Lysosomal Storage Disorders - Biochem Genetics

Lysosomes

• Simple lipid membranes surrounding degradative enzymes

• Found in all mammalian cells except RBCs

  • MACROPHAGES IN PARTICULAR have high number of lysosomes

• Clinical features of lysomal dieases depdends on

  • Distribution/expression of he deficient lysosomal Enzyme

  • Distribution of the substrate expression

  • Effects of substrate accumulation/End-product defeicieny

Monocyte AMcrophages

• when macrophages in the body are deficient in lysosomes, the substrates they scavenged CANNOT BE degraded and accumulate:

  • Bone Marrow --

  • Liver

  • Brain: Neurodegeneration

  • Spleen: Splenomegaly

  • Lung

Lysosomal Storage Disorder Categoreis

1. Sphingolipidoeses: white matter neorudegrantion and organ dysfucntion

2. Mucopolysaccharidoses: numverous body tissues + skeletal dysostosis

3. Oligosaccharidoses: involving numerous tissues with skeltal dystosis

4. Glycogenoses: Progressive glycogen accumualtion in the muscle leades to myopathy and weakness

Lysomomal Storage Disorders: Typically, Progressive Disease

• most affected individuals appear normal at birth

• clinical signs/symptoms develop in weeks/months

  • organomegaly and organ dysfunction

  • loss of motor and cognitive skills

  • cherry red macule

• Often present with lethal/infantile onset but milder/later onset (attenuated) variants exist

Lysosomal Storage Disorders: Phenotypic Variability

• All LSDs, regardless of Age of Onset, are Progressive Disorders: MOST are asymptomatic at birth

  • There is a progressive ACUMULATION OFSUBSTRATE over the lifetime of the affected patient

• Many LSDs have subtypes:

  • Earlier Onset, Severe Phenotype

  • Later Onset, Mild/Attenuated Phenotype

• Many have CNS degradation

Fabry Disease: Metabolic Pathway

• One of the few non-neuronopathic LDS

• Deficiency of Alpha-Galactosidase → Accumulation of Globotriaosylceramide (GL-3)

Fabry Disease: General

• Cardiac, Renal and Cutaneous affect

• Inheritance: X-Linked Recessive

• Genetic Defect: Alpha-Galactosidase (GLA) Gene Deficiency

  • GB3 accumulates in vascular endothelial cells: Kidney, Heart, Skin Nerves/Brain (but no damage)

Fabry Disease: Untreated Features

Classic: Typically, Males with <1% Enzyme Activity —> Onset 4-8yo, but diagnosed much later in life

• Burning Painful episodes (Acropathies): in extremities, stress triggered

• Angiokeratomas (small red/purple skin spots): bellybutton to knees, more w/ age

• Abnormally increased or decreased sweating

• Ocular Opacities: corneal haze/opacity, cataracts (even in carrier females)

• ***Renal Failure: progressive, end-stage renal diease 30-50s yo

• ***Cardiovascular: HTN, Hypertrophic Cardiomyopathy, CAD)

• ***Cerebrovascular Disease: Strokes

Fabry Disease: Variants

• Cardiac Variant (Males >1-20% enzyme activity)

• Renal Variant: presents with relatively isolated renal disease

• Heterozygous Females: varies from asymptomatic to classic

  • Typically milder with later age of onset

  • Rarely progresses to End Stage Renal Diase

Fabry Diease: Diagnosis

• NBS: not done in every state

• Diagnostic test:

  • measure of A-Galactosidase Enzyme activity (Plasma. WBC, Fibroblast)

  • GB3 and Lyso-GB3 levels

  • GLA genotyping: del/dup 100% in positives

• Prenatal Tests

  • Molecular testing

  • GLA enzyme activity on Amnio/CVS

• Other Routine Tests

  • Renal function: BUN/Creatine, urinalysis

  • Cardiac Function: Echocardiogram, EKG, stress test

  • Vision Hearing: eye and ear testing

  • Cerebrovascular function: Brain MRI/MRA

Fabry Disease: Treatment

Preventative

• Recombinant enzyme Replacement Therapy (ERT) → shows increased GL03 clearance and decreased symptoms

Symptomatic

• pain meds

• Ace inhibitors

• Dialysis/Renal transplantation

• Routine care if cardiac/cerebrovascular complication

Gaucher Disease: Metabolic Pathway

• One of the most Common

• Deficney of gluccocerebrosidase → Build-up of Glucocerebroside in tissue

  

Gaucher Disease: Overview

• Glucosylceramides Deficiency

• Inheritance: Autosomal Recessive

• Incidence: seen highly in Ashkenazi Ancestry (Type I)

• Genetic Defect: GBA gene deficiency

  • Build-up of Glucocerebroside in monocyte macrophages: Liver, Spleen, Bone Marrow, Lungs Brain

Gaucher Disease: Untreated

Type 1 (Non-Neuronopathic) most common in Ashkenazi

Onset from Childhood to adult (some remain asymptomatic)

