Tay-Sachs Disease

Overview

Etiology

Tay-Sachs disease is a lysosomal storage disorder caused by a deficiency in the hexosaminidase A (Hex-A) enzyme. 

• Mutation Mutation Genetic mutations are errors in DNA that can cause protein misfolding and dysfunction. There are various types of mutations, including chromosomal, point, frameshift, and expansion mutations. Types of Mutations of the HEXA 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 (15q23-p24) 
• > 130 HEXA 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 mutations have been identified.
• 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 

Classification

Tay-Sachs disease is classified into 3 variants based on age of onset and enzyme activity.

• Infantile, classic acute:
  • Most common
  • Type I GM₂ gangliosidosis
  • < 0.1% of normal Hex-A enzyme activity
• Juvenile onset, subacute:
  • Rare
  • Type III GM₂ gangliosidosis
  • 1% of normal Hex-A enzyme activity
• Adult onset:
  • Very rare
  • Chronic GM₂ gangliosidosis
  • < 10% of normal Hex-A enzyme activity

Epidemiology

• In the general population: 
  • 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 320,000 live births
  • Carrier Carrier Vaccination rate in the general population: 1 in every 250–300 people.
• Higher prevalence Prevalence The total number of cases of a given disease in a specified population at a designated time. It is differentiated from incidence, which refers to the number of new cases in the population at a given time. Measures of Disease Frequency in those of Central and Eastern European or Ashkenazi Jewish descent:
  • 100 times more prevalent in Ashkenazi Jewish individuals
  • 1 in every 29 Ashkenazi Jewish individuals in the United States and 1 in every 60 Moroccan Jews carry HEXA mutations.
• Other populations with high carrier Carrier Vaccination rates:
  • Old Order Amish in Pennsylvania
  • French Canadians in Quebec
  • Individuals of Cajun descent in Louisiana
  • Those with Irish ethnicity

Pathophysiology

• Inadequate activity of Hex-A → accumulation of the cell membrane Cell Membrane A cell membrane (also known as the plasma membrane or plasmalemma) is a biological membrane that separates the cell contents from the outside environment. A cell membrane is composed of a phospholipid bilayer and proteins that function to protect cellular DNA and mediate the exchange of ions and molecules. The Cell: Cell Membrane glycolipid GM₂ ganglioside Ganglioside A subclass of acidic glycosphingolipids. They contain one or more sialic acid (n-acetylneuraminic acid) residues. Using the svennerholm system of abbreviations, gangliosides are designated g for ganglioside, plus subscript m, d, or t for mono-, di-, or trisialo, respectively, the subscript letter being followed by a subscript arabic numeral to indicated sequence of migration in thin-layer chromatograms. Fatty Acids and Lipids in the neuronal lysosomes Lysosomes A class of morphologically heterogeneous cytoplasmic particles in animal and plant tissues characterized by their content of hydrolytic enzymes and the structure-linked latency of these enzymes. The intracellular functions of lysosomes depend on their lytic potential. The single unit membrane of the lysosome acts as a barrier between the enzymes enclosed in the lysosome and the external substrate. The activity of the enzymes contained in lysosomes is limited or nil unless the vesicle in which they are enclosed is ruptured or undergoes membrane fusion. The Cell: Organelles 
• This leads to cell death Cell death Injurious stimuli trigger the process of cellular adaptation, whereby cells respond to withstand the harmful changes in their environment. Overwhelmed adaptive mechanisms lead to cell injury. Mild stimuli produce reversible injury. If the stimulus is severe or persistent, injury becomes irreversible. Apoptosis is programmed cell death, a mechanism with both physiologic and pathologic effects. Cell Injury and Death → progressive neurodegeneration

Clinical Presentation

Tay-Sachs disease is a neurodegenerative disorder with a variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables clinical presentation depending on the variant.

Infantile, classic acute Tay-Sachs disease

• Time course:
  • Normal appearance at birth
  • Onset by 5 months of age
  • Rapid disease progression
  • Death by 4 years of age, often due to pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia
• Signs and symptoms:
  • Exaggerated startle reaction Startle Reaction Primitive Reflexes to sounds ( hyperacusis Hyperacusis An abnormally disproportionate increase in the sensation of loudness in response to auditory stimuli of normal volume. Cochlear disease, vestibulocochlear nerve diseases, facial nerve diseases, stapes surgery, and other disorders may be associated with this condition. Cranial Nerve Palsies)
  • Unusual eye movements
  • Blindness Blindness The inability to see or the loss or absence of perception of visual stimuli. This condition may be the result of eye diseases; optic nerve diseases; optic chiasm diseases; or brain diseases affecting the visual pathways or occipital lobe. Retinopathy of Prematurity
  • Macular “cherry-red” spot on fundoscopic exam Fundoscopic Exam Head and Neck Examination
  • Progressive hearing loss Hearing loss 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
  • Muscle weakness
  • Hypotonia Hypotonia Duchenne Muscular Dystrophy → spasticity Spasticity Spinal Disk Herniation
  • Myoclonic jerks Myoclonic Jerks Neonatal Abstinence Syndrome
  • 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
  • Difficulty swallowing Swallowing The act of taking solids and liquids into the gastrointestinal tract through the mouth and throat. Gastrointestinal Motility
  • Paralysis

