Abstract
The skeleton provides the framework and anchor points against which muscles, attached via tendons, can exert force. Three types of cells are involved in making bone: osteoblasts, osteoclasts, and cartilage. The human muscle system is made up of three types of muscle tissue: skeletal, cardiac, and smooth. The neonate period of life is the first 4 weeks after the birth of an infant. This chapter presents 11 genetic disorders that affect muscles, connective tissue, and newborns. These include achondroplasia, Charcot-Marie tooth syndrome, Duchenne Muscular Dystrophy, Ellis-Van Creveld syndrome, amyotrophic lateral sclerosis, Marfan syndrome, fibrodysplasia ossificans progressive, myotonic dystrophy, Angelman syndrome, Prader-Willi syndrome, fragile-X syndrome, and Waardenburg syndrome.
TopChapter Outline
17.1 Overview
17.2 Achondroplasia
17.3 Charcot-Marie-Tooth Syndrome
17.4 Duchenne Muscular Dystrophy
17.5 Ellis-Van Creveld Syndrome
17.6 Amyotrophic Lateral Sclerosis
17.7 Marfan Syndrome
17.8 Fibrodysplasia Ossificans Progressiva
17.9 Myotonic Dystrophy
17.10 Angelman Syndrome and Prader-Willi Syndrome
17.11 Fragile-X Syndrome
17.12 Waardenburg Syndrome
Chapter Summary
TopLearning Outcomes
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Identify each genetic disorder affecting each system
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Outline the symptoms of each disorder
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Explain the genetic basis of each disorder
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Summarize the current therapies available to treat each disorder
Top17.1 Overview
Humans have endoskeletons which are rigid internal body parts made up of bone that receive the applied force of muscles. The skeleton provides the framework and anchor points against which muscles, attached via tendons, can exert force (Figure 1). It is made up of 206 bones divided into 2 systems: a) axial skeleton with skull bones, 12 pairs of ribs, the sternum, and the 26 vertebrae; b) appendicular skeleton which is made up of the pectoral girdles (shoulders); pelvic girdle (hips) and pairs of arms, hands, legs and feet. Bones are complex organs that function in movement, providing support by anchoring muscles, protecting internal organs, storage of minerals particularly calcium and phosphorous, and blood cell production (white blood cells, red blood cells and platelets). There are two types of bone tissue: compact bone which is found in the shaft and at both ends of long bones. Compact bone is made up many thin, cylindrical, dense layers around interconnected canals for blood vessels and nerves and it resists mechanical shock. Spongy bone tissue has abundant air spaces but very firm and is found inside both ends and shaft of bone. Spongy tissue contains red bone marrow where blood cells are formed. It also contains yellow bone marrow which is largely fat but can be converted to red marrow in severe blood loss cases.
Figure 1. The structure and bones of the human skeleton
Three types of cells involved in making bone. 1) Osteoblasts: In the developing embryo cartilage models are first constructed, into which osteoblasts secrete organic substances which mineralize; cartilage then breaks down to form bone marrow cavities. Once osteoblasts are imprisoned by these secretions, they become osteocytes or mature living bone cells. In adults, large amounts of minerals and many osteocytes are removed and replaced routinely in a process called bone remodeling which adjusts bone strength and maintains calcium and phosphorous levels in the blood. 2) Osteoclasts secrete enzymes that digest bone in the routine bone remodeling activities in the body. 3) Cartilage are collagen fibres embedded in a rubbery matrix of protein and carbohydrate secreted by cells called chondrocytes. In the adult body cartilage is retained in the flexible parts of our skeleton (ears, nose, intervertebral discs, and windpipe). Physical exercise stresses bone such that the process of mineral deposition exceeds withdrawal—making the bones denser and stronger. With age, bones decline in mass where mineral deposits lag behind withdrawal making the bones hollow and brittle—a condition known as osteoporosis.