Aplasia

Aplasia (/əˈpleɪʒə/ ^ⓘ; from Greek a, "not", "no" + plasis, "formation") is a birth defect where an organ or tissue is wholly or largely absent. It is caused by a defect in a developmental process.

Aplastic anemia is the failure of the body to produce blood cells. It may occur at any time, and has multiple causes.

Pure red cell aplasia (PRCA) is caused by the selective destruction or inhibition of erythroid progenitor or precursor cells. It is characterized by anemia and reticulocytopenia and can be chronic or acute. Diamond–Blackfan anemia is a type of PRCA that occurs at birth. PRCA can be acquired as a primary disorder or as a result of another disorder. Immunosuppressive drugs, particularly corticosteroids, will usually result in a temporary or permanent remission. The final outcome is primarily determined by the underlying disorder.

Aplasia cutis congenita is a condition in which some or large portions of the skin is missing at birth. The disorder is most commonly seen on the scalp, often as a solitary lesion without other abnormalities. The condition may be caused by epidermolysis bullosa, specific teratogens, or intrauterine infections, or it may be caused by chromosomal abnormalities, ectodermal dysplasias, or other malformation syndromes.

Radial aplasia is a condition in which the radius does not form. The radius runs from the elbow to the wrist, where the thumb is located. With radial aplasia, the arm can look misshapen and bent. The thumb could also be absent or shorter than usual.

Sertoli cell-only syndrome (SCOS), also known as germ cell aplasia, is defined by azoospermia where the testicular seminiferous tubules are lined solely with sertoli cells. Sertoli cells contribute to the formation of the blood-testis barrier and aid in sperm generation. These cells respond to follicle-stimulating hormone, which is secreted by the hypothalamus and aids in spermatogenesis. Men often learn they have Sertoli cell-only syndrome between the ages of 20 and 40 when they are checked for infertility and found to produce no sperm. Other signs and symptoms are uncommon, yet in some cases, an underlying cause of SCO syndrome, such as Klinefelter syndrome, may produce other symptoms.

Most cases of SCO syndrome are idiopathic, however, causes may include deletions of genetic material on Y-chromosome regions, particularly the azoospermia factor area. Other factors include chemical or toxin exposure, previous exposure to radiation therapy, and a history of severe trauma. A testicular biopsy confirms the diagnosis of SCO syndrome. Although there is no effective treatment at the moment, assisted reproductive technology may help some men with SCO syndrome reproduce.

Pulmonary aplasia is a rare congenital pathology characterized by the unilateral or bilateral absence of lung tissue. It is distinct from pulmonary agenesis, which, while similar, has a short-blind ending bronchus in aplasia. Because bilateral pulmonary aplasia is not feasible, it is usually unilateral. It is frequently associated with other congenital abnormalities, primarily cardiovascular, and has been shown to occur with the VACTERL syndrome.^{[citation needed]}