Metachromatic Leukodystrophy

Overview

Definition

Metachromatic leukodystrophy (MLD) is an autosomal recessive Autosomal recessive Autosomal inheritance, both dominant and recessive, refers to the transmission of genes from the 22 autosomal chromosomes. Autosomal recessive diseases are only expressed when 2 copies of the recessive allele are inherited. Autosomal Recessive and Autosomal Dominant Inheritance white matter White Matter The region of central nervous system that appears lighter in color than the other type, gray matter. It mainly consists of myelinated nerve fibers and contains few neuronal cell bodies or dendrites. Brown-Séquard Syndrome disease caused by a deficiency in arylsulfatase A resulting in accumulation of cerebroside Cerebroside Neutral glycosphingolipids that contain a monosaccharide, normally glucose or galactose, in 1-ortho-beta-glycosidic linkage with the primary alcohol of an n-acyl sphingoid (ceramide). In plants the monosaccharide is normally glucose and the sphingoid usually phytosphingosine. In animals, the monosaccharide is usually galactose, though this may vary with the tissue and the sphingoid is usually sphingosine or dihydrosphingosine. Fatty Acids and Lipids sulfate. This accumulation leads to the destruction of myelin and causes neurologic deficits Neurologic Deficits High-Risk Headaches.

Classification

Based on age at symptom onset:

• Late infantile form
• Juvenile form Juvenile Form Spinal Muscular Atrophy
• Adult form

Epidemiology

• Rare, autosomal recessive Autosomal recessive Autosomal inheritance, both dominant and recessive, refers to the transmission of genes from the 22 autosomal chromosomes. Autosomal recessive diseases are only expressed when 2 copies of the recessive allele are inherited. Autosomal Recessive and Autosomal Dominant Inheritance inherited condition
• Incidence Incidence The number of new cases of a given disease during a given period in a specified population. It also is used for the rate at which new events occur in a defined population. It is differentiated from prevalence, which refers to all cases in the population at a given time. Measures of Disease Frequency: 1 in 40,000 live births in the United States
• No racial or sexual predilection
• Most common form of inherited leukodystrophy

Etiology

• Caused by deficiency in gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics for arylsulfatase A (ARSA): 
  • Gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics located on chromosome Chromosome In a prokaryotic cell or in the nucleus of a eukaryotic cell, a structure consisting of or containing DNA which carries the genetic information essential to the cell. Basic Terms of Genetics 22 (22q13.31qter).
  • Function of ARSA: hydrolyzes sulfated glycosphingolipids
• Pseudodeficiency: partial loss of enzyme activity; no clinical consequences
• MLD can also be caused by deficiency in sphingolipid activator protein B (SAP-B) deficiency. SAP-B acts with ARSA to hydrolyze sulfated glycosphingolipids.

Pathophysiology

• Deficiency in ARSA activity → excessive white matter White Matter The region of central nervous system that appears lighter in color than the other type, gray matter. It mainly consists of myelinated nerve fibers and contains few neuronal cell bodies or dendrites. Brown-Séquard Syndrome storage of sulfated glycosphingolipids
• Accumulate in oligodendrocytes, macrophages Macrophages The relatively long-lived phagocytic cell of mammalian tissues that are derived from blood monocytes. Main types are peritoneal macrophages; alveolar macrophages; histiocytes; kupffer cells of the liver; and osteoclasts. They may further differentiate within chronic inflammatory lesions to epithelioid cells or may fuse to form foreign body giant cells or langhans giant cells. Innate Immunity: Phagocytes and Antigen Presentation, and other subtypes of neurons Neurons The basic cellular units of nervous tissue. Each neuron consists of a body, an axon, and dendrites. Their purpose is to receive, conduct, and transmit impulses in the nervous system. Nervous System: Histology
• Results in demyelination Demyelination Multiple Sclerosis and neurodegeneration

