Female carriership of X-linked adrenoleukodystrophy

Björn M. van Geel, MD, PhD
Neurologist, Medical Center Alkmaar, the Netherlands

Adapted and translated from: van Geel BM. Draagsterschap van X-gebonden adrenoleukodystrofie (The carrier state for X-linked adrenoleukodystrophy). Ned Tijdschr Geneeskd 2000;144:1764-1768. By permission of the Nederlands Tijdschrift voor Geneeskunde.

X-linked adrenoleukodystrophy (X-ALD) is an X-chromosome linked disorder that affects the function of the nervous system and some of the hormone producing organs. Although at present there is no cure for the disease, some treatments such as bone marrow or stem cell transplantation and supplementation of hormone deficiencies are available. And, as prenatal testing is available, new cases can be prevented.

For many years X-ALD has been regarded as a disease that only affects boys and men. However, over the last 15 years it has become clear that at least 20 to 50% of all female carriers develop neurological symptoms as well. Only very rarely female carriers develop deficient function of the adrenal glands. This paper addresses the complaints and symptoms female carriers may develop, and what can be done about it.

Introduction

Contrary to earlier concepts, it has now clearly been demonstrated that X-chromosome linked disorders not only affect male, but to a lesser extent female carriers of the defective genes as well. X-ALD is no exception. The Hollywood movie "Lorenzo's oil" was released in 1992, and tells the true story of five year old Lorenzo Odone, who developed problems with his hearing, his vision, and not much later his motor skills and memory. He was found to have the childhood cerebral form of X-ALD (CCALD), in which a severe immune or inflammatory reaction in the brain causes destruction of the white matter. Lorenzo has been severely affected by the disease, but is still alive today.

Besides CCALD, other variants (also known as phenotypes) of X-ALD are recognized, based upon the age of the onset of symptoms, and the organs that are primarily affected (Table 1). The most frequent phenotypes are CCALD and adrenomyeloneuropathy (AMN). AMN is a milder variant that causes a spastic weakness and sensory disturbances of the legs, bladder and bowel dysfunction, and insufficient production of cortisol and other hormones by the adrenal glands in mainly young adult men. Somehow the different phenotypes can occur in one and the same family. It has been estimated that approximately one in every 20.000 newborns is affected by X-ALD.

In 1981 the underlying defect was localized in the long arm of the X-chromosome (Xq28). It took another 12 years to identify the defective gene, initially named ALD-gene, but now known as the ABCD1-gene. It contains the information for the production of a protein in peroxisomes, known as the ALD-protein (ALDP). These peroxisomes are minute organisms, present in most human cells, that have several very special functions. One of these is the degradation of specific fatty acids, the so-called saturated very long chain fatty acids (VLCFA). The consequent accumulation of the VLCFA in the absence of other metabolic abnormalities is the biochemical hallmark of X-ALD. So far, no associations between the different phenotypes of X-ALD and the amount of VLCFA in the blood or the abnormalities in the ABCD-1 gene have been found.

The central nervous system consists of the brain and the spinal cord and is affected by X-ALD. Both the long extensions of the nerve cells, called axons, and the substance that insulates these structures, named myelin, can be damaged. It is hypothesized that abnormal levels of VLCFA result in an abnormal high level of these fatty acids in lipids that are built into cell membranes, thus impairing the membrane function of the axons. Furthermore, at some point the accumulation of VLCFA may result in a complicated immune reaction in the brain, which eventually causes irreparable destruction of myelin. With regard to the effect of VLCFA in membranes of hormone producing organs, some data strongly suggest that these fatty acids are toxic, and by this mechanism cause insufficient production of cortisol in the adrenal glands

Unfortunately, it is not well known that many if not most female carriers also develop symptoms. Frequently, symptoms are attributed to other causes, and therefore symptomatic treatment may be delayed. In our experience in the Netherlands, undiagnosed women carriers had undergone surgical procedures (hip replacement, cervical spine operations), some more than once, for what was later shown to be spastic weakness of their legs as a result of spinal cord disease due to X-ALD. Even worse, failing to recognise carriership of X-ALD prevented genetic counselling and appropriate diagnosis and therapy of other family members.

