Adrenoleukodystrophy (ALD) is a genetic neurodegenerative condition caused by a mutation in the ABCD1 gene, which contains the information necessary to make the adrenoleukodystrophy protein (ALDP). This protein is responsible for the transport of molecules called very long-chain fatty acids (VLCFA) to the peroxisomes — a specialized compartment within the cells — where they are broken down.
Due to the mutation, VLCFA transport is hindered, and it accumulates in most tissues of the body. The majority of VLCFA accumulation happens in the brain and adrenal glands, which causes the neurological and hormonal symptoms observed in ALD patients, but the accumulation can also be detected in other cells and tissues.
Detection of VLCFA levels in the blood is used for the diagnosis of ALD. A skin biopsy can also be used to detect VLCFA accumulated in fibroblasts — cells made up of collagen and fiber, and responsible for skin repair. Fibroblasts obtained using a skin biopsy are cultured in the laboratory, and used in the diagnostic test.
What is a skin biopsy?
A skin biopsy is a procedure where a small sample of the skin is obtained, after local anesthetic is applied to numb the area. The sampling leaves a small wound that heals in a short period of time. The skin sample is then processed and tested in the laboratory.
The procedure takes about 15 minutes and can be performed at an outpatient facility. Fibroblast cell cultures take about two to three weeks to grow. Therefore, an ALD diagnosis can take up to three weeks.
Skin biopsy and ALD
Fibroblasts are then isolated from the skin sample. They are grown in the laboratory, and the concentration of VLCFA is measured.
Since VLCFA breakdown in the peroxisomes is disturbed in ALD, the level of enzymes in the peroxisomes that help in this process could be affected. So, the levels of peroxisomal enzymes in the fibroblasts are also tested.
Taken together, these results help doctors to diagnose ALD in their patients.
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