Carbohydrate and Amino Acid Metabolism DISORDERS - NEET PG Pediatrics

Carbohydrate disorders are an important topic for the NEET PG exam because they are a group of metabolic disorders that affect the way the body processes carbohydrates. Understanding the symptoms, causes, and treatment options for carbohydrate disorders is crucial for medical students as it can help them diagnose and manage these conditions effectively.

In the NEET PG exam, questions related to carbohydrate disorders test a candidate's knowledge of endocrine anatomy and physiology, as well as their ability to diagnose and manage metabolic disorders.

In this blog, we cover - 

• Glycogen Storage Disease (GSD)
• Galactosemia 
• Hereditary fructose Intolerance (HFI)

Glycogen storage disease (GSD)

• Some have predominant liver involvement, some have predominant muscle involvement 
• Predominantly Liver Involvement 

Type	Name	Enzyme deficient
I	Von Gierke disease	Glucose 6 Phosphatase
III	Cori disease	Debranching enzyme
IV	Anderson disease	Branching enzyme
VI	Hers disease	Hepatic phosphorylase

• Predominantly Muscle Involvement (2+5=7)

Type	Name	Enzyme deficient
2	Pompe disease	Acid Maltase / α - glucosidase
5	Mc Ardle disease - m/c to present in adolescence with myoglobinuria	Muscle phosphorylase
7	Tarui disease	Phosphofructokinase

Von Gierke Disease (Type I GSD)

• Children have doll like facies 
• H/o of repeated episode of Hypoglycemia / especially in early morning          Lethargy, Seizure
• H/o of abdominal distension due to huge hepatomegaly 
• Investigations 
  • Hypoglycemia – check blood sugar levels
  • ↑ lactic acid levels
  • Hyperlipidemia 
  • ↑ Uric Acid Levels
• Treatment 
  • Corn starch diet recommended  

	Von Gierke disease(Type I GSD)	Cori’s disease(Type III GSD)
Muscle involvement	Not seen, CPK level normal	CPK level – ↑
Response to glucagon	No ↑ in blood glucose but LA level may rise	↑ In blood glucose in Fed state, not in fasting state

POMPE disease 

• Due to deficiency of acid maltase / α – glucosidase 
• C/F
  • Coarse facies 
  • Hepatomegaly 
  • Muscle involvement: Hypotonia – Floppy child  
  • Cardiomegaly: EGC changes seen 
• Important to diagnose as ERT is available for Pompe disease 

Galactosemia

• Due to deficiency of 
  • Galactose 1 PO₄ Uridyl Transferase – Most common 
  • Galactokinase 
  • Epimerase 
• C/F
  • Hepatomegaly
  • Jaundice due to liver involvement  
  • Vomiting, Diarrhea 
  • Failure to thrive 
  • Cataract 
• Reducing substance positives in urine 
• Rx – Milk free (lactose free) diet

Hereditary fructose intolerance 

• It is due to deficiency of Aldolase B.
• There is inability to digest fructose 
• C/F
  • Aversion to sweet food (due to some adverse response on consuming sweet food)
  • Jaundice 
  • Hepatomegaly 
  • Vomiting, diarrhea 
  • Liver dysfunction 
• Rx – Fructose free diet 

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DISORDERS OF AMINO ACID METABOLISM

Phenylketonuria 

• It is due to deficiency of phenylalanine hydroxylase. 
• Phenylalanine PA Hydroxylase→ Tyrosine 
• If there is deficiency of PA hydroxylase enzyme, tyrosine is not synthesized in the body.

Important Information  Tyrosine becomes essential AA in phenylketonuria  Excess phenylalanine accumulates in body, which is toxic to CNS: Neurological manifestations are seen

• If there is excess phenylalanine in the body, other metabolites like phenyl acetate, pyruvate are excreted in large amounts through urine & other body fluids. As Tyrosine is not synthesized melanin will also be not synthesized, so child presents with hypopigmentation
• Rx: Low phenylalanine diet & tyrosine supplementation 

Alkaptonuria 

• It is due to deficiency of homogentisate oxidase.
• There is accumulation of homogentisic acid polymer known as alkapton bodies which are present all over body causing black pigmentation or Oochronosis 
  • Blackening of sclera, ear cartilage 
  • Deposition in vertebral bodies 
  • Joint abnormalities
  • Cardiac valve abnormalities
  • Darkening of urine on standing – most common 

Homocystinuria 

• It is most commonly due to deficiency of cystathionine β-synthase
• C/F:
  • Just like Marfan syndrome 
  • Tall stature 
  • Skeletal abnormalities 
  • Recurrent strokes 
  • Lens dislocation of eye
    • In Marfan syndrome, lens dislocation is superolateral (MSL)
    • In homocystinuria, lens dislocation is inferomedial.

Multiple Carboxylase Deficiency

• Biotin is a cofactor 
• Because of which there is skin & hair change 
• Tomcat urine odor 
• Rx – Biotin supplementation 

Hartnup disease

• It is due to mutation of SLC 6 A19 gene. 
• Transport of neutral AA is affected 
• Most kids remain asymptomatic 
• If symptoms seen – due to niacin deficiency, then they are similar to pellagra 
  • Photosensitivity 
  • Rash around neck area & sun exposed part of body. It is known as pellagra like rash 
• Rx: Niacin Supplementation

Tyrosinemia

• It is due to deficiency of fumarylacetoacetate hydrolase: Most common
• There is hepatic involvement 
• C/f
  • Hepatomegaly
  • Bleeding manifestation (coagulation factor not synthesized)
• These children are really sick with what they present. 

Maple Syrup Urine Disease (MSUD)

• It is due to a problem in metabolizing branched chain AA like leucine, Isoleucine & Valine. It is due to deficiency of an enzyme α– ketoacid dehydrogenase. It presents with burnt sugar / maple sugar odor in body fluids
• Rx: Diet with low branched chain AA

Body fluid / Urine odor	Disorder
Burnt sugar odor Sweaty feet odor  Boiled cabbage odor  Tomcat odor Mousy / Musty odor	MUSD Glutaric acid urea Tyrosinemia  Multiple carboxylase deficiency  Phenylketonuria

Screening test for inborn errors of metabolism

• TMS (Tandem Mass Spectrometry) or LCMS / MS: Done using dry blood spots 
• GCMS (Gas Chromatography – mass spectrometry): Done using urine 
• Plasma or urine HPLC: Done to identify elevated levels of various metabolites 
• Electrophoresis 

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