Definition of Albinism, oculocutaneous

Albinism, oculocutaneous: An hereditary disorder characterized by deficiency of the pigment melanin in the eyes, skin and hair. The lack of eye pigment causes photophobia (sensitivity to light), nystagmus, and decreased visual acuity.
Oculocutaneous albinism is conventionally classified as to whether it is tyrosinase-negative or tyrosinase-positive. In the tyrosinase-negative class, there is absence of the enzyme tyrosinase. In the tyrosinase-positive class, tyrosinase is present but it cannot enter pigment cells to do its job and make melanin. There are a number of specific types of oculocutaneous albinism, all of which are inherited in an autosomal recessive manner:

Type IA is characterized by absence of tyrosinase with complete absence of melanin, marked photophobia, and nystagmus. It is due to mutation of the tyrosinase gene (TYR) on chromosome 11q.
Type IB has reduced activity of tyrosinase. It has been called yellow albinism. The child looks "dead white" at birth and has the usual eye problems, but soon develops normal skin pigmentation and yellow hair.
Type II has normal tyrosinase activity. It is the most common type of oculocutaneous albinism. The hair darkens and freckles and nevi (moles) develop normally on the skin. The disorder is due to mutation of the oculocutaneous albinism gene (OCA2) on chromosome 15q.
Type III is characterized by absence of tyrosinase with the presence of pigmentation of the iris in the first decade of life. It is due to mutation of the tyrosine-related protein-1 gene (TYRP1) on chromosome 9p.
Type IV is characterized by normal tyrosinase and is due to mutation of the MATP gene on chromosome 5p. MATP stands for membrane-associated transporter protein.

Oculocutaneous albinism is also a feature of certain other genetic conditions including the Hermansky-Pudlak syndrome and Chediak-Higashi syndrome.

Definition of ADAMTS2

ADAMTS2: A gene that encodes a metalloproteinase enzyme. This enzyme is responsible for processing type I, type II, and type V procollagen proteins. Procollagens are the precursors of collagens, the proteins that add strength and support to many body tissues. Specifically, this enzyme clips a short chain of amino acids off of one end of the procollagen. The clipping step is necessary for proper assembly and function of collagen molecules.
Mutations in the ADAMTS2 gene have been identified in patients with Ehlers-Danlos syndrome, dermatosparaxis type. These mutations greatly reduce the production of the enzyme made by ADAMTS2. Procollagen cannot be processed correctly without this enzyme. As a result, type I collagen fibrils are not assembled properly; they appear ribbon-like and disorganized under the microscope. Cross-links, or chemical interactions, between collagen fibrils are also affected. These defects weaken connective tissue, particularly in the skin, which causes the symptoms of the disorder.
The ADAMTS2 gene is located on the long (q) arm of chromosome 5 at the end (terminal) of the arm. ADAMTS2 stands for A disintegrin-like and metalloprotease with thrombospondin type 1 motif, 2.

Definition of Acoustic neurofibromatosis

Acoustic neurofibromatosis: See: Neurofibromatosis type 2.

Definition of Achondrogenesis-hypochondrogenesis, type II

Achondrogenesis-hypochondrogenesis, type II: See: Achondrogenesis type II.

Definition of ACG2

ACG2: Achondrogenesis type II.

Definition of ABO blood group

ABO blood group:
The major human blood group system. A person's ABO type depends upon the presence of absence of two genes --the A and B genes. These genes are encoded on chromosome 9 (in band 9q34.1). They determine part of the configuration of the red blood cell surface.
A person can be A, B, AB, or O. If a person has two A genes, their
red blood cells are type A. If a person has two B genes, their red
cells are type B. If the person has one A and one B gene, their red
cells are type AB. If the person has neither the A nor B gene, they
are type O.
The situation with antibodies in blood plasma is just the opposite. Someone with type A red cells has anti-B antibodies (antibodies directed against type B red cells) in their blood plasma. Someone with type B red cells has anti-A antibodies in
plasma. Someone who is type O has both anti-A and anti-B antibodies
in plasma. And someone who is type AB has neither anti-A nor anti-B
antibodies in plasma.
It is most important to determine the ABO status of both donor and recipient in transplants and transfusions by typing and cross-matching. ABO incompatibility in such procedures can be a disaster.
The first
recorded blood transfusion may have taken place in 1492 when Pope
Innocent VIII, laying in a coma, was given the blood of 3 young men.
Blood typing and crossmatching was not done. The pope died, as did
the 3 donors.
In 1901 a Viennese pathologist named Karl Landsteiner (1868-1943)
published an article entitled "On Agglutination Phenomena of Normal
Human Blood," in which he observed that, when blood was transfused
from one human to another, the body often clumped the transfused
blood cells and rejected the transfusion, sometimes going in shock.
In 1909 Landsteiner classified red blood cells into types A, B, AB
and O and showed that the body rejects transfusions of a different
blood type. After moving to the Rockefeller Institute in New York,
Landsteiner received the Nobel Prize in 1930 for his pioneering
research in immunology and blood grouping.