Amino acid disorders. Phenylketonuria (PKU) Enzyme defect: phenylalanine hydroxylase (12th...

Amino acid disorders

4-OH-fenilpirüvik asit

Homogentisik asit

Malleoloasitik asit

Fümarilasetoasetik asit

Süksinil- aseton

Fümarik asit + asetoasetik asit

Fenilalanin hidroksilaz

4-OH fenilpirü- vik asit dioksijenaz

Tirozin aminotrasferaz

Homogentisik

asit oksidaz

İzomeraz

Fümarilasetoasetat

hidrolaz

Fenilpirüvat

Parahidroksifenilasetat

Fenillaktat

Fenilasetat

Fenilasetilglütamin

ALKAPTONÜRİ

FENİLKETONÜRİ

NTBC (-)

Tirozin hidroksilaz + BH4, folik asit, niasin, demir)

ALBİNİZM

FENİLALANİN TİROZİN

Delta-amino- Levülinik asit (d-ALA)

Porfobilinojen

d-ALA Dehidraz

Dihidroksifenilalanin (DOPA)

Triptofan

5-hidroksi-

triptofan (5-HT)

Triptofan

dihidroksilaz

BH4

Serotonin

Norepinefrin

Melanin

Metionin Adenozil- metionin

Metionin adenoziltransferaz

Melanositik tirozin hidroksilaz

Tetrahidrobiyopterin (BH4)

TETRAHİDROBİOPTERİN YETERSİZLİĞİ

Tiroksin

TİROZİNEMİ TİP III HAWKİNSİNÜRİ YENİDOĞANIN GEÇİCİ HİPERTİROZİNEMİSİ

TİROZİNEMİ TİP II

TİROZİNEMİ TİP I

Epinefrin

Dopamin

B6 vit(+)

Homovalinik asit

C vit(+)

C vit(+)

C vit(+)

B6 vit(+)

Phenylketonuria (PKU)

• Enzyme defect: phenylalanine hydroxylase (12th chromosome): more than 400 mutations

• Incidence: Average 1:10,000 (Highest incidence in Turkey, 1: 4,000)

Phenylketonuria (PKU): Variants

1. Classical phenylketonuria (complete or near complete enzyme deficiency): phenylalanine levels above 20 mg/dL (<1200 mmol/L) require diet therapy

2. Atypical phenylketonuria (partial enzyme deficiency): (enzyme activity %1-5) require partial diet therapy

3. Benign phenylketonuria. phenylalanine levels below: 10 mg/dL (<600 mmol/L) no clinical findings, not requiring diet therapy

3. Malign phenylketonuria: Tetrahydrobiopterin (BH4=cofactor of phenylalanine hydroxylase): Severe neurologic findings, does not respond diet therapy. Dopamine and setotonin may be helpful.

Phenylketonuria (PKU): Clinical findings

• Severe brain damage, progressive motor-mental retardation

• Spasticity

• Paralysis

• Convulsions

• Self-mutilation

• Light colored skin and eye (yellow hair, blue eyes; tyrosine deficiency)

• Mouse-like odor in urine and sweat.

Phenylketonuria: Diagnosis

• High phenylalanine (N: <2mg/dL) and low tyrosine (N: <2mg/dL) levels,

• Ferric chloride test gives green color in urine (not reliable).

• Neonatal screening: Guthrie-card (taken between 3rd and 7th days of life)

Phenylketonuria:Therapy• Phenylalanine restricted diet, supplementation of

tyrosine, essential amino acids and trace elements.