A carrier’s story

When she was 38 years of age, Mrs. H., born in the Netherlands, lived in the US together with her family. She had noticed that keeping her balance gradually became more and more difficult. Also, her legs started to feel a little stiff. She had had problems with her bladder function for several years, but assumed that giving birth to her two children had caused this. One of her cousins, who at first was thought to have a brain tumor, died at the age of 13 years. Another cousin, who had progressive problems with walking, was diagnosed with multiple sclerosis. Having read an article on X-ALD in a popular magazine in 1985, she recognized her symptoms and those of her cousins, and she decided to contact Dr. Hugo Moser at the Kennedy Krieger Institute in Baltimore, MD. A blood sample was taken, and analysis revealed an elevation of the VLCFAs, thus confirming the diagnosis.

When Mrs. H. was 55, she visited my clinic for the first time, at that time in the Academic Medical Center in Amsterdam, the Netherlands. It appeared that some of her relatives had been reported in the medical literature, but apparently many were not yet tested for X-ALD. Some chose not to be screened, but many had never been offered the VLCFA analysis. On physical examination, her lower back was sore with the muscles very tense. The tone in the leg muscles was increased, and there was some weakness. Sensation was abnormal, as light touch, vibration and joint movements were all impaired in the legs and feet. The tendon reflexes were abnormally elevated in the legs, the plantar responses clearly abnormal.

Magnetic resonance imaging (MRI) investigation of the brain and spinal cord were all normal. Investigation of nerve function revealed abnormalities in mainly the sensory nerves. Genetic counselling and blood tests were offered to relatives.

Retrospectively, CCALD and AMN were diagnosed in her cousins. Mrs. H. was treated for more than a year with “Lorenzo’s oil” and a very low fat diet. When she developed stomach complaints, the dietary treatment was discontinued, and these symptoms disappeared. Spasticity was successfully treated with baclofen (Kemstro ®), the pain in her lower back and hips responded to diclofenac (Voltaren ®). Furthermore, she was referred to a rehabilitation physician and a physiotherapist.

Together with her husband, the director of the Dutch patient organization, she supported newly diagnosed families and patients for many years. Until she passed away suddenly and unexpectedly, due to a disease unrelated to X-ALD.

The symptoms of carriers

Although it has been the experience that many carriers eventually will develop symptoms as a result of damage done to the nervous system, to date very few studies have addressed this. Some 20 to 50% of female carriers will eventually have sign of neurological dysfunction. In a study conducted in the Netherlands between 1992 and 1999 (Table 2), 32 to 48% of the women of at least 20 years of age had symptoms. Also, it appeared that with increasing age, the frequency of carriers that became symptomatic increased. In the age group of women 60 to 80 years of age, 52 to 79% had signs of neurological involvement.

It is very important to point out that symptoms in childhood are extremely rare. Also, brain disease in older women with spinal cord involvement is very uncommon. The symptoms in affected women are mainly due to abnormalities in the spinal cord and nerves in the legs, just like in AMN. Over decades, weakness and spasticity of the legs, disturbed sensation of the lower limbs, and impaired control over bladder and bowel develop. Unlike the affected men, it is very unlikely that women develop adrenocortical insufficiency, although it has been described in 1% in a large group. None of the Dutch carriers studied had signs of adrenocortical dysfunction.

It is debated what might cause the CCALD like symptomatology in female carriers. Normally, one of the two X-chromosomes that every woman has in her tissue cells is inactivated at random. It is hypothesized and partially supported by laboratory studies that in females who develop brain damage the X-chromosomes are not inactivated randomly, but that for some reason the normal X-chromosomes, those without the mutation in the ABCD1 gene, are inactivated. This results in a situation similar to the boys with CCALD.

