In a newborn boy thought to have Fryns syndrome, Clark and Fenner-Gonzales (1989) found mosaicism for a tandem duplication of 1q24-q31.2. They suggested that the gene for this disorder is located in that region. However, de Jong et al. (1989), Krassikoff and Sekhon (1990), and Dean et al. (1991) found possible Fryns syndrome associated with anomalies of chromosome 15, chromosome 6, chromosome 8(human)and chromosome 22, respectively. Thus, these cases may all represent mimics of the mendelian syndrome and have no significance as to the location of the gene for the recessive disorder.

By array CGH, Slavotinek et al. (2005) screened patients with DIH and additional phenotypic anomalies consistent with Fryns syndrome for cryptic chromosomal aberrations. They identified submicroscopic chromosome deletions in 3 probands who had previously been diagnosed with Fryns syndrome and had normal karyotyping with G-banded chromosome analysis. Two female infants were found to have microdeletions involving 15q26.2 (see 142340), and 1 male infant had a deletion in band 8p23.1 (see 222400).

In France, Aymé, "et al." (1989) estimated the prevalence of Fryns syndrome to be 0.7 per 10,000 births based on the diagnosis of 6 cases in a series of 112,276 consecutive births (live births and perinatal deaths).

Muir–Torre was observed to occur in 14 of 50 families (28%) and in 14 of 152 individuals (9.2%) with Lynch syndrome, also known as HNPCC.

The 2 major MMR proteins involved are hMLH1 and hMSH2. Approximately 70% of tumors associated with the MTS have microsatellite instability. While germline disruption of hMLH1 and hMSH2 is evenly distributed in HNPCC, disruption of hMSH2 is seen in greater than 90% of MTS patients.

Gastrointestinal and genitourinary cancers are the most common internal malignancies. Colorectal cancer is the most common visceral neoplasm in Muir–Torre syndrome patients.

Roberts syndrome is an extremely rare condition that only affects about 150 reported individuals. Although there have been only about 150 reported cases, the affected group is quite diverse and spread worldwide. Parental consanguinity (parents are closely related) is common with this genetic disorder. The frequency of Roberts syndrome carriers is unknown.

Schimmelpenning syndrome appears to be sporadic rather than inherited, in almost all cases. It is thought to result from genetic mosaicism, possibly an autosomal dominant mutation arising after conception and present only in a subpopulation of cells. The earlier in embryological development such a mutation occurs, the more extensive the nevi are likely to be and the greater the likelihood of other organ system involvement.

While not always pathological, it can present as a birth defect in multiple syndromes including:

- Catel–Manzke syndrome

- Bloom syndrome

- Coffin–Lowry syndrome

- congenital rubella

- Cri du chat syndrome

- DiGeorge's syndrome

- Ehlers-Danlos syndrome

- fetal alcohol syndrome

- Hallermann-Streiff syndrome

- Hemifacial microsomia (as part of Goldenhar syndrome)

- Juvenile idiopathic arthritis

- Marfan syndrome

- Noonan syndrome

- Pierre Robin syndrome

- Prader–Willi syndrome

- Progeria

- Russell-Silver syndrome

- Seckel syndrome

- Smith-Lemli-Opitz syndrome

- Treacher Collins syndrome

- Trisomy 13 (Patau syndrome)

- Trisomy 18 (Edwards syndrome)

- Wolf–Hirschhorn syndrome

- X0 syndrome (Turner syndrome)

It is likely that this syndrome is inherited in an autosomal dominant fashion, however there may be a recessive form with hypotonia and developmental delay.

It can be detected by the naked eye as well as dental or skull X-Ray testing.

The original report was of a family in Cardiff, United Kingdom. There are subsequent reports of patients from the USA, France, Australia, UAE, India and from Cuba.

Café au lait spots can arise from diverse and unrelated causes:

- Having six or more café au lait spots greater than 5 mm in diameter before puberty, or greater than 15 mm in diameter after puberty, is a diagnostic feature of neurofibromatosis type I, but other features are required to diagnose NF-1.

- Familial multiple café au lait spots have been observed without NF-1 diagnosis.

- They can be caused by vitiligo in the rare McCune–Albright syndrome.

- Legius syndrome

- Tuberous sclerosis

- Fanconi anemia

- Idiopathic

- Ataxia-telangiectasia

- Basal cell nevus syndrome

- Benign congenital skin lesion

- Bloom syndrome

- Chédiak–Higashi syndrome

- Congenital naevus

- Gaucher disease

- Hunter syndrome

- Jaffe–Campanacci syndrome

- Maffucci syndrome

- Multiple mucosal neuroma syndrome

- Noonan syndrome

- Pulmonary Stenosis

- Silver–Russell syndrome

- Watson syndrome

- Wiskott–Aldrich syndrome

The specific cause of camptodactyly remains unknown, but there are a few deficiencies that lead to the condition. A deficient lumbrical muscle controlling the flexion of the fingers, and abnormalities of the flexor and extensor tendons.

