Neurofibromatosis 1 (NF1) is a multisystem disorder characterized by multiple café au lait macules, intertriginous freckling, multiple cutaneous neurofibromas, and learning disability or behavior problems. About half of people with NF1 have plexiform neurofibromas, but most are internal and not suspected clinically. Plexiform neurofibromas can cause pain, neurologic deficits, and abnormalities of involved or adjacent structures. Less common but potentially more serious manifestations include optic nerve and other central nervous system gliomas, malignant peripheral nerve sheath tumors, scoliosis, tibial dysplasia, vasculopathy, and gastrointestinal, endocrine, or pulmonary disease.

Neurofibromatosis 2 (NF2) is characterized by bilateral vestibular schwannomas with associated symptoms of tinnitus, hearing loss, and balance dysfunction. The average age of onset is 18 to 24 years. Almost all affected individuals develop bilateral vestibular schwannomas by age 30 years. Affected individuals may also develop schwannomas of other cranial and peripheral nerves, meningiomas, ependymomas, and, very rarely, astrocytomas. Because NF2 is considered an adult-onset disease, it may be underrecognized in children, in whom skin tumors and ocular findings (retinal hamartoma, thickened optic nerves, cortical wedge cataracts, third cranial nerve palsy) may be the first manifestations. Mononeuropathy that occurs in childhood is an increasingly recognized finding; it frequently presents as a persistent facial palsy or hand/foot drop.

Werner syndrome is characterized by the premature appearance of features associated with normal aging and cancer predisposition. Individuals with Werner syndrome develop normally until the end of the first decade. The first sign is the lack of a growth spurt during the early teen years. Early findings (usually observed in the 20s) include loss and graying of hair, hoarseness, and scleroderma-like skin changes, followed by bilateral ocular cataracts, type 2 diabetes mellitus, hypogonadism, skin ulcers, and osteoporosis in the 30s. Myocardial infarction and cancer are the most common causes of death; the mean age of death in individuals with Werner syndrome is 54 years.

Neurocutaneous melanosis, or neuromelanosis, is characterized by the presence of melanin-producing cells within the brain parenchyma or leptomeninges, which may lead to clinically apparent neurologic signs and symptoms, such as seizures. Other neurologic abnormalities, including hydrocephalus, arachnoid cysts, tumors, and syringomyelia, may also occur. The disorder is a rare but severe manifestation of congenital melanocytic nevus syndrome (CMNS; 137550). Some patients with neurocutaneous melanosis or CMNS may develop malignant melanoma. The incidence of neurologic involvement, development of malignant melanoma, and death is significantly associated with the projected adult size of the largest congenital melanocytic nevus, particularly those greater than 40 cm (summary by Kinsler et al., 2008; Kinsler et al., 2013).

Li-Fraumeni syndrome is a rare disorder that greatly increases the risk of developing several types of cancer, particularly in children and young adults.\n\nA very similar condition called Li-Fraumeni-like syndrome shares many of the features of classic Li-Fraumeni syndrome. Both conditions significantly increase the chances of developing multiple cancers beginning in childhood; however, the pattern of specific cancers seen in affected family members is different.\n\nThe cancers most often associated with Li-Fraumeni syndrome include breast cancer, a form of bone cancer called osteosarcoma, and cancers of soft tissues (such as muscle) called soft tissue sarcomas. Other cancers commonly seen in this syndrome include brain tumors, cancers of blood-forming tissues (leukemias), and a cancer called adrenocortical carcinoma that affects the outer layer of the adrenal glands (small hormone-producing glands on top of each kidney). Several other types of cancer also occur more frequently in people with Li-Fraumeni syndrome.

