Advances in Biochemical Genetics: Pathophysiology, Diagnosis, and Treatment of Inborn Errors of Metabolism

Introduction:

The management and diagnosis of inborn errors of metabolism are dealt with in biochemical genetics. It deals with those patients who have enzymatic deficiencies that disturb the biochemical pathways involved in the metabolism of lipids, carbohydrates, and amino acids. If there is an inherited abnormality in the biochemistry of the body, then it is known as a biochemical genetic disorder. Variation in these diseases is high and incurable. Some of the diseases are related to mental retardation and other developmental issues. Some of them can be life-threatening. Severe effects of such diseases can be prevented if they are detected and treated early. Early treatment can change the natural progression of the disease. Some of the metabolic disorders are glycogen storage diseases, lysosomal storage disorders, phenylketonuria (a birth defect that builds up amino acids in the body).

What Is the Pathophysiology of Biochemical Genetics?

Single gene defects result in abnormalities during the synthesis or catabolism of carbohydrates, fats, or proteins. Most of them are due to a defect in an enzyme or transport protein, resulting in a block in the metabolic pathway. The effects are due to the toxic accumulation of substrates before the block, intermediates from alternative metabolic pathways, defects in energy production, deficiency of the products beyond the block, or a combination of both of these metabolic deviations.

What Is Biochemical Genetic Testing?

Biochemical genetic testing deals with the study of proteins or enzymes in the body that can be unusual in some way. These enzymes or proteins may work differently and lead to conditions such as birth defects in children. These types of problems are usually called inborn errors of metabolism.

What Is the Role of a Genetic Pathologist in Biochemical Testing?

The role of a genetic pathologist working in biochemical genetics is as follows:

• Population-based screening for the inborn errors of metabolism by protein, enzyme, and metabolite assays.

• Diagnostic screening for inborn errors of metabolism in symptomatic patients by analysis of metabolites such as organic acids in urine, amino acids in urine, plasma, and cerebrospinal fluid.

• Diagnostic assays for specific disorders by analyzing specific analytes in the body fluids, enzymatic studies, or deoxyribonucleic acid (DNA) studies of specific genes.

• Predictive assays in unaffected relatives (or a fetus) to determine the risk of developing the disorder known to be present in the family.

• Pedigree analysis (it is a chart designed to understand the inheritance of genes from parents to offspring).

• Diagnostic assessment of segregation in kinds of disease-causing mutations or genomic regions.

• They monitor the biochemical status of a patient for long-term care or to guide them with acute care during a metabolic crisis.

• They provide advice to the laboratory and clinical personnel for test selection and interpretation of biochemical and genetic assay results.

• Biochemical genetic pathologists also contribute to the diagnostic assessment of acutely ill patients who may be diagnosed with an inborn error of metabolism. They assist in the test selection and determining the significance of abnormalities in these test results.

What Are Inborn Errors of Metabolism?

An inherited enzyme deficiency leads to the disruption of normal body metabolism that may have pathological consequences at birth, for example, phenylketonuria, and later in life, diabetes, as a result of the accumulation of toxic substrate or a toxic metabolite or impaired formation of a critical product.

What Are the Types of Inborn Errors of Metabolism?

The types are as follows:

Silent Disorders:

• They do not manifest life-threatening crises.

• If left untreated could lead to brain damage and developmental disabilities.

• For example, phenylketonuria.

Acute Metabolic Crises:

• It can be life-threatening in infants.

• Maternal circulation protects children in utero, providing a missing product or removing toxic substances.

• For example, urea cycle disorders.

Neurological Deterioration:

• For example, Tay-Sachs disease and Gaucher disease.

What Is the Genetics of Inborn Errors of Metabolism?

These disorders follow one gene-one enzyme concept, and the main types of mutations are single base pair substitutions, deletions, or insertions. They can be heterogeneous and have racial and ethnic variations. The mode of inheritance determines the male-to-female ratio. They are usually autosomal recessive, and a few are inherited as an autosomal dominant trait.

How Are Metabolic Disorders Tested?

There are two types of testing for metabolic conditions available. One is screening tests, and the other is disease-specific diagnostic testing.

1. Screening Tests - Screening tests allow the detection of the presence of a particular class of conditions which includes serum electrolytes, glucose and ammonia levels, blood and urine amino acids for disorders of amino acid metabolism, urine organic acids for disorders of organic metabolism acid, acylcarnitine profile for disorders of fatty acid, blood lactate, and pyruvate for disorders of carbohydrate metabolism and mitochondrial disorders.

2. Specific Diagnostic Testing - It is used to measure the activity of the involved protein or enzyme that is available for most conditions. It can be done on blood but sometimes requires skin, liver, or muscle biopsy.

What Are the Treatment Options for Inborn Errors of Metabolism?

The treatment options for inborn errors of metabolism are listed below:

• Dietary restrictions of specific amino acids.

• Providing enzyme and co-enzyme replacement therapy and the removal of harmful substances.

• Gene therapy.

• Prenatal diagnosis.

• Vitamin supplementation.

• Bone marrow transplantation.

What Are Biochemical Methods?

Biochemical methods in genetics are based on the principle that the underlying genetic characteristics can be concluded by identifying and measuring the physiological compounds or phenotypic characteristics controlled by genetics.

1. Quantitative Method - In general, quantitative methods are more accurate and reproducible, and therefore, their application is more widespread. Quantitative methods allow the identification and measurement of one or more analytes produced in vivo, which are contained within a physiological sample, like blood or urine, or in vitro determination of an enzyme-catalyzed chemical reaction rate, usually from physiological samples or cultured cells.

2. Qualitative Method - These include various forms of two-dimensional chromatography and electrophoresis for the separation and visualization of analytes capable of generating distinct normal and abnormal patterns.

Conclusion:

The background of biochemical genetics is mainly focused on the pathophysiology, diagnosis, and treatment options of inborn errors of metabolism. Recent development in biochemical and genetic methods, both quantitative and qualitative, can rapidly evaluate the patient’s metabolic status during acute illness and can provide a piece of conclusive diagnostic information through the measurement of specific enzyme activities.