If the number of nucleotides in a gene is changed by insertion or deletion, and if the number of bases added or deleted is not a multiple of 3, the reading frame of the mes-sage is changed.

Frameshift mutation

When a large segment of DNA is deleted, the coding region of a gene may be entirely removed, in which case the protein product is absent.

Large deletions

Inherited neurodegen-erative disease caused by expansion of a CAG repeat within the coding sequence of the gene, IT15, that codes for the protein huntingtin.

Huntington disease

This genetic disorder is due to expansion of a CGG repeat in a noncoding region immediately adjacent to the FMR1 gene on the X chromosome.

Fragile X syndrome

The most common form of autosomal muscular dystrophy caused by ex-pansion of a CTG repeat in the 3'-untranslated region of the MD gene.

Myotonic dystrophy

A single gene defect can have several consequences. Select what best describes the illustration.

Failure to complete a metabolic pathway

A single gene defect can have several consequences. Select what best describes the illustration.

Accumulation of unmetabolized substrate

A single gene defect can have several consequences. Select what best describes the illustration.

Storage of an intermediary metabolite

In this situation, a mutant gene codes for an abnormal protein.

Formation of an abnormal end-product

Disorders characterized by the development of multiple neurofibromas, which are benign tumors of peripheral nerves of Schwann cell origin

Neurofibromatosis

An autosomal dominant disorder characterized by high levels of LDLs in the blood, and deposition of cholesterol in arteries, tendons, and skin.

Familial hypercholesterolemia

Virtually all lysosomal storage diseases result from mutations in genes that encode lysosomal hydrolases.

True

Characterized by accumulation of glucosylceramide, primarily in macrophage lysosomes.

Gaucher disease

Catastrophic infantile variant of a class of lyso-somal storage diseases known as the GM2gangliosidoses, in which this ganglioside is deposited in neurons of the CNS, owing to a failure of lysosomal degradation

Tay-Sachs disease

Refers to lipidoses that are characterized by the lysosomal storage of sphingomyelin in macrophages of many organs, in hepatocytes, and in the brain.

Niemann-Pick disease

An assortment of lysosomal stor-age diseases characterized by accumulation of glycosaminoglycans (mucopolysaccharides) in many organs.

Mucopolysaccharidoses

A group at least 10 distinct inherited disorders characterized by glycogen accumulation, principally in the liver, skele-tal muscle, and heart.

Glycogenoses

An autosomal reces-sive deficiency of the hepatic enzyme phenylalanine hydroxylase. The disorder is characterized by high levels of circulating phenylalanine, leading to progressive mental deterioration in the first few years of life.

Phenylketonuria

Autosomal recessive inborn error of tyrosine catabolism that manifests as acute liver disease in early infancy or as a more chronic disease of the liver, kidneys, and brain in children.

Tyrosinemia

Autosomal recessive deficiency of hepatic and re-nal homogentisic acid oxidase. It features excretion of homogentisic acid in the urine, generalized pigmentation and arthritis.

Alkaptonuria

Heterogeneous group of at least 10 inherited disor-ders in which absent or reduced biosynthesis of melanin causes hy-popigmentation.

Albinism

Expression of a trait only in the female, since the hemizygous state in the male precludes a dis-tinction between dominant and recessive inheritance.

X-Linked dominant

Heterozygous females do not have clinical disease. Sons of women who are carriers have a 50% chance of inher-iting the disease; daughters are not symptomatic. However, 50% of daughters will also be carriers.

X-Linked recessive

X-linked recessive disorder of blood clotting that re-sults in spontaneous bleeding, particularly into joints, muscles, and in-ternal organs.

Hemophilia A

The most common form of inherited mental retar-dation and is caused by expansion of a CGG repeat at the Xq27 fragile site.

Fragile X syndrome

Deficiency of lysosomal a-galactosidase A

Fabry disease

The observation that the phenotype associ-ated with some genes differs, depending on whether the allele is inher-ited from the mother or the father.

Genetic imprinting

Mitochondrial proteins are encoded only by mitochondrial genes.

False

Most mitochondrial respiratory chain proteins are encoded by nuclear genes.

True

All vertebrate mitochondria are in-herited from the mother via the ovum.

True

Describes a process by which a disease results from the effects of a number of abnormal genes and environmental factors.

Multifactorial inheritance

Involves isolating and purifying nucleic acids from clinical samples, using methods that disrupt cells, remove proteins and contaminants, and recover analyzable nucleic acid, which is essential for effective pathogen detection.

Nucleic acid extraction

Highly sensitive diagnostic tool that amplifies specific target regions of nucleic acid from complex mixtures, allowing for rapid and specific detection of pathogens, and can be used for both DNA and RNA analysis

Polymerase chain reaction

Allows for the amplification and detection of RNA molecules by first converting them into complementary DNA (cDNA) using the enzyme reverse transcriptase, and then using PCR to amplify the cDNA for analysis.

Reverse transcription PCR

Used to determine the order of nucleic acid bases in a gene, enabling the detection and characterization of pathogens with PCR-based sequencing.

Genome sequencing

Culture-independent applications of HTS for investigating the complete viral and microbial genetic composition (microbiome) of samples

Metagenomics

What is the recommended timing for prenatal genetic testing?

First trimester