Organic Acidemias- BioChem Genetics

Organic Acidemias Background

• Primarily disorders of Amino Acid Catabolism: Mainly

  • Branch Chain Amino Acids (BCAA)

  • Lysine

• Toxicity comes from accumulation of ORGNIC ACIDS not from an A.A. acid accumulating

  • Causes metabolic acidosis with increased “Anion Gap”: Decrease in main anion Bicarbonate (HCO3-)

  • Secondary toxic effects of acidosis

    • Mitochondria→ Lactic acidemia

    • Urea Cycle → Hyperammonemia

    • Bone marrow→ Bone marrow suppression

    • CNS function→ Encephalopathy/Mental retardation

• Major Presentations: Neonatal encephalopathic acidosis, late chronic/intermediate

• All autosomal recessive

Metabolic Acidosis

• Blood pH low due to excess acid (H+) vs Base (HCO3-)

  • normal range pH 7.3-7.45 (measure via Atrial Blood Gas)

  • Normal HCo3- level: 22-26 mEq/L

• Mutiple etiologies for Metabolic Acidosis

  • Lowered HCo3- : loss through GI (diahrria), Renal tubule acidosis, Medications

  • Elevated H+: creation of abnormal acids in blood due to starvation, diabetes; Lactic acidosis due to mitochondrial dysfunction, Organic Acidosis

• Clinical Consequences

  • Neonatal: non-specfic, similar to UCDs presenations,

    • Lethargy, vomting, Tachypena, Hypotonia, Seizures, Coma, Death

  • Adult: Devleopmental Delay, Ataxia, Neurological Deficits, (then the neonatal presenations)

Organic Acidemias

Newborn Screening detects many Organic Acidemias

Organic Acidemias Treatment

• Restrict Dietary Protein disease specific amino acid free formulas

• Prevent Catabolism provide sufficient protein free calories

• Reverse Acidosis ± Hyperammonemia

  • Hemodialysis

  • Ammonia and lactic acid scavengers

    • Sodium bicarbonate, sodium benzoate, phenylbutyrate

• Cofactor therapy for specific Disorders

Propionic Acidemia Metabolism

• Failure of Propionyl-CoA carboxylase

• Step 11 of Isoleucine and Valine metabolism:

• Propionyl-CoA → Methylmalonyl-CoA via Propionyl-CoA carboxylase activity

Propionic Acidemia

• Also known as Ketonic hyperglycemia: high level of glycine and ketone bodies

• Autosomal Recessive

• Incidence 1:100,00 (higher in Saudia Arabia and Inuit)

Genetic Defect

• Propinyl-CoA Carboxylase (PCC) alpha or beta subunit genes

  • some genotype/phenotype correlation (null alleles/deletions more severe)

  • Biotin cofactor for PCC

• PA accumulation due to PA production from

  • MET/THR/VAL/ISO catabolism,

  • gut bacteria,

  • odd chain FAs

Untreated Propionic Acidemia

Classical Neonatal Encephalopathic Form

• Normal at birth

• Within a few days

  • Poor feeding, lethargy, vomiting hypotonia →encephalopathy, seizures, coma, death

Late-Onset Form

• Developmental delays/regression

• cyclic vomiting

• protein intolerance

• growth impairment

• hypotonia

• metabolic basal ganglia stroke

• cardiomyopathy

• Acute episode of toxic encephalopathy

Rare Cardiac Subtype isolated cardiomyopathy

Diagnosing Propionic Acidosis (PA)

Newborn Screening

• Elevated Propinoyl Acylcarnitine and ratio to other carnatine species

  • other etiologies: Methylmolic Acidmia, Cobalamin Defects, Maternal B12 Deficiency, False +

Confirmatory Testing

• Atrial Blood Gas: Elevated ammonia, low glucose, high acidosis, increased anion gap

• Complete blood count: suppression of bone marrow→ less blood cells

• Urine Organic Acid Analysis: High 3-OH-proprionate, mthylcitrate, tigly/proprionylglycine but NOT MMA

• Plasma Amino Acid profile:

  • elevated glycine + glutamine, not homocysteine (seen with Cobalamin defects)

