Lysosomal Storage Diseases - Etiology, Types, Symptoms, Diagnosis, and Treatment

What Are Lysosomal Storage Diseases?

Lysosomal storage diseases (LSDs) are metabolic diseases caused by single gene defects. Enzyme defects account for the incidence of nearly 70 percent of lysosomal storage diseases (LSDs), and the rest occur due to defects in proteins or enzyme activators. Lysosomes inside the cells contain hydrolytic enzymes that can digest large molecules into fragments. This unique function of lysosomes requires several enzymes. Therefore, the defective functioning of any of these enzymes results in the accumulation of large molecules within the cell and cell damage. Similar to other genetic disorders, lysosomal storage diseases are inherited from parents to their children. Therefore, it mainly affects children and results in serious complications.

How Do Lysosomes and Enzymes Function Together?

Lysosomes in cells utilize enzymes to help with metabolism. These enzymes assist lysosomes in metabolizing carbohydrates, fats, and proteins. The buildup of these compounds harms other cells and organs. The disorder can affect the brain, central nervous system, and heart.

Who Is at Risk of Lysosomal Storage Disease?

Though it can affect any individual, this is more common in specific ethnic groups and some areas. Certain lysosomal storage disorders are more prevalent in people residing in Finland and also in Jews from Eastern Europe.

What Are the Etiological Factors Responsible for Lysosomal Storage Diseases?

The main cause of LSDs is the mutation in genes encoding for lysosomal proteins. This leads to the generation of defective enzymes resulting in lysosome dysfunction and cellular damage. Most lysosomal storage diseases (LSDs) have an autosomal recessive type of inheritance. Recessive genetic disorders occur when the child inherits the same faulty abnormal gene for the trait from each parent. If the child receives only one abnormal gene, they are considered a disease carrier.

What Are the Different Types of Lysosomal Storage Diseases?

Lysosomal storage diseases (LSDs) are classified based on the accumulated substrates in the body. They can be divided into lipid storage diseases, glycoprotein storage diseases, mucopolysaccharidoses, and mucolipidosis. More than 70 diseases have been identified and named based on the enzyme defect, substance accumulated, or scientist identified.

It consists of the following.

• Farber disease.

• Fabry disease.

• Tay-Sachs disease.

• Schindler disease.

• Krabbe disease.

• Sphingolipidoses.

• Gaucher disease.

• Lysosomal acid lipase deficiency.

• Niemann-Pick disease.

• Galactosialidosis.

• Salla disease.

• Metachromatic leukodystrophy.

• Hurler syndrome.

• Sanfilippo syndrome.

• Maroteaux-Lamy syndrome.

• Cholesteryl ester storage disease.

• Pompe disease.

• Infantile-free sialic acid storage disease.

• Danon disease.

• Cystinosis.

• Beta-mannosidosis.

• Mucopolysaccharidosis.

• Fucosidosis.

• Pycnodysostosis.

• Wolman disease.

• Sly syndrome.

• Hurler-Scheie syndrome.

• Multiple sulfatase deficiency.

• Sandhoff disease.

• Galactosialidosis.

What Are the Common Symptoms of Lysosomal Storage Diseases?

Signs and symptoms associated with lysosomal storage diseases (LSDs) vary depending on the age of onset, enzyme defect involved, and stage of progression (mild to severe).

The most commonly observed symptoms are the following.

• Developmental delay.

• Seizures.

• Movement disorders.

• Deafness.

• Dementia.

• Cardiac problems.

• Enlarged liver.

• Blindness.

• Pulmonary diseases.

• Enlarged spleens.

• Abnormal bone growth.

• Skin rashes.

• Tiredness.

• Anemia.

• Kidney failure.

• Memory loss.

• Depression.

• Muscle weakness.

• Numbness in hands and feet.

• Heart failure.

• Inability to walk.

• Stiff extremities.

How Can We Diagnose Lysosomal Storage Diseases?

