What Is Storage Disorder?
Storage disorder or disease is a rare genetic condition group with more than 50 rare diseases. It causes a buildup of toxic materials in the body's cells by affecting the lysosome (a structure in the cells that helps break down substances such as carbohydrates, proteins, and old cell parts for recycling them by the body). People with these disorders lack important enzymes or substances that help in the functioning of the enzymes. Enzymes are necessary for the lysosome to break down sugar, fats, and other substances. If the breakdown does not happen, it builds up and becomes harmful, causing damage to cells and organs in the body.
There are more than 50 types of storage diseases. It typically appears during pregnancy or soon after birth. This disease can affect one in 7,700 births. In rare cases, adults may develop this disorder. When storage disorder occurs early, it will be more severe, and when it occurs in later stages, it will be mild. Most storage disorders, except Fabry disease and Hunter syndrome, are autosomal recessive disorders; both parents must have the abnormal gene, preventing the body from making a normal enzyme. There are no permanent cures for storage diseases; treatments can help manage the symptoms and reduce the damage to organs and tissues.
What Are the Causes of Storage Disorder?
Storage diseases are caused by an inherited error of metabolism resulting in the absence or deficiency of an enzyme, leading to the storage of harmful material in various body cells. Storage disorder occurs when the child carries a mutant gene from both parents. The parents caring for these gene mutations will not necessarily have a storage disease. Storage diseases can also get triggered by a protein deficiency as it plays a vital role in modifying enzymes in lysosomes, inflammation, and interaction between the byproducts of metabolism and the body. When both parents have a mutated gene, the child has a one in four chance of inheriting and the same chance of having no risk of developing the condition.
What Are the Symptoms of Storage Disorder?
The signs and symptoms of storage disorder vary from disease to disease in their group. Patients are symptomatic due to an enzyme deficiency that inhibits the lysosome's ability to perform its normal function in the body's cells. The symptoms are often progressive over a period of time. The followings are some common storage diseases and their characteristic signs and symptoms:
Gaucher Disease Types I, II, and III - This is one of the common types of a lysosomal storage disorder. Gaucher disease is classified into different types based on the absence or presence and extent of neurological complications.
-
Type I is the most common, and the symptoms include chronic fatigue, easy bruising, and an abnormally enlarged liver and spleen.
-
Type II is seen in newborns and infants, and the symptoms include neurological complications like difficulty swallowing, involuntary muscle spasms, and the loss of acquired motor skills.
-
Type III is seen during the first decade of life, with neurological complications like an inability to coordinate voluntary movements, mental deterioration, and muscle spasms of the arms, legs, or whole body.
Cystinosis - The early signs of this disorder typically involve the kidneys and the eyes. This occurs due to excessive amino acid cystine storage in all the body cells. There are different types of cystinosis infantile, juvenile, and adult forms. The symptoms include
-
Weakened kidney function.
-
Increased sensitivity to light.
-
Growth retardation.
Batten Disease - It is the juvenile form of a progressive neurological disorder called neuronal ceroid lipofuscinoses (NCL). It causes lipopigment, a fatty substance accumulation in the brain and in tissue without nerve cells. The symptoms include
-
Optic atrophy (rapidly progressive vision failure).
-
Neurological disturbances may begin before eight years of age and cause deterioration of both neurological and intellectual functions.
Fabry Disease: Fabry disease symptoms normally begin during early childhood or adolescence. But mostly, it becomes evident in the second or third decade of life. The symptoms include:
-
Severe burning sensation in the hands and feet.
-
Decrease in sweat production.
-
Discomfort in warm temperatures.
-
Reddish to dark blue skin rash appears in the skin, mainly between the hips and knees, which may be a flat or raised lesion.
Glycogen Storage Disease II: This is also called pompe disease. It appears in two forms: an infantile form and a delayed onset form.
-
The infantile form is further divided into a childhood form and an adult form. Infantile form patients are the most severely affected, and the symptoms include diminished muscle tone (hypotonia), rapidly progressive muscle weakness, and hypertrophic cardiomyopathy (abnormal thickening of heart muscles). Also, infants suffer from feeding problems and respiratory difficulties.
-
The adult form occurs between the first and seventh decades, causing slowly progressive muscle weakness or symptoms of respiratory insufficiency. Cardiac involvement is absent with this form.
Metachromatic Leukodystrophy: This condition's early signs and symptoms may appear gradually and be vague. So it is often difficult to diagnose this disorder. The symptoms include
-
Unsteadiness when walking.
-
Delay in developmental or school performance.
-
Muscle spasm.
-
Seizures.
-
Mental retardation.
How Is Storage Disorder Diagnosed?
Diagnosis of storage disorder is quite difficult as the symptoms vary among the different types and individuals. Prenatal diagnosis is possible for all storage disorders and is carried out in a specialized laboratory. Tissue biopsies are also used to diagnose storage disorders in the patient by analyzing the cells or tissues collected from the patient's body for analysis. Blood, urine, amniotic fluid, and skin fibroblast tests are a few tests used to test the presence of storage disorder in a patient's samples. Early detection of storage diseases, before birth or as soon as possible afterward, is very important as it can limit the impact and long-term course of the disease.
What Is the Treatment for Storage Disorder?
At present, there are no known treatments or cures for storage disorders. However, researchers continue to progress toward treatment options beyond treating symptoms to treat underlying causes, as there are around 50 to 60 types of storage disorders with different symptoms. Few therapies are carried out to treat these diseases.
-
Enzyme Replacement Therapy (ERT): The health care professionals insert a genetically engineered enzyme into the patient's vein (intravenously).
-
Stem Cell Transplants: Stem cells from umbilical cord blood or donor help in producing the missing enzymes. It can also reduce tissue damage and inflammation.
-
Substrate Reduction Therapy (SRT): Medications can reduce the substances that build up in the cells. Miglustat helps in treating Gaucher's disease. Currently, many clinical trials are being carried out to treat different other storage disorders.
Conclusion:
Storage disorders are caused by buildups of toxic substances in the body's cells leading to cell and organ damage. At present more than 70 types of storage disorders have been identified. The symptoms of this disorder vary based on the type. Diagnosis is carried out during pregnancy or after birth for children and adults with genetic testing, biopsy, blood tests, and urine tests. However, treatments can not cure this disorder; they can manage symptoms and improve the quality of life.