• Acyl-Carnitine Profile: Elevated C3 acylcarnitine, not C4-DC unless SUCLA2 deficiency

• PCC enzyme activity: can measure PC enzyme in leukocytes or fibroblasts

PCC Genotyping

• Gene sequencing w del/dup analysis (99% detection rate)

Treating Propionic Acidosis

Acute Acidotic Encephalopathy

• Remove acids and ammonia hemodialysis

  • severe hyperammonia: ammonia scavengers

• Reduce PA production Protein restriction 24-25hr

• Prevent catabolism: glucose and lipids IV

• Enhance PA excretion: IV Carnitine

• Decreased PA production in Gut: Antibiotics (Metronidzole

• Biotin:

Chronic Treatment

• protein restriction and MTVI-free metabolic formula

• Oral Carantine, Biotin, and Antibiotics

• Avoid decompensation

• unresponsive to Tx → liver transplantation

Propionic Acidemia Deficiency Outcome

Treamtnet improves surivial, but invariable there is an affect to some degree

• Neurodevleopmatl disabilty

• metabolic basal ganglia stroke

• seiures

• pancreatisis

• cardiomyopathy

• gorwth impairment

• nuetorpnia, AA defience

• renal failure

• premature ovarian fialure

• hearing and vidual defecits (optic nerve atrphy)

Propionic Acidemia Deficiency Screening

• Carrier Screening:

• PRenatal Diaongis:

  • amontic fluid orgnaic acid measurment possible (some false negatives)

Methylmalonic Acidemia Pathway

• Isoleucine and Valine

• Methlymalonyl-CoA → Succinyl CoA via Methylmalonic-CoA mutase activity

• Methlymalonyl-CoA accumulates

Methylmalonic Acidemia

• Increased Methylmalonic Acid but not homocysteine (other forms of MMA have elevated homocysteine→ not primary MMA, but related to Adenosyl Cobalamin - A )

Genetic Defect: mutation of multiple genes cause similar phenotype

• 60% Methlymalonyl-Co mutase gene mutation (MUT)

• 37% Cobalamin A,B,D2 (MMAA, MMAB, MMADHC)→ the upstream vitamins that will be converted into Adenosyl Cobalamin→ leads to dysfunctional MM-Co mutase

Untreated Methylmolaynic Acdiemia

Infantile Subtype: Most common mut0, cblB mutations

• Normal at Birth

• Within days to weeks: poor feeding, lethargy, vomiting, hypotonia, encephalopathy→ progress to seizures, coma, death

Intermediate phenotype: mut-, cblA, cblD2

• Normal for month to years: fialure to thrive, devleopmental delay, hypotonia, poriten aversion→ risk of carastrophic decompensations

Benign Adult form: typically asymptomatic, can decomapnste

Diagnosing Methylmolaynic Acdiemia

Newborn screening: Elevated Propinoyl Acylcarnitine (and ratios) → but non specific

Confirmatory testing

• Atrial Blood Gas, Ammonia Levels, Completel blood ocunt:

  • Hi AG metabolic acidsosi

  • Elevated ammonia

  • Low gluclose

  • pancytopenia

• Urine Organic Acid: High MMA

• Plasma Amino Acid profile: high glycine + glutamine, no Homocystine (Hcy)

  • CblC/D/F - Hcf + MMA high ;

  • cblD2/E/G - Just hcf High

• Enzyme activity: fibroblasts

Genotyping on genes = 95%

Treating MethylMonlic Acdicema

Treat acute acidotic encephalopathy

• Remove acids+amonia: hemodialysis

• Reduce MMA production: protein restriction

• Prevent catabolism: IV glucose and lipids

• Severe hyperammonemia: Amonia scavengers

• Decrease gut bacteria: Antibotics

• HYDOXYCOBALAMIN (B12) injects: cofactor

Chronic Treatment

• protien restriciton and MTVI-free meatolibc fomumal

• L-Carnitine + OH-B12

• Avoid decompensation

Methylmalonic Acidemia Treatment outcome

• Most patient will have some degree of mental impairment, long term affects

Methylmalonic Acidemia Diagnosis

• Prenatal/Preimplantation:

