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Examples of Genetic Disorders
Genetic disorders can be organized not only by their underlying cause but also by the body systems or processes they most affect. Below are representative examples presented in subgroups, each with a short definition followed by specific conditions.
Monogenic Disorders
Metabolic disorders are caused by defects in enzymes or metabolic pathways. These conditions often require strict dietary or metabolic management to prevent toxic buildup of substances in the body.
- Phenylketonuria (PKU). An inherited disorder in which phenylalanine accumulates, leading to neurological damage without dietary restriction.
- Maple syrup urine disease. Defect in breaking down branched-chain amino acids; urine has a sweet odor.
- Galactosemia. Inability to metabolize galactose properly, which can damage the liver and nervous system if untreated.
- Tay–Sachs disease. Deficiency of beta-hexosaminidase causes progressive destruction of neurons.
Neurological disorders primarily affect the brain and nervous system. They often present with developmental delay, cognitive decline, or movement disorders.
- Huntington’s disease. Progressive degeneration of neurons in the brain, leading to movement, cognitive, and psychiatric symptoms.
- Fragile X syndrome. Caused by alterations in the X chromosome; leads to characteristic developmental and behavioral features.
Hematologic (blood) disorders affect red blood cells, hemoglobin, or clotting factors. They often present with anemia, pain crises, or bleeding tendencies.
- Sickle-cell anemia. Red blood cells become sickle shaped, causing pain crises, anemia, and organ damage.
- Beta-thalassemia. Reduced hemoglobin production results in varying degrees of anemia.
- Hemophilia. Blood clotting factors are deficient, leading to prolonged bleeding.
Connective tissue and musculoskeletal disorders affect bone, muscle, and connective tissue. They can alter growth patterns, body structure, or muscular function.
- Achondroplasia. Impairs growth of long bones, affecting the spine and skull.
- Marfan syndrome. Connective tissue disorder; individuals are often tall and thin with long limbs, and cardiovascular issues are common.
- Duchenne muscular dystrophy. Progressive weakening of skeletal and cardiac muscles over time.
Chromosomal Disorders
Trisomies occur when individuals inherit an extra chromosome, leading to characteristic physical and developmental features.
- Down syndrome (Trisomy 21). Extra chromosome 21; associated with distinctive features and intellectual disability.
- Edwards syndrome (Trisomy 18). Extra chromosome 18; severe congenital anomalies.
- Patau syndrome (Trisomy 13). Extra chromosome 13; multiple congenital anomalies, often severe.
Sex chromosome syndromes arise from missing or extra sex chromosomes, affecting sexual development and physical traits.
- Klinefelter syndrome (47,XXY). Males with an extra X chromosome; tall stature and infertility are common.
- Triple X syndrome (47,XXX). Females with an extra X chromosome; often mild features.
- Turner syndrome (Monosomy X). Females missing one X chromosome; short stature and characteristic features such as a webbed neck.
Deletion syndromes occur when parts of a chromosome are missing, often causing distinct developmental and clinical features.
- Cri du chat syndrome. Deletion on chromosome 5; infants have a high-pitched “cat-like” cry.
- Prader–Willi syndrome. Deletion on chromosome 15 from the paternal copy; associated with hypotonia and obesity.
- Angelman syndrome. Disruption of the maternal UBE3A gene on chromosome 15; associated with seizures and developmental delay.
- DiGeorge syndrome. Deletion on chromosome 22; linked to congenital heart disease and immune dysfunction.
- Wolf–Hirschhorn syndrome. Deletion on chromosome 4; distinctive facial features and intellectual disability.
- WAGR syndrome. Deletion on chromosome 11; associated with Wilms tumor, aniridia, and developmental delay.
Translocation disorders result from exchange of material between chromosomes, sometimes creating cancer-causing fusion genes.
- Philadelphia chromosome. Reciprocal translocation between chromosomes 9 and 22, producing a shortened chromosome 22. Commonly associated with chronic myelogenous leukemia (CML).
Select one disorder from the lists above. In 1–2 paragraphs, summarize:
- Inheritance pattern and causal variant or chromosomal change
- Key clinical features and typical age of onset
- Diagnostic approach
- Prognosis and current treatment or management
Compare your selection with a second disorder that differs in category or mechanism. Highlight at least two similarities and two differences.
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