genetic disease
Introduction
Introduction to genetic diseases Genetic disease refers to a disease caused by a change in genetic material or controlled by a disease-causing gene. Genetic disease refers to a disease that is determined in whole or in part by genetic factors, often congenital or acquired. Such as congenital, multi-finger (toe), congenital hoarseness, hemophilia, etc., these genetic diseases are completely determined by genetic factors, and only occur after a certain period of time, sometimes after several years, ten years or even a few Significant symptoms can occur after ten years. At the time of examination, chromosome analysis technique was used to prenatally diagnose fetal chromosomal disease. In the past, amniotic fluid was extracted by amniocentesis at 14 to 16 weeks of gestation, and the cells were cultured for chromosome analysis. The main advantage of this is that the time for examination can be advanced to the early pregnancy (about 8 weeks), and the specimens obtained do not have to undergo cell culture, and can be directly analyzed by chromosomes, and the inspection report can be obtained on the same day. This technique is generally considered to be quite safe with amniotic cell chromosome analysis techniques. basic knowledge The proportion of sickness: 0.01% Susceptible people: no special people Mode of infection: non-infectious Complications: ventricular septal defect
Cause
Cause of genetic disease
1. Chromosomal abnormality: refers to diseases caused by the number or shape of chromosomes, structural abnormalities:
A. Structural abnormality meow syndrome (partial deletion of chromosome 5); B. abnormal number of autosomes: trisomy 21.
Sex chromosome: Gonadal dysplasia (X0, XXY, XYY).
2. Gene abnormalities:
A. Single gene: A genetic disease caused by an abnormality of a gene on a pair of chromosomes from a father or mother in a homologous chromosome.
a. Autosome:
Dominant: (chondral hypoplasia, polydipsia, colon polyps);
Recessive: (alienopathy, phenylketonuria, black urine, congenital hoarseness, high myopia);
Not fully dominant (thalassemia).
b. Sex chromosome:
I, with X:
Dominance: The incidence of women is higher than that of men: (Xg blood type, as well as anti-vitamin D rickets);
Recessive: male incidence rate is higher than female: (red and green blind, hemophilia, etc. are more common).
II, with Y only male incidence (external auditory canal hirsutism).
B. Multiple genes: genetic diseases associated with two or more genes. There is no dominant or recessive relationship between each pair of genes, and each disease is caused by multiple pairs of genes and environmental factors.
Prevention
Genetic disease prevention
Spouse selection:
1. Avoid falling in love with people with the same genetic disease and prevent the same genetic patients from marrying each other. Because of the mating of such patients, the chances of their offspring suffering from the same genetic disease as their parents will increase significantly. Such as essential hypertension, atherosclerosis, diabetes, congenital heart disease, myasthenia gravis, spina bifida, cleft lip, congenital dislocation of the hip, congenital asthma, congenital hoarseness and high myopia, prevention A generation of genetic diseases. If two patients with essential hypertension are married, the probability of their offspring suffering from essential hypertension will be as high as 47%.
2. Avoid the marriage of close relatives, the incidence of recessive genetic diseases of offspring due to close relatives will be significantly higher than the general population.
3. The results of the study indicate that the offspring of the birth of a variety of serious diseases, the possibility of hereditary diseases will also increase. Patients who are suffering from viral hepatitis, tuberculosis, sexually transmitted diseases and other serious organic diseases are not rushing to get married.
Birth:
1. To choose the timing of conception. The age of both spouses should be appropriate. The woman is over 35 years old, and the chances of her children suffering from congenital stupidity can be increased by about 10 times. The age of the man is preferably no more than 50 years old.
2. Pay attention to the external environment of the body of both men and women at the time of conception, such as being in close contact with toxic and hazardous substances (such as receiving radiation therapy or spraying pesticides), or applying certain drugs that can cause damage to the embryo. , can not be pregnant immediately. Avoid pregnancy after avoiding harmful external environment for a while.
3. If there are more than two consecutive spontaneous abortions, a chromosomal examination should be performed to determine whether it is related to genetic factors, and the doctor decides whether to re-pregnancy.
4. The last child is a teratogenic woman. Before giving birth again, it must be thoroughly examined by a doctor to find out the cause of the teratology before deciding whether to have a pregnancy.
Complication
Genetic disease complications Complications, ventricular septal defect
(a) Phenylketonuria:
This congenital metabolic disease is caused by the pathogenic gene that prevents the formation of phenylalanine hydroxylase (PAH) in the liver of the human body. This enzyme can promote the conversion of phenylalanine to tyrosine. The conversion of the amino acid is blocked, resulting in the accumulation of phenylalanine in human blood and other tissues. Excess phenylalanine and its derivative, phenylpyruvate, are excreted in the urine, so it is called phenylketonuria. If phenylpyruvate and its metabolites accumulate in the brain, it will cause disturbance of the biochemical metabolism of brain tissue, hinder the growth and development of the brain, and cause mental retardation, which is the cause of dementia in patients with this disease. In addition, excessive phenylalanine and its metabolites may inhibit the conversion of tyrosine to melanin, so patients are often accompanied by skin color and lighter hair traits. The gene controlling phenylalanine hydroxylase was localized at 12q22 to 12q24.2.
