Although cutaneous hemangiomas are common benign tumors in neonates, they can be life-threatening when they are associated with thrombocytopenia, consumptive coagulopathy, microangiopathic hemolytic anemia, and rapid enlargement, a clinical presentation known as Kasabach-Merritt syndrome (KMS). Untreated, KMS has a 10 to 37% mortality rate (Szlachetka, 1998). With giant hemangiomas in small children, thrombocytopenia and red cell changes compatible with trauma ('microangiopathic hemolytic anemia') have been observed. The mechanism of the hematologic changes is obscure. No evidence of a simple genetic basis has been discovered. Reviews Szlachetka (1998) reviewed the approximately 205 reported cases of KMS and discussed the pathophysiology, clinical manifestations, differential diagnosis, and treatment modalities of the disorder.

Emery-Dreifuss muscular dystrophy (EDMD) is characterized by the clinical triad of: joint contractures that begin in early childhood; slowly progressive muscle weakness and wasting initially in a humero-peroneal distribution that later extends to the scapular and pelvic girdle muscles; and cardiac involvement that may manifest as palpitations, presyncope and syncope, poor exercise tolerance, and congestive heart failure along with variable cardiac rhythm disturbances. Age of onset, severity, and progression of muscle and cardiac involvement demonstrate both inter- and intrafamilial variability. Clinical variability ranges from early onset with severe presentation in childhood to late onset with slow progression in adulthood. In general, joint contractures appear during the first two decades, followed by muscle weakness and wasting. Cardiac involvement usually occurs after the second decade and respiratory function may be impaired in some individuals.

LMNA-related dilated cardiomyopathy (DCM) is characterized by left ventricular enlargement and/or reduced systolic function preceded (sometimes by many years) by or accompanied by conduction system disease and/or arrhythmias. LMNA-related DCM usually presents in early to mid-adulthood with symptomatic conduction system disease or arrhythmias, or with symptomatic DCM including heart failure or embolus from a left ventricular mural thrombus. Sudden cardiac death can occur, and in some instances is the presenting manifestation; sudden cardiac death may occur with minimal or no systolic dysfunction.

An autosomal dominant subtype of dilated cardiomyopathy caused by mutation(s) in the LDB3 gene, encoding LIM domain-binding protein 3.

Naxos disease (NXD) is characterized by arrhythmogenic right ventricular cardiomyopathy associated with abnormalities of the skin, hair, and nails. The ectodermal features are evident from birth or early childhood, whereas the cardiac symptoms develop in young adulthood or later. Clinical variability of ectodermal features has been observed, with hair anomalies ranging from woolly hair to alopecia, and skin abnormalities ranging from mild focal palmoplantar keratoderma to generalized skin fragility or even lethal neonatal epidermolysis bullosa (Protonotarios et al., 1986; Cabral et al., 2010; Pigors et al., 2011; Erken et al., 2011; Sen-Chowdhry and McKenna, 2014). Another syndrome involving cardiomyopathy, woolly hair, and keratoderma (DCWHK; 605676) is caused by mutation in the desmoplakin gene (DSP; 125647). Also see 610476 for a similar disorder caused by homozygous mutation in the DSC2 gene (125645).

Any familial isolated dilated cardiomyopathy in which the cause of the disease is a mutation in the MYH7 gene.

An autosomal dominant subtype of dilated cardiomyopathy caused by mutation(s) in the PLN gene, encoding cardiac phospholamban.

ARVC may not cause any symptoms in its early stages. However, affected individuals may still be at risk of sudden death, especially during strenuous exercise. When symptoms occur, they most commonly include a sensation of fluttering or pounding in the chest (palpitations), light-headedness, and fainting (syncope). Over time, ARVC can also cause shortness of breath and abnormal swelling in the legs or abdomen. If the myocardium becomes severely damaged in the later stages of the disease, it can lead to heart failure.\n\nArrhythmogenic right ventricular cardiomyopathy (ARVC) is a form of heart disease that usually appears in adulthood. ARVC is a disorder of the myocardium, which is the muscular wall of the heart. This condition causes part of the myocardium to break down over time, increasing the risk of an abnormal heartbeat (arrhythmia) and sudden death.

Left ventricular noncompaction (LVNC) is characterized by numerous prominent trabeculations and deep intertrabecular recesses in hypertrophied and hypokinetic segments of the left ventricle (Sasse-Klaassen et al., 2004). The mechanistic basis is thought to be an intrauterine arrest of myocardial development with lack of compaction of the loose myocardial meshwork. LVNC may occur in isolation or in association with congenital heart disease. Distinctive morphologic features can be recognized on 2-dimensional echocardiography (Kurosaki et al., 1999). Noncompaction of the ventricular myocardium is sometimes referred to as spongy myocardium. Stollberger et al. (2002) commented that the term 'isolated LVNC,' meaning LVNC without coexisting cardiac abnormalities, is misleading, because additional cardiac abnormalities are found in nearly all patients with LVNC. Genetic Heterogeneity of Left Ventricular Noncompaction A locus for autosomal dominant left ventricular noncompaction has been identified on chromosome 11p15 (LVNC2; 609470). LVNC3 (see 605906) is caused by mutation in the LDB3 gene (605906) on chromosome 10q23. LVNC4 (see 613424) is caused by mutation in the ACTC1 gene (102540) on chromosome 15q14. LVNC5 (see 613426) is caused by mutation in the MYH7 gene (160760) on chromosome 14q12. LVNC6 (see 601494) is caused by mutation in the TNNT2 gene (191045) on chromosome 1q32. LVNC7 (615092) is caused by mutation in the MIB1 gene (608677) on chromosome 18q11. LVNC8 (615373) is caused by mutation in the PRDM16 gene (605557) on chromosome 1p36. LVNC9 (see 611878) is caused by mutation in the TPM1 gene (191010) on chromosome 15q22. LVNC10 (615396) is caused by mutation in the MYBPC3 gene (600958) on chromosome 11p11. LVNC can also occur as part of an X-linked disorder, Barth syndrome (302060), caused by mutation in the TAZ gene (300394) on chromosome Xq28.

