What are cilia?
Cilia are microscopic hair-like structures that are attached on the outside of many cells that make up our tissues and organs. For a good introduction to cells and what they do please see How Stuff Works which will open in a new tab or window depending on your browser’s default settings. A picture of a human airway cilia can be seen above. Cilia play a number of vital roles during everyday life, and the role they play depends on which organ their cell is part of. In some tissues, such as in our upper airways (including the middle ear), the cilia undergo a rhythmic waving or beating motion. These so-called “motile” (or “moving”) cilia work to keep our airways clear of mucus and dirt, allowing us to breathe easily and without irritation.
“Non-motile” cilia, also known as “primary” cilia, carry out various roles in the body without moving. These cilia may act as an antenna for the cell, receiving signals from other cells or fluids nearby, and telling their cell what is going on in the body. In the kidney, these cilia tell the cells that there is a flow of urine, and that the cells need to do some work to filter the urine. In the eye, non-motile cilia are found inside the light-sensitive cells (“photoreceptors”) of the retina. These cilia act like microscopic train-tracks, and allow the transport of vital molecules from one end of the photoreceptor to the other.
A large number of the symptoms of Alström Syndrome can be readily explained by cilia not working properly. For example, blindness results from the cilia not delivering the vital molecules, leading to death of the photoreceptors. However, some symptoms of Alström Syndrome are difficult to explain, and defective cilia may not be the direct cause of everything related to the disease (see Future Research, below).
Why do cilia go wrong in Alström Syndrome?
Alström Syndrome is a genetic disease. Like other genetic diseases, it is caused when you inherit an altered copy of a gene from both parents. For a good introduction to genes and genetic inheritance try the following link: How Stuff Works Genetics Dictionary. which will open in either a new tab or window depending on your browser’s default settings.
In Alström Syndrome there is a problem with a gene called ALMS1. In only 2002, research carried out simultaneously in two laboratories identified the gene, and then further research shed light on what this gene might be doing in all of us, and why alterations of the gene may cause Alström Syndrome. ALMS1 acts as an instruction manual for cells to make a single protein called Alms1, a molecule that does a particular job within the cell. Scientists have shown that this protein is found very near to the cilia in a number of cell-types, and so it most probably controls how cilia work or how they are built. In people with Alström Syndrome the protein is not made correctly and so cannot do its job, making the cilia work incorrectly. In other ciliopathies (see above), other genes are affected, but the proteins they code for are likely to play similar roles to Alms1. This results in similar symptoms to those seen in Alström Syndrome.
What is the future of research into Alström Syndrome?
There are a number of questions that need to be tackled by future scientific and clinical research:
- “What does the protein Alms1 actually do, and how does it contribute to the function of cilia”?
- We need a clearer picture of how and why cilia function goes wrong.
- What is the cause of cardiomyopathy in Alström Syndrome, and why does it sometimes “go away”?
- This unusual feature is hard to explain by cilia not working properly, but is a contributing factor to the severity of the disease. Research into this problem is essential.
- What is the cause of the fibrosis that affects various organs in Alström Syndrome (e.g. heart, kidney, liver)?
- Again, fibrosis is a complex problem that is probably not caused by cilia not working properly, and it is not clear why it is so common in Alström Syndrome.
- Why is there so much variability in the symptoms between different Alström Syndrome patients, even between affected siblings?
- We need a clearer picture as to why subtle variations of the ALMS1 gene cause differences in the severity of the disease.
This information is intended as a guide for patients and their families. For further information please contact us by email.