Continuing Education Activity

Adrenoleukodystrophy is a peroxisomal disorder resulting from abnormal metabolism of the very-long-chain fatty acids (VLCFA). It is classified into different subtypes based on the mode of inheritance, clinical presentation, age of onset, and organs involved. The prognosis is poor, and the majority of affected patients will develop neurological disabilities and death. This activity reviews the pathophysiology, evaluation, management, and prognosis of the different adrenoleukodystrophy types and highlights the new updates about the diagnosis and treatment options that are available or under investigation for this condition.

Objectives:

• Describe the pathophysiology of the different types of adrenoleukodystrophy.
• Outline the clinical presentation of the different types of adrenoleukodystrophy disorders.
• Review the diagnostic workup for adrenoleukodystrophy.
• Review the treatment options and prognosis of adrenoleukodystrophy.

Introduction

Adrenoleukodystrophy (ALD) is a genetic disorder that follows X linked inheritance pattern in most cases (X-ALD).[1] A unique neonatal form classified as one form of Zellweger syndrome has an autosomal recessive inheritance pattern (N-ALD). Although, the earlier report in the 1900s described the clinical presentations suggestive of this disease.; the terminology and pathophysiology were first reported in the 1970s.[2] The brain, spinal cord, adrenal glands, and testes are the most commonly affected organs. Given the multiple organs, involvement multidisciplinary team approach is highly recommended in the management plan.

Etiology

X-ALD disease has links with the ABCD1 gene mutation.[2] ABCD1 gene plays a significant role in the very-long-chain fatty acids (VLCFA)s transport system in the peroxisomes, where VLCFAs can undergo further metabolism. The abnormal ABCD1 gene mutation interferes with this process and results in abnormal accumulation of VLCFA in different body organs and subsequently interferes with the organs' normal physiological function. A mutation causes the neonatal form in any of the PTS1 receptor, PXR 1, PEX1, PEX 10 or PEX 13 genes.[3] Four main subtypes of ALD have been described based on organs affected and age of presentation:

• Neonatal
• Childhood cerebral form
• Adrenomyeloneuropathy 
• Adrenal insufficiency

Epidemiology

ALD is the most common genetic disease that affects the peroxisomes. It has an approximated prevalence of 1 in 20,000. The disease incidence is higher in patients with Latino or African descent.[4] N-ALD has a prevalence of 1 in 50000.[5]

Histopathology

On gross examination, affected adrenal glands appear small and atrophied. Histological findings at the microscopic level consist of nodular swelling affecting mainly the zona fasciculata and zona reticularis. Celluar vacuoles and clefts may be visible as well. The medulla is usually spared and appears normal.[6]

Central nervous system pathological findings in ALD consist of symmetrical demyelination of the white matter. These effects commonly occur in the corpus callosum and the occipitoparietal region. In severe cases, the spinal cord may get affected. At the cellular level, swelling and vacuolization are caused by infiltrates of active inflammatory cells ( macrophages and astrocytes). These changes usually result in the loss of the myelin sheets, oligodendrocytes, and neuronal axons. Ultimately dystrophic mineralization is seen on the histological examination.[7]

History and Physical

Clinical manifestations vary significantly according to the disease severity and the age at presentation.

N-ALD can manifest immediately after birth. However, some infants will be mildly affected. Hence diagnosis is usually delayed in these cases. Typical signs and symptoms in N-ALD include [8]:

1. Seizures, hypotonia, hearing dysfunction
2. Vision, cataracts, optic nerve dysplasia
3. Jaundice, hepatomegaly
4. Failure to thrive and facial dysmorphism (hypertelorism and flat midface)

X-ALD usually has three phenotypes, classified based on the age of presentation and the organs affected:

1. Childhood cerebral ALD, typically affect children between the age of three to ten years. The hallmark feature that characterizes this form is developmental regression. More progressive sensory and severe neurological deficits, severe disability, coma, and death are generally followed by more progressive sensory and severe neurological deficits. A small percentage of adults may present in a similar pattern to the childhood cerebral ALD. 
2. Addison disease. The adrenal gland dysfunction characterizes this form. The manifestations associated with this subtype are the result of decreased production of:
   1.  Aldosterone (hyponatremia, fatigue, hypotension, dehydration)
   2.  Cortisol (hypoglycemia and generalized weakness)
   3.  Hyperpigmentation of the skin may also occur.
3. Adrenomyeloneuropathy; the typical age of presentation is in the third decade of life. It presents a milder spectrum of ALD. Walking difficulties, unbalanced gait, and bowel/bladder sphincter dysfunction are typical manifestations.[2]  

Females who are carriers may develop milder symptoms (unbalanced gait, neuropathy, mild paresis). The adrenal glands and cerebrum are rarely involved.[9]

Evaluation

Typical Clinical presentation, characteristics, symptoms and signs, and suggestive family history are considered the starting point for adrenoleukodystrophy evaluation. Several states started using newborn screening tests as a screening tool to identify newborns with a potential genetic predisposition for X-ALD.[3] The driving principle behind adding X-ALD to the newborn screening is to identify newborns with the mutation to receive treatment before the symptoms appear.