Juvenile onset, subacute

• Time course:
  • Increased heterogeneity of disease 
  • Onset between 2 and 10 years of age
  • Slow disease progression
  • Death by age 15, often due to pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia
  • Some cases may be aggressive, resulting in death in 2‒4 years.
• Signs and symptoms:
  • Deterioration of gait Gait Manner or style of walking. Neurological Examination:
    • Clumsiness
    • Incoordination ( 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)
  • Worsening cognition and speech
  • Blindness Blindness The inability to see or the loss or absence of perception of visual stimuli. This condition may be the result of eye diseases; optic nerve diseases; optic chiasm diseases; or brain diseases affecting the visual pathways or occipital lobe. Retinopathy of Prematurity due to: 
    • 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
    • Retinitis pigmentosa
  • Frequent infections Infections Invasion of the host organism by microorganisms or their toxins or by parasites that can cause pathological conditions or diseases. Chronic Granulomatous Disease
  • 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

Adult onset, chronic

• Time course:
  • Heterogeneity in phenotype Phenotype The complete genetic complement contained in the DNA of a set of chromosomes in a human. The length of the human genome is about 3 billion base pairs. Basic Terms of Genetics and progression of disease
  • Onset from adolescence to anytime in adulthood
  • Death in the 5th‒6th decade of life
• Signs and symptoms:
  • Subtle clumsiness
  • Progressive muscle weakness
  • 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
  • Tremor Tremor Cyclical movement of a body part that can represent either a physiologic process or a manifestation of disease. Intention or action tremor, a common manifestation of cerebellar diseases, is aggravated by movement. In contrast, resting tremor is maximal when there is no attempt at voluntary movement, and occurs as a relatively frequent manifestation of parkinson disease. Myotonic Dystrophies
  • Dystonia Dystonia Dystonia is a hyperkinetic movement disorder characterized by the involuntary contraction of muscles, resulting in abnormal postures or twisting and repetitive movements. Dystonia can present in various ways as may affect many different skeletal muscle groups. Dystonia
  • 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
  • Dyskinesis
  • Choreoathetosis
  • Psychosis 
  • Proximal muscle wasting Muscle Wasting Duchenne Muscular Dystrophy and weakness

Diagnosis and Management

Diagnosis

Testing is pursued following clinical suspicion. Prenatal screening Screening Preoperative Care is also possible via chorionic villus sampling or amniocentesis Amniocentesis Percutaneous transabdominal puncture of the uterus during pregnancy to obtain amniotic fluid. It is commonly used for fetal karyotype determination in order to diagnose abnormal fetal conditions. Polyhydramnios.

• Hex-A assay: identification Identification Defense Mechanisms of low to no levels of Hex-A and normal to elevated levels of beta-hexosaminidase
• Molecular 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: confirms HEXA 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 mutations

Management

There is no cure for Tay-Sachs disease. Management is supportive, focused on controlling symptoms and improving quality Quality Activities and programs intended to assure or improve the quality of care in either a defined medical setting or a program. The concept includes the assessment or evaluation of the quality of care; identification of problems or shortcomings in the delivery of care; designing activities to overcome these deficiencies; and follow-up monitoring to ensure effectiveness of corrective steps. Quality Measurement and Improvement of life.

