Glycosylation, Creatine, Nucleic Acids and Peptides - BioChem Genetics

Congenital Disorders of Glycosylation (CDGs)

• errors in enzymes that bind carbohydrates to organic molecules via glycosylation

• Carbohydrates (-glycans)s help with protein folding + stability → effects cell trafficking, identification and cohesion

• Exceedingly broad group of disorders: >80 identified so far and more each year b/c of WGS

  • 2% of genes cod for glycosylation enzymes: Most endoplasmic reticulum proteins are glycosylated

Congenital Disorders of Glycosylation (CDGs): General clinical features

• CNS (80%)

  • Seizures

  • Dystonia

  • Mental Retardation

• Ophthalmology

  • Optic Atrophy

  • Coloboma

• Growth Failure

• Immunodeficiency

• Coagulopathy

5 Major Types of Glycan Classes

• ***N-linked: Glycan on Nitrogen*** most common disorder → CDG1-a most often

• O-linked: Glycan on Oxygen

• Glypilation: Glycolipid on Amino Acid c-terminus

• C-Linked: Glycans on carbon of TRYPTOPHAN

• Phospho-Glycans: glycan on Phospho-SER (?)

Phosphomannomutase 2 (PMM2) Deficiency: Overview

• ***MOST COMMON N_GLYCOSATION DISORDER**8

• N-Glycosylation Defect

• Inheritance: Autosomal defect

Phosphomannomutase 2 (PMM2) Deficiency: Presentation

• Infantile onset:

  • can be lethal form or nonlethal, neurological form

  • Fail to thrive, low muscle tone, and UNUSUAL PATTERN OF FAT (fat pads over chest + inversion of nipples)

• Childhood Axatia:

  • Ataxia, Intellecualt diabiltiy, Hypotoinia, Nerupathy

• Stablizes in Adulthood

Phosphomannomutase 2 (PMM2) Deficiency: General Diagnosis + Treatment

Diagnosis

• Transferrin Isoform analysis screening: transferrin is N-linked glycosylation —> deficiency of glycosylated transferrin = CDG

• CDG-1a: PMM2 enzyme analysis

• CDG-1A: PMM2 mutation analysis

Treatment: Primarily supportive —> no effective treatments

Mannose-6-Phosphate Isomerase (MPI) Deficiency: Overview

• An N-Glycosylation Defect

• Autosomal Recessive

• MPI gene mutation

Mannose-6-Phosphate Isomerase (MPI) Deficiency: Presentation

• Infantile Failure to thrive

  • Cyclic Vomiting

  • Liver Dysfunction

  • Coagulopathy (bleeding) / Thrombosis (abnormal clotting)

*** NO NEUROLOGICAL EFFECTS***

Mannose-6-Phosphate Isomerase (MPI) Deficiency: Diagnosis + Treatment

Diagnosis

• Transferrin Isoform analysis (low glycosylated transferrin = n-linked CDG)

• CDG-1b: MPI Gene Mutation Analysis

Treatment

• Oral Mannose Supplementation 1gm/kg/day

CDG: O-Linked Glycosylation

• More Dysmorphic features than N-Linked CDGs

• “Hereditary Multiple Exostosis” → Auto. Dominant

  • EXT1/EXT2 (AD)

• “Progeroid Ehlers-Danlos Syndrome”

  • B4GALT7 (AR)

• “Muscle-Eye-Brain Disease” (Walker-Warburg Syndrome)

  • POMT1, POMT2, POMGT1 (AR)

Cerebral Creatine Deficiency Syndromes (CCDS): Metabolic Pathway

• Creatine primary created in the liver from → Glycine + Arginine to Orthenine + Guanidinoacetate

• Creatine can be an energy storage molecule → conversion to Creatine Phosphate Kinase

  • Can be converted to CREATININE: released in the urine

    

Cerebral Creatine Deficiency Syndromes (CCDS): Overview

• 3 Main Disorder: 3 main enzymes: 2 biosynthesis + 1 transporters

  • L-Argiine:Glycine Amidino Transferase (AGAT) Deficiency - AR

  • GuandiaoAcetate Methyl Transferase (GAMT) Deficiency - AR

  • Creatine Transporter Deficiency (SLC6A8) Deficiency - XLR

Cerebral Creatine Deficiency Syndromes (CCDS): Presentation

Similar features: Onset in childhood

• Global developmental delay —> Mild/Sever mental retardation

• Autism (self-injury in GAMT)

• Muscle weakness

• Movement Disorders: Ataxia, Dystonia (NOT in AGAT)

• Dysmorphic Features (SLC6A8)

Milder Cases may have later Onset

Cerebral Creatine Deficiency Syndromes (CCDS): Diagnosis

• Brain MR Spectroscopy: Creatine peaks in the brain can be detected

• Screening Tests (Urine/Plasma/Spinal Fluid)

  • Guanidinoacetate (GAA) → High in GAMT :: Low in AGAT

  • Creatine → Low in GAMT + AGAT :: High in SLC6A8

  • Creatinine → Low in GAMT, AGAT and SLC6A8

• Diagnostic

  • Enzyme Activity: AGAT + GAMT

  • Creatine uptake (fibroblasts) : SLC6A8

  • Gene Analysis: GATM (AGAT), GAMT (““) , SLC6A8 (transporter)

Cerebral Creatine Deficiency Syndromes (CCDS): Treatment

• AGAT: Oral Creatine Monohydrate

• GAMT: Oral Creatine Monohydrate and Decrease Guanidinoacetate production

  • Orthinine: Inhibits AGAT, lowers GAA

  • Arginine restriction: inhibits AGAT, lowers GAA

  • Benzoate: reduces glycine, lowers GAA

• SLC6A8: Oral Creatine Monohydrate

Purine synthesis

• Ribos-5-Phosphate → steps → Inosine Monophosphate (IMP) → either:

  • Adenosine monophosphate

  • Guanosine monophosphate

• Inosine monophosphate can be converted to hypoxanthine via HPRT→ can be storge molecule for later conversation to IMP (?)