(2) Black urine disease:
Another important metabolic pathway for tyrosine in the human body is the conversion to acetoacetate, which is further broken down into carbon dioxide and water, making the presence of urinary acid in the urine. However, when urinary acid oxidase is deficient due to a genetic defect, uric acid is discharged from the urine because it cannot be oxidatively decomposed. Uroic acid itself has no color, but it will turn black in the air for a while, so the urine will also turn black. Under alkaline conditions, the uric acid can be further blackened, so the diapers of such children are washed with soap and the more they wash, the darker they are. However, black urine is a benign disorder of autosomal recessiveness, which is generally not harmful to patients, but sometimes it can cause pigmentation in parts such as cartilage and joints, and it can cause arthritis in severe cases.
(3) Albinism:
In normal humans, tyrosine also has an important metabolic pathway, which is the formation of melanin with the participation of tyrosinase. Melanin makes human hair appear black, and people who have been working in the field for a long time will have darkened skin. This is because the formation of melanin is accelerated by the sunlight, and there are more melanin deposits in the skin cells. To. The increase of melanin can prevent the sun's ultraviolet rays from being irradiated to the human body and has a certain protective effect. However, if the gene controlling tyrosine synthase is recessively mutated or two recessive genes are obtained from both parents, this person cannot synthesize tyrosinase, resulting in hindered formation of melanin in the body, lacking melanin. As a result, the body is whitish, even the hair and eyebrows are white. This is commonly known as albinism, commonly known as "sheep whitehead." Other aspects of albinos are normal, unlike phenylketonuria, which affects people's intellectual development. The only defect of this kind of person is that he is afraid of exposure to sunlight, especially the eyes are particularly photophobic. The whitening patients who are commonly seen are almost blindfolded, especially in the case of blindness caused by excessive light stimulation.
(4) Congenital glucose and galactose malabsorption:
The child presented with diarrhea, a watery stool, similar to urine. The incidence and degree of diarrhea are related to the time and amount of feeding sugar. Diarrhea occurs 24 hours after feeding. The more eating, the more serious, but the food intake of the child is very large, so the weight quickly declines. It is then dehydrated, weightless, and malnourished. As long as the child does not use fructose as the main source of sugar, diarrhea will occur, so it is necessary to limit the consumption of glucose and galactose for life. However, it is resistant to glucose and galactose with age.
(5) sickle-shaped red blood cell anemia:
This disease is often considered to be autosomal recessive, more like incomplete dominance, the homozygous anemia of the disease-causing gene is severe, dysplasia, joint, abdomen and muscle pain, mostly in childhood. However, most of the hybrids with pathogenic genes are asymptomatic, or some have only mild anemia. However, if this heterozygous person is in the highland area or if long-term high-intensity exercise training leads to hypoxia in the body, the red blood cells will "transform", block the blood vessels, cause systemic fever, muscle soreness, and a lot of red blood cells are spleen. Phagocytosis, decreased hemoglobin, decreased ability of the body to transport O2 and CO2, causing a vicious circle of red blood cell destruction and hypoxia. It has been reported that such heterozygous people will die under special circumstances such as anesthesia, blood transfusion, and physical exertion. For example, in 1970, in Texas, four heterozygous black recruits died of stress.
Symptom
Genetic disease symptoms Common symptoms Anemia appearance bleeding tendency Red blind green blind blue-yellow blind repeated bleeding
First, hemophilia:
Hemophilia is a group of hemorrhagic diseases of hereditary coagulopathy. The common feature is the active thromboplastin formation disorder, prolonged clotting time, and a tendency to post-traumatic bleeding after life.
Second, albinism:
Albinism is a hereditary leukoplakia caused by melanin deficiency or synthetic disorders in the skin and accessory organs caused by tyrosinase deficiency or dysfunction. The patient's retina has no pigment, and the iris and pupil are pale pink, afraid of light. Skin, eyebrows, hair and other body hairs are white or yellowish white. Albinism is a family hereditary disease that is autosomal recessive and often occurs in close relatives. Genetic map of albinism: Both parents of the patient carry the albinism gene, which does not itself. If both couples pass the disease-causing gene they carry to their children, the child will become ill. Ocular albinism is X-linked recessive inheritance. It is caused by the albinism gene carried by the mother when it is passed on to the son. It is generally not transmitted to the daughter.
Third, color blindness:
Congenital color vision disorder is usually called color blindness. It can't distinguish various colors or certain colors in the natural spectrum. The poor color discrimination ability is called weak color. The weak color can see the color seen by normal people. However, the ability to recognize colors is slow or poor. When the light is dim, some are almost the same as color blindness, or appear as color vision fatigue. The boundary between it and color blindness is generally difficult to distinguish. Color blindness and color weakness are more common in congenital factors. There are far more male patients than female patients.
