Mucolipidosis

Society for Mucopolysaccharide Diseases
MPS House, Repton Place, White Lion Road, Amersham, Buckinghamshire, HP7 9LP, UK
Tel: 0845 389 9901 Fax: 0845 389 9902
National Registered Charity No. 287034

Mucolipidosis II and Mucolipidosis III (ML II and ML III)

MLll (I-Cell disease) and MLIII (Pseudo-Hurler Polydystrophy) were once thought to be two separate forms of a condition known as mucolipidosis. It is now known that both MLII and MLIII have the same biochemical cause and that they represent two ends of a spectrum of severity. The name I-Cell in Mucolipidosis type II comes from the characteristic appearance of the cells under a microscope (see below). One of the first doctors to write about the condition in the 1960s was Dr Jules Leroy from Belgium and his name is sometimes used to refer to MLll. MLIII was described in 1966 by Dr. Maroteaux and Dr Lamy from France. They called it Pseudo-Hurler Polydystrophy as it resembled a mild form of Hurler disease, one of the mucopolysaccharide diseases. 'Polydystrophy' means that many organs are abnormal.

MPS diseases are closely related to the mucolipidoses. There is no magic cure for either MPS or ML diseases, but there are ways of helping children and adults to enjoy their lives and to manage the problems they will have.

What causes MLll and MLIII?
Many complex chemicals are used in the building of cells in the body. There is a continuous process in the body of replacing used materials and breaking them down for disposal. This activity takes place in a special part of the body's cells called the lysosome. Substances known as enzymes which are responsible for breaking down the used material can only reach the lysosomes after a special signal has been attached to them. In MLII and MLIII the signal is not attached so the enzymes cannot get to the right place and are lost outside the cell.

How common is it?
The MPS Society which co-ordinates the Registry for Mucopolysaccharide and Related Diseases has shown that in the United Kingdom between 1980 and 1990 23 babies were born with MLII and 14 with MLIII. This gives a live birth figure of 1: 326,000 for MLII and 1: 536,000 for MLIII.

How is it inherited?
We all have genes inherited from our parents which control whether we are tall, short, fair, etc. Some genes we inherit are 'recessive', that is to say we carry the gene but it does not have any effect on our development. MLII and MLIII are caused by a recessive gene. If an adult carrying the abnormal gene has a partner who is another carrier there will be a one in four chance with every pregnancy that the child will inherit the defective gene from each parent and will suffer from the disease. There is a two in three chance that unaffected brothers and sisters of ML sufferers 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 provided their partner is not a cousin or other close family member.

All families of affected children should seek further information from their doctor or genetic counsellor before planning to have more children. There is a more detailed explanation of this complex subject in the booklet on inheritance which is available from the MPS Society.

Prenatal diagnosis
If you already have a child with MLII or MLIII it is possible to have tests during a subsequent pregnancy to find out whether the baby you are carrying is affected. It is important to consult your doctor as soon as you suspect you may be pregnant if you wish tests to be arranged.

Is there a cure?
At present there is treatment for symptoms as they arise, but no cure for the underlying disease. Bone marrow transplantation has been tried in a small number of cases of MLll but this had no effect on the progress of the disease. This treatment is not recommended for patients with MLll or MLlll.

Click here to read Luke's Story (ML II)

Click here to read Tetsuya's Story (ML III)