs. These technologies allow the identification of aneuploidies (numerical alterations of chromosomes) and structural alterations (unbalanced translocations, deletions, duplications, etc.) associated with the loss or gain of DNA. Some variants of these tests allow “molecular karyotyping” to be performed by massively parallel sequencing. Overall, these tests can identify more than 95% of all chromosomal alterations detectable by traditional karyogram.

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مواضيع ذات صلة

Prenatal Diagnosis of Hereditary Genetic Diseases

Clinical Applications of Gene Testing in Muscular Dystrophy

The Genetics of Duchenne Muscular Dystrophy and Becker Muscular Dystrophy

Pathogenic Variants of an Enzyme Inhibitor: α1-Antitrypsin Deficiency

Lysosomal Storage Diseases: A Unique Class of Enzymopathies

Aminoacidopathies

Diseases due to pathogenic variants in different classes of proteins

Renal cysts and diabetes (HNF1B MODY)

Maternally inherited diabetes and deafness

Genetic testing in neonatal diabetes

Human Hemoglobin and Associated Diseases

The Relationship Between Genotype and Phenotype in Genetic Disease