Fourth, congenital heart disease:
Congenital heart disease is the most common type of congenital malformation, accounting for 28% of all kinds of congenital malformations. It refers to anatomical abnormalities caused by abnormalities in cardiac and macrovascular formation during embryonic development, or birth. The channel that should be automatically closed afterwards cannot be closed (in the case of a normal fetus). The incidence of congenital heart disease can not be underestimated, accounting for 0.4% to 1% of the life of infants, which means that China has an annual increase of 150,000 to 200,000 patients with congenital heart disease. Congenital heart disease has a wide spectrum, including hundreds of specific types. Some patients can have multiple malformations at the same time. The symptoms vary widely. The lightest ones can be asymptomatic for life. If they are born, they will have serious symptoms such as hypoxia, shock or even death. . According to hemodynamics combined with pathophysiological changes, congenital heart disease can be divided into cyanotic or non-cyanotic, or divided into three categories according to the presence or absence of shunt: no shunt (such as pulmonary stenosis, aortic coarctation), left to Right shunt (such as atrial septal defect, ventricular septal defect, patent ductus arteriosus) and right to left shunt (such as tetralogy of Fallot, large blood vessel dislocation).
A small number of congenital heart diseases have a chance to heal before the age of 5, and a small number of patients have mild deformities and no significant effect on circulatory function, without any treatment, but most patients need surgery to correct the deformity. With the rapid development of medical technology, the surgical effect has been greatly improved. At present, most patients, such as timely surgical treatment, can return to normal as normal people, growth and development are not affected, and can be qualified for ordinary work, study and life needs.
Five, phenylketonuria:
Phenylketonuria (PKU) is a common amino acid metabolic disease caused by an enzyme deficiency in the phenylalanine (PA) metabolic pathway, which prevents phenylalanine from being converted into tyrosine, resulting in phenylalanine and Its ketoacid accumulates and is excreted in large quantities from the urine. The disease is more common in hereditary amino acid metabolism-deficient diseases, and its genetic pattern is autosomal recessive inheritance. The clinical manifestations were not uniform. The main clinical features were mental retardation, mental and neurological symptoms, eczema, skin scratch marks, pigmentation and rat odor, and abnormal EEG. If early diagnosis and early treatment are available, the aforementioned clinical manifestations may not occur, intelligence is normal, and EEG abnormalities can be restored.
Examine
Genetic disease examination
1. Using chromosome analysis technology, prenatal diagnosis of fetal chromosomal disease, in the past 14 to 16 weeks of pregnancy with amniocentesis to extract amniotic fluid, the cells were cultured for chromosome analysis. The main advantage of this is that the time for examination can be advanced to the early pregnancy (about 8 weeks), and the specimens obtained do not have to undergo cell culture, and can be directly analyzed by chromosomes, and the inspection report can be obtained on the same day. This technique is generally considered to be quite safe with amniotic cell chromosome analysis techniques.
2. Make a prenatal diagnosis using biochemical assays. There are more than 80 congenital metabolic defects that can be diagnosed at this time. For the specimens used for prenatal biochemical diagnosis, cultured amniocytes have been used in the past. In recent years, there has also been a trend toward using this specimen for the diagnosis of fluff specimens.
3. Congenital malformations with skeletal abnormalities can be diagnosed prenatally by x-ray examination.
4. Applying a fetal mirror, the doctor can directly see certain parts of the fetus and obtain first-hand information on prenatal intrauterine diagnosis. In addition to direct "pepper", fetal biopsy (such as fetal blood, etc.) can also be used for examination. It can even be used to inject a drug into a sick fetus for "intrauterine treatment."
Diagnosis
Genetic diagnosis
1. Congenital diseases and genetic diseases:
Congenital diseases refer to symptoms of the disease at birth, such as albinism, axillary fingers, and Down's syndrome. Many congenital diseases are not caused by genetic factors, but caused by harmful environmental factors during pregnancy. Pregnant women are exposed to toxic chemicals and improper medications cause abnormal fetal development, such as seal abnormalities and multiple deformities, not genetic diseases, but non- Hereditary congenital diseases. Some of the congenital diseases are genetic diseases; some are non-genetic diseases. However, some congenital diseases have the same clinical manifestations, some are caused by genetic factors, are genetic diseases; some are caused by adverse environmental factors, and are non-hereditary congenital diseases. Neural tube defects, cleft lip, cleft palate, congenital heart disease, etc., both hereditary and non-hereditary.
2. Familial diseases and sporadic genetic diseases:
A family of patients with the same disease for several generations, known as the disease is familial. In theory, genetic diseases are familial. However, due to new mutations in genes, or opportunities for gene delivery, genetic diseases can only occur in one family, and are sporadic genetic diseases. In addition, although some diseases are familial, they are not caused by genetic factors, so they are not genetic diseases. For example, endemic goiter, certain infectious diseases, etc. However, some familial diseases have the same clinical manifestations, some are genetic diseases caused by genetic factors; some are caused by adverse environmental factors, and are non-genetic diseases. For example, goiter, night blindness, etc. The clinical manifestations of some non-hereditary diseases are identical to the clinical manifestations of a genetic disease called phenotypic simulation, or cophenotype. For example, non-genetic diabetes, non-genetic congenital deafness.
