Nutrition and Metabolic Disorders: Classification of Inborn Errors of Metabolism (IEM)

Vocabulary flashcards covering the pathophysiology, inheritance, clinical classifications, examples, and nutritional management strategies of inborn errors of metabolism (IEM).

Inborn Errors of Metabolism (IEM)

A vast group of genetic disorders resulting from defects in specific enzymes, cofactors, transport proteins, or cellular receptors that disrupt normal metabolic biochemical pathways.

Accumulation of Substrate

A pathological mechanism in IEMs characterized by the toxic build-up of precursor compounds or alternative side-products upstream of an enzymatic metabolic block.

Deficiency of Product

A pathological mechanism in IEMs resulting in reduced synthesis of essential downstream molecules required for cellular energy, growth, or physiological function.

Autosomal Recessive Inheritance (in IEM)

The inheritance pattern governing the majority of IEMs, which requires two mutated alleles (one inherited from each carrier parent) for expression of the disorder.

Intoxication Disorders

A functional category of IEMs involving defects in the breakdown of small organic molecules (such as amino acids, organic acids, and urea) that lead to upstream toxic metabolite accumulation, typically presenting after a symptom-free interval once feeding begins.

Phenylketonuria (PKU)

An intoxication disorder caused by a defect in phenylalanine hydroxylase, leading to toxic accumulation of phenylalanine and severe intellectual impairment; treated with strict restriction of dietary protein and phenylalanine supplemented with specialized formula.

Maple Syrup Urine Disease (MSUD)

An intoxication disorder marked by impaired breakdown of branched-chain amino acids (leucine, isoleucine, and valine); nutritionally managed with a BCAA-free synthetic formula and careful leucine titration.

Urea Cycle Disorders (UCD)

A group of intoxication disorders characterized by an inability to convert waste nitrogen into urea, resulting in severe hyperammonemia; treated with natural protein restriction and essential amino acid supplementation.

Energy Deficiency Disorders

A functional category of IEMs caused by the failure to generate sufficient cellular ATP through glycolysis, glycogenolysis, or fatty acid oxidation, primarily affecting organs with high energy requirements such as the brain, heart, and skeletal muscle.

Fatty Acid Oxidation Disorders (FAODs)

A subclass of energy deficiency disorders (such as MCAD deficiency) characterized by impaired fat breakdown during fasting; managed by avoiding prolonged fasting and maintaining regular complex carbohydrate intake.

Glycogen Storage Diseases (GSDs)

A subclass of energy deficiency disorders (such as GSD Type I) marked by impaired glycogen breakdown leading to fasting hypoglycemia; managed with frequent dietary meals and uncooked cornstarch therapy.

Mitochondrial Disorders

A subclass of energy deficiency disorders resulting from respiratory chain defects that lead to multisystem organ dysfunction.

Complex Molecule Disorders

A functional category of IEMs involving organelles (such as lysosomes and peroxisomes) that handle the synthesis, transport, and recycling of complex cellular macromolecules, presenting with slowly progressive, permanent symptoms that are independent of food intake.

Lysosomal Storage Diseases (LSDs)

Complex molecule disorders (including Gaucher disease, Fabry disease, and MPS) marked by macromolecular accumulation in lysosomes, clinical organomegaly, and neurodegeneration; managed via Enzyme Replacement Therapy (ERT).

Peroxisomal Disorders

Complex molecule disorders affecting peroxisome function, with clinical examples including Zellweger syndrome and X-linked Adrenoleukodystrophy (X-ALD).

Enzyme Replacement Therapy (ERT)

A targeted medical intervention noted specifically for the management of lysosomal storage diseases.