Amino Acids in Pediatric Medicine

A comprehensive guide for pediatricians and medical students focusing on amino acid disorders, functions, and clinical relevance.

Essential Amino Acids

Phenylalanine (Phe)

Overview

Primary Functions:

  • Precursor for tyrosine
  • Essential for neurotransmitter synthesis
  • Required for protein synthesis

Associated Disorders:

  • Phenylketonuria (PKU)
    • Incidence: 1:10,000-15,000 births
    • Screening: Part of newborn screening programs
    • Management: Low-Phe diet, medical foods
  • Hyperphenylalaninemia
Clinical Manifestations Monitoring Parameters
- Developmental delay
- Seizures
- Fair skin/hair
- Behavioral problems 		- Blood Phe levels
- Growth parameters
- Development milestones
- Dietary compliance
Tryptophan (Trp)

Overview

Primary Functions:

  • Serotonin synthesis
  • Melatonin production
  • Niacin synthesis

Associated Disorders:

  • Hartnup Disease
    • Incidence: 1:30,000 births
    • Inheritance: Autosomal recessive
    • Management: Niacin supplementation, sun protection
  • Tryptophan Hydroxylase Deficiency
Clinical Manifestations Monitoring Parameters
- Pellagra-like rash
- Cerebellar ataxia
- Mood disorders
- Sleep disturbances 		- Plasma tryptophan
- Urinary amino acids
- Growth monitoring
- Neurological assessment
Lysine (Lys)

Overview

Primary Functions:

  • Collagen formation
  • Carnitine synthesis
  • Calcium absorption

Associated Disorders:

  • Hyperlysinemia
    • Rare genetic disorder
    • Variable clinical significance
    • Management: Monitoring
  • Lysinuric Protein Intolerance (LPI)
Clinical Manifestations Monitoring Parameters
- Growth failure
- Osteoporosis
- Muscle weakness
- Hepatosplenomegaly 		- Plasma lysine
- Bone density
- Growth charts
- Organ function tests

Non-Essential Amino Acids

Tyrosine (Tyr)

Overview

Primary Functions:

  • Catecholamine synthesis
  • Melanin production
  • Thyroid hormone synthesis

Associated Disorders:

  • Tyrosinemia
    • Type I (most severe)
    • Type II (oculocutaneous)
    • Type III (rare)
  • Alkaptonuria
Clinical Manifestations Monitoring Parameters
- Liver failure
- Renal tubular dysfunction
- Eye lesions
- Growth failure 		- Blood tyrosine
- Liver function
- Renal function
- Ophthalmological exam

Branched-Chain Amino Acids (BCAAs)

Leucine (Leu)

Overview

Primary Functions:

  • Protein synthesis stimulation
  • Blood sugar regulation
  • Growth hormone production
  • Wound healing

Associated Disorders:

  • Maple Syrup Urine Disease (MSUD)
    • Incidence: 1:185,000 births
    • Acute metabolic decompensation
    • Emergency protocol required
  • Isovaleric Acidemia
Clinical Manifestations Monitoring Parameters
- Maple syrup odor in urine
- Lethargy/coma
- Feeding difficulties
- Developmental delay 		- BCAA levels
- Ketones
- Brain MRI
- Growth parameters
Valine (Val)

Overview

Primary Functions:

  • Muscle metabolism
  • Cognitive function
  • Immune system support

Associated Disorders:

  • MSUD (with Leucine and Isoleucine)
    • Neurological complications
    • Dietary management essential
Clinical Manifestations Management Approach
- Poor feeding
- Neurological symptoms
- Growth issues
- Metabolic acidosis 		- Medical formula
- Protein restriction
- Emergency protocols
- Regular monitoring
Isoleucine (Ile)

Overview

Primary Functions:

  • Hemoglobin synthesis
  • Blood sugar regulation
  • Muscle metabolism

Associated Disorders:

  • MSUD Component
    • Part of branched-chain organic acidemias
    • Neonatal screening target
Monitoring Aspects Therapeutic Approaches
- Plasma levels
- Nutritional status
- Development tracking
- Metabolic stability 		- BCAA-free formula
- Sick-day protocols
- Dietary planning
- Metabolic team follow-up

