Screening for hereditary diseases

Genetic screening is part of health care programs today. Originally, it was about identifying newborns with a genetically determined disease that is treatable in case of early diagnosis, e.g. PKU. The main role of genetic screening is to improve the health of society.

Newborn Screening Programs
Principles of an adequate screening-test:
 * the disease state must not only be clearly defined, but also treatable and its incidence in the monitored population must be significant
 * the examination itself must be done quickly and easily on a large number of samples
 * the test should have few false positives and, if possible, zero false negatives
 * completion of diagnosis and initiation of treatment must be well organized and prompt
 * if these conditions are not met, complications will occur

Screening of heterozygotess
'Conditions for enabling the screening test:
 * significant occurrence of the disease in a specific population group
 * availability of a test suitable for mass screening
 * possibility of prenatal diagnosis
 * the following diseases meet these criteria:

1. Tay-Sachs disease

 * often occurs in Ashkenazi Jews
 * this is one of several different forms of familial amaurotic idiocy (amaurotic = unclear)
 * the enzyme disorder in this disease is a significant deficiency of hexosaminidase A (hex A), in a wide range of tissues; the role of hex A is to cleave the N-acetyl-galactosamine residue from the polysaccharide chain of the ganglioside molecule. In case of its deficiency, ganglioside accumulates, mainly in brain tissue
 * heterozygotess can be detected by screening blood samples for hexosaminidase activity
 * the disease can be detected by biochemical analysis of cultured amniocytes

2. Sickle cell anemia

 * manifests itself practically exclusively in blacks
 * the molecular basis is abnormal hemoglobin – HbS
 * this is a severe hemolytic disease with a characteristic tendency of red blood cells to take an obviously abnormal form in an environment with reduced partial pressure of oxygen
 * clinical picture: anemia, icterus and "crisis", vascular obstruction and painful infarcts of various organs (bones, spleen, lungs)

3. Thalassemia

 * heterogeneous group of disorders of HbA chain formation
 * caused by damaged genes for hemoglobin, possibly. deletions

Screening α-fetoprotein in maternal serum (MSAFP)

 * possibility of detection of split defects, event. fetal Down syndrome warning

Related Articles

 * Indication of chromosomal examination
 * Inherited disorders of amino acid metabolism
 * Newborn Screening

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