Acalvaria usually occurs in less than 1 of every 100,000 births. By way of epidemiological data, it is thought that females are more prone to have this defect. Currently, acalvaria is not thought to have much of a risk of recurrence.

Usually babies with this malformation do not survive past birth. However, there have been cases of survival. As of 2004, there were only two reported living cases. Of these two, one was severely cognitively impaired and physically disabled. The status of the other was unreported. If the fetus progresses to full term, there is the risk that it will have head trauma from the pressure applied to the head while being delivered. A few other cases of acalvaria have been reported, which did not progress to birth. In addition to the lack skull cap, there were brain malformations present in each case, and all of the pregnancies were terminated either electively or the fetuses were spontaneously aborted.

Ring chromosome 14 syndrome is extremely rare, the true rate of occurrence is unknown (as it is "less than" 1 per 1,000,000), but there are at least 50 documented cases in the literature.

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

Many sources classify Proteus syndrome to be a type of nevus syndrome. The lesions appear to be distributed in a mosaic manner. It has been confirmed that the disorder is an example of genetic mosaicism.

In 2011 researchers determined the cause of Proteus syndrome. In 26 of 29 patients who met strict clinical criteria for the disorder, Lindhurst "et al." identified an activating mutation in AKT1 kinase in a mosaic state gene.

Previous research had suggested the condition linked to PTEN on chromosome 10, while other research pointed to chromosome 16. Prior to the findings regarding AKT1 in 2011, other researchers expressed doubt regarding the involvement of PTEN or GPC3, which codes for glypican 3 and may play a role in regulating cell division and growth regulation.

The tumor is rare, affecting adults in the 4th decade most commonly. Patients are usually younger than those who present with a lipoma. There is a slight male predominance. Hibernoma are most commonly identified in the subcutaneous and muscle tissue of the head and neck region (shoulders, neck, scapular), followed by thigh, back, chest, abdomen, and arms. In rare cases hibernoma may arise in bone tissue, however it is an incidental finding.

By 1990, 65 patients had been reported in the literature, with no sex or ethnic preference notable. Some individuals present with minimal malformation; rarely patients have died during infancy as a result of severe central nervous system involvement or respiratory complications. Several syndromes are related to the Freeman–Sheldon syndrome spectrum, but more information is required before undertaking such nosological delineation.

Benign lipoblastomatosis (also known as an "embryonic lipoma") is a tumor frequently confused with a liposarcoma, affecting exclusively infants and young children, with approximately 90% occurring before 3 years of age.

Phakomatoses are inconsistently defined, and there is a lack of consensus about what conditions are included in this category.

Conditions included are:

- Ataxia telangiectasia

- Incontinentia pigmenti

- Neurofibromatosis

- Nevoid basal cell carcinoma syndrome

- Sturge-Weber syndrome

- Tuberous sclerosis

- Wyburn-Mason syndrome (Bonnet–Dechaume–Blanc syndrome)

- von Hippel-Lindau disease

There are little data on prognosis. Rarely, some patients have died in infancy from respiratory failure; otherwise, life expectancy is considered to be normal.

The syndrome is caused by the loss of genetic material near the end of the long arm (q) of chromosome 14 . The break that causes the telomere(s) to be lost occurs near the end of the chromosome, and is called a "constitutional ring". These rings arise spontaneously ( it is rarely inherited).Ring chromosome 14 syndrome finds itself at 14:0-107,043,718 which are the genomic coordinates.

The genetic abnormality occurs randomly in sperm or egg cells or it may occur in early embryonic growth, if it occurs during embryonic growth the ring chromosome may be present in only some of a person's cells.

Neurocristopathy is a diverse class of pathologies that may arise from defects in the development of tissues containing cells commonly derived from the embryonic neural crest cell lineage. The term was coined by Robert P. Bolande in 1974.

Accepted examples are piebaldism, Waardenburg syndrome, Hirschsprung disease, Ondine's curse (congenital central hypoventilation syndrome), pheochromocytoma, paraganglioma, Merkel cell carcinoma, multiple endocrine neoplasia, neurofibromatosis type I, CHARGE syndrome, familial dysautonomia, DiGeorge syndrome, Axenfeld-Rieger syndrome, Goldenhar syndrome (a.k.a. hemifacial microsomia), craniofrontonasal syndrome, congenital melanocytic nevus, melanoma, and certain congenital heart defects of the outflow tract, in particular.

Multiple sclerosis has also been suggested as being neurocristopathic in origin.

The usefulness of the definition resides in its ability to refer to a potentially common etiological factor for certain neoplasms and/or congenital malformation associations that are otherwise difficult to group with other means of nosology.

Complete surgical excision is the treatment of choice, associated with an excellent long term clinical outcome.

