Autosomal syndromes

Role of heredity and mutation outcomes

Depending on the severity of consequences for the organism, genetic defects are classified by clinical outcomes:

• Lethal mutations: accompanied by the death of the individual during prenatal development. Clear examples include autosomal monosomies, haploidies, and the overwhelming majority of polyploidies.
• Sublethal mutations: the patient dies before puberty, losing the ability to leave offspring. This group includes Swiss-type agammaglobulinemia, Louis-Bar syndrome (Ataxia-telangiectasia), and certain forms of hemophilia.
• Hypogenital mutations: patients survive, but the pathology is combined with infertility (e.g., Klinefelter and Turner syndromes).

According to the degree of environmental and genomic contribution, pathologies are divided into strictly hereditary diseases (direct consequence of a mutation), ecogenetic (a specific environmental factor provokes the mutation), diseases of genetic predisposition (mutations act as risk factors), and diseases caused by environmental factors (the genetic contribution to their development is extremely negligible).

Mechanisms of development of monogenic diseases

Gene diseases are the most frequent form of hereditary pathology. In most cases, these are monogenic (Mendelian) diseases, the differentiation of which is based on the function of the altered polypeptide. The mutant gene can disrupt the work of structural proteins, receptors, or transmembrane transporters. If enzyme synthesis fails, enzymopathy develops—a severe disruption of cellular metabolism.

The most important characteristic of any monogenic disease is its type of inheritance:

1. Autosomal dominant: Marfan syndrome, polydactyly, Huntington's chorea.
2. Autosomal recessive: phenylketonuria, cystic fibrosis, albinism. It is important to remember that the heterozygote phenotype with this type of inheritance may be completely indistinguishable from normal—manifestations are either mild or completely absent.

Treatment of genetic diseases can be symptomatic, pathogenetic (dietary therapy, replacement therapy with insulin or blood clotting factors, toxin removal), and etiological (the most promising direction is gene therapy).

Autosomal chromosomal diseases

Chromosomal pathologies arise due to impaired chromosome segregation during gametogenesis, leading to a change in their exact number or structure. Among autosomal syndromes, trisomies are the most well-known—the presence of an extra third chromosome in a pair:

• Down syndrome: trisomy of the 21st pair;
• Edwards syndrome: trisomy of the 18th pair;
• Patau syndrome: trisomy of the 13th pair.

To detect them, the cytogenetic method is used: microscopic study of chromosomes, karyotyping, and graphic idiogram creation (where chromosomes are arranged in descending order of size). As a rapid diagnostic, dermatoglyphics can be used—evaluation of palm skin patterns (e.g., detecting a "simian crease" in Down syndrome).

Pathogenesis using Gaucher disease as an example

Gaucher disease is the most common hereditary enzymopathy from the group of lysosomal storage diseases. It is inherited in an autosomal recessive manner. In the general population, the disease frequency ranges from 1:40,000 to 1:100,000, and in the Ashkenazi Jewish population, it reaches 1:45.

The basis of the pathology is a mutation in the GBA gene (chromosomal region 1q22) encoding the lysosomal enzyme β-D-glucocerebrosidase. The pathogenetic cascade develops sequentially:

1. The presence of biallelic pathogenic variants of the gene reduces the catalytic activity of the enzyme.
2. Unutilized lipids begin to accumulate in the lysosomes of macrophages.
3. Lipid-overloaded, specific "Gaucher cells" are formed.
4. Chronic activation of the macrophage system occurs.
5. Autocrine stimulation of monocytopoiesis increases the absolute number of macrophages in target organs—the spleen, liver, and bone marrow.

As a result of the metabolic defect, hepatomegaly, splenomegaly, and bone marrow infiltration develop, while impaired regulatory functions of macrophages become the basis for cytopenic syndrome and bone-articular system lesions.

Class and exam questions

What else to study on this topic

• Diseases linked to sex chromosomes (hemophilia, color blindness) and their pedigrees.
• Maternal-fetal incompatibility diseases (e.g., Rhesus conflict mechanisms).
• Features of multifactorial pathologies and diseases with mitochondrial (maternal) inheritance.
• Invasive prenatal diagnostic methods: amniocentesis, cordocentesis, and chorionic villus sampling.
• Principles of medical genetic counseling to predict risks in offspring.

Other topics in the "Additional Topics" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.