Q.ELISA technique is based on the principles of antigen-antibody interaction. Can this techique be used in the molecular diagnosis of a genetic disorder, such as phenyketonuria?

No, ELISA cannot be used for the molecular diagnosis of phenylketonuria (PKU). Here is why.

ELISA detects the presence of a specific protein (antigen) or an antibody against it. It works on the principle of antigen-antibody interaction, meaning it identifies a gene product — a protein that is already made.

Phenylketonuria is a genetic disorder caused by a mutation in the DNA that codes for the enzyme phenylalanine hydroxylase. The defect is at the gene level, not at the level of a protein that is abnormally present or absent in a way ELISA can detect. In PKU, the enzyme is simply non-functional or missing, but ELISA cannot distinguish a normal enzyme from a defective one unless the defective protein has a different shape that a specific antibody can recognise — which is not the standard diagnostic approach. …

ELISA — short for Enzyme-Linked Immunosorbent Assay — is a laboratory technique that relies on the highly specific binding between an antigen and its corresponding antibody. In essence, it is a tool for detecting and measuring the presence of a particular protein (the antigen) in a sample, using an enzyme-linked antibody that produces a visible colour change. This makes ELISA extremely useful for diagnosing infectious diseases (like HIV or hepatitis) where the pathogen’s proteins or the body’s antibodies against them are present in blood.

Now, consider a genetic disorder such as phenylketonuria (PKU). PKU is caused by a mutation in the gene that codes for the enzyme phenylalanine hydroxylase. This mutation is a change in the DNA sequence — it is not a protein that circulates in the blood. The defective enzyme may be produced in reduced amounts or may be non-functional, but the core problem lies at the genetic level.

So, can ELISA be used for molecular diagnosis of PKU? The answer is no — not directly. Molecular diagnosis of a genetic disorder requires identifying the specific mutation in the DNA. Techniques like PCR (polymerase chain reaction) followed by DNA sequencing or restriction fragment length polymorphism (RFLP) analysis are used for that purpose. ELISA works with proteins, not DNA. …

Method — check what ELISA can physically detect vs what PKU actually is

ELISA detects a PROTEIN (antigen or antibody) — it needs the abnormal molecule to be PRESENT and DIFFERENT in a way an antibody can recognise.

PKU's defect is a MUTATED GENE causing a non-functional enzyme — the enzyme may still be structurally similar enough that no antibody distinguishes "faulty" from "normal" PAH protein. …