Carbohydrate and Amino Acid Metabolism DISORDERS - NEET PG Pediatrics
Apr 10, 2023
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)
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
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 cystathionineβ-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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