Syndactyly can be simple or complex.

- In simple syndactyly, adjacent fingers or toes are joined by soft tissue.

- In complex syndactyly, the bones of adjacent digits are fused. The kangaroo exhibits complex syndactyly.

Syndactyly can be complete or incomplete.

- In complete syndactyly, the skin is joined all the way to the tip of the involved digits.

- In incomplete syndactyly, the skin is only joined part of the distance to the tip of the involved digits.

Complex syndactyly occurs as part of a syndrome (such as Apert syndrome) and typically involves more digits than simple syndactyly.

Fenestrated syndactyly means the skin is joined for most of the digit but in a proximal area there is gap in the syndactyly with normal skin. This type of syndactyly is found in amniotic band syndrome.

Simple syndactyly can be full or partial, and is present at birth (congenital). In early human fetal development, webbing (syndactyly) of the toes and fingers is normal. At about 6 weeks of gestation, apoptosis takes place due to a protein named sonic hedgehog, also known as SHH, which dissolves the tissue between the fingers and toes, and the webbing disappears. In some fetuses, this process does not occur completely between all fingers or toes and some residual webbing remains.

This condition is normally discovered at birth. If other symptoms are present, a specific syndrome may be indicated. Diagnosis of a specific syndrome is based on family history, medical history, and a physical exam. Webbed toes are also known as "twin toes," "duck toes," "turkey toes" and "tiger toes."

Severity can vary. Most cases involve the second and third toes but any number of toes can be involved. In some cases the toes are joined part way while in some the webbing can extend right up to the nails. In some cases the entire toes, including the nails and bones, can be fused.

This is a very rare situation, in which the extra digit is on the ring, middle or index finger. Of these fingers, the index finger is most often affected, whereas the ring finger is rarely affected.

This type of polydactyly can be associated with syndactyly, cleft hand and several syndromes.

Polysyndactyly presents various degrees of syndactyly affecting fingers three and four.

Classification is performed by using x-ray imaging to see the bone structures.

Hypophalangism is a congenital absence of one or more phalanges (bones of the fingers and toes).

Syndactyly (from Greek συν- meaning "together" and δακτυλος meaning "finger") is a condition wherein two or more digits are fused together. It occurs normally in some mammals, such as the siamang and diprotodontia, but is an unusual condition in humans.

Characteristics are:

- A fibrous band instead of the fibula

- Short deformed leg

- Absence of the lateral part of the ankle joint (due to absence of the distal end of the fibula), and what is left is unstable; the foot has an equinovalgus deformity

- Possible absence of part of the foot requiring surgical intervention to bring the foot into normal function, or amputation.

- Possible absence of one or two toes on the foot

- Possible conjoined toes or metatarsals

Partial or total absence of fibula is among the most frequent limb anomalies. It is the most common long bone deficiency and is the most common skeletal deformity in the leg. It most often is unilateral (present only on one side). It may also present as bilateral (affecting both legs). Paraxial fibular hemimelia is the most common manifestation in which only the postaxial portion of the limb is affected. It is commonly seen as a complete terminal deficiency, where the lateral rays of the foot are also affected. Hemimelia can also be intercalary in which case the foot remains unaffected. Although the missing bone is easily identified, this condition is not simply a missing bone. Males are affected twice as often as females in most series.

Webbed toes is the common name for syndactyly affecting the feet. It is characterised by the fusion of two or more digits of the feet. This is normal in many birds, such as ducks; amphibians, such as frogs; and mammals, such as kangaroos. In humans it is considered unusual, occurring in approximately one in 2,000 to 2,500 live births.

There are various levels of webbing, from partial to complete. For example, the rare Hose's civet, a viverrid endemic to northern Borneo, has partially webbed feet. Most commonly the second and third toes are webbed or joined by skin and flexible tissue. This can reach either part way up or nearly all the way up the toe.

Specific types of additional body parts include:

- Accessory breast – one or more additional breasts

- Accessory spleen – one or more additional spleens

- Cervical rib – an additional rib

- Diphallia - Having two penes/penises.

- Hermaphroditism – having both sexes' sex organs

- Hyperdontia – additional teeth

- Pelvic digit – a bony growth in the soft tissue of the pelvic region

- Polycephaly – an extra head

- Polydactyly – additional fingers or toes

- Polymelia — an extra arm or leg.

