X-Linked Adrenoleukodystrophy (ALD) By Megan Martinez and Shelbi Green

Nature of ALD: Overview ALD is an X-linked peroxisomal disorder characterized by the demyelination of the central nervous system and degradation of adrenal function (Aubourg, 1993). Caused by the inability of peroxisomes to degrade very-long chain fatty acids (VLCFAs). VLCFAs build up in the tissues of the body, especially the brain and adrenal glands (Mosser, 2010).

The Peroxisomes and β-Oxidation Peroxisomes: digestive organelles in all eukaryotic cells that carry oxidative enzymes that are involved in the break down of fatty acids by oxidation. Fatty Acids: necessary and vital components of all cells (i.e. triglycerides for energy storage). VLCFAs: very hydrophobic fatty acids with tails longer than 22 carbons. They are normal components in membranes such as the myelin sheath. VLCFAs Oxidation: too long to be broken down in the mitochondria. Therefore, are broken down in the peroxisomes in a series of chemical reactions called the β-oxidation cycle which the VLCFAs are broken down by the successive removal of two carbons (Mosser, 2010).

ALD Protein ALD Protein: the cause of the peroxisome’s inability to oxidize VLCFAs is the absence of a protein named the ALD protein (ALDP). It was shown that the expression of the ALDP in ALD patient cells restored normal β-oxidation of VLCFAs (Shinnoh et al, 1995). ALDP function: transports VLCFAs across the peroxisomal membrane. When it does not fuction properly, VLCFA accumulates in the cytosol and does not get degraded. ALDP deficiency has two effects: Impairs β oxidation of VLCFAs Allows the VLCFAs waiting in the cytosol to become substrates for further elongation.

Consequences of Excess VLCFAs Demyelination: the destruction of myelin impairs the conduction of signals in affected neurons. Adrenal Insuffiency: damage to the adrenal glands causes their inability to produce the necessary amount of steroid homones

Cause of ALDP deficiency: Mutation ALDP deficiency is caused by a mutation in the ATP-binding cassette, sub-family D (ABCD1) gene which is located on the long arm of the X chromosome at position 28 (Xq28)

Pattern of Inheritance: X-Linked Recessive The ABCD1 gene is located on the X-chromosome, and the mutation causing ALDP deficiency is a recessive allele. Disorder is passed from mother to son and daughter are carriers.

History of ALD 9 documented cases of ALD between 1910-1963. Disease was elusive and unknown, but by 1963 was suspected to be X-linked recessive because only male patients had been documented. Very little was known about the disease except that it involved degeneration of the white matter in the CNS and adrenocortical insufficiency. Major breakthrough was made in 1972 Schaumburg and Johnson observed that adrenal cells of ALD patients contained characteristic lipid inclusions (fat droplets), and showed that these fat droplets consisted of cholesterol esters that contained VLCFAs (Engelen & Kemp, 2010). 1986: Lorenzo’s Oil 1988: First successful bone marrow transplant 1993: ABCD1 mutation identified allowing for improvements in diagnosis and genetic counseling 2006: advancement in VLCFA screening in blood tests 2007: two 7-year-old boys successfully treated using gene therapy 2010: discovery ALDP transports VLCFAs across the peroxisomal membrane

ALD Diagnosis and Facts The most common leukodystrophy affecting 1:17,000 (Engelene & Kemp, 2010). Affects all ethnic groups Progressive demyelination and adrenocortical insuficiency eventually leads to long-term coma (vegetative state) usually within 2 years of the first neurological symptoms. Patient can live up to 10 years in this state (Englene & Kemp, 2010). Lorenzo Odone, the inspiration for the film Lorenzo’s Oil three days before his death in May 2008.

Untreated ALD If ALD goes untreated Myelin sheaths of the nerve cells continues to degrade leading to failure of adrenal glands, brain damage and in sever cases, vegetation or even death.

Demyelination of ALD Healthy myelin Damaged Myelin

Untreated ALD Healthy Brain Brain damaged by ADL

Current Treatment of ALD Dietary therapy Transplant Gene therapy Adrenal insufficiency

Dietary therapy Dietary restrictions of very-long-chain fatty acids lead to the discovery of Lorenzo's oil

Transplant Therapy Allogeneic Hematopoietic Stem Cell Transplants

Gene therapy Appropriate vectors are selected and modified to express wild type ABCD1 and then transplanted into the patients

Adrenal insufficiency Hormone replacement is standard treatment for ALD patients demonstrating adrenal insufficiency, but it cannot resolve any of the neurological symptoms.

Recent Research A gene therapy trial in two ALD patients showed results that strongly suggest that hematopoietic stem cells were transduced in the patients and that gene therapy of hematopoietic stem cells can provide clinical benefits in ALD.

References Amorosi, C., Myskóva, H., Monti, M., Argaraña, C., Morita, M., Kemp, S., & ... de Ramírez, A. (2012). X-Linked Adrenoleukodystrophy: Molecular and Functional Analysis of the ABCD1 Gene in Argentinean Patients. Plos ONE, 7(12), 1-8. Aubourg, P., Mosser, J., Douar, AM., Sarde, CO., Lopez, J., Mendel, JL. (1993). Adrenoleukodystrophy gene: Unexpected homology to a protein involved in peroxisome biogenesis. Biochimie, 75(3-4), 293-302. Cartier N., Hacein-Bey-Abina S., Bartholomae C.C., Veres G. (2009). Hematopoietic Stem Cell Gene Therapy with a Lentiviral Vector in X-Linked Adrenoleukodystrophy. Science Journal, 326:818-823 Engelen, M., Kemp, S. (2010). History of X-ALD. X-ALD Database. Moser, HW. (2010). X-linked Adrenoleukodystrophy database. Kennedy Krieger Institute. Shinnoh N., Yamada T., Yoshimura T., Furuya H., Yoshida Y., Suzuki Y., Shimozawa N., Orii T., Kobayashi T. (1995). Adrenoleukodystrophy: the restoration of peroxisomal beta-oxidation by transfection of normal cDNA. Biochem Biophys Res Commun 210(3), 830-6.