Prenatal diagnostic tests can be done to identify the presence of lysosomal storage diseases (LSDs) in the baby during pregnancy. A definitive diagnosis can be made using an enzyme assay. Apart from specific diagnostic tests, other investigations like X-rays, audiometry, pulmonary function tests, visual assessment tests, magnetic resonance imaging (MRI), echocardiogram, liver function test, hemogram, and renal function tests can be done to identify and evaluate a patient's condition and associated complications.

LSDs can be diagnosed by performing certain prenatal screening tests during pregnancy. The test includes amniocentesis and chorionic villus sampling. The newborn babies will be examined for LSDs by doing a blood test. The blood test will help to determine the missing enzyme. In children and adults, the condition is diagnosed by performing various tests, which include blood tests, urinalysis, genetic testing, and biopsy. The physician may advise you to take a few more tests to identify any damage to the organs. This includes kidney function tests, liver function tests, eye checkups, and MRI (magnetic resonance imaging).

How Can We Manage Lysosomal Storage Diseases?

There is no specific treatment available for lysosomal storage diseases (LSDs). Furthermore, few therapies have been developed for patients suffering from lysosomal storage diseases to improve their quality of life and increase life expectancy.

It includes the following:

• Bone Marrow Transplantation Therapy - It is effective in preventing the progression of mental retardation in children with Hurler disease. Bone marrow transplantation is done before two years of age. It is considered a standard treatment option for infants with Hurler disease.

• Enzyme Replacement Therapy - It has been proven effective in the treatment of Gaucher disease type I. Enzyme replacement therapy improves lung and cardiac function and the patient's overall condition.

• Substrate Reduction Therapy - Some specific substances can be used to reduce the formation of toxic substrates by inhibiting the enzymes responsible for their synthesis. Thus, the progression of neuropathic defects associated with lysosomal storage diseases can be slowed.

• Proteostasis Regulators - They help to control different steps involved in the progression of metabolic diseases associated with lysosomal storage diseases.

• Pharmacological Chaperone Therapy (PCT) - Chaperons are small molecules that correct misfolding and improve enzyme function. Pharmacological chaperone therapy (PCT) helps to improve the enzymatic defect associated with lysosomal storage diseases.

• Anti-inflammatory Agents - Immunosuppressive agents, along with anti-inflammatory agents, reduce inflammatory agents responsible for the pathogenesis of lysosomal storage diseases.

• Hematopoietic Stem Cell Transplantation (HSCT) - Stem cells obtained from the umbilical cord or donors can also be used instead of bone marrow tissues to improve the patient's condition and outcomes.

• Small Molecule Assisted Substrate Transportation (SMAST) - In this substrate accumulated in the cells due to lack of transporter mechanism is converted to another compound that can be easily transported.

• Supportive Treatments - Apart from specific therapies directed at improving enzyme function, substrate removal, and stem cell therapy, other individual treatments can also be used to reduce the complications associated with lysosomal storage diseases.

Is It Possible to Reduce the Likelihood of Lysosomal Storage Diseases?

It is impossible to reduce the risk, but one can improve the quality of life with prompt treatment.

What Is the Prognosis of Lysosomal Storage Disease?

Life expectancy varies with the stage of the disease. Individuals with mild LSD have better life spans if they initialize the treatment early than individuals with severe forms of LSD.

How to Take Care of Myself With Lysosomal Storage Disease?

Take help from a psychologist if you are diagnosed with lysosomal storage disease. They can give some suggestions on how to cope with mental stress and connect with support groups, which helps you connect with people who face similar situations.

Conclusion

Lysosomal storage diseases cause the deposition of abnormal substances in the cells. It will result in damage to other cells and organs. The LSDs occur due to alterations in the genes encoding the lysosomal enzyme. The condition can be diagnosed while pregnant by doing certain prenatal screening tests, in children and adults by performing certain blood tests. Managing lysosomal storage diseases includes specific therapies to improve enzyme function and other supportive therapeutic agents to improve difficulties.