Aplasia

Aplasia is the failure of an organ or tissue to develop or to form normally. It can be congenital (present at birth) or acquired later in life due to injury, disease, or environmental factors. Aplasia is distinguished from hypoplasia, which is underdevelopment, and from atrophy, which is the shrinking or loss of tissue after it has formed.

The most clinically significant use of the term is bone marrow aplasia, or aplastic anemia, in which the bone marrow becomes hypocellular and fails to produce adequate numbers of red blood cells, white blood cells, and platelets. Aplasia can also refer to failure or absence of development in other tissues or organs, such as gonads or glands, though such uses are less common in routine clinical language.

Causes of aplasia can be congenital or acquired. Congenital aplasia arises from genetic mutations that disrupt normal development. Acquired aplasia results from factors that damage or suppress tissue formation, including radiation, chemotherapy, toxins (for example benzene), autoimmune processes, or certain infections. In some contexts, aplasia may be part of broader developmental syndromes or may reflect complete absence of a structure (true aplasia) or a severely underdeveloped one (hypoplasia with minimal tissue).

Diagnosis typically relies on clinical presentation and laboratory findings. In bone marrow aplasia, blood counts show pancytopenia, and a bone marrow biopsy reveals marked cellularity loss. Evaluation excludes other causes of cytopenias, such as nutritional deficiencies or malignancy.

Treatment depends on cause and severity and may include immunosuppressive therapy, hematopoietic stem cell transplantation, and supportive care (transfusions, antibiotics, growth factors) aimed at preventing complications and restoring hematopoiesis.

See also hypoplasia, atrophy, pancytopenia, bone marrow failure.