• Medications to control 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 and treatment of psychosis in adults
• Nonmedical and supportive care:
  • Protect airway Airway ABCDE Assessment and provide respiratory support:
    • Manage chest congestion with chest physiotherapy Physiotherapy Spinal Stenosis.
    • Oxygen administration
    • Tracheostomy Tracheostomy Surgical formation of an opening into the trachea through the neck, or the opening so created. Laryngomalacia and Tracheomalacia tube when at risk of aspiration
    • Assisted ventilatory support based on expected disease course and family preference
  • Proper nutrition and hydration:
    • High-calorie diet with semisolid or puréed food (administer via gastrostomy tube, if necessary)
    • Special techniques and strategies for nursing infants
    • Percutaneous endoscopic gastrostomy
  • Physical therapy Physical Therapy Becker Muscular Dystrophy to improve motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology skills and decrease spasticity Spasticity Spinal Disk Herniation
• Other therapeutic modalities in development:
  • Bone marrow transplant Bone marrow transplant Transfer of hematopoietic stem cells from bone marrow or blood between individuals within the same species (homologous transplantation) or transfer within the same individual (autologous transplantation). Hematopoietic stem cell transplantation has been used as an alternative to bone marrow transplantation in the treatment of a variety of neoplasms. Organ Transplantation
  • Enzyme-replacement therapy
  • Enzyme-enhancing therapy
  • Cell transplantation
  • Substrate-reduction therapy
  • 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 therapy