Clinical Presentation

Late infantile form

• Most common (50% of cases)
• Age at presentation: < 30 months
• Symptoms:
  • Initial developmental milestones Developmental milestones Developmental milestones are the skills or abilities that most children are able to perform when they reach a certain age. Understanding the appropriate milestones and at what age they are reached helps clinicians identify symptoms of delayed development. Developmental milestones are divided into 5 important domains: gross motor, fine motor, language, social, and cognitive. Developmental Milestones and Normal Growth are met MET Preoperative Care and then progressively lost.
  • Regression Regression Corneal Abrasions, Erosion, and Ulcers of motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology skills
  • Seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures
  • Hypotonia Hypotonia Duchenne Muscular Dystrophy
  • Extensor plantar posturing
  • Optic atrophy Atrophy Decrease in the size of a cell, tissue, organ, or multiple organs, associated with a variety of pathological conditions such as abnormal cellular changes, ischemia, malnutrition, or hormonal changes. Cellular Adaptation
• Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship die at < 5 years of life if untreated.

Juvenile form Juvenile Form Spinal Muscular Atrophy

• Age at presentation: 3 to < 16 years
• Symptoms:
  • Initial developmental milestones Developmental milestones Developmental milestones are the skills or abilities that most children are able to perform when they reach a certain age. Understanding the appropriate milestones and at what age they are reached helps clinicians identify symptoms of delayed development. Developmental milestones are divided into 5 important domains: gross motor, fine motor, language, social, and cognitive. Developmental Milestones and Normal Growth are met MET Preoperative Care and then progressively lost.
  • Intellectual regression Regression Corneal Abrasions, Erosion, and Ulcers
  • Behavioral and personality changes
  • Peripheral neuropathy Neuropathy Leprosy
  • Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship presenting at later ages often have seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures
• Death usually occurs < 2 decades after symptom onset.

Adult form

• Similar to juvenile form Juvenile Form Spinal Muscular Atrophy but more protracted course 
• Age at presentation: > 20 years
• Slow progression
• Symptoms:
  • Dementia Dementia Major neurocognitive disorders (NCD), also known as dementia, are a group of diseases characterized by decline in a person’s memory and executive function. These disorders are progressive and persistent diseases that are the leading cause of disability among elderly people worldwide. Major Neurocognitive Disorders
  • Seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures
  • Diminished reflexes
  • Optic atrophy Atrophy Decrease in the size of a cell, tissue, organ, or multiple organs, associated with a variety of pathological conditions such as abnormal cellular changes, ischemia, malnutrition, or hormonal changes. Cellular Adaptation

Diagnosis

Consider diagnostic testing in patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship expressing typical clinical features.

• Diagnosis is confirmed with biochemical, urine, and genetic analysis:
  • Decreased or absent ARSA activity in leukocytes Leukocytes White blood cells. These include granular leukocytes (basophils; eosinophils; and neutrophils) as well as non-granular leukocytes (lymphocytes and monocytes). White Myeloid Cells: Histology or cultured skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Skin: Structure and Functions fibroblasts Fibroblasts Connective tissue cells which secrete an extracellular matrix rich in collagen and other macromolecules. Sarcoidosis
  • Increased urinary sulfatide secretion Secretion Coagulation Studies ( Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with pseudodeficiency have normal secretion Secretion Coagulation Studies.)
  • Genetic analysis for common mutations
• Brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification MRI is diagnostic adjunct and may show: 
  • Hyperintensity in periventricular white matter Periventricular White Matter Multiple Sclerosis
  • Hyperintensity in subcortical supratentorial white matter White Matter The region of central nervous system that appears lighter in color than the other type, gray matter. It mainly consists of myelinated nerve fibers and contains few neuronal cell bodies or dendrites. Brown-Séquard Syndrome
• Electroneurographic recordings show decreased nerve conduction velocities.
• Other results consistent with MLD but not required for diagnosis:
  • Increased CSF protein
  • Metachromatic deposits in sural nerve
  • Metachromatic granules in urinary sediment

Management

No curative therapy for MLD is widely available. Umbilical cord Umbilical cord The flexible rope-like structure that connects a developing fetus to the placenta in mammals. The cord contains blood vessels which carry oxygen and nutrients from the mother to the fetus and waste products away from the fetus. Placenta, Umbilical Cord, and Amniotic Cavity blood transplantation for children with presymptomatic late-infantile MLD or minimally symptomatic juvenile MLD can slow disease progression.