Goals of the therapy:• 0-10 years: phenylalanine values: 0.7-4 mg/dL• 11-16 years: phenylalanine values: <15 mg/dL• 16+ years: phenylalanine values: <20 mg/dL• Pregnant mothers with PKU: phenylalanine

values < 7mg/dL

Prognosis: with immediate and efficient treatment, normal development and intelligence

Maternal PKU= phenylketonuric fetopathy

• Normal phenylalanine levels

• Microcephaly

• Cardiac defects

• Motor-mental retardation

• No therapy


Homogentisik asit

Malleoloasitik asit


Süksinil- aseton





Homogentisik

asit oksidaz

İzomeraz

Fümarilasetoasetat

hidrolaz

Fenilpirüvat


Fenillaktat

Fenilasetat


ALKAPTONÜRİ

FENİLKETONÜRİ

NTBC (-)


ALBİNİZM



Porfobilinojen

d-ALA Dehidraz


Triptofan

5-hidroksi-

triptofan (5-HT)

Triptofan

dihidroksilaz

BH4

Serotonin

Norepinefrin

Melanin






Tiroksin




Epinefrin

Dopamin

B6 vit(+)

Homovalinik asit

C vit(+)

C vit(+)

C vit(+)

B6 vit(+)

Tyrosinemia Type I

Enzyme defect: Fumarylacetoacetate hydroxylase

Clinical findings

• Acute infantile form: Severe liver failure, vomiting, bleeds, sepsis, hypoglycemia, renal tubulopathy (Fanconi syndrome)

• Chronic form: Hepatomegaly, cirrhosis, growth retardation, rickets, hematoma, tubulopathy, neuropathy, and abdominal pain (due to porphyrines)

Tyrosinemia Type I: Diagnosis

• High succinylacetone levels (diagnostic). tyrosine levels: normal or slightly elevated.

• Methionine: high

• Delta-aminolevulinic acid: high (colic)

• Alfa-feto protein: very high (marker of hepatocellular carcinoma)

Tyrosinemia Type I: Therapy

• NTBC 1 mg/kg: blocks the accumulation of toxic metabolites (succinylacetone); beware tyrosine elevation and give tyrosine-restricted diet

• If this therapy fails consider liver transplantation.

Tyrosinemia Type I: Complications

• Renal failure• Hepatocellular carcinoma

(monitor alfa-feto protein), check periodically liver ultrasongraphy and biopsy.

Prognosis: Relatively good under NTBC treatment.


Homogentisik asit

Malleoloasitik asit


Süksinil- aseton





Homogentisik

asit oksidaz

İzomeraz

Fümarilasetoasetat

hidrolaz

Fenilpirüvat


Fenillaktat

Fenilasetat


ALKAPTONÜRİ

FENİLKETONÜRİ

NTBC (-)


ALBİNİZM



Porfobilinojen

d-ALA Dehidraz


Triptofan

5-hidroksi-

triptofan (5-HT)

Triptofan

dihidroksilaz

BH4

Serotonin

Norepinefrin

Melanin






Tiroksin




Epinefrin

Dopamin

B6 vit(+)

Homovalinik asit

C vit(+)

C vit(+)

C vit(+)

B6 vit(+)

Tyrosinemia Type II

• Enzyme defect: Cytosolic tyrosine aminotransferase

• Clinical findings: Painful corneal lesions (lacrimation, photophobia, scars), mild mental retardation

• Diagnosis: High tyrosine and phenylalanine levels

• Therapy: Tyrosine and phenylalanine-restricted diet


Homogentisik asit

Malleoloasitik asit


Süksinil- aseton





Homogentisik

asit oksidaz

İzomeraz

Fümarilasetoasetat

hidrolaz

Fenilpirüvat


Fenillaktat

Fenilasetat


ALKAPTONÜRİ

FENİLKETONÜRİ

NTBC (-)


ALBİNİZM



Porfobilinojen

d-ALA Dehidraz


Triptofan

5-hidroksi-

triptofan (5-HT)

Triptofan

dihidroksilaz

BH4

Serotonin

Norepinefrin

Melanin






Tiroksin




Epinefrin

Dopamin

B6 vit(+)

Homovalinik asit

C vit(+)

C vit(+)

C vit(+)

B6 vit(+)

Alcaptonuria• Enzyme defect: Homogentisate

oxygenase

• Clinical findings: black discoloration in urine at acid pH; mild arthritis in adults

• Diagnosis: High homogentisic acid levels in urine

• Therapy: Protein-restricted diet? NTBC?

