Patient's question:
What are the major genetic diseases? If my elders suffer from this disease, what is the probability that I will get it?Doctor's answer:
Genetic diseases are caused by abnormal changes in genetic material (including chromosomes and genes). To date, approximately 3,000 genetic diseases have been discovered worldwide, including over 300 types of chromosomal disorders and over 2,700 types of genetic disorders. Some common genetic diseases include:(1) Autosomal dominant genetic diseases: These are diseases caused by dominant pathogenic genes located on autosomes and are the most common among single-gene genetic diseases. If one of the parents is a patient, the risk of the disease occurring in both males and females is equal, and half of the offspring will be affected. Examples include:
- Brachydactyly: Due to shortening or absence of finger (or toe) bones or metacarpals (metatarsals), resulting in short fingers (or toes).
- Familial hypercholesterolemia: Characterized by cholesterol deposition in the vessel walls, causing atherosclerosis, which may lead to early coronary heart disease or myocardial infarction.
(2) Autosomal recessive genetic diseases: These are diseases caused by recessive pathogenic genes located on autosomes. Both parents of the affected individual are carriers or patients of the pathogenic gene, and the risk of the disease is equal for both males and females. The incidence rate increases significantly in offspring of consanguineous marriages. Common examples include:
- Albinism: Caused by a metabolic disorder in melanin production, resulting in white skin and hair, pale red irises and pupils, and depigmented retinas with photophobia.
- Phenylketonuria: Due to a hereditary deficiency of phenylalanine hydroxylase, leading to normal appearance in infants but gradual onset of intellectual disability, abnormal gait, small steps, simian-like posture, and a special foul odor in urine.
- Galactosemia: Caused by a deficiency of galactose-1-phosphate uridyltransferase, resulting in vomiting and diarrhea after breastfeeding, intolerance to dairy products, and later complications such as liver cirrhosis, cataracts, and intellectual disability.
(3) Sex-linked genetic diseases: These are genetic diseases caused by pathogenic genes on sex chromosomes. Most sex-linked pathogenic genes are located on the X chromosome, and male patients are far more common than female patients. Examples include:
- Red-green color blindness: The affected individual has impaired or reduced ability to distinguish red and green.
- Antivitamin D rickets: Primarily caused by impaired phosphate transport mechanisms in the distal renal tubules, leading to increased phosphate excretion in urine and decreased blood phosphate levels, which affects bone calcification. Patients are short-statured and do not respond to vitamin D treatment.
(4) Polygenic genetic diseases: These are genetic diseases controlled by multiple pairs of pathogenic genes and have a lower incidence rate. Common examples include:
- Congenital hip dislocation
- Spina bifida
- Cleft lip or palate (commonly referred to as "harelip")
- Anencephaly
(5) Chromosomal diseases: These are diseases caused by congenital abnormalities in chromosome number or structure. Examples include:
- Trisomy 21 (Down syndrome): Caused by the presence of three copies of chromosome 21, primarily characterized by intellectual disability, wide-set eyes, slanted eyelid corners, open mouth with protruding tongue, and drooling.