A number of congenital syndromes may also cause camptodactyly:

- Jacobsen syndrome

- Beals Syndrome

- Blau syndrome

- Freeman-Sheldon syndrome

- Cerebrohepatorenal syndrome

- Weaver syndrome

- Christian syndrome 1

- Gordon Syndrome

- Jacobs arthropathy-camptodactyly syndrome

- Lenz microphthalmia syndrome

- Marshall-Smith-Weaver syndrome

- Oculo-dento-digital syndrome

- Tel Hashomer camptodactyly syndrome

- Toriello-Carey syndrome

- Stuve-Wiedemann syndrome

- Loeys-Dietz syndrome

- Fryns syndrome

- Marfan's syndrome

- Carnio-carpo-tarsal dysthropy

3C syndrome is very rare, occurring in less than 1 birth per million. Because of consanguinity due to a founder effect, it is much more common in a remote First Nations village in Manitoba, where 1 in 9 people carries the recessive gene.

Heart-hand syndrome type 2 is also known as Berk–Tabatznik syndrome. Berk–Tabatznik syndrome is a condition with an unknown cause that shows symptoms of short stature, congenital optic atrophy and brachytelephalangy. This condition is extremely rare with only two cases being found.

Heart-hand syndrome type 3 is very rare and has been described only in three members of a Spanish family. It is also known as Heart-hand syndrome, Spanish type.

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.

Nevus sebaceous was first identified in 1895 by Jadassohn. Sebaceous nevi occur in 1 to 3 of 1000 births, with equal incidence by sex. There is no test to determine whether an individual born with a sebaceous nevus will go on to develop further symptoms of Schimmelpenning syndrome. It has been reported that up to 10% of individuals with epidermal nevi may develop additional syndrome symptoms, but that number appears to be inconsistent with the rarity of the syndrome and may be overstated. Prevalence is unknown, but Epidermal nevus syndrome is listed with the National Organization for Rare Disorders, which defines "rare" as affecting "fewer than 200,000 people in the United States."

Acrocephalosyndactylia (or acrocephalosyndactyly) is the common presentation of craniosynostosis and syndactyly.

The incidence of Fraser syndrome is 0.043 per 10,000 live born infants and 1.1 in 10,000 stillbirths, making it a rare syndrome.

Orofaciodigital syndrome 1 (OFD1), also called Papillon-League and Psaume syndrome, is an X-linked congenital disorder characterized by malformations of the face, oral cavity, and digits with polycystic kidney disease and variable involvement of the central nervous system.

At this time, there are no other phenotypes (observable expressions of a gene) that have been discovered for mutations in the ESCO2 gene.

Both autosomal dominant and recessive forms of Larsen syndrome have been reported. The former is significantly more common than the latter. Symptoms such as syndactyly, cleft palate, short stature, and cardiac defects are seen more commonly in individuals with the autosomal recessive form of the disorder. A lethal form of the disorder has been reported it is described as being a combination of the Larsen phenotype and pulmonary hypoplasia.

Respiratory complications are often cause of death in early infancy.

3C syndrome, also known as CCC dysplasia, Craniocerebellocardiac dysplasia or Ritscher–Schinzel syndrome, is a rare condition, whose symptoms include heart defects, cerebellar hypoplasia, and cranial dysmorphism. It was first described in the medical literature in 1987 by Ritscher and Schinzel, for whom the disorder is sometimes named.

Recent findings in genetic research have suggested that a large number of genetic disorders, both genetic syndromes and genetic diseases, that were not previously identified in the medical literature as related, may be, in fact, highly related in the genotypical root cause of these widely varying, phenotypically-observed disorders. Orofaciodigital syndrome has been found to be a ciliopathy. Other known ciliopathies include primary ciliary dyskinesia, Bardet-Biedl syndrome, polycystic kidney disease and polycystic liver disease, nephronophthisis, Alstrom syndrome, Meckel-Gruber syndrome and some forms of retinal degeneration.

Overgrowth syndromes in children constitute a group of rare disorders that are typical of tissue hypertrophy. Individual overgrowth syndromes have been shown to overlap with regard to clinical and radiologic features. The details of the genetic bases of these syndromes are unfolding. Any of the three embryonic tissue layers may be involved.The syndromes may manifest in localized or generalized tissue overgrowth. Latitudinal and longitudinal growth may be affected. Nevertheless, the musculoskeletal features are central to the diagnosis of some syndromes such as Proteus syndrome. The time of presentation of children with overgrowth syndromes is an important contributor to the differential diagnosis. Children with some overgrowth syndromes such as Klippel-Trenaunay-Weber syndrome can be readily detectable at birth. In contrast other overgrowth syndromes such as Proteus syndrome usually present in the postnatal period characteristically between the 2nd and 3rd year of life. In general, children with overgrowth syndromes are at increased risk of embryonic tumor development.

Examples of overgrowth syndromes include; Beckwith-Wiedemann syndrome, Proteus syndrome, Sotos syndrome, neurofibromatosis, Simpson-Golabi-Behmel syndrome, Weaver syndrome, Sturge–Weber syndrome, Macrocephaly-capillary malformation, CLOVES syndrome, fragile X syndrome and Klippel-Trenaunay-Weber syndrome.