What is the primary characteristic of metabolic errors?

The primary characteristic of metabolic errors is impaired processing of substances. Metabolic disorders often arise from defects in the biochemical pathways that process nutrients, waste products, or energy. This impaired processing can lead to the accumulation of toxic substances or a deficiency in critical compounds necessary for normal bodily functions. For example, in metabolic disorders such as phenylketonuria (PKU), the body lacks the enzyme needed to metabolize the amino acid phenylalanine, resulting in toxic buildup that can cause serious health issues.

Genetic defects may contribute to metabolic disorders, but they are not the defining characteristic—rather, they are a cause. Developmental delays and neurological disorders can be outcomes or associated conditions that arise from metabolic errors, but the core issue lies in the impaired biochemical processes themselves. Thus, the focus on impaired processing of substances encapsulates the essence of what defines metabolic errors, making it the correct answer.