Hypoplasia

Underdevelopment or incomplete development of a tissue or organ. For example, there can be hypoplasia (underdevelopment) of the enamel of the teeth. Hypoplasia is less drastic than aplasia where there is no development at all.

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1. Underdevelopment of a tissue or organ, usually due to a deficiency in the number of cells. 2. Atrophy due to destruction of some of the elements and not merely to their general reduction in size. [hypo- + G. plasis, a molding]

- cartilage-hair h. [MIM*250250 & MIM*250460] a skeletal dysplasia prevalent among the Amish, characterized by short-limb dwarfism, sparse, light-colored hair, T-cell immunologic defect rendering them susceptible to infections, and radiographic findings of metaphyseal dysplasia. Autosomal recessive inheritance, the gene maps to 9p. SYN: McKusick metaphyseal dysplasia.

- enamel h. a developmental disturbance of teeth characterized by deficient or defective enamel matrix formation; may be hereditary, as in amelogenesis imperfecta, or acquired, as encountered in dental fluorosis, local infection, childhood fevers, and congenital syphilis.

- focal dermal h. [MIM*305600] inherited as an X-linked dominant with in utero lethality in males; characterized by linear areas of dermal atrophy or h., herniation of fat through the dermal defects, and papillomata of the mucus membranes or skin; may be associated with digital, ocular, and oral anomalies; mental retardation; and bony striations. SYN: Goltz syndrome.

- optic nerve h. congenitally small optic disk resulting from a reduced number of retinal ganglion cells and, therefore, a reduced number of axons; visual impairment may be marked. See de Morsier syndrome.

- renal h. an abnormally small kidney that is morphologically normal but has either a reduced number of nephrons or smaller nephrons.

- h. of right ventricle failure of development of the right ventricle resulting in its having little muscle and much connective tissue instead of the reverse.

- right ventricular h. SYN: parchment heart.

- thymic h. SYN: DiGeorge syndrome.

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hy·po·pla·sia -'plā-zh(ē-)ə n a condition of arrested development in which an organ or part remains below the normal size or in an immature state

hy·po·plas·tic -'plas-tik adj

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n.

underdevelopment of an organ or tissue. Dental hypoplasia is the defective formation of parts of a tooth due to illnesses such as measles or starvation while the tooth is being formed. It is marked by transverse lines of brown defective enamel, which define the date of the illness.

• hypoplastic adj.

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hy·po·pla·sia (hi″po-plaґzhə) [hypo- + -plasia] incomplete development or underdevelopment of an organ or tissue; it is less severe in degree than aplasia. hypoplastic adj