Differential Diagnosis

• Sandhoff disease ( SD SD The standard deviation (SD) is a measure of how far each observed value is from the mean in a data set. Measures of Central Tendency and Dispersion): a lysosomal storage disorder caused by a deficiency in both Hex-A and B. Juvenile SD SD The standard deviation (SD) is a measure of how far each observed value is from the mean in a data set. Measures of Central Tendency and Dispersion is characterized by progressive neurodegeneration starting at the age of 6 months. Clinical manifestations are similar to infantile Tay-Sachs disease, including hyperacusis Hyperacusis An abnormally disproportionate increase in the sensation of loudness in response to auditory stimuli of normal volume. Cochlear disease, vestibulocochlear nerve diseases, facial nerve diseases, stapes surgery, and other disorders may be associated with this condition. Cranial Nerve Palsies, macular cherry-red spot, blindness Blindness The inability to see or the loss or absence of perception of visual stimuli. This condition may be the result of eye diseases; optic nerve diseases; optic chiasm diseases; or brain diseases affecting the visual pathways or occipital lobe. Retinopathy of Prematurity, and 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. Organomegaly and skeletal abnormalities are distinct from Tay-Sachs disease. Diagnosis is made by measurement of Hex-A and B as well as genetic analysis. Management is supportive. 
• Niemann-Pick disease Niemann-Pick disease Niemann-Pick disease (NPD) is a rare, inherited, lysosomal storage disorder. The disease is classified on the basis of the genetic mutation. Type A and type B result from mutations in the SMPD-1 gene, resulting in acid sphingomyelinase enzyme deficiency. Type C results from NPC1 or NPC2 gene mutations, which are needed for intracellular transport of lipids. Niemann-Pick Disease type A (NPD-A): a lysosomal storage disorder caused by an acid sphingomyelinase Acid sphingomyelinase Niemann-Pick Disease enzyme deficiency. The disease is characterized by progressive neurodegeneration starting within a few months of life and resulting in death by age 3. Clinical manifestations are similar to Tay-Sachs disease, including a macular cherry-red spot, difficulty feeding, loss of motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology skills, and hypotonia Hypotonia Duchenne Muscular Dystrophy. The presence of organomegaly distinguishes NPD NPD Niemann-pick disease (NPD) is a rare, inherited, lysosomal storage disorder. The disease is classified on the basis of the genetic mutation. Type a and type B result from mutations in the smpd-1 gene, resulting in acid sphingomyelinase enzyme deficiency. Type c results from npc1 or npc2 gene mutations, which are needed for intracellular transport of lipids. Niemann-Pick Disease from Tay-Sachs disease. Diagnosis includes measurement of sphingomyelinase enzyme activity 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. Management is supportive. 
• Pompe disease ( glycogen storage disease Glycogen storage disease A group of inherited metabolic disorders involving the enzymes responsible for the synthesis and degradation of glycogen. In some patients, prominent liver involvement is presented. In others, more generalized storage of glycogen occurs, sometimes with prominent cardiac involvement. Benign Liver Tumors II): a lysosomal and glycogen storage disorder caused by acid alpha-glucosidase (GAA) deficiency. There are 3 types of Pompe disease, with variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables onset and presentations. Clinical manifestations include failure to thrive Failure to Thrive Failure to thrive (FTT), or faltering growth, describes suboptimal weight gain and growth in children. The majority of cases are due to inadequate caloric intake; however, genetic, infectious, and oncological etiologies are also common. Failure to Thrive, feeding difficulty, hypotonia Hypotonia Duchenne Muscular Dystrophy, progressive muscle weakness, hypertrophic cardiomyopathy Hypertrophic Cardiomyopathy Hypertrophic cardiomyopathy (HCM) is the most commonly inherited cardiomyopathy, which is characterized by an asymmetric increase in thickness (hypertrophy) of the left ventricular wall, diastolic dysfunction, and often left ventricular outflow tract obstruction. Hypertrophic Cardiomyopathy, and respiratory failure Respiratory failure Respiratory failure is a syndrome that develops when the respiratory system is unable to maintain oxygenation and/or ventilation. Respiratory failure may be acute or chronic and is classified as hypoxemic, hypercapnic, or a combination of the two. Respiratory Failure. The diagnosis is made by measuring enzyme activity and molecular 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 analysis. Management includes supportive measures and enzyme replacement Enzyme replacement Therapeutic replacement or supplementation of defective or missing enzymes to alleviate the effects of enzyme deficiency (e.g., glucosylceramidase replacement for gaucher disease). Severe Combined Immunodeficiency (SCID).
• Fabry disease Fabry disease Fabry disease (FD), also known as Anderson-Fabry disease, is an X-linked recessive lysosomal storage disorder and the 2nd most common of the lysosomal storage disorders. Fabry disease is caused by a deficiency in the alpha-galactosidase enzyme (alpha-Gal A), resulting in the accumulation of the glycosphingolipid globotriaosylceramide (Gb3) in lysosomes. Fabry Disease: a lysosomal storage disorder caused by alpha-galactosidase Alpha-galactosidase An enzyme that catalyzes the hydrolysis of terminal, non-reducing alpha-d-galactose residues in alpha-galactosides including galactose oligosaccharides, galactomannans, and galactolipids. Fabry Disease A (GLA) deficiency. The deficiency results in glycophospholipid deposition in the vascular endothelium Endothelium A layer of epithelium that lines the heart, blood vessels (vascular endothelium), lymph vessels (lymphatic endothelium), and the serous cavities of the body. Arteries: Histology and smooth muscle cells. Clinical manifestations include paresthesias Paresthesias Subjective cutaneous sensations (e.g., cold, warmth, tingling, pressure, etc.) that are experienced spontaneously in the absence of stimulation. Posterior Cord Syndrome involving the hands and feet, purplish 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 lesions (angiokeratomas), decreased sweating, cardiovascular complications, and renal disease. Diagnosis is made with measurement of GLA enzyme activity. Management includes supportive measures and enzyme replacement Enzyme replacement Therapeutic replacement or supplementation of defective or missing enzymes to alleviate the effects of enzyme deficiency (e.g., glucosylceramidase replacement for gaucher disease). Severe Combined Immunodeficiency (SCID).
• Gaucher disease Gaucher disease Gaucher Disease (GD) is an autosomal recessive lysosomal storage disorder caused by a deficiency of glucocerebrosidase enzyme activity, resulting in accumulation of glucocerebroside in cells and certain organs. The disease is categorized into 3 types with variable clinical presentation. Gaucher Disease ( GD GD Gaucher disease (GD) is an autosomal recessive lysosomal storage disorder caused by a deficiency of glucocerebrosidase enzyme activity, resulting in accumulation of glucocerebroside in cells and certain organs. The disease is categorized into 3 types with variable clinical presentation. Gaucher Disease): a lysosomal storage disorder caused by a deficiency of glucocerebrosidase enzyme activity, resulting in accumulation of glucocerebrosidase. Infantile GD GD Gaucher disease (GD) is an autosomal recessive lysosomal storage disorder caused by a deficiency of glucocerebrosidase enzyme activity, resulting in accumulation of glucocerebroside in cells and certain organs. The disease is categorized into 3 types with variable clinical presentation. Gaucher Disease presents within 6 months of life with progressive neurodegeneration, loss of motor Motor Neurons which send impulses peripherally to activate muscles or secretory cells. Nervous System: Histology skills, hypotonia Hypotonia Duchenne Muscular Dystrophy, feeding difficulties, and death before the age of 3 years. Hepatosplenomegaly Hepatosplenomegaly Cytomegalovirus makes GD GD Gaucher disease (GD) is an autosomal recessive lysosomal storage disorder caused by a deficiency of glucocerebrosidase enzyme activity, resulting in accumulation of glucocerebroside in cells and certain organs. The disease is categorized into 3 types with variable clinical presentation. Gaucher Disease distinct from Tay-Sachs disease. Diagnosis is made by measurement of acid beta-glucosidase Beta-glucosidase An exocellulase with specificity for a variety of beta-d-glucoside substrates. It catalyzes the hydrolysis of terminal non-reducing residues in beta-d-glucosides with release of glucose. Gaucher Disease activity and confirmed with genetic analysis. Management is supportive.