Why female carriers should be identified

Many female carriers with mild AMN symptoms remain unrecognized for many years. This may result in withholding specific treatment for spasticity and lower back or joint pain, and bladder and bowel dysfunction. Once diagnosed, these symptoms can be treated more easily. Most importantly, once a woman is diagnosed as a carrier of X-ALD, her children and relatives can be screened, in order to diagnose boys and men with adrenocortical insufficiency. In addition, prenatal testing (using amniotic fluid or chorionic villus biopsy) allows early identification of an affected fetus. Boys and men who are affected and who have a yet unrecognized dysfunction of the adrenal glands can be identified. If left untreated, adrenocortical dysfunction can result in serious complications, and even death. Boys affected by the disease can be monitored closely; when they develop brain involvement, they can undergo bone marrow or stem cell transplantation. This has been proven to be beneficial in boys with only mild brain involvement. Daughters of carriers who desire to have children can also be offered VLCFA and DNA testing.

Establishing the diagnosis

X-ALD used to be diagnosed by analysis of VLCFA in blood samples or cultured skin cells (fibroblasts). For the females at risk for carriership however, these procedures were not sufficient, as many of the carriers have normal values of VLCFAs in blood or fibroblasts. After the ABCD1 gene and its product, the X-ALD protein (ALDP), had been identified, diagnosis became more reliable for those potential carriers with normal VLCFA levels.

VLCFA analysis
In boys and men, abnormally elevated levels of VLCFAs in blood plasma or cultured fibroblasts confirm X-ALD. But in at least 10 to 15% of the female carriers, VLCFA levels are within normal limits. Apparently, their unaffected X-chromosomes have enough residual activity and are able to mask the biochemical deficiency. Therefore, it is impossible to exclude that a woman in an affected family does not have X-ALD based upon finding normal VLCFA concentrations in blood or cultured cells! On the other hand, once elevated levels of VLCFA are found, this confirms the diagnosis.

Immunocytological tests
This diagnostic tool uses antibodies directed against the ALDP, and is used to study the presence of the ALDP in membranes of peroxisomes. The ALDP is abnormal in approximately 70% of the mutations found in the ABCD1. If the ALDP is deficient, the antibody will not recognize the protein. In cells from affected boys and men of a family in which the ALDP is known to be abnormal, the ALDP antibody will fail to recognize the protein, and the test result will be abnormal. In X-ALD carriers, half of the cells have normal ALDP (the cells in which the unaffected X-chromosome is active), and about 50% have deficient ALDP (the cells with the mutated ABCD1 gene). This results in a mixed pattern when cultured cells are stained with the ALDP antibody. This test should only be used in those families in which the ALDP is known to be absent! In 30% of the affected families abnormalities in the ABCD1 gene will not result in the absence of ALDP, this test can not be used. With the availability of DNA diagnostic testing, this test is now rarely used.

DNA or mutational analysis
Nowadays, this is the golden standard for the identification of female carriers. It should never be omitted in women of affected families in which VLCFA analysis or immunocytological stains are within normal limits. So far, more than 600 mutations in the ABCD1 gene have been identified. DNA analysis can be performed blood or other tissue samples, including chorionic villus biopsies and amniotic fluid cells, or previously cultured cells. The mutations are updated regularly in the X-ALD mutation database (http://www.x-ald.nl), a result of the cooperation between Dr. Hugo Moser, Kennedy Krieger Institute in Baltimore, MD, and Dr.Stephan Kemp, Academic Medical Center in Amsterdam, the Netherlands.

