Lysosomal storage diseases

Lysosomal storage diseases are a group of inherited metabolic disorders caused by a deficiency of specific enzymes. This causes an accumulation of abnormal substances that are usually degraded within lysosomes, resulting in cell damage and death. These substances include specific lipids and glycoproteins such as sphingolipids, glycosaminoglycans, and gangliosides, among others. Lysosomal storage diseases have a progressive course and, depending on the exact disease and subtype, can also be fatal in early childhood.

Sphingolipidoses are a group of lysosomal storage diseases caused by inherited deficiencies of lysosomal enzymes leading to alteration of sphingolipid catabolism. This will eventually lead to accumulation of pathologic cellular inclusions and cell damage, ultimately resulting in cell death. There are three main types of pathologic cellular inclusions:

• Sphingomyelin: derived from a ceramide with phosphorylcholine as a hydrophilic group
• Cerebrosides: derived from a ceramide with a single sugar residue (galactose or glucose)
• Gangliosides: derived from a ceramide with an oligosaccharide chain and one or more sialic acids linked to the chain

• Etiology: autosomal recessive inherited disease ^[1]
• Epidemiology
  • Most common lysosomal lipid storage disease
  • Increased incidence of type I in the Ashkenazi Jewish population ^[2]
• Pathophysiology: deficiency of β-glucocerebrosidase → accumulation of glucocerebroside (sphingolipid found in cell membranes that can accumulate in the lysosome of macrophages) in the brain, liver, spleen, and bone marrow
• Clinical features
  • Vary according to the exact subtype of Gaucher disease
    • Type I: non-neuronopathic Gaucher disease
    • Type II: acute neuronopathic Gaucher disease
    • Type III: chronic neuronopathic Gaucher disease
  • All types
    • Hepatosplenomegaly
    • Bone: bone crises , osteoporosis, avascular necrosis of the femur
    • Blood abnormalities: anemia, thrombocytopenia, pancytopenia
    • Pulmonary manifestations
    • Growth delays
  • Type II
    • Congenital ichthyosis (collodion baby), acute neurodegeneration
    • Death within the first years of life ^[3]
  • Type III
    • Gradual onset of symptoms
    • Neurodegeneration
• Diagnostics
  • Reduced glucocerebrosidase activity in leukocytes or fibroblasts
  • Accumulation of glucocerebroside in leukocytes or fibroblasts
  • Gaucher cell: lipid-rich macrophages with an enlarged cytoplasm with inclusions that resemble crumpled tissue paper on microscopy
• Treatment: : enzyme replacement therapy with recombinant glucocerebrosidase or substrate reduction therapy with eliglustat

“The Girl HaS Painted A Bone Meticulously on a Crumpled Tissue Paper:” Glucocerebrosidase, HepatoSplenomegaly, Pancytopenia, Avascular necrosis of the femur, Bone crises, Macrophage inclusions that resemble crumpled tissue paper.

• Etiology: autosomal recessive inherited disease ^[4]
• Pathophysiology: lack of or reduced activity of the lysosomal enzyme galactocerebrosidase (GALC; also called galactosylceramidase) → accumulation of galactocerebroside and psychosine (toxic myelin degradation products) and formation of globoid cells → demyelination and destruction of oligodendrocytes up to decerebration
• Clinical features
  • Major mental and motor deficits
    • Developmental delay
    • Peripheral neuropathy
    • Limb stiffness
    • Opisthotonic posture
  • Loss of vision (atrophy of the optical nerve)
• Diagnostics: globoid cell (a large multinucleated cell of mesodermal origin that is found clustered in the brain tissue )
• Treatment
  • Before symptom onset, stem cell transplantation may improve outcome.
  • Only supportive treatment is possible after symptom onset.

• Etiology: autosomal recessive inherited disease ^[5]
• Epidemiology: : more common in the Ashkenazi Jewish population ^[6]
• Pathophysiology: hexosaminidase A deficiency → intracellular accumulation of GM₂ ganglioside → progressive neurodegeneration
• Clinical features: Rapid reduction of physical and mental abilities begins around the age of 3–6 months ^[5]
  • Developmental delay
  • Macula showing a “cherry-red” spot
  • Hypotonia
  • Seizures, hyperreflexia
  • Hyperacusis
  • Note: no hepatomegaly (unlike in Niemann-Pick disease)
  • Affected individuals typically die around the age of 2–3 years ^[5]
• Diagnostics: lysosomes with onion-skin appearance
• Treatment: supportive

“After they Hexed Tay's Sax, his playing became deficient.”

• Etiology: X-linked recessive inherited disease ^[7]
• Epidemiology
  • Typical onset is during childhood but may also appear in 60–80-year-old adults
  • Mainly affects boys
• Pathophysiology: α-Galactosidase A deficiency → accumulation of ceramide trihexoside (also known as globotriaosylceramide; a glycolipid found in multiple body tissues) in the endothelium of vessels, in the epithelium of many organs, and in smooth muscle cells → disorder affecting many organ systems
• Clinical features
  • Early symptoms manifest as a typical triad, consisting of
    • Periodically occurring dysesthesia; in the hands and feet caused by small fiber neuropathy , which manifests as burning pain (Fabry crises)
    • Anhidrosis or hypohidrosis
    • Angiokeratomas
  • Other early symptoms include:
    • Nonspecific gastrointestinal disturbances
    • Corneal clouding
    • Cataract
  • Late symptoms
    • Cardiomyopathy
    • Cerebrovascular lesions (TIA and stroke)
    • Fabry nephropathy, causing progressive renal failure
• Treatment: enzyme replacement therapy with α-galactosidase A

FABRYC: Foamy urine (Fabry nephropathy), α-galactosidase A deficiency/Angiokeratomas, Burning pain in hands and feet, Really sweaty/dry, YX genotype (male), Cardio-Cerebrovascular disease/Ceramide trihexoside accumulation.