• Bone Disease: bone pain

• Hepatosplenomegaly: swelling of spleen and liver

• Cytopenia decreased RBC/WBC

• Pulmonary involvement: plumonary hypertension

• Parkinsons DieaseL 20-30x increased risk

• Miscellaneous

  • depression, gallstone, possibly myeloma/lymphoma/liver carcinoma

• No primary Early Neurodegeneration

Gaucher Disease: non-type 1

• Type II/III (Neuronopathic):

  • Type II: onset before 2yo, progressive, lethal neurodegeneration

  • Type III: Children at any age, more slowly progressive, death by 20-30yo

• Perinatal Letha Variant (RARE)

  • Hydrops Fetalis, Ichthyotic Skin changes

• Cardiovascular Variant (Atypical)

  • Mild Symptoms but Prominet Valvular heart Disease

Gaucher Disease: Diagnosis

NBS: not in all states

Diagnostic Tests

• Glucocerbrosidae Enzyme Activity (WBC, Fibroblast)

• GBA Genotyping

  • 4 mutations cover 90% of alleles in Ashkenazi (N370S, L444P, 84GG, IVS2+1)

  • N370S allele limits disease to Type I Non-Neuronopathic Type

Prenatal Tests: Molecular, GBA Enzyme Activity on Amnio/CVS

Gaucher Disease: Treatment

Preventative (Not in type II)

• Recombinant Enzyme Replacement Therapy (ERT): prevents type 1 complications, no effect in Type II, mixed benefit for Type III

• Oral Substrate Reduction Therapy (SRT) → inhibits glucocerbroside formation

• Bone marrow transplantation

Symptomatic

• Splenectomy

• Tranplation

• Pain meds/joint replacment for bone complications

Niemann-Pick Disease: Metabolic Pathway

• Has Neuropathic and Non-neuropathic forms

• Deficiency of slingomaylonase enzyme → buildup of Phosphocholine

  

Neimann-Pick Disease: Overview

Two Types:

• Type A (Neuronopathic)

• Type B( Non-Neuronopathic)

• Type C does exist, but non LSD

Inheritance: Autosomal Recessive

Incidence: Higher prevalence (Type A) in Ashkenazi

Genetic Defect

• Sphingomyelin Phosphodiesterase 1 (SMPD1) Gene

  • Sphingomyelin accumulation on monocyte macrophage cells in Brain, Liver, Spleen, Lung

Neiman Pick Disease: Untreated, Type A

Neuronopathic form of Neiman Pick: similar to the Neuronopathic Form of Gaucher Diease

• Onset within 1st year, death usually before 3-4 years of age

• Neurodegeneration: typical onset between 6-12 months of age

• Hepatosplenomegaly (HSM): present by 3 months of age

• Pulmonary Involvement

• Miscellaneous

  • Cherry red spot on Macual of Eye ****UNIQUE TO NB but NOT GAUCHER****

Neiman Pick Disease: Untreated, Type B

Non-Neuronopathic form of Neiman Pick, less common

• Later onset and milder variable symptoms, survival to adulthood

  • More organ swelling: massive hepatosplenomegaly

  • Deterioration of pulmonary function

  • Miscellaneous: Abnormal Lipids (low HDLc/high LDL)

Neiman Pick Disease: Diagnosis

NBS not done for all states

Diagnostic Tests

• Acid Sphingomyelinase Enzyme Activity (WBC, Fibroblast)

• SMPD1 Genotyping

  • 3 mutations (L302P, R496L, fsP330) in 90% of alleles in Ashkenazim Type A

  • R610del very common Type B allele

Prenatal Tests

• Molecular, SMPD1 enzyme activity on Amnio/CVS

Other Routine Tests

• Pulmonary Assessment, Lipid/Cholesterol levels, blood counts

• Liver function tests, Bone Density, Opthalmogic Evalutation

Neimann Pick Disease: Treatment

Preventative (Not Type A)

• Bone marrow transplant:

• Recombinant Enzyme Replacement therapy (ERT)

Symptomatic

• Platelet transfusion

• Avoid splenectomy

• Cholesterol lowering meds

• Supplemental oxygen and respiratory support

Tay-Sachs Disease: Metabolic Pathway

• Deficiency of Hexosaminidase A → Accumulation of GalNAc

Tay-Sachs Disease: Overview

Most common: early onset, neuropathic form

Inheritance: Autosomal Recessive

Incidence: High in Ashkenazi and French Candain

Genetic Defect

• Hexosaminidase A (HEXA) Gene → GM2 ganglioside accumulation primarily in CNS (neurodegeneration)

• HEX A: 1a and 1b subunit, HEXB contain 2 beta subunits

Tay-Sachs: Infantile Form, Untreated

0-5% HEX A activity

• Onset by 6 months, Death usally by 2-4 years of Age

• Neurodegeneration - Starting 3-6 months of age

  • Decreased attentiveness with increased startle repsonse

Tay-Sachs: Juvenile+Adult Form, Untreated

5-15% HEX A activity

• Later onset and slower progression

• Progressive dystonia,

• Speech and cognitive decline

• Death

  • Juvenile: 10-15 years old

  • Adult: variable

Tay-Sachs: Diagnosis

NBS: Not done

Diagnostic Testing

• Hexosaminidase A Enzyme Activity (serum, WBC, Fibroblast)