Sulfur-Containing Amino Acids

Methionine (Met)

Overview

Primary Functions:

  • SAM-e synthesis
  • Protein synthesis initiation
  • Homocysteine metabolism
  • Antioxidant production

Associated Disorders:

  • Homocystinuria
    • Incidence: 1:200,000-335,000
    • CBS deficiency
    • Thrombotic risk
  • MTHFR Deficiency
Clinical Manifestations Monitoring Parameters
- Marfanoid features
- Lens dislocation
- Thromboembolism
- Developmental delay 		- Homocysteine levels
- Methionine levels
- Ophthalmologic exam
- Clotting studies
Cysteine (Cys)

Overview

Primary Functions:

  • Glutathione synthesis
  • Taurine production
  • Disulfide bond formation
  • Detoxification

Associated Disorders:

  • Cystinuria
    • Incidence: 1:7,000
    • Kidney stones
    • Renal damage risk
  • Cystinosis
Clinical Manifestations Management Approach
- Renal stones
- Growth failure
- Crystal arthropathy
- Fanconi syndrome 		- Hydration therapy
- Urinary alkalinization
- Dietary modification
- Stone prophylaxis

Essential Amino Acids (continued)

Histidine (His)

Overview

Primary Functions:

  • Hemoglobin synthesis
  • Histamine production
  • pH buffer in blood
  • Growth and repair of tissues

Associated Disorders:

  • Histidinemia
    • Incidence: 1:8,000
    • Generally benign
    • Speech delays reported
  • Urocanic aciduria
Clinical Manifestations Monitoring Parameters
- Speech delay
- Learning difficulties
- Behavioral changes
- Generally asymptomatic 		- Plasma histidine
- Urocanic acid
- Development screening
- Speech assessment
Threonine (Thr)

Overview

Primary Functions:

  • Collagen and elastin formation
  • Fat metabolism
  • Immune system support
  • Intestinal mucin production

Associated Disorders:

  • Threonine Dehydratase Deficiency
    • Very rare condition
    • Neurological impact
    • Developmental concerns
Clinical Manifestations Management Approach
- Developmental delay
- Spasticity
- Seizures
- Failure to thrive 		- Dietary supplementation
- Neurological monitoring
- Growth tracking
- Physical therapy

Conditionally Essential Amino Acids

Arginine (Arg)

Overview

Primary Functions:

  • Nitric oxide synthesis
  • Urea cycle
  • Growth hormone secretion
  • Wound healing

Associated Disorders:

  • Urea Cycle Disorders
    • Incidence: 1:35,000
    • Hyperammonemia
    • Emergency protocols needed
  • Arginase Deficiency
Clinical Manifestations Monitoring Parameters
- Hyperammonemia
- Neurological symptoms
- Protein aversion
- Developmental delay 		- Ammonia levels
- Plasma amino acids
- Neurological status
- Growth parameters
Glutamine (Gln)

Overview

Primary Functions:

  • Intestinal cell fuel
  • Immune system support
  • Acid-base balance
  • Nitrogen transport

Associated Disorders:

  • Glutamine Synthetase Deficiency
    • Extremely rare
    • Severe brain malformations
    • Multi-organ involvement
  • Secondary deficiencies in critical illness
Clinical Manifestations Therapeutic Approaches
- Seizures
- Brain malformations
- Multi-organ dysfunction
- Metabolic acidosis 		- Supplementation
- Anticonvulsants
- Supportive care
- Nutritional support

Non-Essential Amino Acids with Clinical Significance

Glycine (Gly)

Overview

Primary Functions:

  • Collagen formation
  • Neurotransmitter function
  • Heme synthesis
  • Bile acid conjugation

Associated Disorders:

  • Nonketotic Hyperglycinemia
    • Incidence: 1:60,000
    • Severe neurological impact
    • Poor prognosis
  • Glycine Encephalopathy
Clinical Manifestations Management Approach
- Neonatal seizures
- Hypotonia
- Respiratory issues
- Lethargy/coma 		- Sodium benzoate
- Dextromethorphan
- Seizure control
- Respiratory support
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