• Prognosis: Relatively good without treatment

Methionine metabolism

CLASSICAL HOMOCYSTINURIA

• Enzyme defect: Cystationine-ß-synthase

• Mechanism: Accumulation of homocysteine (collagen disorder)

• Clinical findings: Progressive disease, usually starting with school age. Marfan-like appearance (archnodactyly), progressive myopia (the earliest finding), lens dislocation, epilepsy, mental retardation, osteoporosis, thromboembolism !!!

Marfan syndrom

HOMOCYSTINURIA

• Diagnosis: High methionine, high homocysteine (N: 0-3.5 µmol/L) and low cysteine levels. Positive nitroprusside test in fresh urine

• Therapy: Pyridoxine (Vit. B6): 50-1000 mg/day + folic acid 10 mg/day.

• If this fails diet + betaine (100 mg/kg) up to 3X3 g

• Goal: Keep homocysteine <30µmol/L.

MILD HYPERHOMOCYSTEINEMIACauses

• Methylene tetrahydrofolate reductase (MTHFR) polymorphism, thermolabile variant, homozygosity, up to 5% in Europeans, 60% in Asiasns

• Heterozygosity for cystationine-ß-synthase

• Endogenous and exogenous disorders of folic acid metabolism

• Vitamin B12 deficiency

MILD HYPERHOMOCYSTEINEMIA

Clinical findings:• Premature vascular disease in the 3rd

and 4th decade (infarctions, thrombosis embolies)

Maternal hyperhomocysteinemia: congenital defects

• Neural tube defects• Cardiac output defects• Renal defects• Pyloric stenosis?

Maple syrup urine disease

Enzyme: Branched-chain alfa-ketoacid dehydrogenase complex

Incidence: 1:200,000, autosomal recessive

Clinical findings

• Severe form: Progressive encephalopathy, cerebral edema, lethargy, coma after the 3rd day of life, “çemen” odor in urine and sweat

• Mild form: Developmental retardation, recurrent ketoacidotic decompensation

Diagnosis:• “Çemen” odor in urine and sweat, positive DNPH

test in urine (non-spesific), • Aminoacid analysis: high valine, leucine,

isoleucine and alloisoleucine (diagnostic) levels.

Therapy: • Acute: Detoxification (dialysis, exchange

transfusion)Augmentation of anabolism : Glucose + insulin

• Chronic: Diet (monitor leucine level) ± vitamin B1 (thiamin): 5 mg/kg/day

Disorders of amino acid transport

Methionine Malabsorption

• Methionine malabsorption in renal tubules and intestines.

• Clinical findings: White hair, convulsions,, diarrhea, edema , mental retardation, odor (like beer).

• Therapy: Diet deficient in methionine.

HARTNUP DISEASE• Defect: Intestinal and renal tubular reabsorption

defect of the neutral amino acids (alanine, valine, threonine, leucine, isoleucine, phenylalanine, tyrosine, tryptophan, histidine, glycine; tryptophan deficiency leads nicotinic acid and serotonine deficiency.

• Clinical finding: Photodermatitis, cerebellar ataxia; often asymptomatic

• Diagnosis: High levels of neutral amino acids in urine low levels of neutral amino acids in plasma.

• Therapy: Nicotinamide 40-300 mg/day, sun protection

LYSINURIC PROTEIN INTOLERANCE

• Defect: Intestinal and renal tubular reabsorption defect of the dibasic amino acids (lysine, arginine and ornithine) lead blockage of urea cycle; lysine deficiency

• Clinical findings: Intestinal protein intolerance, failure to thrive, osteoporosis, and hyperammonemia with progressive encephalopathy

• Diagnosis: Hyperammonemia, low lysine, arginine and ornithine in plasma, high LDH levels.

• Therapy: Citrulline substitution, protein restriction

CYSTINURIA

• Defect: Renal tubular reabsorption defect of the dibasic amino acids (lysine, arginine, ornithine and cystine)

• Clinical findings: Neprolithiasis (cystine crystallizes above 1250 µmol/L at pH 7.5)

• Diagnosis: Positive nitroprusside test in urine, increased levels of acids lysine, arginine, ornithine and cystine in urine, plasma levels are generally normal.

