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

The inheritance of Impossible syndrome is suspected to be autosomal recessive, which means the affected gene is located on an autosome, and two copies of the gene - one from each parent - are required to have an infant with the disorder.

Genetic counseling for VWS involves discussion of disease transmission in the autosomal dominant manner and possibilities for penetrance and expression in offspring. Autosomal dominance means affected parents have a 50% chance of passing on their mutated "IRF6" allele to a their child. Furthermore, if a cleft patient has lip pits, he or she has a ten times greater risk of having a child with cleft lip with or without cleft palate than a cleft patient who does not have lip pits. Types of clefting between parents and affected children are significantly associated; however, different types of clefts may occur horizontally and vertically within the same pedigree. In cases where clefting is the only symptom, a complete family history must be taken to ensure the patient does not have non-syndromic clefting.

Type VII of radial polydactyly is associated with several syndromes:

Holt–Oram syndrome, Fanconi anemia (aplastic anemia by the age of 6), Townes–Brocks syndrome, and Greig cephalopolysyndactyly (also known to occur with ulnar polydactyly).

Three main support groups of this syndrome are the ASGA in Australia, The Association for Children with Genetic Disorders in Poland, and the Association of People of Genetic Disorders in Greece.

The syndromes associated with central polydactyly are:

Bardet–Biedl syndrome,

Meckel syndrome,

Pallister–Hall syndrome,

Legius syndrome,

Holt–Oram syndrome,

Also, central polydactyly can be associated with syndactyly and cleft hand.

Other syndromes including polydactyly include acrocallosal syndrome, basal cell nevus syndrome, Biemond syndrome, ectrodactyly-ectodermal dysplasias-cleft lip/palate syndrome, mirror hand deformity, Mohr syndrome, oral-facial-digital syndrome, Rubinstein-Taybi syndrome, short rib polydactyly, and VATER association.

It can also occur with a triphalangeal thumb.

Very few risk factors for choanal atresia have been identified. While causes are unknown, both genetic and environmental triggers are suspected. One study suggests that chemicals that act as endocrine disrupters may put an unborn infant at risk. A 2012 epidemiological study looked at atrazine, a commonly used herbicide in the U.S., and found that women who lived in counties in Texas with the highest levels of this chemical being used to treat agricultural crops were 80 times more likely to give birth to infants with choanal atresia or stenosis compared to women who lived in the counties with the lowest levels. Another epidemiological report in 2010 found even higher associations between increased incidents of choanal atresia and exposure to second-hand-smoke, coffee consumption, high maternal zinc and B-12 intake and exposure to anti-infective urinary tract medications.

In regard to the epidemiology of multicystic dysplasia kidney, the incidence of MCDK is estimated to be 1 in every 4,000 live births, making it rare in terms of the general population.

The Wassel classification is used to categorise radial polydactyly, based upon the most proximal level of skeletal duplication.

Synpolydactyly is a joint presentation of syndactyly (fusion of digits) and polydactyly (production of supernumerary digits). This is often a result of a mutation in the HOX D13 gene.

Types include:

Congenital limb deformities are congenital musculoskeletal disorders which primarily affect the upper and lower limbs.

An example is polydactyly.

Ectrodactyly can be caused by various changes to 7q. When 7q is altered by a deletion or a translocation ectrodactyly can sometimes be associated with hearing loss. Ectrodactyly, or Split hand/split foot malformation (SHFM) type 1 is the only form of split hand/ malformation associated with sensorineural hearing loss.

Triphalangeal thumb can occur in syndromes but it can also be isolated. The triphalangeal thumb can appear in combination with other malformations or syndromes.

Syndromes include:

- Holt-Oram syndrome

- Aase syndrome

- Blackfan-Diamond syndrome

- Townes-Brocks syndrome

Malformations include:

- Radial polydactyly

- Syndactyly

- Claw-like hand or foot

A large number of human gene defects can cause ectrodactyly. The most common mode of inheritance is autosomal dominant with reduced penetrance, while autosomal recessive and X-linked forms occur more rarely. Ectrodactyly can also be caused by a duplication on 10q24. Detailed studies of a number of mouse models for ectrodactyly have also revealed that a failure to maintain median apical ectodermal ridge (AER) signalling can be the main pathogenic mechanism in triggering this abnormality.

A number of factors make the identification of the genetic defects underlying human ectrodactyly a complicated process: the limited number of families linked to each split hand/foot malformation (SHFM) locus, the large number of morphogens involved in limb development, the complex interactions between these morphogens, the involvement of modifier genes, and the presumed involvement of multiple gene or long-range regulatory elements in some cases of ectrodactyly. In the clinical setting these genetic characteristics can become problematic and making predictions of carrier status and severity of the disease impossible to predict.

In 2011, a novel mutation in DLX5 was found to be involved in SHFM.

Ectrodactyly is frequently seen with other congenital anomalies. Syndromes in which ectrodactyly is associated with other abnormalities can occur when two or more genes are affected by a chromosomal rearrangement. Disorders associated with ectrodactyly include Ectrodactyly-Ectodermal Dysplasia-Clefting (EEC) syndrome, which is closely correlated to the ADULT syndrome and Limb-mammary (LMS) syndrome, Ectrodactyly-Cleft Palate (ECP) syndrome, Ectrodactyly-Ectodermal Dysplasia-Macular Dystrophy syndrome, Ectrodactyly-Fibular Aplasia/Hypoplasia (EFA) syndrome, and Ectrodactyly-Polydactyly. More than 50 syndromes and associations involving ectrodactyly are distinguished in the London Dysmorphology Database.