Diagnostic strategy
When X-ALD is diagnosed in a boy or man, it cannot be emphasized enough how important it is that the family must be screened thoroughly. This may prevent unnecessary new cases, and helps to identify those relatives with adrenocortical insufficiency and those who may benefit from bone marrow or stem cell transplantation. To make identification of affected relatives easier and more reliable, not only VLCFA analysis, but also immunocytological studies and DNA analysis should be carried once X-ALD is diagnosed in a family previously unknown with the disease. Once the mutation has been found, mutational analysis in relatives is much easier, as the test can be focused on that specific abnormality. The DNA analysis should be performed in specialized centers.

What to do after carriership has been established?

Obligate carriers
These are females who due to the sex chromosome linked inheritance of X-ALD must be carriers of the mutated ABCD1 gene. All daughters of men with one of the variants of X-ALD are obligate carriers, just as the women who have an affected child and an affected relative on their mother’s side of the family. Theoretically, it is not necessary to test these females, but in order to take away any doubt it is advisable to carry out DNA analysis. Remember that, although most female carriers eventually will develop some neurological symptoms, being free of symptoms does not exclude carriership!

Females at risk in an affected family
When the carriership is considered or suspected, diagnostic tests should never be omitted. Although it may be convenient to do VLCFA assays and immunocytological tests, the only way to confirm or exclude carriership reliably is mutation analysis.

Suspected female carriership with a negative family history
The spontaneous mutation rate in X-ALD is in the range of 3 to 5%. Therefore, only very exceptionally, a woman might be the index patient in a family. Among the Dutch carriers in the 50 families identified so far, just one was the only person in her family affected by X-ALD. In these females mutation analysis should be performed. But as the test cannot be pinpointed at a specific part of the ABCD1 gene, this is more difficult compared to the families with a well-known mutation.

Hormonal dysfunction

Although endocrine dysfunction has been described in carriers, it is very rare. Approximately 1% has some signs of impaired function of the adrenals. Abnormal function of the thyroid gland has been reported, but is encountered frequently in the overall population as well, making it difficult to say whether there is any relation with X-ALD. In general, endocrine tests should only be carried out when endocrine insufficiency is suspected.

Neuroimaging and electrophysiology

Only very occasionally severe white matter abnormalities in carriers have been reported. Suspected brain involvement can be demonstrated with MRI investigations. Electrophysiological examinations, such as the electroencephalogram (EEG) or evoked response investigations, may be abnormal in these cases as well. When the peripheral nerves are involved, nerve conduction studies and electromyography (EMG) may be abnormal as well.

For research purposes these investigations are interesting, but it is not essential to carry out these tests in every carrier, unless there are clear abnormalities on physical examination that warrant further investigation.

Treatment and management

Curative treatment
Over the last decades many therapies have been tried in X-ALD. Treatment with Lorenzo’s oil, ß-interferon, intravenous immunoglobulins, immunosuppression with cytostatic drugs, and plasma exchange so far have not been able to arrest or delay the disease progression once neurological symptoms are present. So far, bone marrow or stem cell transplantation in boys with mild brain involvement is the only treatment that has been shown to be beneficial.

In men and women with AMN like symptoms however, bone marrow or stem cell transplantation should not be performed, as this aggressive treatment is directed against the brain inflammation, and not at the slowly progressive loss of function of the nerve cells in the spinal cord and peripheral nerves, which occurs in AMN and female carriers.

Symptomatic treatment
Spasticity can be treated with drugs that reduce the muscle tone, such as baclofen (Kemstro ®), tizanidine (Zanaflex ®) and dantrolene (Dantrium ®). Alternatives for short-term use are benzodiazepines, such as diazepam (Valium ®) or clonazepam (Klonopin ®).

Many carriers experience lower back pain, or pain in the ankles, knees and hips, caused by the increased muscle tone in the legs and consequent abnormal walking. Nonopioid analgesics, such as acetaminophen and nonsteroidal anti-inflammatory drugs (e.g. ibuprofen, naproxen or diclofenac) may be particularly useful in the treatment of pain. The main side effects are stomach complaints, which results in discontinuation of the drugs in 10 to 15%. Selective COX-2 inhibitors (such as celecoxib (Celebrex ®), rofecoxib (Vioxx ®) and valdecoxib (Bextra ®) have become available in the recent years: in comparison they need to be taken less frequently, but have the same side effects as the nonsteroidal anti-inflammatory drugs.

