Trichorhinophalangeal syndrome (TRPS) comprises TRPS I (caused by a heterozygous pathogenic variant in TRPS1) and TRPS II (caused by contiguous gene deletion of TRPS1, RAD21, and EXT1). Both types of TRPS are characterized by distinctive facial features; ectodermal features (fine, sparse, depigmented, and slow growing hair; dystrophic nails; and small breasts); and skeletal findings (short stature; short feet; brachydactyly with ulnar or radial deviation of the fingers; and early, marked hip dysplasia). TRPS II is characterized by multiple osteochondromas (typically first observed clinically on the scapulae and around the elbows and knees between ages 1 month and 6 years) and an increased risk of mild-to-moderate intellectual disability.

Proteus syndrome is characterized by progressive segmental or patchy overgrowth most commonly affecting the skeleton, skin, adipose, and central nervous systems. In most individuals Proteus syndrome has modest or no manifestations at birth, develops and progresses rapidly beginning in the toddler period, and relentlessly progresses through childhood, causing severe overgrowth and disfigurement. It is associated with a range of tumors, pulmonary complications, and a striking predisposition to deep vein thrombosis and pulmonary embolism.

A rare acquired dermis elastic tissue disorder with increased elastic tissue characterized by focal dermal elastosis and transepidermal elimination of abnormal elastic fibers, presenting as small keratotic papules or plaques arranged in groups in serpiginous or annular patterns on the neck, face, and arms, while other areas are less frequently affected. Although spontaneous regression is possible, the lesions often persist over longer periods of time. The condition typically occurs during childhood or early adulthood and is more frequent in men than in women.

The NSDHL-related disorders include: CHILD (congenital hemidysplasia with ichthyosiform nevus and limb defects) syndrome, an X-linked condition that is usually male lethal during gestation and thus predominantly affects females; and CK syndrome, an X-linked disorder that affects males. CHILD syndrome is characterized by unilateral distribution of ichthyosiform (yellow scaly) skin lesions and ipsilateral limb defects that range from shortening of the metacarpals and phalanges to absence of the entire limb. Intellect is usually normal. The ichthyosiform skin lesions are usually present at birth or in the first weeks of life; new lesions can develop in later life. Nail changes are also common. The heart, lung, and kidneys can also be involved. CK syndrome (named for the initials of the original proband) is characterized by mild to severe cognitive impairment and behavior problems (aggression, attention deficit hyperactivity disorder, and irritability). All affected males reported have developed seizures in infancy and have cerebral cortical malformations and microcephaly. All have distinctive facial features, a thin habitus, and relatively long, thin fingers and toes. Some have scoliosis and kyphosis. Strabismus is common. Optic atrophy is also reported.

Buschke-Ollendorff syndrome (BOS) is an autosomal dominant connective tissue disorder manifest by multiple subcutaneous nevi or nodules. They may be either elastin-rich (elastoma) or collagen-rich (dermatofibrosis lenticularis disseminata) on histologic examination. The lesions are usually nontender and firm. Affected individuals also have osteopoikilosis (OPK), literally meaning 'spotted bones,' which are osteosclerotic foci that occur in the epiphyses and metaphyses of long bones, wrist, foot, ankle, pelvis, and scapula. Some individuals have both skin and bone manifestations, whereas others may lack skin or bone manifestations. Some individuals may also have melorheostosis (155950), which is characterized by 'flowing' hyperostosis of the cortex of tubular bones. Most reported cases of BOS and OPK are benign, and the bone lesions are found incidentally, although some patients may have joint pain (reviews by Hellemans et al., 2004 and Zhang et al., 2009).

Bazex-Dupre-Christol syndrome (BDCS) is an X-linked dominant disorder characterized by a triad of congenital hypotrichosis, follicular atrophoderma affecting the dorsa of the hands and feet, the face, and extensor surfaces of the elbows or knees, and the development of basal cell neoplasms, including basal cell nevi and basal cell carcinomas from the second decade onward (Yung and Newton-Bishop, 2005). Rombo syndrome (180730) has similar features, but shows autosomal dominant inheritance.

