Human Genetic Diseases

Section 3: Human Genetic Diseases

With the improvement of living standards and medical conditions, most infectious diseases in humans have gradually been brought under control. However, the incidence and mortality rates of human genetic diseases have shown a trend of increasing year by year. Human genetic diseases have become an important factor threatening human health.

Types of Common Human Genetic Diseases

Human genetic diseases generally refer to diseases caused by changes in genetic material. They can mainly be divided into three categories: single-gene genetic diseases, polygenic genetic diseases, and chromosomal abnormality genetic diseases.

Single-Gene Genetic Diseases
Single-gene genetic diseases are those controlled by a pair of alleles. More than 8,000 types of such genetic diseases have been discovered worldwide. Single-gene genetic diseases may be caused by dominant pathogenic genes, such as polydactyly, syndactyly, and achondroplasia (Figure 5-8). They can also be caused by recessive pathogenic genes, such as sickle cell anemia, albinism, and phenylketonuria.

Polygenic Genetic Diseases
Polygenic genetic diseases are those controlled by two or more pairs of alleles. These diseases mainly include some congenital developmental abnormalities and some common diseases, such as primary hypertension, coronary heart disease, asthma, and juvenile diabetes. The incidence of polygenic genetic diseases in the population is relatively high.

Chromosomal Abnormality Genetic Diseases
Chromosomal abnormality genetic diseases are those caused by chromosomal variations (commonly referred to as chromosomal diseases). Over 500 such diseases have been identified, affecting almost every pair of human chromosomes. Among them, Down syndrome, also known as trisomy 21 syndrome, is a common chromosomal disease. Patients with Down syndrome have below-average intelligence, slow physical development, and characteristic facial features. Chromosome testing of patients reveals an extra 21st chromosome compared to normal individuals (Figure 5-9).

After understanding the types of common human genetic diseases, let us further explore human genetic diseases through investigations.

Detection and Prevention of Genetic Diseases

In China, 20% to 25% of people suffer from genetic diseases, with more than 600,000 individuals affected by Down syndrome alone. Genetic diseases not only cause suffering to the affected individuals but also place a burden on families and society. Through genetic counseling (Figure 5-10) and prenatal diagnosis, genetic diseases can be detected and prevented to some extent, effectively reducing the occurrence and development of these diseases.

Prenatal diagnosis refers to the methods used by doctors to determine whether a fetus has a genetic or congenital disease before birth. These methods include amniocentesis (Figure 5-11), ultrasound, maternal blood cell tests, and genetic testing.

Genetic testing involves analyzing the DNA sequences in human cells to understand the genetic status of an individual. Blood, saliva, semen, hair, or tissue from the human body can all be used for genetic testing.

Genetic testing can accurately diagnose the cause of a disease. For example, certain diseases are associated with gene mutations; identifying the mutated gene can lead to a precise diagnosis (Figure 5-12), allowing doctors to prescribe appropriate treatments. By analyzing an individual's genetic status and combining it with disease genomics, the risk of developing a disease can be predicted, helping individuals avoid or delay the onset of diseases by improving their living environment and lifestyle. Additionally, by detecting whether parents carry pathogenic genes for genetic diseases, the probability of offspring inheriting such diseases can be predicted.

However, genetic testing also raises concerns, as people worry about facing unequal treatment in employment, insurance, and other areas due to the detection of defective genes.How do you think this issue should be properly addressed?