• Therapy: High (>5L) fluid intake, alkalisation of the urine (urinary infections!). Consider penisillamine (1-2 g/day), mercaptopropionylglycine or captopril in selected cases.

ORGANIC ACIDEMIAS

Pahogenesis • Mitochondrial accumulation of related CoA-

metabolites

Clinical findings

Acute neonatal form• Lethargy * Coma• Feeding problems *

Hypotonia/hypertonia• Myoclonic jerks * Cerebral edema• Dehydration * Unusual odor

ORGANIC ACIDEMIAS: Forms

Acute intermittent form• Recurrent episodes of acidotic coma• Ataxia• Focal neurologic signs

Chronic progressive form• Failure to thrive, Anorexia • Chronic vomiting• Hypotonia• Developmental retardation

ORGANIC ACIDEMIAS

Laboratory findings• Acidosis (increased anion gap)• Hyperammonemia• Hyperlactatemia

Diagnosis• Organic acids in urine (GC-MS)• Enzyme and DNA studies

ORGANIC ACIDEMIAS:Therapy

Acute• Remove toxins: dialysis, hemofiltration and

exchange transfusion• Interrupt catabolic state• Stop protein intake• Give carnitine (100-300 mg/kg)

Long term• Protein restricted diet (special formulas if

available)• Carnitine• Vitamins (Vit. B12, Vit. B1, Vit. B2, biotin)

Features of some organic acidemias

Izovaleric acidemia Ketoacidosis, dehydration, neutropenia, thromboscytopenia, hyperammonemia, sweety feet odor

Propionic acidemia Motor-mental retardation, ketoacidosis, dehydration, neutropenia, thromboscytopenia, hyperammonemia, hipoglycemia

Methylmalonic acidemia Motor-mental retardation, ketoacidosis, neutropenia, thromboscytopenia, hyperammonemia, hypoglycemia, response to vit B12 (+)

Biotinidase deficiencyBiotin (complex)

Biotin (free)

piruvate carboxylase propionyl

CoA carboxylase

beta-methylcrotonyl CoA carboxylase

asetyl CoA carboxylase

Biotinidase

Biotinidase deficiencyIncidenseWorld. 1:60,000 Turkey: 1:10,000

Clinical and laboratory findings• Severe metabolic acidosis • Alopecia • Seborrheic skin eruptions• Refractory convulsions

Therapy 5-10 mg/day biotin (life long).

Urea cycle defects

Carbaglu (+)

Urea cycle defects

Incidence: 1:10,000 (cumulative)

Genetics

• Ornitine transcarbabamylase deficiency (most common urea cycle defect, X-linked)

• Argininosuccinate synthase deficiency (citrullinemia, (the second most common urea cycle defect, OR)

• Carbamylphosphate synthase I deficiency (OR)

• Argininosuccinate lyase deficiency (argininosuccinic aciduria, OR)

• Arginase deficiency (argininemia, OR)

Urea cycle defects: Clinical findings

Main symptom (acute/or chronic encephalopathy) is related to high protein intake, increased catabolism, infections or stress

Neonates: * Poor feeding * Temperature lability* Lethargy * Hyperventilation (respiratory alkalosis)* Loss of reflexes * Intracranial hemorrhages * Seizures * Progressive encephalopathy

Infants and children* Failure to thrive * Episodic encephalopathy* Feeding problems * Ataxia* Nausea, vomiting * Convulsions

Adolescents and adults* Chronic neurologic symptoms * Episodic encephalopathy* Chronic psychiatric symptoms * Behavioral problems

Urea cycle defectsLaboratory findings

• Hyperammonemia (generally >400 µmol/L in urea cycle defects)

• Amino acids in serum• Organic acids in urine

Differential diagnosis• Organic acidurias: • Liver diseases: neonatal hepatitis, galactosemia,

tyrosinemia, respiratory chain defects• Transient hyperammonemia of newborn due to

patent ductus venosus.