- Polyorchidism – having three or more testicles

- Supernumerary bones – these additional bones are fairly common, particularly in the feet, and are frequently mistaken for fractures on x-rays.

- Supernumerary kidney – a third kidney

- Supernumerary nipples – an additional nipple

- Supernumerary phantom limbs – where the brain acts as though a limb were there, but it is not.

- Syndactyly – webbing between the fingers or toes

- Uterus didelphys – two vaginal canals and/or uteri

The differential diagnosis includes;

- Symbrachydactyly

- Chorionic villus sampling

- Congenital amputations

- Hypoplasias of hand, digit, thumb

- Adams-Oliver syndrome

- ADAM complex

ADAM Complex; CRS is sometimes mislabeled as ADAM complex. ADAM is an abbreviation for Amniotic Deformity, Adhesions Mutilations. CRS is the malformation due to a constriction ring around mostly a limb. ADAM-complex is the association of limb defects (caused by constriction rings) and certain craniofacial clefts

“Adams-Oliver syndrome is often mislabeled as CRS and consists of cutis aplasia of the scalp in which a longitudinal defect can vary in size and can often be associated with full-thickness skullcap loss. The distal digital or toe hypoplasia-aplasia is often confused with CRS. Constriction rings with or without edema are not present. The digital or toe hypoplasia-aplasia usually contains diminutive nails or nail folds”.

The diagnosis of constriction ring syndrome can be confirmed with an ultrasonography. The clinical manifestations can be extremely variable. It could be a single or multiple manifestation. This can be confirmed at the end of the first trimester or at the beginning of the second trimester. But not every patient will be diagnosed at that moment, most will get this diagnosis at birth.

Symptoms are related to defects in connective tissue.

- Congenital anterior dislocation of the knees

- Dislocation of hips and shoulders

- Flattened facial appearance

- Prominent forehead

- Depressed nasal bridge

- Club foot

- Cervical kyphosis

Carpenter syndrome presents several features:

- Tower-shaped skull (craniosynostosis)

- Additional or fused digits (fingers and toes)

- Obesity

- Reduced height

Intellectual disability is also common with the disorder, although some patients may have average intellectual capacity.

These symptoms were found in rare cases of Larsen syndrome.

- Cataracts

- Cleft palate

- Extra bones of wrist

- Malocclusion

- Microdontia and hypodontia

- Complete agenesis of anus

- uterus

- Bifid tongue

Fibular hemimelia or longitudinal fibular deficiency is "the congenital absence of the fibula and it is the most common congenital absence of long bone of the extremities." It is the shortening of the fibula at birth, or the complete lack thereof. In humans, the disorder can be noted by ultrasound in utero to prepare for amputation after birth or complex bone lengthening surgery. The amputation usually takes place at six months with removal of portions of the legs to prepare them for prosthetic use. The other treatments which include repeated corrective osteotomies and leg-lengthening surgery (Ilizarov apparatus) are costly and associated with residual deformity.

Additional findings that may be present in HFGS according to the latest research are:

- Limited metacarpophalangeal flexion of the thumb or limited ability to oppose the thumb and fifth finger

- Hypoplastic thenar eminences

- Medial deviation of the great toe (hallux varus), a useful diagnostic sign when present

- Small great toenail

- Fifth-finger clinodactyly, secondary to a shortened middle phalanx

- Short feet

- Altered dermatoglyphics of the hands; when present, primarily involving distal placement of the axial triradius, lack of thenar or hypothenar patterning, low arches on the thumbs, thin ulnar loops (deficiency of radial loops and whorls), and a greatly reduced ridge count on the fingers

Radiographic findings

- Hypoplasia of the distal phalanx and first metacarpal of the thumbs and great toes

- Pointed distal phalanges of the thumb

- Lack of normal tufting of the distal phalanges of the great toes

- Fusions of the cuneiform to other tarsal bones or trapezium-scaphoid fusion of the carpals

- Short calcaneus

- Occasional bony fusions of the middle and distal phalanges of the second, third, fourth, or fifth toes