Supportive therapy is preferred for patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with symptoms and for all patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with juvenile and late-onset forms MLD:

• Seizure prophylaxis Prophylaxis Cephalosporins with antiepileptics (e.g., levetiracetam Levetiracetam A pyrrolidinone and acetamide derivative that is used primarily for the treatment of seizures and some movement disorders, and as a nootropic agent. Second-Generation Anticonvulsant Drugs) 
• Treatment for spasticity Spasticity Spinal Disk Herniation (e.g., with baclofen Baclofen A gamma-aminobutyric acid derivative that is a specific agonist of gaba-b receptors. It is used in the treatment of muscle spasticity, especially that due to spinal cord injuries. Its therapeutic effects result from actions at spinal and supraspinal sites, generally the reduction of excitatory transmission. Spasmolytics)
• Mood/behavioral issues should be addressed with behavioral therapy and medication (e.g., antidepressants).

Clinical trials of recombinant human arylsulfatase A (rhARSA) enzyme demonstrated its safety in children with late-infantile MLD.

Differential Diagnosis

• Krabbe disease Krabbe disease Krabbe disease, also known as globoid cell leukodystrophy or galactosylceramide lipidosis, is a rare autosomal recessive lysosomal storage disorder caused by a deficiency of the enzyme galactocerebrosidase. Accumulation of galactocerebroside results in destruction of myelin-producing cells throughout the peripheral and central nervous systems, leading to demyelination and clinical symptoms. Krabbe Disease: autosomal recessive Autosomal recessive Autosomal inheritance, both dominant and recessive, refers to the transmission of genes from the 22 autosomal chromosomes. Autosomal recessive diseases are only expressed when 2 copies of the recessive allele are inherited. Autosomal Recessive and Autosomal Dominant Inheritance lysosomal storage disease Lysosomal storage disease Lysosomal storage diseases are a group of metabolic disorders caused by genetic mutations in the enzymes responsible for normal lysosomal function. The dysfunction of enzymatic processes causes an accumulation of undigested metabolites, resulting in cellular death. The main groups include sphingolipidoses, oligosaccharidoses, and mucolipidoses. Overview of Lysosomal Storage Diseases caused by deficiency in beta-galactosidase ( GALC GALC An enzyme that hydrolyzes galactose from ceramide monohexosides. Deficiency of this enzyme may cause globoid cell leukodystrophy. Krabbe Disease). Krabbe disease Krabbe disease Krabbe disease, also known as globoid cell leukodystrophy or galactosylceramide lipidosis, is a rare autosomal recessive lysosomal storage disorder caused by a deficiency of the enzyme galactocerebrosidase. Accumulation of galactocerebroside results in destruction of myelin-producing cells throughout the peripheral and central nervous systems, leading to demyelination and clinical symptoms. Krabbe Disease can present during all stages of life. All patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship present with peripheral motor-sensory neuropathy Neuropathy Leprosy. Common symptoms also include irritability, hypertonia Hypertonia Abnormal increase in skeletal or smooth muscle tone. Skeletal muscle hypertonicity may be associated with pyramidal tract lesions or basal ganglia diseases. Neurological Examination, hyperesthesia, hypotonia Hypotonia Duchenne Muscular Dystrophy, and abnormal deep tendon reflexes Deep Tendon Reflexes Neurological Examination. Diagnosis is confirmed through GALC GALC An enzyme that hydrolyzes galactose from ceramide monohexosides. Deficiency of this enzyme may cause globoid cell leukodystrophy. Krabbe Disease enzyme activity.