  • Ammonitic organic acid fluid analysis possible

  • Enzyme activity of CVS and amniocentesis

Iso-valeric Acidemia

• issues with the Isovaleryl-CoA dehygroenase enzyme

• LEUCINE PATHWAY ONLY

• Build up of Isovalryl-CoA (Isovaleric Acid)

Isovaleric Acidemia (IVA)

• Disorder of Leucine metabolism

Genetic Defect

• IsoValeryl-CoA Dehydrogenase (IVD) Gene Mutation

  • results in increased Isovaleric Acid

  • Sweaty feet odoer is prominent

Untreated Isovaleric Acidemia

Severe Neonatal Onset form

• Normal at birth

• Within day: poor feeding, lethargy, hypotonia, Sweaty feet order —> encephalophagy, seizure, coma, death

Mid/Late Onset Form

• unexplained failure to thrive and developmental delay

Benign Adult Form : typically asymptomatic but can mildly decompensate

Diagnosing Isovaleric Acidemia

Newborn screening: elevated Isovaleryl Acylcarnitine → can also be increased in 2MBG+Antibitoic

Confirmatory testing

• Blood tests:

  • High ammonia

  • Low glucose

  • High metabolic acidosis

• Urine organic acid

  • High IVA

  • High isovaleryl glycine

• Plasma AA levels:

  • High glycine

  • High glutamine

• Enzyme activity: Fibroblast

Genotyping: exact genes unknown

Treating Isovaleric Acidemia

Treat Acute Acidotic encephalopathy

• Remove acids and ammonia: hemodialysis

• Reduce IVA production: protein restriction 24-26hrs

• Prevent Catabolism: IV glucose and lipids

• Enhance IVA excretion: IV carnitine

• If hyper ammonia: ammonia scavengers

• GLYCINE SUPPLMENTAITON-BINDS IVA

Chronic Treatment

• Protein rection and LEUCINE-free metabolic formula

• Oral L-Carnitine and L-Glycine

• Avoid decompensation

Isovaleric Acdiemia Otucome

• Outlook with Treatment is one of the best if treatment done early and effecetively enough

  • can be comepltely asymptomatic as long condition is monitored

  • Leucine tolerance gets better with age

• Even if diaognsis is after neonatal period, and evne with major encaplapthic event in neonatal period—> longer term out look is vairable : CAN BE OK

Isovaleric Acidemia Prenatal Diagnosis

• Ammniotic fluid can be checked for organic acids

Biotinidase Deficiency Pathway

• Biotin is a vital cofactor for of number of different enzymes:

  • ALL ARE CARBOXYLASES

• 3-Methylcrontoyl-CoA carboxylase (Leucine)

• Propinoyl-CoA Carboxylase (Isoleucine and Valine)

• Malonyl-CoA decarboxylase

When there are mutations in the BIOTINADASE gene: Biotin is not properly recycled → these blocks develop

Biotinidase Deficiency (BTD)

• Late multiple Carboxylase Deficiency

• Slightly increased incidence in Hispanic and Middle Easter

Gene Defect: Biotinidase (BTD) gene

• failure to recycle biotin = biotin deficiney

• Biotin co-factor for the carboxylases: cannot combine and make function enzyme

Untreated Biotinidase Deficiency

Affect depends on the residual enzyamtic acitvity when biotin absent

Profound Defcieny (<10% enzyme)

• Normal at birth

• Symptoms devleop after few months

  • Developmental delay, seziures, hypotonia, ataxia, hearing loss, visual problems, ***alopecia***, ***eczema*** (uniquie to BTD)—>

Partial Defieciney (10-30% enzyme)

• intermeinet symptoms with stress

Symptoms can be irreversible once present

Diagnosing Biotinadase

Newborn Screening: Elevated C5-OH Acylcarnitine, but not specfic to BTD

Confirmatory Testing

• Blood:

  • High ammonia

  • High acidosis

  • Low gluclose

• Urine Organic Acids: multiple organic acids b/c Bitonaisde affects multiple enzymes

  • ( )

• Elevated C5-OH Acylcarnitine

• Enzyme activity: If Biotinadase activity is normal—> then issue is probably Holocarboxylase deficiency (presents the same way but is earlier)