- Delayed carpal or tarsal maturation

- Metacarpophalangeal profile reflecting shortening of the first metacarpal, the first and second phalanges, and the second phalanx of the second and fifth digits

Urogenital Defects

Females may have the following:

- Vesicoureteral reflux secondary to ureteric incompetence

- Ectopic ureteral orifices

- Trigonal hypoplasia

- Hypospadiac urethra

- Subsymphyseal epispadias

- Patulous urethra

- Urinary incontinence (related to structural anomalies and weakness of the bladder sphincter muscle)

- Small hymenal opening

- Various degrees of incomplete Müllerian fusion with or without two cervices or a longitudinal vaginal septum

Males may have the following:

- Retrograde ejaculation (related to structural anomalies and weakness of the bladder sphincter muscle)

Carpenter Syndrome belongs to a group of rare genetic disorders known as acrocephalopolysyndactyly, abbreviated ACPS (RN, 2007). There were originally five types of ACPS, but this number has been decreased because they have been found to be closely related to one another or to other disorders (Paul A. Johnson, 2002).

The most common physical manifestation of Carpenter Syndrome is early fusing of the fibrous cranial sutures which results in an abnormally pointed head. The fusion of the skull bones is evident from birth (National Organization for Rare Disorders, Inc., 2008). Babies’ mobile cranial bones form a cone shape as the pass through the birth canal and soon thereafter return to a normal shape; however, a baby affected by carpenter syndrome maintains a cone shaped head.

A baby affected by Carpenter Syndrome will also display malformations of the face. An individual affected by the syndrome may have broad cheeks, a flat nasal bridge, and a wide upturned nose with abnormally large nasal openings. Their ears will most commonly be low, unevenly set, and malformed in structure. In addition to these facial abnormalities, individuals also have an underdeveloped maxilla and/ or mandible with a highly arched and narrow palate which makes speech a very difficult skill to master. Teeth are usually very late to come in and will be undersized and spaced far apart (Carpenter Syndrome-description).

Other physical abnormalities often associated with Carpenter Syndrome include extra digits. Extra toes are more commonly seen than fingers. Often both the toes and fingers are webbed, a process that occurs before the sixth week gestational period. Often their digits will be abnormally short, and the fingers are commonly missing an interphalangeal joint. Roughly half of the babies born with Carpenter Syndrome have some type of heart defect, and seventy five percent of individuals with this disease will experience some degree of development delay due to mild mental retardation (Carpenter Syndrome-description).

Supernumerary body parts are most commonly a congenital disorder involving the growth of an additional part of the body and a deviation from the body plan. Body parts may be easily visible or hidden away, such as internal organs.

Many additional body parts form by the same process as conjoined twins: the zygote begins to split but fails to completely separate. This condition may also be a symptom of repeated occurrences of continuous inbreeding in a genetic line.

Diplopodia is a congenital anomaly in tetrapods that involves duplication of elements of the foot on the hind limb. It comes from the Greek roots diplo = "double" and pod = "foot". Diplopodia is often found in conjunction with other structural abnormalities and can be lethal. It is more extreme than polydactyly, the presence of extra digits.

Hand-foot-genital syndrome (HFGS) is characterized by limb malformations and urogenital defects. Mild bilateral shortening of the thumbs and great toes, caused primarily by shortening of the distal phalanx and/or the first metacarpal or metatarsal, is the most common limb malformation and results in impaired dexterity or apposition of the thumbs. Urogenital abnormalities include abnormalities of the ureters and urethra and various degrees of incomplete Müllerian fusion in females and hypospadias of variable severity with or without chordee in males. Vesicoureteral reflux, recurrent urinary tract infections, and chronic pyelonephritis are common; fertility is normal.

Congenital causes include: Aarskog syndrome, Albright's hereditary osteodystrophy, and Apert syndrome. Can be caused by a trauma, although the exact mechanism is not known.

Phenotypic expression varies greatly between individuals with CFND. Some of the more prominent characteristics are:

- Craniosynostosis of the coronal suture(s) (fusion of the coronal sutures),

- Orbital hypertelorism (increased interocular distance),

- Bifid nasal tip,

- Dry frizzy curled hair,

- Longitudinal ridging and / or splitting of the nails,

- Facial Asymmetry.