• Etiology: autosomal recessive inherited disease ^[8]
• Pathophysiology: arylsulfatase A deficiency → cerebroside sulfate accumulation in neural and non-neural tissue → progressive demyelination of the central and peripheral nervous system
• Clinical features
  • Infantile onset
    • Motor regression and developmental delay
    • Impaired memory
    • Ataxia
    • Hypotonia and hyporeflexia
    • Optic nerve atrophy → loss of vision
    • Flaccid paralysis followed by spastic paralysis
  • Childhood and juvenile onset
    • Ataxia
    • Neurocognitive and behavioral changes (e.g., worsening school performance)
    • Peripheral neuropathy
• Treatment: supportive

• Etiology: autosomal recessive inherited disease ^[9][10]
• Epidemiology: type A and B are more common in the Ashkenazi Jewish population ^[11]
• Pathophysiology
  • Type A and B: genetic deficiency of sphingomyelinase → accumulation of sphingomyelin
  • Type C: defective NPC proteins (mainly NPC1)
• Clinical features
  • Progressive neurodegeneration (mainly type A and C) ^[12]
  • Cherry-red spot in the macula
  • Hepatosplenomegaly
• Diagnostics
  • Light microscopy: lipid-laden macrophages (foam cells) in the bone marrow, spleen, and liver
  • Electron microscopy: Zebra bodies (abnormal configuration of myelinoid membranes into parallel palisading lamellae in the lysosomal cytoplasm )
• Treatment: mainly conservative

“No Man Pictures the Sphinx Proudly Holding Cherries:” Niemann-Pick disease (Sphingomyelinase deficiency, Progressive neurodegeneration, Hepatosplenomegaly, Cherry-red spots in the macula).

Mucopolysaccharidoses are a group of metabolic disorders that result in the impaired breakdown of glycosaminoglycans (previously known as mucopolysaccharides), due to mutations in lysosomal enzymes. At least nine different types of mucopolysaccharidosis have been identified. The two most common conditions are Hurler syndrome and Hunter syndrome. ^[13][14]

“Hunters with good eyesight will catch the aggressive chupacabra active in TeXas:” Hunter syndrome (no corneal clouding, aggressive behavior, carpal tunnel syndrome, hyperactivity, and X-linked recessive inheritance).

Mucolipids are complex lipid polymers that contain sialic acid or a related substance. Mucolipidoses were originally phenotypically confused with the mucopolysaccharidoses. However, the storage material in tissues includes not only mucopolysaccharides but also lipids. Additionally, glycosaminoglycans are not present in the urine of patients with mucolipidosis, while patients affected by mucopolysaccharidoses may have mucopolysacchariduria. ^[15]

The four main types of mucolipidosis include:

• Sialidosis (mucolipidosis type I)
• I-cell disease (mucolipidosis type II)
• Pseudo-Hurler disease (mucolipidosis type III)
• Sialolipidosis (mucolipidosis type IV)

• Definition: an autosomal recessive disease caused by a defect in N-acetylglucosaminyl-1-phosphotransferase activity
• Pathophysiology
  • Defective N-acetylglucosaminyl-1-phosphotransferase → impaired phosphorylation of mannose residues of glycoproteins in the Golgi apparatus that should be transported to lysosomes (glycoproteins do not have mannose-6-phosphate) → extracellular secretion of these glycoproteins instead of delivery to lysosomes → inability to degrade lysosomal content → accumulation of abnormal lysosomal substances in the serum
• Clinical features
  • Coarse facial features
  • Corneal clouding : progresses to blindness
  • Gingival hyperplasia
  • Claw hand deformity
  • Kyphoscoliosis
  • Abnormal bone growth and restricted joint movements
  • Failure to thrive (growth failure by 2 years of age) ^[16]
  • Developmental delay
• Diagnostics
  • Prenatal: low levels of N-acetylglucosamine-1-phosphodiesterase enzyme activity in amniotic fluid or chorionic villi
  • Postnatal
    • Increased plasma levels of lysosomal enzymes
    • Inclusion bodies in peripheral blood lymphocytes (I-cells)
    • Note: negative urinary glycosaminoglycans (compared with mucopolysaccharidoses)
    • Low levels of N-acetylglucosamine-1-phosphodiesterase activity in white blood cells
    • Decreased concentration of lysosomal enzymes in cultured fibroblasts
• Treatment
  • No cure available
  • Only symptomatic treatment
    • Nutritional support
    • Physical therapy for musculoskeletal problems
• Complications
  • Pneumonia
  • Otitis media
  • Congestive heart failure
  • Atlantoaxial instability
• Prognosis: Affected individuals typically die from cardiopulmonary complications during childhood.