  • Reduced HEX A, but elevated HEX B activity

• HEX A Genotyping

  • Null genes

  • Pseudodeficieny mutations: there is decreased enzyme activity in the lab but not IN VIVIO (in the actual body) : can cause positive carrier screening result → appear to be disease carrier but actually just a pseduo-deficiency carrier which does not cause the disease

• Prenatal: molecular, HEX A Enzyme activity on Amnio/CVS

• Brain MRI shows atrophy and white matter demyelination

Tay-Sachs: Treatment

• NO PREVENATIVE OR CURATIVE CARE

• Supportive care only: little effect on mortality

  • Antiepileptics, Respiratory support, Supplemental nutrition

Krabbe Disease: Metabolic Pathway

• A common leukodystrophy;

• Deficiency of Gal-cerebroside-B-galactosidase → Galactosylceramide accumulation

  

Krabbe Disease: Overview

Inheritance: Autosomal Recessive

two forms

• 90% Infantile Leukodystrophy

• 10 Late Onset Leukodystrophy

Genetic Defect

• Beta-Galactosidase (GALC) Gene → Accumulation and deposition of galactosylceramide and pyschosine primarily in brain leading to oligodendoglial destruction and white matter demyelination (leukodystrophy)

Krabbe: Infantile, untreated

Onset by 6 months, death by 2yo

Unlike neuronopathic Neiman Pick type A, or Tay Sach Disease → No Cherry Red Spot

More similar to Type II Gauches: BUT no organ enlargement

• Initial (Stage I):

• Initial (Stage II):

• Intial (Stage III):

Krabbe: Later onset, untreated

Variable onset, severity and progression of:

• Weakness, ataxia, neuropathy

• Visual deterioration

• Psychomotor regression ± death when earlier onset

Krabbe: Diagnosis

NBS: tested in many state -→ Low GALC Activity leads to targeted DNA analysis ± reflex to sequencing

Diagnostic Tests

• Beta-Galactosidase Enzyme Activity (WBC, Fibroblast)

• GALC Genotyping

  • specific deletion = infantile Krabbe (45%)

  • 857G>A results in late onset Krabbe (50%)

Prenatal Tests

• Molecular, GALC enzyme activity on Amnio/CVS

Other Routine Tests

• Brain neuroimaging (atrophy and white matter changes)

• Elevated CSF Protein, abnormal NCV/EMG

Krabbe Disease: Treatment

Preventative:

• Hematopoietic Stem Cell Transplantation:

  • only benefits presymptomatic infants and mildly symptomatic late-onset cases

  • Can preserve function and slow down progression

• Hromeon Replacement therapy not shown to be affective in human

Symptomatic

• directed at maximizing/Prolonging Function and Minimizing Discomfort/Suffering

Metachromatic Leukodystrophy: Metabolic Pathway

• Cerebroside Sulphatase deficiency → Sulphatide accumulation

Metachromatic Leukodystrophy: Overview

3 sub-type: Late-Infantile, Juvenile and Adult

Inheritance: Autosomal Recessive

Genetic Defect

• Arylsulfatase A (ARSA) Gene

  • Accumulation of sulfogalactosylcermide and other sulfatides in brain and Kidney → White Matter Demyelination (Leukodystrophy)

Untreated Metachromatic Leukodystrophy: Late Infantile

Onset between 1-2 yo, death in 3-10 years

• Initial: 6-12 month normal development

• Followed by regression, neurodegeneration, neuropathy,

• Leading to prolonged: blindness,, unaware, decerabte posturing, Death

• No organomegaly, cherry-red eye spot

Untreated Metachromatic Leukodystrophy: Juvenile + Adult

Juvenlie: Onset 4-14yo

Adult: Onset after 14yo

• Initial: De;cine in school or job prefmeona, behcviour/perosnality changes

• Followed by: deterioting gait, speech, behaviour, neuropathy, coginton : with or without death

Diagnosing Metachromatic Leukodystrophy

No NBS

Diagnostic

• Arylsufacte A Enzyme activity (WBC, Fibroblast)

• ARSE Genotyping

  • Null/nonsense genes

  • Psuedodefiencney alleles → low ARSA enzyme activity (5-20%) but no disease

• Prenatal test: molecular + enzyme activity (if no pseudodeficiney)

• Other routine testing

  • Brain neuroimaging (atrophy and white matter change)

  • Elevated CSF protein

Treating Metachromatic Leukodystrophy

Preventive

• Hematopoietic stem cell transplantation

  • Best outcomes when presymptomatic → no universally affective

  • Progression after a time in some patient

Symptomatic

• Treatment directed at maximizing/prolonging function and minimizing discomfort/suffering