Mosaicism

A family from a very remote eastern region of the Russian Federation applied. Parents are physically healthy. The mother's first child from her first marriage is healthy (girl, 4 years old). The father had no children before. The mother's pregnancy with the second child proceeded with peculiarities: the fetus was small, there was oligohydramnios, the child did not move much. Parents were worried about the health of the unborn baby. Since mom already had a healthy child from her first marriage, dad was worried that "all the problems are coming from him." On his line, there was a story unconfirmed by doctors about the peculiarities of the development of relatives. A girl was born with low weight, lethargic, with low muscle tone (hung on the arm "like a rag"). From 4-5 months, a lag in physical development became deviations: the girl ate very poorly, did not gain body weight, she had to be transferred to feeding from a syringe, there was also a lag in psychomotor development: the girl acquired motor and mental skills very slowly (she was not interested in others, toys, did not make sounds). Based on the results of several hospitalizations in specialized hospitals, it was assumed that the cause of everything is the girl's impaired metabolism, poor digestion of food. Because of this, the child does not gain weight and develops incorrectly.

Against the background of the treatment, the child began to gain weight, motor skills quickly improved, but the delay in psychoverbal development became apparent. Numerous conducted biochemical studies, genetic study did not reveal the possible causes of the disease. The geneticist recommended whole genome sequencing in the trio format (mother, father and child), taking into account the erased manifestations of the disease in relatives and previous genetic studies. The family could not pay for this study on their own and turned to the foundation for help.

The results of the study were very interesting: no genetic changes were found in the father of the child. And the mother of the child turned out to be a “mosaic”. This means that a small part of her body is made up of cells with a genetic breakdown that leads to the development of mental retardation with clinical changes that coincide with those that a child has (such a breakdown is well known and described). But most of her body is represented by cells without genetic damage. It is likely that some of the ovarian cells are also represented by cells with genetic damage, and some without it. With the first pregnancy, the woman was lucky: the fetus developed from the egg without genetic damage. But the second pregnancy was a fetus that developed from an egg with a genetic breakdown.

The disease, identified in the family, has a dominant inheritance. This means that the signs of the disease appear in every person who has this genetic breakdown (even in one gene from a pair). But the mother, given the small number of cells with genetic damage in the body, did not have classic mental retardation. It is also likely that it was all the brain tissues that were represented by cells without breakage.

The family is planning a childbearing and information about the mosaicism of the mother is very important for the birth of a healthy child.