PIK3CA-related overgrowth spectrum (PROS) encompasses a range of clinical findings in which the core features are congenital or early-childhood onset of segmental/focal overgrowth with or without cellular dysplasia. Prior to the identification of PIK3CA as the causative gene, PROS was separated into distinct clinical syndromes based on the tissues and/or organs involved (e.g., MCAP [megalencephaly-capillary malformation] syndrome and CLOVES [congenital lipomatous asymmetric overgrowth of the trunk, lymphatic, capillary, venous, and combined-type vascular malformations, epidermal nevi, skeletal and spinal anomalies] syndrome). The predominant areas of overgrowth include the brain, limbs (including fingers and toes), trunk (including abdomen and chest), and face, all usually in an asymmetric distribution. Generalized brain overgrowth may be accompanied by secondary overgrowth of specific brain structures resulting in ventriculomegaly, a markedly thick corpus callosum, and cerebellar tonsillar ectopia with crowding of the posterior fossa. Vascular malformations may include capillary, venous, and less frequently, arterial or mixed (capillary-lymphatic-venous or arteriovenous) malformations. Lymphatic malformations may be in various locations (internal and/or external) and can cause various clinical issues, including swelling, pain, and occasionally localized bleeding secondary to trauma. Lipomatous overgrowth may occur ipsilateral or contralateral to a vascular malformation, if present. The degree of intellectual disability appears to be mostly related to the presence and severity of seizures, cortical dysplasia (e.g., polymicrogyria), and hydrocephalus. Many children have feeding difficulties that are often multifactorial in nature. Endocrine issues affect a small number of individuals and most commonly include hypoglycemia (largely hypoinsulinemic hypoketotic hypoglycemia), hypothyroidism, and growth hormone deficiency.

Any malignant glioma in which the cause of the disease is a mutation in the PTEN gene.

BAP1 tumor predisposition syndrome (BAP1-TPDS) is associated with an increased risk for a specific skin lesion, BAP1-inactivated melanocytic tumors (BIMT; formerly called atypical Spitz tumors), and the following cancers, in descending order of frequency: uveal (eye) melanoma (UM), malignant mesothelioma (MMe), cutaneous melanoma (CM), renal cell carcinoma (RCC), and basal cell carcinoma (BCC). Hepatocellular carcinoma, cholangiocarcinoma, and meningioma may also be associated with BAP1-TPDS. Affected individuals can have more than one type of primary cancer. In general, the median age of onset of these tumors is younger than in the general population. UM tends to be a more aggressive class 2 tumor with higher risk for metastasis and reduced survival compared to UM occurring in the general population. Due to the limited number of families reported to date, the penetrance, natural history, and frequencies of BAP1-associated tumors are yet to be determined. Other suspected but unconfirmed tumors in BAP1-TPDS include (in alphabetic order): breast cancer, neuroendocrine carcinoma, non-small-cell lung adenocarcinoma, thyroid cancer, and urinary bladder cancer.

Individuals with MN1 C-terminal truncation (MCTT) syndrome have mild-to-moderate intellectual disability, severe expressive language delay, dysmorphic facial features (midface hypoplasia, downslanting palpebral fissures, hypertelorism, exophthalmia, short upturned nose, and small low-set ears), and distinctive findings on brain imaging (including perisylvian polymicrogyria and atypical rhombencephalosynapsis). Mild-to-moderate prelingual hearing loss (usually bilateral, conductive, and/or sensorineural) is common. Generalized seizures (observed in the minority of individuals) are responsive to anti-seizure medication. There is an increased risk for craniosynostosis and, thus, increased intracranial pressure. To date, 25 individuals with MCTT syndrome have been identified.

PIK3CA-related overgrowth spectrum (PROS) encompasses a range of clinical findings in which the core features are congenital or early-childhood onset of segmental/focal overgrowth with or without cellular dysplasia. Prior to the identification of PIK3CA as the causative gene, PROS was separated into distinct clinical syndromes based on the tissues and/or organs involved (e.g., MCAP [megalencephaly-capillary malformation] syndrome and CLOVES [congenital lipomatous asymmetric overgrowth of the trunk, lymphatic, capillary, venous, and combined-type vascular malformations, epidermal nevi, skeletal and spinal anomalies] syndrome). The predominant areas of overgrowth include the brain, limbs (including fingers and toes), trunk (including abdomen and chest), and face, all usually in an asymmetric distribution. Generalized brain overgrowth may be accompanied by secondary overgrowth of specific brain structures resulting in ventriculomegaly, a markedly thick corpus callosum, and cerebellar tonsillar ectopia with crowding of the posterior fossa. Vascular malformations may include capillary, venous, and less frequently, arterial or mixed (capillary-lymphatic-venous or arteriovenous) malformations. Lymphatic malformations may be in various locations (internal and/or external) and can cause various clinical issues, including swelling, pain, and occasionally localized bleeding secondary to trauma. Lipomatous overgrowth may occur ipsilateral or contralateral to a vascular malformation, if present. The degree of intellectual disability appears to be mostly related to the presence and severity of seizures, cortical dysplasia (e.g., polymicrogyria), and hydrocephalus. Many children have feeding difficulties that are often multifactorial in nature. Endocrine issues affect a small number of individuals and most commonly include hypoglycemia (largely hypoinsulinemic hypoketotic hypoglycemia), hypothyroidism, and growth hormone deficiency.

