From the third week to the eighth week of the embryo (that is, the mother is pregnant), the fetal face completes the development process, and the tissues meet from both sides of the face to the center. During this period, if the development process is blocked for some reason and the tissues cannot be fused unilaterally or bilaterally, unilateral or bilateral cleft lip will be formed.
Genetic law: the incidence of cleft lip in normal people is about one in a thousand. Human genetic material is mainly carried by chromosomes in cells. There are 23 pairs of chromosomes, of which 1 pair determines sex and the other 22 pairs are autosomes. If the genes carried by chromosomes can show their characteristics, it is called dominant inheritance, and vice versa. Fetuses get a chromosome from both parents, and when both are recessive genes, malformations will occur.
Cleft lip is an autosomal recessive inheritance, and every generation cannot be deformed. Only when their parents with healthy appearance carry the pathogenic gene, 1/4 of their children will have cleft lip, 1/2 children with healthy appearance actually carry the pathogenic gene, and only 1/4 children are healthy. The co-occurrence rate between siblings is 2% ~ 4%.
If one parent carries the pathogenic gene and the other parent is healthy, the next generation of children will not have cleft lip, but 1/2 children carry the pathogenic gene.
If one parent is cleft lip and the other is healthy, half of the next generation of children will be deformed and the other half will carry the disease-causing gene.
If both parents are cleft lip patients, the next generation of children will also suffer from cleft lip. There are slightly more men than women with cleft lip, and the ratio of male to female is about 1.5: 1.