Hunter syndrome is a rare genetic disorder. Its incidence is 1 in every 100,000 male live births to 1 in every 170,000 male live births. This disease almost always occurs in males. Very rarely female might be affected. It is mostly seen in males because this disease is X-linked recessive type of disease. Females are mostly the carriers of the disease and the males get the disease inherited from the mothers. Sometimes females might be affected if the X chromosome inherited from the father becomes inactivated. This is a multisystem disorder because all the organs of the body are affected. This disease needs proper medical care and attention.
Is Hunter Syndrome Dominant Or Recessive?
Dominant and recessive are the terms used to describe the patterns of inheritance of the genetic traits. All the humans possess two copies of one single gene. But these genes also called as alleles can vary from each other slightly. These differences can lead to variation in the production of proteins. If a person has dominant allele then a dominant phenotype will be produced even if only one copy of dominant allele is inherited from one of the parents. If a recessive allele has to produce a recessive phenotype, then the recessive alleles must be two in number, one from each parent. If a person inherits one dominant allele and one recessive allele, then the dominant allele shows dominant phenotype. When a person has one normal and one abnormal recessive allele, such people are called as carriers of the recessive allele, which means that the recessive allele is present, but its phenotype is not produced.
In Hunter syndrome the inheritance is X linked recessive in type. The females are mostly not affected but are carriers of the diseased X chromosome. Males contain two sex chromosomes one X chromosome and one Y chromosome while the females possess two sex chromosomes and both of them are X chromosomes. (1)
When an embryo is produced, if the sex of it is female then each of the parents pass on their X chromosomes to the child. If the sex of the fetus is male, then it gets one X chromosome from mother and one Y chromosome from father.
This is the reason why females are rarely affected by this disease. Even if a diseased X chromosome is inherited by the female but because of the other healthy X chromosome the phenotype is not produced and such females become carriers of the disease. But in case of males, if a diseased X chromosome is inherited, it will produce its phenotype because they possess only one X chromosome and other is Y chromosome.
Pathophysiology Of Hunter Syndrome
Lots and lots of biochemical reactions take place in our body in order for it to function normally. Breaking down of large biomolecules is one of the important functions and this function is disrupted in Hunter syndrome. There is an extra cellular matrix that is present outside the cells of our body. This extracellular matrix is made of several of proteins and sugars. These sugars and proteins help in maintaining the architecture of the body. This matrix acts like a glue surrounding the cells and holds all the cells together. One of the components of this matrix is proteoglycan that is a type of molecule. These molecules of proteoglycans must be broken down and then replaced by new molecules. When these proteoglycans are broken down, one of the byproducts formed are mucopolysaccharides (GAGs).
In Hunter syndrome, there is difficulty in breaking down two important GAGs that are heparan sulfate and dermatan sulfate. For breaking down these two GAGs, an enzyme named iduronate-2-sulfatase (I2S) is necessary. In patients with Hunter syndrome, this enzyme I2S is either totally inactive or only lightly active. Due to this, the GAGs are not broken down and this results in accumulation of these GAGs in all the cells of the body. This accumulation in the body is not the same in all the people, in some people there is more accumulation and in some there is less amount of collection of GAGs and the severity depends on the amount collection of GAGs. The more the collection, more severe is the disease.
Conclusion
Hunter syndrome is a recessive disorder that is X linked in nature. Recessive genetic disorders are the ones in which the presence of one recessive allele and one normal allele makes the person a carrier and presence of two recessive alleles or presence of single recessive allele produces the recessive phenotype means that the disease is produced. Because of this the females are mostly the carriers and the males present the disease.
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