What is Mannosidosis?
Alpha Mannosidosis is a rare lysosomal storage disorder of the Glycoprotein family of diseases and is closely related to Mucopolysaccharidoses.
Alpha Mannosidosis was fi rst described by Dr Oekerman, from Lund in Sweden in 1967. There is another variant known as ‘Beta Mannosidosis’ which is extremely rare and has produced a wide range of clinical abnormalities in the few patients described with this disorder.
Alpha Mannosidosis is an enzyme deficiency disorder which results in defective mannosidase activity (the accumulation of mannose-rich oligosaccharide chains). This accumulation is responsible for many problems that affect individuals with Alpha Mannosidosis.
What causes this disease?
Oligosaccharides are long chains of sugar molecules used in the building of bones, cartilage, skin, tendons and many other tissues in the body. “Oligo” means a small number and “saccharide” is a general term for a sugar molecule.
In the course of normal life there is a continuous recycling process of building new Oligosaccharides and breaking down old ones. This process requires a series of special biochemical tools called enzymes. Children and adults affected with Alpha Mannosidosis have a malfunctioning or missing enzyme called Alpha Mannosidase.
Partially broken down Mannose-containing chemicals remain stored in the body and over time begin to build up. This causes progressive damage to the cells.
Babies may show little sign of the disease but as more and more cells become damaged by accumulation of oligosaccharides, symptoms start to appear.
Does Alpha Mannosidosis affect individuals differently?
Alpha Mannosidosis, like most MPS and related disorders is very variable. Some individuals with Alpha Mannosidosis will have mild to moderate learning difficulties which may develop in childhood or adolescence.
How common is Alpha Mannosidosis?
The MPS Society, which co-ordinates the MPS Registry for MPS and related diseases, knows of 30 affected individuals in the UK. There has only been approximately 200 cases reported worldwide but there are probably many more patients that have not been diagnosed or reported.
How is the disease inherited?
Genes are inherited from our parents and control how tall we are as well as the colour of our eyes and skin. Some genes we inherit are “recessive” which means we carry that gene but it does not have any effect on our development.
Alpha Mannosidosis is caused by a recessive gene. If an adult carrying the abnormal gene has a partner who is also a carrier, there will be a 25% chance with every pregnancy that the foetus will inherit the defective gene from each parent and will suffer from the disease. There is a two out of three chance that unaffected brothers and sisters of those affected by Alpha Mannosidosis will be carriers. They can be reassured, however that as the disease is so rare, the chance of having a partner who is another carrier is very slight, unless the individuals are of the same family.
There is a more detailed explanation of this complex subject in the booklet on inheritance available from the MPS Society.