MedGen

Von Willebrand disease (VWD), a congenital bleeding disorder caused by deficient or defective plasma von Willebrand factor (VWF), may only become apparent on hemostatic challenge, and bleeding history may become more apparent with increasing age. Recent guidelines on VWD have recommended taking a VWF level of 30 or 40 IU/dL as a cutoff for those diagnosed with the disorder. Individuals with VWF levels greater than 30 IU/dL and lower than 50 IU/dL can be described as having a risk factor for bleeding. This change in guidelines significantly alters the proportion of individuals with each disease type. Type 1 VWD (~30% of VWD) typically manifests as mild mucocutaneous bleeding. Type 2 VWD accounts for approximately 60% of VWD. Type 2 subtypes include: Type 2A, which usually manifests as mild-to-moderate mucocutaneous bleeding; Type 2B, which typically manifests as mild-to-moderate mucocutaneous bleeding that can include thrombocytopenia that worsens in certain circumstances; Type 2M, which typically manifests as mild-moderate mucocutaneous bleeding; Type 2N, which can manifest as excessive bleeding with surgery and mimics mild hemophilia A. Type 3 VWD (<10% of VWD) manifests with severe mucocutaneous and musculoskeletal bleeding. [from GeneReviews]

Platelet-type bleeding disorder-24 (BDPLT24) is an autosomal dominant form of congenital macrothrombocytopenia associated with platelet anisocytosis. It is a disorder of platelet production. Affected individuals may have no or only mildly increased bleeding tendency. In vitro studies show mild platelet functional abnormalities (summary by Kunishima et al., 2011 and Nurden et al., 2011). For a discussion of genetic heterogeneity of Glanzmann thrombasthenia-like with macrothrombocytopenia, see 187800. [from OMIM]

Glanzmann thrombasthenia-2 (GT2) is an autosomal recessive bleeding disorder characterized by failure of platelet aggregation and by absent or diminished clot retraction. The abnormalities are related to quantitative or qualitative abnormalities of the GPIIb (607759)/IIIa platelet surface fibrinogen receptor complex resulting from mutations in the GPIIIa gene (Rosenberg et al., 1997). For a general phenotypic description and a discussion of genetic heterogeneity of Glanzmann thrombasthenia, see 273800. [from OMIM]

Platelet-type bleeding disorder-16 (BDPLT16) is an autosomal dominant form of congenital macrothrombocytopenia associated with platelet anisocytosis. It is a disorder of platelet production. Affected individuals may have no or only mildly increased bleeding tendency. In vitro studies show mild platelet functional abnormalities (summary by Kunishima et al., 2011 and Nurden et al., 2011). Genetic Heterogeneity of Glanzmann Thrombasthenia-like with Macrothromocytopenia See BDPLT24 (619271), caused by mutation in the ITGB3 gene (173470) on chromosome 17q21.32. Together the ITGB2B and ITBG3 genes form an integrin, known as platelet glycoprotein GPIIb/III, that is expressed on platelets. [from OMIM]

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. [from GeneReviews]

Visual impairment and progressive phthisis bulbi is characterized by poor vision at birth, with development of bilateral phthisis by adulthood (Ansar et al., 2018). [from OMIM]

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). [from OMIM]

Primary familial and congenital polycythemia (PFCP) is characterized by isolated erythrocytosis in an individual with a normal-sized spleen and absence of disorders causing secondary erythrocytosis. Clinical manifestations relate to the erythrocytosis and can include plethora, the hyperviscosity syndrome (headache, dizziness, fatigue, lassitude, visual and auditory disturbances, paresthesia, myalgia), altered mental status caused by hypoperfusion and local hypoxia, and arterial and/or venous thromboembolic events. Although the majority of individuals with PFCP have only mild manifestations of hyperviscosity such as dizziness or headache, some affected individuals have had severe and even fatal complications including arterial hypertension, intracerebral hemorrhage, deep vein thrombosis, coronary disease, and myocardial infarction. To date 116 affected individuals from 24 families have been reported. [from GeneReviews]

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. [from GeneReviews]

The Houge type of X-linked syndromic intellectual developmental disorder (MRXSHG) is characterized by delayed development, intellectual disability, speech and language delay, and early-onset seizures. EEG tends to show continuous spike-wave activity or centrotemporal spikes. Some patients may have remission of seizures by adolescence. Carrier females may be mildly affected (summary by Damiano et al., 2017). [from OMIM]

