Medical Genetics - V. M. Zaporozhan 2005

Classification, general characteristics, and symptoms of hereditary diseases. General clinical diagnostics
Syndromological diagnosis in clinical genetics

Hereditary diseases are the result of genotype alterations that cause disruptions in embryonic development or specific metabolic pathways. Since each Gene has a distinct function, identical Mutations manifest with a similar phenotype in different individuals (typically as a complex of symptoms rather than a single manifestation). This specific combination of external disease traits can be explained by the pleiotropic (multiple) effects of genes, creating a patient phenotype so characteristic that it is sometimes reflected in the name of the condition (e.g., "elfin face" syndrome, fetal face syndrome, "happy puppet" syndrome, and "mongoloid idiocy" — an obsolete term for Down syndrome, among others).

Knowing the symptoms typical of a given hereditary disease makes it possible to diagnose it based on an Analysis of the patient's phenotype. A consistent set of symptoms united by a single Pathogenesis is referred to as a syndrome. Thus, the Diagnosis of hereditary diseases is syndromological in nature.

Most hereditary syndromes are diagnosed solely on The basis of a characteristic clinical picture. The diagnosis of hereditary conditions, frequently grounded in the patient's specific phenotype, is known as portrait (syndromological) Diagnostics. To facilitate portrait-based diagnosis, diagnostic atlases containing photographs of patients with hereditary pathologies, as well as computer-aided diagnostic software, have been developed. An accurate diagnosis is essential for the physician to properly determine the life prognosis and choose the appropriate Treatment strategy. For instance, in Patau syndrome, performing complex cleft palate surgeries is futile, as infants with this condition are not viable. Esophageal atresia may be an isolated developmental defect or a symptom of the lethal DiGeorge syndrome. In the former case, surgical intervention is recommended, whereas in the latter, it is pointless.

Furthermore, an accurate diagnosis allows for the Determination of the trait's inheritance pattern, making it possible to calculate the probability of having an affected child in the future and to select adequate prenatal diagnostic measures.