While the majority of individuals with Costello syndrome share characteristic findings affecting multiple organ systems, the phenotypic spectrum is wide, ranging from a milder or attenuated phenotype to a severe phenotype with early lethal complications. Costello syndrome is typically characterized by failure to thrive in infancy as a result of severe postnatal feeding difficulties; short stature; developmental delay or intellectual disability; coarse facial features (full lips, large mouth, full nasal tip); curly or sparse, fine hair; loose, soft skin with deep palmar and plantar creases; papillomata of the face and perianal region; diffuse hypotonia and joint laxity with ulnar deviation of the wrists and fingers; tight Achilles tendons; and cardiac involvement including: cardiac hypertrophy (usually typical hypertrophic cardiomyopathy), congenital heart defect (usually valvar pulmonic stenosis), and arrhythmia (usually supraventricular tachycardia, especially chaotic atrial rhythm/multifocal atrial tachycardia or ectopic atrial tachycardia). Relative or absolute macrocephaly is typical, and postnatal cerebellar overgrowth can result in the development of a Chiari I malformation with associated anomalies including hydrocephalus or syringomyelia. Individuals with Costello syndrome have an approximately 15% lifetime risk for malignant tumors including rhabdomyosarcoma and neuroblastoma in young children and transitional cell carcinoma of the bladder in adolescents and young adults.

The core phenotype of Elsahy-Waters syndrome consists of brachycephaly, facial asymmetry, marked hypertelorism, proptosis, blepharochalasis, midface hypoplasia, broad nose with concave nasal ridge, and prognathism; radicular dentin dysplasia with consequent obliterated pulp chambers, apical translucent cysts, recurrent infections, and early loss of teeth; vertebral fusions, particularly at C2-C3; and moderate mental retardation. Skin wrinkling over the glabellar region seems common, and in males, hypospadias has always been present. Inter- and intrafamilial variability has been reported regarding the presence of vertebral fusions, hearing loss, and dentigerous cysts. Midface hypoplasia, facial asymmetry, progressive dental anomalies, and impaired cognitive development become more evident in adulthood (summary by Castori et al., 2010).

Noonan syndrome (NS) is characterized by characteristic facies, short stature, congenital heart defect, and developmental delay of variable degree. Other findings can include broad or webbed neck, unusual chest shape with superior pectus carinatum and inferior pectus excavatum, cryptorchidism, varied coagulation defects, lymphatic dysplasias, and ocular abnormalities. Although birth length is usually normal, final adult height approaches the lower limit of normal. Congenital heart disease occurs in 50%-80% of individuals. Pulmonary valve stenosis, often with dysplasia, is the most common heart defect and is found in 20%-50% of individuals. Hypertrophic cardiomyopathy, found in 20%-30% of individuals, may be present at birth or develop in infancy or childhood. Other structural defects include atrial and ventricular septal defects, branch pulmonary artery stenosis, and tetralogy of Fallot. Up to one fourth of affected individuals have mild intellectual disability, and language impairments in general are more common in NS than in the general population.

Becker nevus (BN) is a cutaneous hamartoma affecting approximately 1 in 200 individuals that appears in childhood as a unilateral tan patch, and increases in thickness, pigmentation, and hair growth during adolescence. Histologically, epidermal acanthosis is accompanied by irregularly dispersed ectopic smooth muscle bundles and increased terminal hair follicles (summary by Cai et al., 2017). Becker nevus syndrome (BNS) is a phenotype characterized by the presence of a Becker nevus in association with unilateral hypoplasia of breast or other cutaneous, muscular, or skeletal defects (Happle and Koopman, 1997).

Noonan syndrome (NS) is characterized by characteristic facies, short stature, congenital heart defect, and developmental delay of variable degree. Other findings can include broad or webbed neck, unusual chest shape with superior pectus carinatum and inferior pectus excavatum, cryptorchidism, varied coagulation defects, lymphatic dysplasias, and ocular abnormalities. Although birth length is usually normal, final adult height approaches the lower limit of normal. Congenital heart disease occurs in 50%-80% of individuals. Pulmonary valve stenosis, often with dysplasia, is the most common heart defect and is found in 20%-50% of individuals. Hypertrophic cardiomyopathy, found in 20%-30% of individuals, may be present at birth or develop in infancy or childhood. Other structural defects include atrial and ventricular septal defects, branch pulmonary artery stenosis, and tetralogy of Fallot. Up to one fourth of affected individuals have mild intellectual disability, and language impairments in general are more common in NS than in the general population.