Tetra-amelia syndrome has been reported in only a few families worldwide.

According to a 2011 study by Bermejo-Sanchez, amelia – that is, the lacking of one or more limbs – occurs in roughly 1 out of every 71,000 pregnancies.

Phakomatoses refers to a group of neuro-oculo-cutaneous syndromes or neurocutaneous disorders involving structures arising from the embryonic ectoderm. These multisystem disorders involve the ectodermal structures like central nervous system, skin and eyes. The lesions have a variable severity. However, it has been subsequently noted that mesodermal and endodermal tissues too are involved.

A number of genetic and acquired diseases come in this category and may affect one or more of these tissues. However, in some conditions, such as von Hippel-Lindau disease, ectodermal presentation is minimal.

The cause of fibular hemimelia is unclear. Purportedly, there have been some incidents of genetic distribution in a family; however, this does not account for all cases. Maternal viral infections, embryonic trauma, teratogenic environmental exposures or vascular dysgenesis (failure of the embryo to form a satisfactory blood supply) between four and seven weeks gestation are considered possible causes.

In an experimental mouse model, change in the expression of a homeobox gene led to similar, but bilateral, fibular defects.

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.

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

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.

Michelin tire baby syndrome (also known as "Folded skin with scarring"), is characterized by multiple, symmetric, circular skin creases, or bands, on the forearms, lower legs, and often the neck that are present at birth. The creases disappear later in life. But it is a dangerous skin disease as it resides in the body rest of life, it can lead to death. They are reminiscent of those of Bibendum, the mascot of the tire manufacturer, Michelin, hence the name of the syndrome. Associated abnormalities vary and may include facial dysmorphism, upslanting palpebral fissures, hypertelorism, cleft palate, genital anomalies, mild developmental delay, ureterocele, smooth muscle hamartoma, nevus lipomatosus, Laron syndrome (dwarfism with high growth hormone and low somatomedin activity), and other defects.

It was originally described by Ross in 1969.

Twenty cases of this disorder have been reported.

Incidence of Crouzon syndrome is currently estimated to occur in 1.6 out of every 100,000 people. There is a greater frequency in families with a history of the disorder, but that doesn't mean that everyone in the family is affected (as referred to above).

Congenital epulis is a proliferation of cells most frequently occurring on the alveolar ridge of the upper jaw at birth. Less frequently the mass may arise from the mandibular alveolus. Rare cases can arise from the tongue. This lesion is more commonly found in female babies, suggesting hormonal involvement during embryonic development. The cause of this type of epulis is unknown. Also known as congenital granular cell tumor or Neumann's tumor; historically referred to as granular cell myoblastoma.

Multiple lesions occur in 10% of affected neonates. The tumor is typically pedunculated and varies in maximum size from 0.5 cm to 9 cm. The lesion is typically painless and does not increase in size after discovery. Some small lesions may regress over time. Treatment is surgical excision. Recurrence is extremely rare even after incomplete excision.

Diprosopus (Greek , "two-faced", from , ', "two" and , ' [neuter], "face", "person"; with Latin ending), also known as craniofacial duplication (cranio- from Greek , "skull", the other parts Latin), is an extremely rare congenital disorder whereby parts (accessories) or all of the face are duplicated on the head.

In teratology, proboscis is a blind-ended, tubelike structure, commonly located in the midface.

Proboscis formation are classified in four general types: holoprosencephalic proboscis, lateral nasal proboscis, supernumerary proboscis, and disruptive proboscis.

- Holoprosencephalic proboscis is found in holoprosencephaly. In cyclopia or ethmocephaly, proboscis is an abnormally formed nose. In cyclopia, a single median eye is associated with arrhinia (absence of the nose) and usually with proboscis formation above the eye. In ethmocephaly, two separate hypoteloric eyes are associated with arrhinia and supraocular proboscis formation. In cebocephaly, no proboscis formation occurs, but a single-nostril nose is present.

- Lateral nasal proboscis (proboscis lateralis) is a tubular proboscis-like structure and represents incomplete formation of one side of the nose; it is found instead of a nostril. The olfactory bulb is usually rudimentary on the involved side. The lacrimal duct (tear duct), nasal bone, nasal cavity, vomer, maxillary sinus, cribriform plate, and ethmoid cells are often missing on the involved side. Ocular hypertelorism may be present. The proboscis lateralis is a rare nasal anomaly.

- Supernumerary proboscis (Accessory proboscis) is found when both nostrils are formed and a proboscis occurs additionally. Accessory proboscis arise from a supernumerary olfactory placode.

- Disruptive proboscis occur if an early embryonic hamartoneoplastic lesion arises in the primitive prosencephalon.