Sometimes surgery may be considered. Knees and hips can be replaced, bladder surgery may help in coping with incontinence. It should be clear though that the underlying disease is not treated with these procedures, and that things may not get better.

A multidisciplinary approach
Female carriers with neurological symptoms may benefit from a multidisciplinary approach. The neurologist can treat some of the symptoms, but a symptomatic carrier should also consult a physical therapist, rehabilitation physician and urologist. A specialized nurse who knows the ins and outs of X-ALD is invaluable. If necessary, a psychologist or psychiatrist may be consulted, in order to cope with the disease itself, or the feeling of guilt that may overwhelm a carrier once it has been established that one of her children is affected. Last but not least, the clinical geneticist should not be forgotten, as the mode of inheritance of X-ALD, the availability of prenatal testing, and the need for family screening must be discussed.

Other therapies at this moment, and in the near future
Several drugs have been studied over the last years. Lovastatin was reported to lower the VLCFA levels in X-ALD, but so far data supporting this finding and demonstrating a beneficial effect are lacking. It was reported that 4-phenylbutyrate induced pharmacological gene therapy in laboratory tests, but its effectiveness so far could not be studied sufficiently in patients. Other promising drugs are studied at present, but it is very unlikely that one of them will become available for clinical use shortly.

When the ABCD1 gene was identified in 1993, it was expected that it was only a matter of time before the defective gene could be repaired by gene therapy. In cultured fibroblasts from X-ALD patients, gene therapy corrected the metabolic defect for several months. However, this kind of treatment is still not possible in X-ALD, and it remains unclear if and when it will become available.

Concluding remarks

Many if not most of the female carriers of the mutated ABCD1 gene will develop neurological symptoms caused by abnormalities in the spinal cord and peripheral nerves. It is important to recognize these symptoms, as symptomatic treatment and multidisciplinary support can make life a little easier. It should be kept in mind that at present very reliable and powerful diagnostic tools are available to demonstrate or exclude female carriership of X-ALD. It cannot be emphasized enough that the golden standard for the diagnosis in females is DNA analysis, as VLCFA test may very well be normal in 10 to 15% of the carriers. Once a carrier has been identified, the family should be screened and affected male relatives must be identified. These tests and family screening preferably should be performed in specialized centers

Acknowledgement

I would like to thank Dr. Gerald Raymond for his very helpful comments and suggestions.

Further reading

van Geel BM, Assies J, Wanders RJ et al. X-linked adrenoleukodystrophy: clinical presentation, diagnosis and therapy. Journal of Neurology, Neurosurgery and Psychiatry 1997;63:4-14.

Moser HW. Adrenoleukodystrophy: phenotypes, genetics, pathogenesis and therapy. Brain 1997;120:1485-1508.

El-Deiry SS, Naidu S, Blevins LS, et al. Assessment of adrenal function in women heterozygous for adrenoleukodystrophy. Journal of Clinical Endocrinology and Metabolism 1997;82:856-860.

Moser AB, Kreiter N, Bezman L, et al. Plasma very long chain fatty acids in 3,000 peroxisome disease patients and 29,000 controls. Annals of Neurology 1999;45:100-110.

van Geel BM, Bezman L, Loes D, et al. Evolution of phenotypes in adult male patients with X-linked adrenoleukodystrophy. Annals of Neurology 2001;49:186-194.

Bezman L, Moser AB, Raymond GV, et al. Adrenoleukodystrophy: incidence, new mutation rate, and results of extended family screening. Annals of Neurology 2001;49:512-517.

Last update: 03-Mar-2009