Hunter syndrome is an X linked recessive genetic disorder and is also known as mucopolysaccharidosis type II (MPS II). It is a disease with multisystem involvement. There are long chains of sugar and carbohydrates in the cells of our body called glycosaminoglycans (GAG) that must be broken down. An enzyme named iduronate-2-sulfatase does the work of breaking down these glycosaminoglycans. But in hunter syndrome, there is deficiency of this enzyme and hence the GAGs build up and accumulate in the cells and tissues and cause troubles with normal functioning of the body. These GAGs are very crucial for the development of skin, tendons, cartilage, bones, etc. and hence they need to be broken down for its functioning.
How Often Does Hunter Syndrome Occur?
Hunter syndrome is an X-linked recessive genetic disorder that is characterized by accumulation of the glycosaminoglycans in the body.
Normally the mother has two X chromosomes and the father has one X chromosome and one Y chromosome. The mother inherits the X chromosome with the abnormal gene on it. The females are not affected because of healthy X chromosome that is inherited from the father; they are just the carriers of the abnormal gene. Males are affected always because they inherit the X chromosome from mother, which has the abnormal gene and other Y chromosome is inherited from the father that is normal.
Females are the carriers and do not show any symptoms because only one X chromosome is abnormal and the other X chromosome is normal. (1) (2)
But all the sons of such mothers are not affected. There are 25% chances that the mother will give birth to a son with this disease and 25% chances that she will give birth to a normal unaffected son. Also there are 25% chances that the daughter of a carrier mother will transfer the carrier chromosome to the daughter and 25% chances that she will give birth to a non-carrier daughter.
If a male has this disease, he will pass his abnormal X chromosome to all his daughters who will then become carriers but his sons will not be affected because the father passes on the Y chromosome and not the X chromosome. But in some cases, females can also be affected because of inactivation of the X chromosome that is inherited from the father.
Hunter syndrome can be diagnosed at the age of 2-4 years. This disease has an incidence rate of 1 in 100,000 to 1 in 170,000 male live births. It has been found that around 2,000 people worldwide have been afflicted with this disease.
Signs And Symptoms Of Hunter Syndrome
Hunter syndrome is a multisystem disorder so the signs and symptoms are related to all the organs and systems in the body and they are as follows:
- Macroglossia (abnormal enlargement of the tongue)
- Broad nose
- Depressed and broad nasal bridge
- Round cheeks
- Thickened lips
- Prominence of supraorbital ridges
- Short stature
- Macrocephaly
- Swelling of the optic nerve (papilledema)
- Retinopathy- retinal degeneration may lead to night blindness and poor vision
- Enlargement of tonsils
- Enlargement of adenoids
- Hoarseness of voice– due to glycosaminoglycans (GAG) deposition in the larynx
- Hypertrophy of gingival tissue
- Teeth- irregularly shaped teeth
- Hearing loss– may be sensorineural or conductive deafness
- Otosclerosis- may also lead to loss of hearing
- Respiratory system- increased frequency of respiratory tract infections
- Obstruction of airway- this is due to accumulation of GAG in trachea, tongue, oropharynx, etc.
- Cardiomegaly
- Hypertension
- Hepatomegaly
- Splenomegaly
- Chronic diarrhea
- Behavioral problems
- Cognitive problems
- Hydrocephalus
The hunter syndrome diagnosis is made on the basis of these symptoms as well as laboratory tests and radiological findings. The treatment is also a tricky part because of the involvement of all the systems; different doctors with specialization in each system have to come together for the treatment.
Conclusion
As described above, hunter syndrome is an autosomal recessive or X linked recessive disorder. So, mainly only the male child is affected but in a few cases female child is also affected but very rarely. So the incidence of this disease in males is 1 in 100,000 to 1 in 170,000 live male childbirths.
References:
- https://ghr.nlm.nih.gov/condition/mucopolysaccharidosis-type-ii#sourcesforpage
- https://www.ncbi.nlm.nih.gov/books/NBK1274/
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