Batten disease is an inherited neurodegenerative disorder, causing seizures, vision problems, and a loss of cognitive and motor skills. It is caused by mutations that affect proteins involved in clearing waste from cells, which is especially sensitive in nerve cells.
The waste substances, called lipofuscins, build up in compartments inside cells called lysosomes, impairing cell function and ultimately causing cell death.
A diagnosis of Batten disease normally involves a genetic test or an enzyme assay. These can determine whether there are any mutations and what level of functional protein the patient has.
In some cases, other tests such as a tissue biopsy may be carried out to check for signs of Batten disease.
What is a tissue biopsy?
A tissue biopsy is a minor procedure to remove a small piece of tissue from the patient. This is examined under a microscope to check for known abnormalities, or used in other tests.
In Batten disease, the most common type of biopsy is a skin biopsy. This is most likely done by a punch biopsy, a method that obtains a small section through all the relevant skin layers. A local anesthetic is applied before starting the procedure. A small circular blade is then inserted into the skin and rotated to remove a small cylindrical skin sample.
If the results from this biopsy are inconclusive, then a muscle or nerve biopsy may be conducted. This involves the use of surgical tools inserted under the skin and into the tissue to cut and remove a small piece of tissue.
Historically, a rectal biopsy was used for the diagnosis of Batten disease. But this is rarely used now because it is quite invasive and modern enzyme and genetic testing have largely replaced it.
Results of a tissue biopsy
The tissue biopsy is first examined under a microscope. In Batten disease, this can reveal accumulated lipofuscins, identified as greenish-yellow pigmented shapes present in cavities inside the cells. They appear as a distinctive fingerprint or half-moon shape.
These results can confirm if the patient has Batten disease, but if these structures are absent it does not confirm a negative diagnosis. Other tests, such as genetic analyses or enzyme assays are required, and these can also be used to determine the type of Batten disease the patient has.
The tissue biopsy can also be used for the enzyme assay. Fibroblasts, a type of skin cell, from the skin biopsy can be cultured in the laboratory and the levels and functionality of the affected protein can be measured.
The sample may also be used to obtain DNA for genetic testing to check whether there is a mutation in one of the genes known to be associated with Batten disease.
Risks associated with tissue biopsy
Depending on the type of biopsy, the procedure is generally low-risk. A skin biopsy is normally the safest, although it may sometimes result in bleeding, bruising, scarring, infection, or an allergic reaction to topical antibiotics used.
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