Genotyping: sequencing 99% detection

Treating Biotinadase Deficeincy

Rarely severyl acidotic or hyperammonemic

• may occasionally need sodium bi-cabonate (adress acidty)

• may occasionally need amonia scavnerge (adress amonia levels)

• Insitute Biotin therapy immediately

Chronic treatment

• Biotin

• No protien restction

• Avoid raw egg whites (has protein that binds Biotin)

Biotinadase Deficiency outcome

• Extremely great outlook for patients (one of the best for Organic Acidemias)

• As long as treatment is implemented BEFORE the development of severe symptoms

• If detected after symptoms, some are irreversible: optic atrophy, hearing loss, developmental delay can presist

Biotinadase Deficiency Prenatal diagonsis

• Biotinadase enzyme activity can also be measuredin the amniocytes and the amniotic fluid

3-MethylCrotonyl-CoA (3-MCC) Carboxylase Deficiency

• LEUCINE METABOLISM

Diagnosis:

• Newborn screening: VERY COMMONLY FOUND High C5-OH

  • Mom can be asymptomatic

• Urine Organic Acids: High 3-Methylcrotonyglycine, 3-OH-IVA

Cause: 3-MCCC Subunit 1 or 2 Genes : Biotin a cofactor → effected when bitoinadase

Symptoms

• May be asymptomatic

• Some episodic liver dysfunction, hypotonia, hypoglycemia

• May cause development delay + sezures

Treatment

• Restrict LEUCINE

• Carnitine (to excert Leucine) and Biotin suppletion

3-Hydroxy-3-Methylglutaryl (3-HMG) CoA Lyase Deficiency

• LEUCINE METABOLISM

Diagnosis

• Newborn screening: High C5-OH

• Urine Organic Acids: elevated 3-HMG, 3-methylglutacoant, 3-OH-IVA, 3-methylglutarate

Cause: HMGCL gene mutation

Symptoms

• May be asymptomatic until decompaneaion

• Liver dysfucntion

Treatment

• Leucine restriction

• Caritine supplementation (BUT NO NEED FOR BIOTIN)

Glutaric Acidemia Type 1 (GA1) Metabolism

• NOT a Branch Chain Amino Acid metabolism disorder

• Breakdown of LYSINE and TRYPTOPHANE

• Lysine + Tryptophane → Alpha ketoadipic→ Glutyrl-Coa

• Glutyrl-Coa→ Glutaconyl-CoA (shunt to Glutaontic Acid) via Glutaryl-CoA Dehydrogenase activity

Glutaric Acidemia Type 1 (GA1)

• “Cerebral” Organic Acidemia: Often normal

Genetic Defect: Glutaryl-CoA Dehydrogenase (GCDH) gene mutation causing defective Lysine + Tyrptohan metabolism

Glutaric Acidemia Type 1 (GA1) Symptoms

• Often normal at birth or only macrocephalic

• symptoms often begin prior to 2 years of age

  • May start with a Sudden neurologic decompensation: 75% by 14months—> fever, illness, metabolic stress

Primary symptoms

• Stress-induced encephalopathy

• Ataxia

• Epilepsy

• Myoclonus

• Storke-like episodes

Glutaric Acidemia Type 1 (GA1) Diagnosis

Newboarn screening: Elevated C5-DC (glutaryl) Acylcarnitine

• many False negatives

Confirmatory Testing

• Blood: elvated ammonia, low gluclose, Aciditiy

• Plasma + Urine: C5-DC glutaryl acylcarnitine + glutaric acid

• Enzyme activity: fibroblast

• CT/MRI: Cerberallar atrophy, basal ganlia infact and hemorrhage

Genotyping

Glutaric Acidemia Type 1 (GA1) Treatment

Reverse/Prevent Catabolism When sick: protien free calroeis during metaoblic stress

Dietary Mdofication

• Low LYSINE and TRYOPTHAN

MEdicaitons

• B2 (Riboflavin) is a COFATOR

• Carntine: Binds Glutaric acid and remvoes it

Avoid Valproate (Bind Carnitine)