• X-linked X-linked Genetic diseases that are linked to gene mutations on the X chromosome in humans or the X chromosome in other species. Included here are animal models of human X-linked diseases. Common Variable Immunodeficiency (CVID) adrenoleukodystrophy: X-linked X-linked Genetic diseases that are linked to gene mutations on the X chromosome in humans or the X chromosome in other species. Included here are animal models of human X-linked diseases. Common Variable Immunodeficiency (CVID) disorder of peroxisomes Peroxisomes Microbodies which occur in animal and plant cells and in certain fungi and protozoa. They contain peroxidase, catalase, and allied enzymes. The Cell: Organelles caused by mutations in ATP-binding cassette, subfamily D, member 1 gene Gene A category of nucleic acid sequences that function as units of heredity and which code for the basic instructions for the development, reproduction, and maintenance of organisms. Basic Terms of Genetics (ABCD1) that results in accumulation of very-long-chain fatty acids Acids Chemical compounds which yield hydrogen ions or protons when dissolved in water, whose hydrogen can be replaced by metals or basic radicals, or which react with bases to form salts and water (neutralization). An extension of the term includes substances dissolved in media other than water. Acid-Base Balance in most tissues of the body. Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship present with adrenal insufficiency Adrenal Insufficiency Conditions in which the production of adrenal corticosteroids falls below the requirement of the body. Adrenal insufficiency can be caused by defects in the adrenal glands, the pituitary gland, or the hypothalamus. Adrenal Insufficiency and Addison Disease, decreased cognition, behavioral issues, vision Vision Ophthalmic Exam and hearing impairment Hearing impairment Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss, and dysarthria Dysarthria Disorders of speech articulation caused by imperfect coordination of pharynx, larynx, tongue, or face muscles. This may result from cranial nerve diseases; neuromuscular diseases; cerebellar diseases; basal ganglia diseases; brain stem diseases; or diseases of the corticobulbar tracts. The cortical language centers are intact in this condition. Wilson Disease. Brain Brain The part of central nervous system that is contained within the skull (cranium). Arising from the neural tube, the embryonic brain is comprised of three major parts including prosencephalon (the forebrain); mesencephalon (the midbrain); and rhombencephalon (the hindbrain). The developed brain consists of cerebrum; cerebellum; and other structures in the brain stem. Nervous System: Anatomy, Structure, and Classification MRI and genetic testing Genetic Testing Detection of a mutation; genotype; karyotype; or specific alleles associated with genetic traits, heritable diseases, or predisposition to a disease, or that may lead to the disease in descendants. It includes prenatal genetic testing. Myotonic Dystrophies is diagnostic.
• Canavan disease: progressive neurodegenerative autosomal recessive Autosomal recessive Autosomal inheritance, both dominant and recessive, refers to the transmission of genes from the 22 autosomal chromosomes. Autosomal recessive diseases are only expressed when 2 copies of the recessive allele are inherited. Autosomal Recessive and Autosomal Dominant Inheritance leukodystrophy seen primarily in Ashkenazi Jewish populations. Canavan disease is caused by aspartoacylase deficiency. Symptoms include spasticity Spasticity Spinal Disk Herniation, ataxia Ataxia Impairment of the ability to perform smoothly coordinated voluntary movements. This condition may affect the limbs, trunk, eyes, pharynx, larynx, and other structures. Ataxia may result from impaired sensory or motor function. Sensory ataxia may result from posterior column injury or peripheral nerve diseases. Motor ataxia may be associated with cerebellar diseases; cerebral cortex diseases; thalamic diseases; basal ganglia diseases; injury to the red nucleus; and other conditions. Ataxia-telangiectasia, seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures, hypotonia Hypotonia Duchenne Muscular Dystrophy, and optic atrophy Atrophy Decrease in the size of a cell, tissue, organ, or multiple organs, associated with a variety of pathological conditions such as abnormal cellular changes, ischemia, malnutrition, or hormonal changes. Cellular Adaptation. Diagnosis is confirmed by discovering elevated levels of N-acetyl aspartate Aspartate One of the non-essential amino acids commonly occurring in the l-form. It is found in animals and plants, especially in sugar cane and sugar beets. It may be a neurotransmitter. Synthesis of Nonessential Amino Acids (NAA) in urine and abnormal diffuse white matter White Matter The region of central nervous system that appears lighter in color than the other type, gray matter. It mainly consists of myelinated nerve fibers and contains few neuronal cell bodies or dendrites. Brown-Séquard Syndrome disease on MRI.