Types

• missing (aplasia
  Aplasia
  Aplasia is defined in general as "defective development or congenital absence of an organ or tissue." In the field of hematology, the term refers to "incomplete, retarded, or defective development, or cessation of the usual regenerative process."-Examples:*Acquired pure red cell aplasia*Aplasia...
  
  ) limbs
  Limb (anatomy)
  A limb is a jointed, or prehensile , appendage of the human or other animal body....
  
  : amelia
  Amelia (birth defect)
  Amelia is the birth defect of lacking one or more limbs. It can also result in a shrunken or deformed limb. For example, a child might be born without an elbow or forearm. The term may be modified to indicate the number of legs or arms missing at birth, such as tetra-amelia for the absence of all...
  
  , oligodactyly
  Oligodactyly
  Oligodactyly in humans is "the presence of fewer than five fingers or toes on a hand or foot". It is quite often incorrectly called hypodactyly, but the Greek prefixes hypo- and hyper- are used for continuous scales...
  
  , congenital amputation
  Congenital amputation
  Congenital amputation is a congenital disorder that can be caused by fibrous bands of the amnion that constrict foetal limbs to such an extent that they fall off due to missing blood supply. The child is born without one or more limbs or without parts of limbs .-Causes:Congenital amputations can...
  
  
• malformation of limbs: ectrodactyly
  Ectrodactyly
  Ectrodactyly, sometimes referred to as the “Lobster-Claw Syndrome” involves the deficiency or absence of one or more central digits of the hand or foot and is also known as split hand/split foot malformation...
  
  , phocomelia
  Phocomelia
  Phocomelia is an extremely rare congenital disorder involving the limbs . Étienne Geoffroy Saint-Hilaire coined the term in 1836....
  
  , meromelia
  Meromelia
  Meromelia is a birth defect characterized by the lacking of a part, but not all, of one or more limbs with the presence of a hand or foot. It results in a shrunken and deformed extremity...
  
  , syndactyly, brachydactyly
  Brachydactyly
  Brachydactyly , is a medical term which literally means "shortness of the fingers and toes" . The shortness is relative to the length of other long bones and other parts of the body. Brachydactyly is an inherited, usually dominant trait...
  
  , clubfoot
• too many limbs: polymelia
  Polymelia
  Polymelia is a birth defect involving limbs , in which the affected individual has more than the usual number of limbs. In humans and most land-dwelling animals, this means having five or more limbs...
  
  , polydactyly
  Polydactyly
  Polydactyly or polydactylism , also known as hyperdactyly, is a congenital physical anomaly in humans, dogs, and cats having supernumerary fingers or toes....
  
  , polysyndactyly

Causes

• inheritance
  Inheritance
  Inheritance is the practice of passing on property, titles, debts, rights and obligations upon the death of an individual. It has long played an important role in human societies...
  
   of abnormal genes
  Gênes
  Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
  
  , e.g. polydactyly
  Polydactyly
  Polydactyly or polydactylism , also known as hyperdactyly, is a congenital physical anomaly in humans, dogs, and cats having supernumerary fingers or toes....
  
  , ectrodactyly
  Ectrodactyly
  Ectrodactyly, sometimes referred to as the “Lobster-Claw Syndrome” involves the deficiency or absence of one or more central digits of the hand or foot and is also known as split hand/split foot malformation...
  
   or brachydactyly
  Brachydactyly
  Brachydactyly , is a medical term which literally means "shortness of the fingers and toes" . The shortness is relative to the length of other long bones and other parts of the body. Brachydactyly is an inherited, usually dominant trait...
  
  , symptoms of deformed limbs then often occur in combination with other symptoms (syndrome
  Syndrome
  In medicine and psychology, a syndrome is the association of several clinically recognizable features, signs , symptoms , phenomena or characteristics that often occur together, so that the presence of one or more features alerts the physician to the possible presence of the others...
  
  s)
• external causes during pregnancy (thus not inherited), e.g. via amniotic band syndrome
  Amniotic band syndrome
  Amniotic band syndrome is a congenital disorder caused by entrapment of fetal parts in fibrous amniotic bands while in utero.-Epidemiology:Amniotic banding affects approximately 1 in 1,200 live births...
  
  
• teratogenic drugs (e.g. thalidomide
  Thalidomide
  Thalidomide was introduced as a sedative drug in the late 1950s that was typically used to cure morning sickness. In 1961, it was withdrawn due to teratogenicity and neuropathy. There is now a growing clinical interest in thalidomide, and it is introduced as an immunomodulatory agent used...
  
  , which causes phocomelia
  Phocomelia
  Phocomelia is an extremely rare congenital disorder involving the limbs . Étienne Geoffroy Saint-Hilaire coined the term in 1836....
  
  ) or environmental chemicals
• ionizing radiation (nuclear weapon
  Nuclear weapon
  A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...
  
  s, radioiodine, radiation therapy
  Radiation therapy
  Radiation therapy , radiation oncology, or radiotherapy , sometimes abbreviated to XRT or DXT, is the medical use of ionizing radiation, generally as part of cancer treatment to control malignant cells.Radiation therapy is commonly applied to the cancerous tumor because of its ability to control...
  
  )
• infections
• metabolic imbalance