Tetra-amelia syndrome is one of the rarest genetic diseases associated with a mutation of the WMT3 gene. The main symptom of the disease is the complete absence of all four limbs in a person. There are other serious malformations. You can see a photo of tetra-amelia syndrome below.
General information
In addition to the absence of four limbs (Greek "tetra" - four, "amelia" - a limb), with tetraamelia syndrome, malformations of the skeleton, head, heart, lungs and genitourinary system are observed. In some cases, there are microphthalmia, cataracts, hypoplasia or aplasia of the lungs, low-set ears, cleft palate, or cleft lip. Most children with tetra-amelia syndrome have life-threatening malformations. Embryos with this genetic pathology often die in the womb or die during the first days of life.
Tetra-amelia syndrome has similar symptoms to another extremely rare genetic disorder, Roberts syndrome. This disease is characterized by severely underdeveloped limbs, defectsinternal organs, especially the heart and kidneys, cleft palate. Roberts syndrome is caused by a mutation in the ESCO2 gene located on the 8th chromosome. Like tetra-amelia syndrome, the disease is inherited in an autosomal recessive manner. An accurate diagnosis can only be made with a genetic test.
Genetics
The syndrome is caused by a mutation of the WNT3 gene located on the q arm of the 17th chromosome. The WNT3 gene encodes a protein that is involved in the formation of the limbs of the fetus before birth and is responsible for the formation of the skeleton. A mutation in this gene (deletion or duplication) is the cause of tetra-amelia syndrome.
Studies within families show that this syndrome is inherited in an autosomal recessive manner. That is, a child can be born with such a pathology only if both parents are carriers of the mutant WNT3 gene. If only one of the parents has the defective gene, then the child will either be he althy or will be a carrier of the disease. In carriers, the mutated gene on one of the chromosomes is compensated by a he althy gene on the homologous chromosome that encodes the normal WNT3 protein, so tetra-amelia syndrome does not manifest itself in carriers. If both parents are carriers of the disease, then the probability of having a sick child is 25%.
Treatment
There is currently no cure for tetra-amelia syndrome, like most other genetic diseases.
In the future, gene therapy in the early stages of fetal development may make it possible to replace the mutated WNT3 gene withThe 17th chromosome is normal, which will help avoid the development of tetra-amelia syndrome, but so far this operation is at the experimental stage. The extremely low incidence of the disease makes it difficult to find possible treatments.
Epidemiology
Tetra-amelia syndrome is less common than other genetic pathologies. The exact frequency of the disease has not been established. According to some reports, there are now only seven people with this disease in the world.
Diagnosis
The tetra-amelia syndrome can be determined in the fetus by such medical procedures as the analysis of the sequence of the encoded region of the chromosome, the analysis of deletions and duplications of chromosome 17. These tests show whether there is a deletion on the chromosome (absence of gene or gene sections completely) or extra repeats of trinucleotides. Such testing is especially relevant if the family has already had cases of the birth of a child with tetra-amelia syndrome.
Already in the first trimester of pregnancy, a high-resolution ultrasound therapy machine will easily determine the absence of limbs in the fetus. Procedures such as amniocentesis and chorionic biopsy can also detect the presence or absence of a mutation, but they detect the disease later than ultrasound.
With artificial insemination, pre-implantation genetic diagnosis is possible. This procedure will allow you to determine which embryos have the mutated gene and which do not, and selectonly he althy ones. This diagnostic method is very effective when it comes to many genetic pathologies, not only tetra-amelia syndrome, and minimizes the risk of having a child with genetic abnormalities.
Forecast
People with tetra-amelia syndrome learn to lead fulfilling lives. It is impossible to say unequivocally how tetraamelia affects life expectancy. It all depends on the severity of concomitant malformations of the skeleton, heart, lungs, nerves.
As already mentioned, one of the rarest genetic disorders of all possible - tetra-amelia syndrome. How many people in the world suffer from it? According to some reports, only seven people are now living with this disease. The most famous people with tetra-amelia syndrome are American motivational speaker and writer Nicholas Vujicic, Japanese sports journalist Hirotada Ototake, and Joanna O'Riordan.
