Dysmelia can be caused by

- inheritance of abnormal genes, e.g. polydactyly, ectrodactyly or brachydactyly, symptoms of deformed limbs then often occur in combination with other symptoms (syndromes)

- external causes during pregnancy (thus not inherited), e.g. via amniotic band syndrome

- teratogenic drugs (e.g. thalidomide, which causes phocomelia) or environmental chemicals

- ionizing radiation (nuclear weapons, radioiodine, radiation therapy)

- infections

- metabolic imbalance

Dysmelia can refer to

- missing (aplasia) limbs: amelia, oligodactyly, congenital amputation e.g. Tibial or Radial aplasia

- malformation of limbs: shortening (micromelia, rhizomelia or mesomelia), ectrodactyly, phocomelia, meromelia, syndactyly, brachydactyly, club foot

- too many limbs: polymelia, polydactyly, polysyndactyly

- others: Tetraamelia, hemimelia, Symbrachydactyly

According to the National Human Genome Research Institute, Poland syndrome affects males three times as often as females and affects the right side of the body twice as often as the left. The incidence is estimated to range from one in 7,000 to one in 100,000 live births.

The cause of Poland syndrome is unknown. However, an interruption of the embryonic blood supply to the arteries that lie under the collarbone (subclavian arteries) at about the 46th day of embryonic development is the prevailing theory.

The subclavian arteries normally supply blood to embryonic tissues that give rise to the chest wall and hand. Variations in the site and extent of the disruption may explain the range of signs and symptoms that occur in Poland syndrome. Abnormality of an embryonic structure called the apical ectodermal ridge, which helps direct early limb development, may also be involved in this disorder.

A squitten is a cat with unusually short forelegs and/or unusually long hind legs that resembles a squirrel. It is an example of a cat body type genetic mutation. The word is a portmanteau of squirrel and kitten.

The term kangaroo cat is also, rarely, used; this derives from a 1953 specimen known as the Stalingrad Kangaroo Cat.

Life expectancy for individuals with hypochondroplasia is normal; the maximum height is about 147 cm or 4.8 ft.

The term squitten is generally used to refer to cats with the condition radial hypoplasia (underdeveloped radius bones) or foreleg micromelia (small forelegs) and related conditions known as radial aplasia (absent radius bones), radial agenesis (failure of radius bones to form) that produces stunted forelegs. The mutation sometimes occurs in the random-breeding population, particularly in inbred populations where recessive genes may be exhibited. Such cats have also been called twisty cats; In the late 1990s, several were deliberately bred at Karma Farms, a horse farm and cattery in Marshall, Texas, resulting in a public outcry against the operators of the farm.

Radial hypoplasia is related to one form of polydactyly, sometimes called patty feet or hamburger feet by cat lovers to distinguish them from thumb cat polydactyls. Ordinary mitten cat polydactyls are not affected.

Cats with radial hypoplasia or similar mutations often sit on their rump with their forelegs unable to touch the floor; this gives them a resemblance to a squirrel or kangaroo. This raises special care considerations for owners of affected cats. Kittens may be unable to knead effectively with their short forelegs; kneading is required to stimulate milk flow in the mother. The short or twisted forelegs cause mobility problems and such cats may adapt by using their hindlegs in a hopping gait.

A corresponding condition affecting the hind legs is called femoral hypoplasia and has only been reported three times in cats.

Typical characteristics of a squitten are short forelegs, with a short radius and ulna which may be twisted or absent, extra front toes, and normal-length hind legs.

In terms of cause this disorder is transmitted as an autosomal dominant trait affecting the "FGFR3" gene on chromosome 4p16.3, there is currently no cure for this condition.

Microlissencephaly is listed in Orphanet database as a rare disease. There is no much information available about the epidemiology of microlissencepahly in literature. A PhD thesis has estimated the prevalence of microlissencepahly in South–Eastern Hungary between July 1992 and June 2006 to be a case every 91,000 live births (0.11:10,000).

Microlissencephaly (MLIS) is a rare congenital brain disorder that combines severe microcephaly (small head) with lissencephaly (smooth brain surface due to absent sulci and gyri). Microlissencephaly is a heterogeneous disorder i.e. it has many different causes and a variable clinical course. Microlissencephaly is a malformation of cortical development (MCD) that occurs due to failure of neuronal migration between the third and fifth month of gestation as well as stem cell population abnormalities. Numerous genes have been found to be associated with microlissencephaly, however, the pathophysiology is still not completely understood.

The combination of lissencephaly with severe congenital microcephaly is designated as microlissencephaly only when the cortex is abnormally thick. If such combination exists with a normal cortical thickness (2.5 to 3 mm), it is known as "microcephaly with simplified gyral pattern" (MSGP). Both MLIS and MSGP have a much more severe clinical course than microcephaly alone. They are inherited in autosomal recessive manner. Prior to 2000, the term “microlissencephaly” was used to designate both MLIS and MSGP.