Clinical use
To aid in the diagnosis of Adrenoleukodystrophy (X-ALD) is a serious progressive, genetic disorder that affects the adrenal glands, the spinal cord and the white matter of the nervous system.
Background
X-ALD is an inherited metabolic storage disease whereby a defect in a specific enzyme results in the accumulation of very long-chain fatty acids (VLCFA) in tissues of the body, especially the brain and the adrenal glands. Ultimately the myelin sheath that surrounds the nerves is destroyed causing neurologic problems, and the adrenal gland malfunction causes Addison’s disease. While some of the VLCFA that accumulate come from the diet, they are derived mainly from production within the body through elongation of long-chain fatty acids. The accumulation of VLCFA in X-ALD patients results from the impaired capacity to degrade these fatty acids.
The break down of VLCFA normally takes place in a part of the cell, which is referred to as the peroxisome. All cells of the body, except red blood cells, have peroxisomes (Figure 1). Patients with X-ALD lack one of the proteins required for this degradation to take place. The protein that is missing or defective is called ALDP (X-ALD protein). ALDP is crucial for the transport of the VLCFA from the cell into the peroxisome. 20% female X-ALD (adrenoleukodystrophy) carriers reported to have normal VLCFA values – VLCFA in serum reduces as heterozygotes age. X-ALD occurs all over the world and is not limited to certain ethnicities. The incidence of X-ALD has been estimated to be 1:17.000 newborns.
Reference ranges
| C24:0: | 33.1 – 75.0 µmol/L |
|---|---|
| C24:0 | 33.1 – 75.0 µmol/L |
| C22:0 | 38.0 – 90.5 µmol/L |
| C26:0 | 0.30 – 1.49 µmol/L |
| C26:0/C22:0 Ratio | 0.003 – 0.025 |
| C24:0/C22:0 Ratio | 0.35 – 1.10 |
| Phytanic Acid | 0.30 – 11.5 µmol/L |
| Pristanic Acid | 0.0 – 1.5 µmol/L |
Patient preparation
None required
Specimen requirements
EDTA (Purple top) tube preferred but plain (red top) also acceptable.
Turnaround time
4 weeks
Additional information
For diagnosis of peroxisomal disorders e.g. Zellwegers. Patient does not need to be fasted as diet has very little influence on levels. However, if unusual results are obtained, Newcastle may request a fasting sample.
Referred test
Referred test