A mutant or epigenetically altered stem cell may replace the other nearby stem cells by natural selection. Thus, a patch of abnormal tissue may arise. The figure in this section includes a photo of a freshly resected and lengthwise-opened segment of the colon showing a colon cancer and four polyps. Below the photo, there is a schematic diagram of how a large patch of mutant or epigenetically altered cells may have formed, shown by the large area in yellow in the diagram. Within this first large patch in the diagram (a large clone of cells), a second such mutation or epigenetic alteration may occur so that a given stem cell acquires an advantage compared to other stem cells within the patch, and this altered stem cell may expand clonally forming a secondary patch, or sub-clone, within the original patch. This is indicated in the diagram by four smaller patches of different colors within the large yellow original area. Within these new patches (sub-clones), the process may be repeated multiple times, indicated by the still smaller patches within the four secondary patches (with still different colors in the diagram) which clonally expand, until stem cells arise that generate either small polyps or else a malignant neoplasm (cancer).In the photo, an apparent field defect in this segment of a colon has generated four polyps (labeled with the size of the polyps, 6mm, 5mm, and two of 3mm, and a cancer about 3 cm across in its longest dimension).
Diastrophic dysplasia is an autosomal recessive dysplasia which affects cartilage and bone development. ("Diastrophism" is a general word referring to a twisting.) Diastrophic dysplasia is due to mutations in the SLC26A2 gene. Affected individuals have short stature with very short arms and legs and joint problems that restrict mobility. Signs and symptoms
This condition is also characterized by an unusual clubfoot with twisting of the metatarsals, inward- and upward-turning foot, tarsus varus and inversion adducted appearances. Furthermore, they classically present with scoliosis (progressive curvature of the spine) and unusually positioned thumbs (hitchhikers thumbs). About half of infants with diastrophic dysplasia are born with an opening in the roof of the mouth called a cleft palate. Swelling of the external ears is also common in newborns and can lead to thickened, deformed ears. The signs and symptoms of diastrophic dysplasia are similar to those of another skeletal disorder called atelosteogenesis, type 2; however diastrophic dysplasia tends to be less severe. Genetic
It is one of a spectrum of skeletal disorders caused by mutations in the SLC26A2 gene. The protein encoded by this gene is essential for the normal development of cartilage and for its conversion to bone. Cartilage is a tough, flexible tissue that makes up much of the skeleton during early development. Most cartilage is later converted to bone, but in adulthood this tissue continues to cover and protect the ends of bones and is present in the nose and external ears.