CPS= Karbamoil fosfat sentaz OTC= Ornitin transkarbomoilaz ASA=Arjininosüksinik asit AS=Arjininosüksinat sentazAL=Arjininosüksinat liaz(sitrüllinemi)

Urea cycle defects: Acute therapy

• Stop protein intake

• Interrupt catabolic state by high calorie infusion (carbohydrate + lipid)

• Remove ammonia when >400 µmol/L by hemodiafiltration, hemofiltration, or hemodialysis, (periton dialysis is not effective)

• Give arginine 350 mg/kg in order to support urea cycle.

• Give sodium benzoate: 350mg/kg/day

• Give sodium phenylbutyrate 250mg/kg/day

• Aim for an ammonia concentration < 200µmol/L

Urea cycle defects

Chronic therapy• Restriction of protein intake (1.0-1.5

g/kg/day) +arginine +• sodium benzoate + sodium –phenylbutyrate

Prognosis• Poor if there is prolonged coma (>3 days),

and symptoms and signs of increased intracranial pressure

Defects of Fatty acid oxidation

Fatty acid (plasma)

Asetil CoA

Fatty acid (mitochondria)

Carnitine Carnitine enzymes

Beta-oxidation(acyl CoA

dehydrogenases)

131 ATP

Keton bodies

HMG CoA- liaseHMG CoA- synthase

3-ketothiolase (tioforase)

Krebs cycle

Fatty acid oxidation

Ya€ asidi

Açil-CoA

Açil-CoA

ß-oksidasyon

Asetil-CoA Pirüvik asit

Laktik asit

Krebs döngüsü

Elektron transport (solunum)zinciri

ATP

Karnitin transport sistemi

Enoil-CoA

VLCAD LCAD MCAD SCAD

3-OH-açil-CoA

LC-Hidrataz Krotanaz

LCHAD SCHAD

3-keto-açil-CoALC-Tiolaz SC-Tiolaz

Asetoasetat

ß-OH bütirat

NAD

NADH

NAD

NADH

NAD

NADH

FAD

FADH

Glükoz

HMG-sentaz HMG-liaz

Fatty acid oxidation

• Disorders of fatty acid oxidation

• During prolonged fasting mitochonrial oxidation of fatty acids provides up to 80% of the total energy requirement.

Fatty acid oxidation: Etiology

Carnitine transporter deficiency

Defects of carnitine cycle• Carnitine palmitoyltransferase I (CPTI) deficiency• Carnitine translocase deficiency• Carnitine palmitoyltransferase II (CPTII) deficiency

ß-oxidation defects• Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency• Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency• Short-chain acyl-CoA dehydrogenase (SCAD) deficiency• Long-chain hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency• Medium-chain hydroxyacyl-CoA dehydrogenase (LCHAD)

deficiency• Short-chain hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency

Fatty acid oxidation: Pathogenesis

• Insufficient energy production during fasting

• Deficiency of mitochondrial free CoA due to accumulation of toxic intermediary products

Clinical findings (Reyelike syndrome)

• Life-threatening hypoketotic hypoglycemic coma during catabolic states (prolonged fasting, infections, operations)

• Liver failure

• Skeletal myopathy, cardiomyopathy

Fatty acid oxidation: Laboratory findings

• Ketones: low, ammonia: high, glucose: low to normal, liver enzymes: high

• Total carnitine: low (high in CPTI deficiency)

• Acyl carnitine/total carnitine: Low

• Dicarboxilic acids in urine (GS-MS)

• Acylcarnitine profile (Diagnostic)

• Enzyme studies (Fibroblasts, lymphocytes)

Fatty acid oxidation: therapy

Acute therapy • High dose glucose (7-10 mg/kg/min),

no lipids (!)• Carnitine (100mg/kg): not in carnitine

cylce defects, and in LCHAD deficiency

Chronic therapy• Avoid prolonged fasting, careful

monitoring during catabolic states

Amino acid disorders. Phenylketonuria (PKU) Enzyme defect: phenylalanine hydroxylase (12th...

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