Tetraamelia syndrome is one of the rarest genetic diseases associated with a WMT3 gene mutation. The main symptom of the disease is the complete absence of all four limbs in a person. Other serious malformations are also observed. A photo of tetraamelia syndrome you see below.
General information
In addition to the absence of four limbs (Greek "tetra" - four, "amelia" - limb), with tetraamelia syndrome, defects of the skeleton, head, heart, lungs and genitourinary system are observed. In some cases, microphthalmia, cataracts, hypoplasia or aplasia of the lungs, low-set ears, split palate or cleft lip occur. Most children with tetraamelia syndrome have malformations that are incompatible with life. Embryos with this genetic pathology often die in the womb or die during the first days of life.
Tetraamelia syndrome has similar symptoms with another extremely rare genetic pathology - Roberts syndrome. This disease is characterized by severely underdeveloped limbs, defects of internal organs, especially the heart and kidneys, and splitting of the palate. Roberts syndrome causes a mutation of the ESCO2 gene located on the 8th chromosome. Like tetraamelia syndrome, the disease is inherited in an autosomal recessive manner. An accurate diagnosis can only be made using a genetic test.
Genetics
The syndrome is caused by a mutation in 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 fetal limbs before birth and is responsible for the formation of the skeleton. A mutation in this gene (deletion or duplication) is the cause of tetraamelia 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 be either healthy or will be the carrier of the disease. In carriers, a mutated gene on one of the chromosomes is compensated by a healthy gene on a homologous chromosome that encodes a normal WNT3 protein, therefore, tetraamelia 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
The treatment of tetraamelia syndrome currently does not exist, like most other genetic diseases.
In the future, gene therapy in the early stages of fetal development may possibly replace the mutated WNT3 gene on the 17th chromosome with a normal one, which will help to avoid the development of tetraamelia syndrome, but so far this operation is at the experimental stage. The extremely low frequency of the disease makes it difficult to find possible methods of therapy.
Epidemiology
Tetraamelia syndrome is less common than other genetic pathologies. The exact frequency of the disease has not been established. According to some reports, only seven people with this disease currently live in the world.
Diagnostics
Medical procedures such as sequence analysis of the encoded region of the chromosome, analysis of deletions and duplications of chromosome 17 allow the fetus to detect tetraamelia syndrome in the fetus. These tests show whether there are deletions on the chromosome (the absence of the entire gene or gene sections) or extra trinucleotide repeats. Such testing is especially relevant if there have already been cases in the family of the birth of a child with tetraamelia syndrome.
Already in the first trimester of pregnancy, a high-resolution ultrasound therapy device can easily determine the absence of limbs in the fetus. Procedures such as amniocentesis and chorionic biopsy can also reveal the presence or absence of a mutation, but with their help, the disease is detected later than with an ultrasound scan.
With artificial insemination, preimplantation gene diagnosis is possible . This procedure will determine which embryos have a mutated gene and which do not, and select only healthy ones. This diagnostic method is very effective when it comes to many genetic pathologies, not only tetraamelia syndrome, and allows you to minimize the risk of having a baby with genetic anomalies.
Forecast
People with tetraamelia syndrome learn to live a full life. 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 is tetraamelia syndrome. How many people in the world suffer from it? According to some reports, only seven people now live with this disease. The most famous people with tetraamelia syndrome are American motivational speaker and writer Nicholas Vuychich, Japanese sports journalist Hirotada Ototake, and Joanna O'Riordan.