Unit Converter
Serine (Ser)
(Non-Essential Amino Acid - Critical in CNS Development, One-Carbon Metabolism, and Inborn Errors of Metabolism)
Synonyms
- Serine
- L-Serine
- Ser
- 2-Amino-3-hydroxypropanoic acid
- Proteinogenic amino acid Ser
Units of Measurement
- µmol/L
- mg/L
- mg/dL
- mg/100 mL
- mg%
- µg/mL
Unit Conversions
Molecular weight of L-Serine = 105.09 g/mol
µmol/L ↔ mg/L
1 µmol/L=0.105 mg/L1\ \text{µmol/L} = 0.105\ \text{mg/L}1 µmol/L=0.105 mg/L 1 mg/L=9.51 µmol/L1\ \text{mg/L} = 9.51\ \text{µmol/L}1 mg/L=9.51 µmol/L
mg/dL → mg/L
1 mg/dL=10 mg/L1\ \text{mg/dL} = 10\ \text{mg/L}1 mg/dL=10 mg/L
mg% = mg/dL
µg/mL → mg/L
1 µg/mL=1 mg/L1\ \text{µg/mL} = 1\ \text{mg/L}1 µg/mL=1 mg/L
Description
Serine is a non-essential, polar amino acid synthesized from 3-phosphoglycerate.
It plays a crucial role in:
- Central nervous system development
- One-carbon metabolism
- Sphingolipid biosynthesis
- Protein synthesis
- Glutathione and cysteine formation
- Purine and thymidine synthesis
Serine is also a precursor to D-serine, an important co-agonist at the NMDA receptor in the brain.
In laboratory medicine, serine is measured as part of plasma amino-acid profiles to diagnose metabolic disorders.
Physiological Role
1. CNS Development
Essential for brain growth and myelination.
2. One-Carbon Metabolism
Via serine hydroxymethyltransferase → supports:
- DNA synthesis
- Methylation reactions
3. Antioxidant Defense
Precursor for glutathione synthesis.
4. Protein & Sphingolipid Biosynthesis
Required for cell membranes and signaling molecules.
5. Energy Metabolism
Supports mitochondrial function & cellular redox balance.
Clinical Significance
HIGH SERINE
1. Serine Dehydratase Deficiency
- Causes mild elevation
- Often asymptomatic
2. Immature Liver Function
3. Hyperalimentation / TPN
Elevated due to infusion amino acids.
4. Rare Inborn Errors Affecting Glycine/One-Carbon Pathways
- SHMT deficiency
- Mitochondrial folate pathway disorders
LOW SERINE (Hypo-serinemia)
Clinically important finding.
1. 3-Phosphoglycerate Dehydrogenase (3-PGDH) Deficiency
Severe congenital disorder → profound CNS impairment:
- Microcephaly
- Intractable seizures
- Psychomotor retardation
- Hypotonia
Responds to high-dose L-serine therapy.
2. PHGDH / PSAT / PSPH Defects
Serine biosynthesis defects - present in infancy.
3. Malnutrition / Malabsorption
Low protein intake → reduced serine levels.
4. Liver Disease
Impaired conversion from 3-phosphoglycerate.
5. Chronic Alcohol Intake
Lower serine due to malnutrition and poor hepatic metabolism.
6. Renal Losses
Seen in Fanconi syndrome.
7. TPN Deficiency
Inadequate amino-acid mixture.
Reference Intervals
(Tietz 8E + Mayo + ARUP + ACMG Amino Acid Reference Panels)
Plasma Serine
| Age Group | Range |
| Adults | 60 – 170 µmol/L |
| Children | 70 – 200 µmol/L |
| Newborns | 80 – 250 µmol/L |
(Serine is normally higher in newborns due to active CNS development.)
Flags
- <50 µmol/L → consider serine biosynthesis defect
- >250 µmol/L → hyper-serinemia (usually benign unless metabolic disorder suspected)
Diagnostic Uses
1. Evaluation of Metabolic Disorders
Especially in neonates with:
- Seizures
- Microcephaly
- Developmental delay
- Hypotonia
2. Inborn Errors of Serine Biosynthesis
3-PGDH, PSAT, PSPH deficiencies.
3. Monitoring Nutritional Status
Particularly in malnutrition & TPN.
4. Liver Dysfunction Evaluation
As part of amino-acid signature.
5. Investigation of Neurological Disorders
Because serine contributes to NMDA receptor modulation (via D-serine).
Analytical Notes
- Use fasting plasma for best accuracy.
- Avoid hemolysis - releases intracellular amino acids.
- Collected in heparin or EDTA tubes.
- Deproteinize immediately or freeze plasma to prevent degradation.
- Measured by HPLC or LC–MS/MS.
Clinical Pearls
- Very low serine in infants → urgent metabolic work-up for serine biosynthesis defects.
- High-dose serine therapy dramatically improves outcomes in 3-PGDH deficiency.
- Combine serine with glycine levels for one-carbon metabolism interpretation.
- Serine is significantly affected by liver function, nutrition, and TPN composition.
- In neonates, high serine is normal due to active CNS growth.
Interesting Fact
Serine was first isolated from silk fibers (Latin “sericum”), where it constitutes nearly 10% of the protein content.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Amino Acids
- ACMG Guidelines for Evaluation of Inborn Errors of Metabolism
- Mayo Clinic Laboratories - Plasma Amino Acids
- ARUP Consult - Amino Acid Testing
- NIH / MedlinePlus - Amino Acids