Question

In the United States, a major cause of death of babies during the first year is sudden infant death syndrome (SIDS). One study showed a strong corrclation for an increased risk of SIDS with a prolonged \(\mathrm{QT}\) interval in their electrocardiograms. In one child, a gene associated with the Long \(\mathrm{QT}\) syndrome had a substitution of AAC for TCC. This gene codes for a protein associated with the sodium channel. The mutation was detected by single-strand conformation polymorphism \((\mathrm{SSCP})\) Which of the following statement(s) about SSCP is/are correct? A. The electrophoretic mobility on polyacrylamide gel of small, single- stranded DNA during the SSCP technique depends partly on the secondary conformation. B. There must be a restriction endonudease site in the region studied for SSCP to work. C. Radiolabeling is not used in this technique. D. It is not necessary to know the sequence of the DNA to be studied. E. All of the above.

Short answer

A. The electrophoretic mobility on a polyacrylamide gel of small, single-stranded DNA during the SSCP technique depends partly on the secondary conformation. B. There must be a restriction endonuclease site in the region studied for SSCP to work. C. Radiolabeling is not used in this technique. D. It is not necessary to know the sequence of the DNA to be studied. Answer: A and D

Step-by-step solution

Statement A

The electrophoretic mobility on a polyacrylamide gel of small, single-stranded DNA during the SSCP technique depends partly on the secondary conformation. This statement is true. SSCP is an electrophoresis-based technique that separates single-stranded DNA molecules according to their secondary conformation, which influences their mobility on the gel.

Statement B

There must be a restriction endonuclease site in the region studied for SSCP to work. This statement is false. SSCP doesn't require the presence of a restriction endonuclease site to analyze and detect mutations.

Statement C

Radiolabeling is not used in this technique. This statement is false. Radiolabeling can be used in SSCP, although other labeling techniques such as fluorescent labeling can also be applied.

Statement D

It is not necessary to know the sequence of the DNA to be studied. This statement is true. SSCP can be used to detect mutations without prior knowledge of the DNA sequence, making it a valuable screening tool. Now let's look at the answer choices: A. True B. False C. False D. True E. All of the above. Since only statements A and D are true, the correct answer is not E. So, the correct statement(s) about SSCP is/are A and D.

Key concepts

Sudden Infant Death Syndrome (SIDS)

Sudden Infant Death Syndrome (SIDS) refers to the unexplained death, usually during sleep, of a seemingly healthy baby less than a year old. Its cause remains unknown, but research has identified several risk factors such as sleep environment, genetic makeup, and physical factors like brain abnormalities.

One noteworthy area of SIDS research focuses on genetic variables that may predispose a child to SIDS, such as mutations affecting heart function. For instance, mutations that lead to Long QT Syndrome, which affects heart rhythm, have been linked to an increased SIDS risk. Understanding the genetic underpinnings of SIDS is essential for developing preventive strategies and potentially identifying at-risk infants.

Long QT Syndrome

Long QT Syndrome (LQTS) is a genetic condition that can cause sudden, uncontrollable, and dangerous arrhythmias (heart rhythms) in response to exercise or stress. Individuals with LQTS have an elongated QT interval, which can be seen on an electrocardiogram (ECG). This extended interval indicates that the heart's electrical system takes longer than normal to recharge between beats.

In relation to SIDS, certain mutations associated with LQTS may increase the risk of unexpected cardiac arrest in infants. Diagnosing such mutations early can lead to interventions that may reduce the risk of life-threatening events, emphasizing the importance of genetic analyses in newborns and infants with suspicious clinical history.

DNA Electrophoresis

DNA Electrophoresis is a laboratory technique used to separate DNA fragments according to their size. This procedure involves applying an electric current to move DNA molecules through a gel matrix. Smaller fragments move faster and go further than larger ones, permitting the size-based separation of DNA.

This technique is fundamental in genetic analyses, including mutation detection and diagnosis of genetic diseases like LQTS, as it can reveal differences in DNA fragment sizes caused by mutations. Additionally, advanced forms of electrophoresis, such as single-strand conformation polymorphism (SSCP), can detect conformational changes in DNA that denote mutations without prior information of DNA sequence.

Mutation Detection

Mutation Detection is pivotal in genetic research and diagnostic medicine. It involves identifying alterations in the DNA sequence that may lead to disease. Detecting mutations can be challenging, but there are techniques like SSCP that enable researchers and clinicians to find these genetic changes reliably.

SSCP, an electrophoresis-based technique, allows for the identification of DNA sequence variations due to their impact on the shape and, consequently, the movement of single-stranded DNA through a gel. It doesn't always require knowledge of the specific sequence being studied, making it a versatile method for screening an array of genetic disorders including those associated with SIDS and LQTS. Notably, SSCP can even detect single-nucleotide polymorphisms (SNPs), which are the most common type of genetic variation among people.