\n\nThe features of Cowden syndrome overlap with those of another disorder called Bannayan-Riley-Ruvalcaba syndrome. People with Bannayan-Riley-Ruvalcaba syndrome also develop hamartomas and other noncancerous tumors.  Some people with Cowden syndrome have relatives diagnosed with Bannayan-Riley-Ruvalcaba syndrome, and other affected individuals have the characteristic features of both conditions. Based on these similarities, researchers have proposed that Cowden syndrome and Bannayan-Riley-Ruvalcaba syndrome represent a spectrum of overlapping features known as PTEN hamartoma tumor syndrome (named for the genetic cause of the conditions) instead of two distinct conditions.\n\nSome people do not meet the strict criteria for a clinical diagnosis of Cowden syndrome, but they have some of the characteristic features of the condition, particularly the cancers. These individuals are often described as having Cowden-like syndrome. Both Cowden syndrome and Cowden-like syndrome are caused by mutations in the same genes.\n\nCowden syndrome is associated with an increased risk of developing several types of cancer, particularly cancers of the breast, a gland in the lower neck called the thyroid, and the lining of the uterus (the endometrium). Other cancers that have been identified in people with Cowden syndrome include kidney cancer, colorectal cancer, and an agressive form of skin cancer called melanoma. Compared with the general population, people with Cowden syndrome develop these cancers at younger ages, often beginning in their thirties or forties. People with Cowden syndrome are also more likely to develop more than one cancer during their lifetimes compared to the general population. Other diseases of the breast, thyroid, and endometrium are also common in Cowden syndrome. Additional signs and symptoms can include an enlarged head (macrocephaly) and a rare, noncancerous brain tumor called Lhermitte-Duclos disease. A small percentage of affected individuals have delayed development, intellectual disability, or autism spectrum disorder, which can affect communication and social interaction.\n\nAlmost everyone with Cowden syndrome develops hamartomas. These growths are most commonly found on the skin and mucous membranes (such as the lining of the mouth and nose), but they can also occur in the intestine and other parts of the body. The growth of hamartomas on the skin and mucous membranes typically becomes apparent by a person's late twenties.\n\nCowden syndrome is a genetic disorder characterized by multiple noncancerous, tumor-like growths called hamartomas and an increased risk of developing certain cancers.

Schwannomatosis is characterized by a predisposition to develop multiple schwannomas and, less frequently, meningiomas. Individuals with schwannomatosis most commonly present between the second and fourth decade of life. The most common presenting feature is localized or diffuse pain or asymptomatic mass. Schwannomas most often affect peripheral nerves and spinal nerves. Meningiomas occur in about 5% of individuals with schwannomatosis and have only been reported in individuals with SMARCB1-related schwannomatosis. Malignancy remains a theoretic risk especially in individuals with a SMARCB1 pathogenic variant.

NTHL1 tumor syndrome is characterized by an increased lifetime risk for colorectal cancer (CRC), breast cancer, and colorectal polyposis. Colorectal polyps can be adenomatous, hyperplastic, and/or sessile serrated. Duodenal polyposis has also been reported. Additional cancers reported in individuals with NTHL1 tumor syndrome include endometrial cancer, cervical cancer, urothelial carcinoma of the bladder, meningiomas, unspecified brain tumors, basal cell carcinomas, head and neck squamous cell carcinomas, and hematologic malignancies. The cumulative lifetime risk of developing extracolonic cancer by age 60 years has been estimated at 35% to 78%.

Tumor predisposition syndrome-2 (TPDS2) is an autosomal recessive cancer predisposition syndrome characterized by the onset of various types of tumors or malignancies in young adulthood. The most common clinical manifestations include acute myeloid leukemia (AML), myelodysplastic syndrome, colorectal adenomatous polyposis and carcinoma, and uveal melanoma, although other tumors and malignancies have been reported (summary by Palles et al., 2022). For a discussion of genetic heterogeneity of TPDS, see TPDS1 (614327).

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).