Thrombocytopenia-11 with multiple congenital anomalies and dysmorphic facies (THC11) is a syndromic disorder characterized by dysmorphic facial features, multiple congenital anomalies that may involve the heart, brain, genitourinary, endocrine, and/or skeletal systems, chronic and persistent thrombocytopenia, sometimes with leukopenia or anemia, poor growth with microcephaly, hypotonia, and mildly impaired intellectual development or learning disabilities. The disorder results from constitutive activation of the RAS signaling pathway and can be considered a RASopathy (Niemann et al., 2020; Miller et al., 2022). For a discussion of genetic heterogeneity of thrombocytopenia, see 313900. [from OMIM]

Glanzmann thrombasthenia-1 (GT1) is an autosomal recessive bleeding disorder characterized by failure of platelet aggregation and by absent or diminished clot retraction. The abnormalities are related to quantitative or qualitative abnormalities of the GPIIb/IIIa (ITGB3; 173470) platelet surface fibrinogen receptor complex resulting from mutations in the GPIIb gene (Rosenberg et al., 1997). Genetic Heterogeneity of Glanzmann Thrombasthenia See Glanzmann thrombasthenia-2 (GT2; 619267), caused by mutation the ITGB3 gene (173470) on chromosome 17q21.32. See review by Botero et al. (2020). [from OMIM]

Thrombocytopenia-6 is an autosomal dominant hematologic disorder characterized by increased bleeding episodes due to reduced platelet count and abnormal platelet morphology resulting from defective megakaryopoiesis. Patients may also have bone abnormalities, including osteoporosis or tooth loss, as well as an increased risk for myelofibrosis (summary by Turro et al., 2016). For a general phenotypic description and a discussion of genetic heterogeneity of thrombocytopenia, see 313900. [from OMIM]

Nonmedullary thyroid cancer (NMTC) comprises thyroid cancers of follicular cell origin and accounts for more than 95% of all thyroid cancer cases. The remaining cancers originate from parafollicular cells (medullary thyroid cancer, MTC; 155240). NMTC is classified into 4 groups: papillary, follicular, Hurthle cell (607464), and anaplastic. Approximately 5% of NMTC is hereditary, occurring as a minor component of a familial cancer syndrome (e.g., familial adenomatous polyposis, 175100, Carney complex, 160980) or as a primary feature (familial NMTC or FNMTC). Papillary thyroid cancer (PTC) is the most common histologic subtype of FNMTC, accounting for approximately 85% of cases (summary by Vriens et al., 2009). Follicular thyroid cancer (FTC) accounts for approximately 15% of NMTC and is defined by invasive features that result in infiltration of blood vessels and/or full penetration of the tumor capsule, in the absence of the nuclear alterations that characterize papillary carcinoma. FTC is rarely multifocal and usually does not metastasize to the regional lymph nodes but tends to spread via the bloodstream to the lung and bones. An important histologic variant of FTC is the oncocytic (Hurthle cell, oxyphilic) follicular carcinoma composed of eosinophilic cells replete with mitochondria (summary by Bonora et al., 2010). For a general phenotypic description and a discussion of genetic heterogeneity of NMTC, see NMTC1 (188550). [from OMIM]

Dabrafenib is a kinase inhibitor used in the treatment of individuals with unresectable or metastatic melanoma, metastatic non-small cell lung cancer (NSCLC), locally advanced or metastatic anaplastic thyroid cancer (ATC), pediatric low-grade glioma (LGG), and other unresectable or metastatic solid tumors with specific BRAF variants. Dabrafenib can be used as a single agent to treat melanoma with the BRAF valine 600 to glutamic acid (V600E) variant or in combination with the MEK inhibitor trametinib to treat multiple tumor types with BRAF V600E or V600K variants.The BRAF protein is an intracellular kinase in the mitogen-activated protein kinases (MAPK) pathway. Functionally, BRAF regulates essential cell processes such as cell growth, division, differentiation, and apoptosis. The gene BRAF is also a proto-oncogene—when mutated, it transforms normal cells into cancerous cells. Variation in the kinase domain of BRAF is associated with various cancers. The most common BRAF variant, V600E, constitutively activates the kinase and causes cell proliferation in the absence of growth factors that would usually be needed. The V600E variant is detected in approximately 50% of melanomas, 25% of ATC, 2% of NSCLC, and 20% of pediatric LGGs. The FDA-approved label for dabrafenib states that the presence of BRAF mutation in tumor specimens (V600E for dabrafenib monotherapy; V600E or V600K for dabrafenib plus trametinib) should be confirmed using an FDA-approved test before starting treatment with dabrafenib. Dabrafenib is not indicated for the treatment of individuals with wild-type BRAF tumors, or the treatment of colorectal cancer due to intrinsic resistance to BRAF inhibitor monotherapy. The label also states that individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency should be monitored for signs of hemolytic anemia while taking dabrafenib (1). However, it is important to note that an independent literature review by the Clinical Pharmacogenetics Implementation Consortium found no publications to support or refute this risk and thus issued no guidance for G6PD deficiency and dabrafenib therapy. [from Medical Genetics Summaries]