Nonspecific laboratory workup may reveal an abnormal liver function and reduced response to ACTH administration. The more indicative test results will show [10]:

1. Increased VLCFA plasma concentration
2. Decrease red blood cells' plasmalogen concentration
3. Increase in the concentration of pipecolic and phytanic acid concentration in both plasma and fibroblasts

Magnetic resonance imaging (MRI) of the brain is an essential part of the evaluation; Typical findings are:

1. White matter demyelination pattern
2. Microgyria
3. Germinolytic cysts in the caudothalamic groove

Further genetic testing to identify the specific genetic mutation is recommended to confirm the diagnosis.[11]

Treatment / Management

There is no effective treatment for most of the forms of N-ALD or X-ALD. Supportive care by optimizing nutrition, occupational therapy, and respiratory support can help alleviate some of these disorders' severe consequences but typically do not significantly impact survival or long-term outcomes. Coreterosteriod and mineralocorticoid replacement therapy is the recommended therapy in those with impaired adrenal gland function. Some reports have shown that allogeneic hematopoietic cell transplant (HCT) may have beneficial effects. Favorable outcomes with HCT therapy occur in asymptomatic patients at the time of diagnosis or those with mild symptoms and CNS involvement.[12] 

Recent trials to use docosahexaenoic acid (DHA) or the induction of peroxisome proliferation were not conclusive.[13][14] Given the multiple organs affected and the multiple needs for the management of ALD patients, an interprofessional team approach (endocrinologist, neurologist, genetics, psychologist) is recommended.

Differential Diagnosis

The differential diagnosis for N-ALD is comprehensive and includes other genetic syndromes that present in the neonatal period with neurological signs and symptoms ( Angelman, RET syndrome, Prader Willi, hypoxic-ischemic encephalopathy, metabolic disorders, myotonic dystrophy, and others). For X-ALD; Other demyelination disorders (acute disseminated encephalomyelitis (ADEM), multiple sclerosis, specific central nervous system dysfunction) should be excluded as the evaluation, management, and prognosis for these conditions are different from ALD.

Pertinent Studies and Ongoing Trials

Two ongoing clinical trials to evaluate potential therapeutic interventions for ALD are actively recruiting. NCT03727555 clinical trial evaluates the use of lentiviral vector TYF-ABCD1 to correct the defective ABCD1 gene associated with ALD. Another trial, NCT03852498, aims to assess the effect of autologous CD34+ HCT on ALD.

Prognosis

Prognosis is poor with N-ALD and most of the other forms of X-ALD. Treatment is usually limited to symptomatic supportive management. Replacement therapy for patients with Addison disease and HCT for asymptomatic patients ( identified by newborn screen or incidental imaging) or have mild symptoms may be effective in selected cases. Severe disabilities and death are the expected outcomes on the majority of patients with N-ALD or X-ALD. 

Deterrence and Patient Education

Adrenoleukodystrophy is a peroxisome disease that affects neonates ( N-ALD) or children and adult (X-ALD) with multiple organs involvement ( commonly; the central nervous system and the adrenal glands).

• Neonatal ALD inheritance is in an autosomal recessive pattern while X-ALD follows X linked recessive (male predominance)
• Clinical presentation of patients with ALD is variable, with neurological (hypotonia, weakness, developmental regression, cognitive disabilities, severe disabilities) and adrenal insufficiency (hypotension, fatigue, hypoglycemia) been the most common clinical manifestations.
• Diagnosis of ALD requires a detailed history and physical examination, measuring VLCFA levels, brain MRI, and specific genetic testing.
• Treatment for ALD with corticosteroid replacement therapy and hematopoietic stem cell transplant ( HCT) is limited for selected cases. No effective treatment exists for the majority of cases, and management is usually supportive.
• The prognosis of ALD is unfavorable and carries a high rate of mortality and severe disabilities.
• Clinical trials are ongoing to evaluate potential gene therapy for ALD.

Enhancing Healthcare Team Outcomes

• Adrenoleukodystrophy is a peroxisomal disorder that has a variable clinical presentation. It has many types based on; age, organs involved, and mode of inheritance.
• A multidisciplinary team of neurologists, endocrinologists, genetics, dietician, and psychologist is recommended to coordinate the care of patients of ALD.
• Hemapotioc cell transplant (HCT), docosahexaenoic acid (DHA) fatty acid, and peroxisomal induction are possible treatments.