Lesch-Nyhan Syndrome: Metabolic pathway

• Inosine monophosphate can be converted to hypoxanthine via HPRT→ can be storge molecule for later conversation to IMP (?)

• Deficiency in HPRT = inadequate IMP + Hypoxanthine → xanthine → uric acid (which builds up)

Lesch-Nyhan Syndrome: Overview

• X-Linked Recessive

• Etiology HPRT1 Deficiency → Decreased Inosine Monophosphate + Increase Uric acid / Xanthine

Evaluation:

• Screening: Uric Acid levels

• Diagnosis: Enzyme activity (blood, fibroblast, CVS) + HPRT1 gene analysis

Lesch-Nyhan Syndrome: Presentation

• Neurologic

  • Mental retardation, seizures, cerebral palsy

  • motor dysfunction

  • Sel Mutilating (1-8yo)

• Hyperuricemia:

  • uric acid kidney stones, renal failure, gout

Lesch-Nyhan Syndrome: Treatments

• No Cure

• Can lower uric acid, but cannot prevent the Neurologic conditions

• Medications

• Physical restraints are necessary

Monoamine Synthesis

• Tyrosine → Dopa → Dopamine → Norepinephrine→ Epinephrine (Adrenaline)

• Tryptophan → 5-Hydroxytryphtoan → Serotonin

  

Tetrahydrobiopterin (BH4) Deficiency: Metabolic pathways

• BH4 a cofactor for Neurotransmitter synthesis enzymes (also important in the Aminoadipates → look at those cards)

  • ALSO: Phenylalanine Hydroxylase (PAH), associated with PKU, need BH4

• BH4 low → Monoamines Low

• BH4 Synthesis: GTPCH1, PTPS, SR

• BH4 Regeneration: PCD, DHPR

Tetrahydrobiopterin (BH4) Deficiency: Differential Diagnosis

NBS with elevated Phenylalanine (b/c BH4 needs to be high for PHE → Tyrosine)

need to rule out:

• PKU (PHE > 1200uM) (***MOST LIKELY***)

• Fals positive or generalized liver dysfunction

• Hyperphenylmaina (PHE 120uM-1200uM)

Tetrahydrobiopterin (BH4) Deficiency: Diagnosis

• PHE levels usually Heyperphanlamenima (120-1200uM) but not no the PKU range

  • GTPCH

  • PRPS

  • PCD

  • DHPR

• PHE Normal form AD GRPCH1 and SR

• Check for

  • Urine Ptertin

  • RBC DHPR levels

  • Do BH4 load test

• Confirm diagnosis with enzyme activity / gene analysis

Elevated PHE BH4 (GTPCH, PRPS, PCD, DHPR): Presentation

• At birth Asymptomatic

• Infancy

  • Abnormal muscle tone

  • poor sucking

  • seizures

  • delayed motor development

• Long term

  • Irreversible neurologic deterioration

  • mental retardation

  • seizures

  • death

• Phenotypic severity varies response to treatment varies

Elevated PHE BH4 (GTPCH, PRPS, PCD, DHPR): Treatment

• Oral BH4 Supplementation Sapropterin

• Dietary Modification reduced PHE, add TYR

• Neurotransmitter Replacement

  • L-Dopa

  • 5-HT (serotonin) supplementation, SSRIs

  • MAO inhibitors

• Cofactors: Folic Acid

AD GTPCH1 Dopa-Responsive Dystonia: Overview

• *** PHE not ELEVATED *** → But Decreased Neurotransmitters (dopamine)

• Clinical “Segawa Syndrome”: Childhood onset (avg 6yo) dystonia and progressive Parkinsonian: symptoms of dopamine deficiency (Parkinsons Disease) But at a much early age

Diagnosis

• Decreased Neopterin + Biopterin

• CTPCH1 enzyme activity

• GCH1 gene mutation analysis

Treatment

• L-Dopa/Carbidopa

• Dramatic normalization with treatment

Sepiatrin Reductase: Overview

• ***PHE not ELEVATED***

• Parkinson features at an early age → BUT more severe INTELLECTUAL DISABILITY

  • “Diurnal FLucation” : Better in the morning, but get worse throughout the day

• Diagnosis

  • Decreased Homovalnic acid + HIAA (neurotransmitter metabolites) - CSF

  • Increased Neoprtrin - CSF and Urine

• Treatment/Outcomes

  • L-Dope, 5-HT, SSRI, MAOIs

  • Normal outcomes with treatment

Glutathione Synthase Deficiency: Overview

• Impacts pathway for mitigating Oxidative Stress: Glutathione is decreased

Clinical

• Milder Deficney → Anmia and metabolic acidosis

• Sever Deficiney → Neurodegenration and infection

Etiology: AR Glutathione synthease (GSS) mutation = Decreased free radical scavenging

Diagonsis

• Low Glutahione, increased 5-Oxoproline

• Enzyme activity + gene Anylsis

Treatment

• Correct acidsoids

• Supplment with anti-oxidant vitamins

• Avoid oxidative stress

Trimethylaminuria: Overview

• Prominent Fishy Order from body fluids

Etiology: AR FMO3 gene mutation: Increased Trimethylamine (TMA) → Urine TMA levles, gene testing

Treatment:

• Restrict dietary trimethylamine, choline and lecithin

• Decrease gut bacterial production

• Riboflavin

• Acididc skin/oral products