Vemurafenib is a kinase inhibitor used in the treatment of patients with unresectable or metastatic melanoma with the BRAF V600E variant. BRAF is an intracellular kinase in the mitogen-activated protein kinases (MAPK) pathway. BRAF is involved in regulating important cell functions such as cell growth, division, differentiation, and apoptosis. BRAF is also a proto-oncogene—when mutated it has the ability to transform normal cells into cancerous cells. Variation in the kinase domain of BRAF have been associated with various cancers. The most common BRAF variant, V600E, constitutively activates the kinase, and causes cell proliferation in the absence of growth factors that would normally be required. The V600E variant is detected in approximately 50% of melanomas. The FDA-approved drug label for vemurafenib states that the presence of BRAF V600E mutation in tumor specimens should be confirmed, using an FDA-approved test, before starting treatment with vemurafenib. The label also states that vemurafenib is not indicated for treatment of patients with wild-type BRAF melanoma. Variations in NRAS, also an oncogene, are found in up to 30% of all malignancies and in approximately 15-20% of melanomas. NRAS variants activate MAPK and have been implicated in in acquired resistance to BRAF inhibitors. Vemurafenib’s label warns that one adverse effect associated with therapy may be the progression of pre-existing chronic myelomonocytic leukemia with NRAS mutation. Other adverse effects include arthralgia, rash, alopecia, photosensitivity reaction, pruritus, and skin papilloma. [from Medical Genetics Summaries]

Any familial isolated dilated cardiomyopathy in which the cause of the disease is a mutation in the RAF1 gene. [from MONDO]

Cardiofaciocutaneous (CFC) syndrome is characterized by cardiac abnormalities (pulmonic stenosis and other valve dysplasias, septal defects, hypertrophic cardiomyopathy, rhythm disturbances), distinctive craniofacial appearance, and cutaneous abnormalities (including xerosis, hyperkeratosis, ichthyosis, keratosis pilaris, ulerythema ophryogenes, eczema, pigmented moles, hemangiomas, and palmoplantar hyperkeratosis). The hair is typically sparse, curly, fine or thick, woolly or brittle; eyelashes and eyebrows may be absent or sparse. Nails may be dystrophic or fast growing. Some form of neurologic and/or cognitive delay (ranging from mild to severe) is seen in all affected individuals. Neoplasia, mostly acute lymphoblastic leukemia, has been reported in some individuals. [from GeneReviews]

Cardiofaciocutaneous (CFC) syndrome is characterized by cardiac abnormalities (pulmonic stenosis and other valve dysplasias, septal defects, hypertrophic cardiomyopathy, rhythm disturbances), distinctive craniofacial appearance, and cutaneous abnormalities (including xerosis, hyperkeratosis, ichthyosis, keratosis pilaris, ulerythema ophryogenes, eczema, pigmented moles, hemangiomas, and palmoplantar hyperkeratosis). The hair is typically sparse, curly, fine or thick, woolly or brittle; eyelashes and eyebrows may be absent or sparse. Nails may be dystrophic or fast growing. Some form of neurologic and/or cognitive delay (ranging from mild to severe) is seen in all affected individuals. Neoplasia, mostly acute lymphoblastic leukemia, has been reported in some individuals. [from GeneReviews]

Cardiofaciocutaneous (CFC) syndrome is characterized by cardiac abnormalities (pulmonic stenosis and other valve dysplasias, septal defects, hypertrophic cardiomyopathy, rhythm disturbances), distinctive craniofacial appearance, and cutaneous abnormalities (including xerosis, hyperkeratosis, ichthyosis, keratosis pilaris, ulerythema ophryogenes, eczema, pigmented moles, hemangiomas, and palmoplantar hyperkeratosis). The hair is typically sparse, curly, fine or thick, woolly or brittle; eyelashes and eyebrows may be absent or sparse. Nails may be dystrophic or fast growing. Some form of neurologic and/or cognitive delay (ranging from mild to severe) is seen in all affected individuals. Neoplasia, mostly acute lymphoblastic leukemia, has been reported in some individuals. [from GeneReviews]