Malformations of the upper extremities can occur In the third to seventh embryonic week. In some cases the TPT is hereditary. In these cases, there is a mutation on chromosome 7q36. If the TPT is hereditary, it is mostly inherited as an autosomal dominant trait, non-opposable and bilateral. The sporadic cases are mostly opposable and unilateral.

The cause of multicystic dysplastic kidney can be attributed to genetics. Renal dysplasia can be a consequence of a genetic syndrome, which in turn may affect the digestive tract, nervous system, or other areas of the urinary tract. If the mother had been taking certain prescription drugs such as those for hypertension, this may be a precipitating factor as well.

NBCCS has an incidence of 1 in 50,000 to 150,000 with higher incidence in Australia. One aspect of NBCCS is that basal-cell carcinomas will occur on areas of the body which are not generally exposed to sunlight, such as the palms and soles of the feet and lesions may develop at the base of palmar and plantar pits.

One of the prime features of NBCCS is development of multiple BCCs at an early age, often in the teen years. Each person who has this syndrome is affected to a different degree, some having many more characteristics of the condition than others.

It has several different types:

- type 1 - Apert syndrome

- type 2 - Crouzon syndrome

- type 3 - Saethre-Chotzen syndrome

- type 5 - Pfeiffer syndrome

A related term, "acrocephalopolysyndactyly" (ACPS), refers to the inclusion of polydactyly to the presentation. It also has multiple types:

- type 1 - Noack syndrome; now classified with Pfeiffer syndrome

- type 2 - Carpenter syndrome

- type 3 - Sakati-Nyhan-Tisdale syndrome

- type 4 - Goodman syndrome; now classified with Carpenter syndrome

- type 5 - Pfeiffer syndrome

It has been suggested that the distinction between "acrocephalosyndactyly" versus "acrocephalopolysyndactyly" should be abandoned.

Lip pits may be surgically removed either for aesthetic reasons or discomfort due to inflammation caused by bacterial infections or chronic saliva excretion, though spontaneous shrinkage of the lip pits has occurred in some rare cases. Chronic inflammation has also been reported to cause squamous-cell carcinoma. It is essential to completely remove the entire lip pit canal, as mucoid cysts can develop if mucous glands are not removed. A possible side effect of removing the lip pits is a loose lip muscle. Other conditions associated with VWS, including CL, CP, congenital heart defects, etc. are surgically corrected or otherwise treated as they would be if they were non-syndromic.

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

Duane-radial ray syndrome is caused by mutations in the "SALL4" gene which is a part of a group of genes called the SALL family. This gene plays an important role in embryonic development by providing instructions to make proteins that are involved in the formation of tissues and organs. SALL proteins act as transcription factors in that they attach themselves to certain regions in DNA in order to help control certain gene activities. Due to the mutations in the "SALL4" gene, proteins can not be made because one copy of the gene in each cell is stopped from performing its duty. These mutations are heterozygous and can be nonsense, short duplications, or deletions. At this time, there is no clear reason as to why a reduced amount of the SALL4 protein causes the symptoms of Duane-radial ray syndrome and similar conditions.

Duane-radial ray syndrome is inherited through autosomal dominance meaning that a mutation in one copy of the SALL 4 gene is all it takes to cause this syndrome. Those with this condition can have affected parents, but it can also manifest for the first time with no family history which is called de novo. Since Duane-radial ray syndrome is an autosomal dominant disorder, there is a 50% chance of passing the mutation on to offspring.

There is still some discussion on whether FND is sporadic or genetic. The majority of FND cases are sporadic. Yet, some studies describe families with multiple members with FND. Gene mutations are likely to play an important role in the cause. Unfortunately, the genetic cause for most types of FND remains undetermined.

Impossible Syndrome, or Chondrodysplasia situs inversus imperforate anus polydactyly, is a complex combination of human congenital malformations (birth defects).

The malformations include chondrodysplasia (improper growth of bone and cartilage), situs inversus totalis (chest and abdominal organs all a mirror image of normal), cleft larynx and epiglottis, hexadactyly (six digits) on hands and feet, diaphragmatic hernia, pancreatic abnormalities, kidney abnormal on one side and absent on the other side, micropenis and ambiguous genitalia, and imperforate anus.

Only one case of Impossible Syndrome has been reported; the infant was premature and stillborn.

Acromelic frontonasal dysplasia is a rare subtype of FND. It has an autosomal recessive inheritance. Acromelic frontonasal dysplasia is associated with central nervous system malformations and limb defects including a clubfoot, an underdeveloped shin-bone, and preaxial polydactyly of the feet. Preaxial polydactyly is a condition in which there are too many toes on the side of the big toe. The phenotype of AFND is severe: a type Ia DeMyer and a Sedano type D. In contrast to the other subtypes of FND, AFND has a relatively high frequency of underlying malformations of the brain.

The varied signs and symptoms of Duane-radial ray syndrome often overlap with features of other disorders.

- For example, acro-renal-ocular syndrome is characterized by Duane anomaly and other eye abnormalities, radial ray malformations, and kidney defects. Both conditions can be caused by mutations in the same gene. Based on these similarities, researchers are investigating whether Duane-radial ray syndrome and acro-renal-ocular syndrome are separate disorders or part of a single syndrome with many possible signs and symptoms.

- The features of Duane-radial ray syndrome also overlap with those of a condition called Holt-Oram syndrome; however, these two disorders are caused by mutations in different genes.