Manual of Clinical Nutrition

Manual of Clinical Nutrition Management III- 74 Copyright © 2013 Compass Group, Inc.

INBORN ERRORS OF METABOLISM

Discussion

Inborn errors of metabolism are inherited disorders in which there is an absence or reduced activity of a
specific enzyme or cofactor. Impaired metabolism and disease result.

A rational approach to the nutrition intervention of an inborn error of metabolism requires some
understanding of the pathogenic mechanisms and resulting consequences. One or both of the following
mechanisms may be present, depending on the type of disorder:

1. The accumulated substrate or its metabolites may have toxic effects.


2. A harmful deficiency may result from the decreased synthesis of a necessary end product.

The rationale for nutrition intervention depends on which of these mechanisms is thought to be important.
For example, in galactosemia, the goal is to reduce the accumulation of substrate (galactose and galactose- 1 -
phosphate). In type I glycogen storage disease, the aim is to supply the deficient product (glucose). In
phenylketonuria both reduction of the substrate (phenylalanine) and provisions of adequate amounts of the
product (tyrosine) must be accomplished.

Successful nutrition intervention for patients with inborn errors requires a keen appreciation of the
tremendous variability among individuals and a willingness to tailor the therapeutic approaches to the
specific needs of each patient.

Approaches

The following table lists genetic disorders in which nutrition intervention has been employed.

Table III-20: Metabolic Disorders That Respond to Dietary Treatment

Disorder Enzyme Defect

Nutrition

Intervention

Special Formulasa

Possible Outcomes
Without Effective
Medical Treatment
Phenylketonuria
(PKU)

Phenylalanine Diet low in

phenylalanine.

Increase tyrosine in

diet.

Lofenalac® (MJ),

Phenyl-free® (MJ),

Phenex® (RL),

Maxamaid® (SHS)

Growth delay, mental

impairment, seizures

Tyrosinemia Cytosol tyrosine
aminotransferase

Diet low in

phenylalanine and

tyrosine

Product 3200 AB®

(MJ),

XYPHEN® (SHS),

Tyromex® (RL)

Death, growth delay,

mental impairment,

renal disease, liver

dysfunction, seizures,

hypoglycemia,

metabolic acidosis,

hyperammonia

Maple syrup
urine disease
(MSUD)

Ketoacid

decarboxylase

Diet low in leucine,

isoleucine, and

valine

MSUD Diet Powder®

(MJ),

MSUD Maxamaid®

(SHS),

Ketonex® (RL)

Death, growth delay,

mental impairment,

seizures, hypoglycemia,

metabolic acidosis,

hyperammonia