Carney complex (CNC) is characterized by skin pigmentary abnormalities, myxomas, endocrine tumors or overactivity, and schwannomas. Pale brown to black lentigines are the most common presenting feature of CNC and typically increase in number at puberty. Cardiac myxomas occur at a young age, may occur in any or all cardiac chambers, and can manifest as intracardiac obstruction of blood flow, embolic phenomenon, and/or heart failure. Other sites for myxomas include the skin, breast, oropharynx, and female genital tract. Primary pigmented nodular adrenocortical disease (PPNAD), which causes Cushing syndrome, is the most frequently observed endocrine tumor in CNC, occurring in approximately 25% of affected individuals. Large-cell calcifying Sertoli cell tumors (LCCSCTs) are observed in one third of affected males within the first decade and in most adult males. Up to 75% of individuals with CNC have multiple thyroid nodules, most of which are nonfunctioning thyroid follicular adenomas. Clinically evident acromegaly from a growth hormone (GH)-producing adenoma is evident in approximately 10% of adults. Psammomatous melanotic schwannoma (PMS), a rare tumor of the nerve sheath, occurs in an estimated 10% of affected individuals. The median age of diagnosis is 20 years.

A rare genetic bone development disorder with characteristics of hand camptodactyly associated with facial dysmorphism (flat face, hypertelorism, telecanthus, symblepharon, simplified ears, retrognathia) and neck anomalies (short neck with pterygia, muscle sclerosis). Additional features include spinal defects (e.g. cervical and dorso-lumbar spina bifida occulta), congenital shortness of the sternocleidomastoid muscle, flexed wrists and thin hands and feet. Brain structural anomalies, multiple nevi, micropenis and mild intellectual disability are also observed. Imaging reveals widened femoral necks, cortical thickening of long bones and delayed bone age.

Frontonasal dysplasia-2 (FND2) is an autosomal recessive disorder characterized by variable degrees of alopecia, skull defects, hypertelorism, depressed nasal bridge and ridge with notched alae nasi, and abnormal central nervous system findings (summary by Kariminejad et al., 2014).

Cornelia de Lange syndrome (CdLS) encompasses a spectrum of findings from mild to severe. Severe (classic) CdLS is characterized by distinctive facial features, growth restriction (prenatal onset; <5th centile throughout life), hypertrichosis, and upper-limb reduction defects that range from subtle phalangeal abnormalities to oligodactyly (missing digits). Craniofacial features include synophrys, highly arched and/or thick eyebrows, long eyelashes, short nasal bridge with anteverted nares, small widely spaced teeth, and microcephaly. Individuals with a milder phenotype have less severe growth, cognitive, and limb involvement, but often have facial features consistent with CdLS. Across the CdLS spectrum IQ ranges from below 30 to 102 (mean: 53). Many individuals demonstrate autistic and self-destructive tendencies. Other frequent findings include cardiac septal defects, gastrointestinal dysfunction, hearing loss, myopia, and cryptorchidism or hypoplastic genitalia.

Takenouchi-Kosaki syndrome is a highly heterogeneous autosomal dominant complex congenital developmental disorder affecting multiple organ systems. The core phenotype includes delayed psychomotor development with variable intellectual disability, dysmorphic facial features, and cardiac, genitourinary, and hematologic or lymphatic defects, including thrombocytopenia and lymphedema. Additional features may include abnormalities on brain imaging, skeletal anomalies, and recurrent infections. Some patients have a milder disease course reminiscent of Noonan syndrome (see, e.g., NS1, 163950) (summary by Martinelli et al., 2018).

The Cincinnati type of acrofacial dysostosis is a ribosomopathy characterized by a spectrum of mandibulofacial dysostosis phenotypes, with or without extrafacial skeletal defects (Weaver et al., 2015). In addition, a significant number of neurologic abnormalities have been reported, ranging from mild delays to refractory epilepsy, as well as an increased incidence of congenital heart defects, primarily septal in nature (Smallwood et al., 2023).

Fanconi anemia (FA) is characterized by physical abnormalities, bone marrow failure, and increased risk for malignancy. Physical abnormalities, present in approximately 75% of affected individuals, include one or more of the following: short stature, abnormal skin pigmentation, skeletal malformations of the upper and/or lower limbs, microcephaly, and ophthalmic and genitourinary tract anomalies. Progressive bone marrow failure with pancytopenia typically presents in the first decade, often initially with thrombocytopenia or leukopenia. The incidence of acute myeloid leukemia is 13% by age 50 years. Solid tumors – particularly of the head and neck, skin, and genitourinary tract – are more common in individuals with FA.

