Hypoplasia (from Ancient Greek ὑπo- (hypo-) 'under' and πλάσις (plasis) 'formation'; adjective formhypoplastic) is underdevelopment or incomplete development of atissue ororgan.^[1] Although the term is not always used precisely, it properly refers to an inadequate or below-normal number of cells.^[2] Hypoplasia is similar toaplasia, but less severe. It is technicallynot the opposite ofhyperplasia (too many cells). Hypoplasia is acongenital condition, while hyperplasia generally refers to excessivecell growth later in life. (Atrophy, the wasting away of already existing cells, is technically the direct opposite of both hyperplasia andhypertrophy.)

Hypoplasia can be present in any tissue or organ. It is descriptive of manymedical conditions, including underdevelopment of organs such as:

• Breasts duringpuberty
• Testes inKlinefelter's syndrome
• Ovaries inFanconi anemia,gonadal dysgenesis,trisomy X
• Thymus inDiGeorge syndrome
• Labia majora inpopliteal pterygium syndrome
• Corpus callosum, connecting the two sides of the brain, inagenesis of the corpus callosum
• Cerebellum caused by mutation in thereelin gene
• Tooth caused byoral pathology, such asTurner's hypoplasia
• Chambers of theheart inhypoplastic left heart syndrome andhypoplastic right heart syndrome
• Optic nerve inoptic nerve hypoplasia
• Sacrum insacral agenesis
• Facial muscle inasymmetric crying facies
• Thumb frombirth
• Lungs, often as a result ofoligohydramnios during gestation or the existence ofcongenital diaphragmatic hernia
• Small bowel incoeliac disease
• Fingers andears inharlequin-type ichthyosis
• Mandible incongenital hypothyroidism

• Atrophy, when an existing part wastes away
• List of biological development disorders

• Medical terminology
• Anatomical pathology

• Articles with short description
• Short description is different from Wikidata