Other characteristics that are less frequently seen are: broad nasal base, low anterior hair line, low set ears, crowding of the teeth, maxillary hypoplasia, rounded and sloping shoulders, pectus excavatum, scoliosis, high arched palate, orbital dystopia, low implant of the breasts with asymmetric nipples and volume, webbed neck, hand or foot abnormalities such as clinodactyly (most common is a curved 5th finger) and cutaneous syndactyly (webbed fingers / toes).

Females are more commonly and usually more severely affected than males. Males can however have (some of) the same symptoms as females, but this is not frequently seen. Most males have mild symptoms such as hypertelorism and a broad nasal base with bifid nose, but can also be a carrier of the mutation yet stay clinically unaffected.

Individuals affected by ischiopatellar dysplasia commonly have abnormalities of the patella and pelvic girdle, such as absent or delayed patellar and ischial ossification as well as infra-acetabular axe-cut notches. Patellae are typically absent or small in these individuals, when patellae are present they are small and laterally displaced or dislocated. In addition, abnormalities in other parts of their skeleton and dysmorphic features are common in those affected. Other features that have been identified in patients with ischiopatellar dysplasia include foot anomalies, specifically flat feet (pes planus), syndactylism of the toes, short fourth and fifth toes, and a large gap between the first and second toes, femur anomalies, cleft palate, and craniofacial dysmorphisms.

Many of the characteristic facial features result from the premature fusion of the skull bones (craniosynostosis). The head is unable to grow normally, which leads to a high prominent forehead (turribrachycephaly), and eyes that appear to bulge (proptosis) and are wide-set (hypertelorism). In addition, there is an underdeveloped upper jaw (maxillary hypoplasia). About 50 percent of children with Pfeiffer syndrome have hearing loss, and dental problems are also common.

In people with Pfeiffer syndrome, the thumbs and first (big) toes are wide and bend away from the other digits (pollex varus and hallux varus). Unusually short fingers and toes (brachydactyly) are also common, and there may be some webbing or fusion between the digits (syndactyly).

Nasodigitoacoustic syndrome is congenital and is characterized by a number of nasal, facial and cranial features. These include a broad and high, sometimes depressed nasal bridge (top of the nose, between the eyes) and a flattened nasal tip. This can give the nose a shortened, arch-like appearance. Hypertelorism (unusually wide-set eyes), prominent frontal bones and supraorbital ridge (the eyebrow ridge), bilateral epicanthic folds (an extra flap of skin over the eyelids), a broad forehead and an overall enlarged head circumference have also been observed. A bulging of the upper lip with an exaggerated cupid's bow shape, and maxillary hypoplasia (underdevelopment of the upper jaw) with retraction have also been reported.

Several anomalies affecting the digits (fingers and toes) have been observed with the syndrome. A broadening of the thumbs and big toes (halluces) was reported in two brothers. The broadening was apparent in all distal phalanges of the fingers, although the pinkies were unaffected yet appeared to be clinodactylic (warped, or bent toward the other fingers). Additional eports described this broadness of the thumbs and big toes, with brachydactyly (shortness) in the distal phalanges of the other digits except the pinkies in affected individuals. On X-rays of a two-year-old boy with the disorder, the brachydactyly was shown to be caused by shortening of epiphyses (joint-ends) of the distal phalanges. The broadness and brachydactyly of the big toes in particular may give them a stunted, rounded and stub-like appearance.

The auditory, or "acoustic" abnormalities observed with the syndrome include sensorineural hearing loss and hoarseness. Two affected Turkish brothers with a mild form of this hearing loss, and a hoarse voice were reported. A laryngoscopic examination of both brothers revealed swelling of the vocal cords, and a malformed epiglottis. Sensorineural-associated hearing impairment and hoarsness was also observed in a 10-year-old girl and her father, and in a number of other cases.

Other characteristics seen with the syndrome include developmental delay, growth retardation, pulmonary stenosis (an obstruction of blood-flow from the right ventricle of the heart to the pulmonary artery) with associated dyspnea (shortness of breath), and renal agenesis (failure of the kidneys to develop during the fetal period). Undescended testes, hyperactivity and aggressive behavior have also been noted.