The name HIST1H1E syndrome has been proposed as a mnemonic for the characteristic features of this emerging, recognizable phenotype: hypotonia; intellectual disability with behavioral issues; skeletal; testes (undescended) and thyroid; heart anomalies (most commonly atrial septal defect); and ectodermal issues (including sparse hair, thin nails, and abnormal dentition). In the 47 affected individuals reported to date, predominant findings were intellectual disability (ranging from mild to profound) and behavioral problems (combinations of anxiety/phobias, obsessive behaviors, attention-deficit/hyperactivity disorder, and autistic spectrum disorder/traits among others). Skeletal involvement can include scoliosis and decreased bone mineral density. Other findings in some include seizures, craniosynostosis, and hearing loss. Life expectancy does not appear to be reduced in HIST1H1E syndrome.

Schimmelpenning-Feuerstein-Mims syndrome, also known as linear sebaceous nevus syndrome, is characterized by sebaceous nevi, often on the face, associated with variable ipsilateral abnormalities of the central nervous system, ocular anomalies, and skeletal defects (summary by Happle, 1991 and Ernst et al., 2007). The linear sebaceous nevi follow the lines of Blaschko (Hornstein and Knickenberg, 1974; Bouwes Bavinck and van de Kamp, 1985). All cases are sporadic. The syndrome is believed to be caused by an autosomal dominant lethal mutation that survives by somatic mosaicism (Gorlin et al., 2001).

Basilicata-Akhtar syndrome (MRXSBA) is characterized by global developmental delay apparent from infancy, feeding difficulties, hypotonia, and poor or absent speech. Most patients are able to walk, although they may have an unsteady gait or spasticity. Additional findings include dysmorphic facial features and mild distal skeletal anomalies. Males and females are similarly affected (summary by Basilicata et al., 2018).

Developmental delay, impaired speech, and behavioral abnormalities (DDISBA) is characterized by global developmental delay apparent from early childhood. Intellectual disability can range from mild to severe. Additional variable features may include dysmorphic facial features, seizures, hypotonia, motor abnormalities such as Tourette syndrome or dystonia, and hearing loss (summary by Cousin et al., 2021).

Bone marrow failure and diabetes mellitus syndrome (BMFDMS) is an autosomal recessive disorder characterized by the onset of manifestations of bone marrow failure, such as anemia, thrombocytopenia, and dyserythropoiesis, in infancy or early childhood. White blood cell lineages may or may not be affected. Patients with BMFDMS also develop nonautoimmune insulin-dependent diabetes mellitus in the first or second decades, likely due to apoptosis of pancreatic beta cells. Many patients show pigmentary skin abnormalities and short stature. Bone marrow transplant is curative for the bone marrow failure, but does not have an effect on diabetes (Dos Santos et al., 2017).

Diamond-Blackfan anemia-21 (DBA21) is an autosomal recessive bone marrow failure syndrome that includes selective erythroid hypoplasia, anemia with transient thrombocytopenia, short stature, facial dysmorphism, limb abnormalities, cardiac defects, and intellectual disability (O'Donohue et al., 2022). For a general phenotypic description and discussion of genetic heterogeneity of Diamond-Blackfan anemia, see DBA1 (105650).

Mosaic variegated aneuploidy syndrome-7 with inflammation and tumor predisposition (MVA7) is an autosomal recessive disorder characterized by increased susceptibility to benign and malignant neoplasms beginning in early childhood. Affected individuals show dysmorphic facies and may have early developmental delay. Patient cells show a high level of aneuploidy due to defects in cell division (Villarroya-Beltri et al., 2022). For a discussion of genetic heterogeneity of MVA, see MVA1 (257300).

Tessadori-Bicknell-van Haaften neurodevelopmental syndrome-3 (TEBIVANED3) is characterized by global developmental delay with poor overall growth, impaired intellectual development, and speech difficulties. More variable features include hypotonia, microcephaly, and dysmorphic facies. The severity and manifestations of the disorder are highly variable (Tessadori et al., 2022). For a discussion of genetic heterogeneity of Tessadori-Bicknell-van Haaften neurodevelopmental disorder, see TEBIVANED1 (619758).

The basal cell nevus syndrome (BCNS), also known as Gorlin syndrome, is characterized by numerous basal cell cancers and epidermal cysts of the skin, calcified dural folds, keratocysts of the jaws, palmar and plantar pits, ovarian fibromas, medulloblastomas, lymphomesenteric cysts, fetal rhabdomyomas, and various stigmata of maldevelopment (e.g., rib and vertebral abnormalities, cleft lip or cleft palate, and cortical defects of bones) (summary by Koch et al., 2002). For a discussion of genetic heterogeneity of BCNS, see BCNS1 (109400).