Arrhythmogenic right ventricular dysplasia (ARVD) is a clinical and pathologic entity for which the diagnosis rests on electrocardiographic and angiographic criteria; pathologic findings, replacement of ventricular myocardium with fatty and fibrous elements, preferentially involve the right ventricular free wall. It is inherited in an autosomal dominant manner with reduced penetrance and is one of the major genetic causes of juvenile sudden death. When the dysplasia is extensive, it may represent the Uhl anomaly ('parchment right ventricle'). The presenting finding is usually recurrent, sustained ventricular tachycardia with left bundle branch block configuration. Basso et al. (2009) provided a detailed review of ARVD, including diagnosis, pathogenesis, treatment options, and genetics. Genetic Heterogeneity of Familial Arrhythmogenic Right Ventricular Dysplasia Other forms of ARVD include ARVD3 (602086), mapped to chromosome 14q12-q22; ARVD4 (602087), mapped to chromosome 2q32.1-q32.3; ARVD5 (604400), caused by mutation in the TMEM43 gene (612048) on chromosome 3p23; ARVD6 (604401), mapped to chromosome 10p14-p12; ARVD8 (607450), caused by mutation in the DSP gene (125647) on chromosome 6p24; ARVD9 (609040), caused by mutation in the PKP2 gene (602861) on chromosome 12p11; ARVD10 (610193), caused by mutation in the DSG2 (125671) on chromosome 18q12; ARVD11 (610476), caused by mutation in the DSC2 gene (125645) on chromosome 18q12.1; ARVD12 (611528), caused by mutation in the JUP gene (173325) on chromosome 17q21; ARVD13 (615616), caused by mutation in the CTNNA3 gene (607667) on chromosome 10q21; ARVD14 (618920), caused by mutation in the CDH2 gene (114020) on chromosome 18q12; and ARVD15 (see 617047), caused by mutation in the FLNC gene (102565) on chromosome 7q32. The designation ARVD2 had been used for patients reported to have a form of arrhythmogenic cardiomyopathy resulting from mutation in the RYR2 gene (180902); it was later recognized that the patients had catecholamine-induced ventricular tachycardia (CPVT1; 604772) rather than arrhythmogenic cardiomyopathy (Karmouch et al., 2018). ARVD7 is a former designation for a form of myopathy and ARVD mapped to chromosome 10q22, which was later found to be a form of myofibrillar myopathy (MFM1; 601419) caused by mutation in the DES gene (125660) on chromosome 2q35. Christensen et al. (2010) screened 65 ARVD probands for mutations in 5 desmosomal genes as well as the TGFB3 gene (190230), and identified 19 different mutations in the desmosomal genes in 12 of the families, including 7 with more than 1 mutation. In 6 families, digenic mutation carriers were identified, with at least 1 of the mutations being absent in the control population. The authors stated that their findings partially supported a gene dosage effect, although phenotypic variation was large. Nitoiu et al. (2014) reviewed desmosome biology in cardiocutaneous syndromes and inherited skin disease, including discussion of the involvement of the DSP, PKP2, DSG2, DSC2, and JUP genes.

Any familial isolated arrhythmogenic right ventricular dysplasia in which the cause of the disease is a mutation in the DSC2 gene.

Familial arrhythmogenic right ventricular dysplasia-4 (ARVD4) is characterized by progressive degeneration of the myocardium of the right ventricle, with focal necrosis of muscle cells followed by adipose and connective tissue replacement. The left ventricle may be partially involved. Patches of replacement tissue result in electrical instability and arrhythmias. Patients experience syncopal episodes, and sudden death may occur (summary by Rampazzo et al., 1997). For phenotypic information and evidence of genetic heterogeneity in this disorder, see ARVD1 (107970).

ARVC may not cause any symptoms in its early stages. However, affected individuals may still be at risk of sudden death, especially during strenuous exercise. When symptoms occur, they most commonly include a sensation of fluttering or pounding in the chest (palpitations), light-headedness, and fainting (syncope). Over time, ARVC can also cause shortness of breath and abnormal swelling in the legs or abdomen. If the myocardium becomes severely damaged in the later stages of the disease, it can lead to heart failure.\n\nArrhythmogenic right ventricular cardiomyopathy (ARVC) is a form of heart disease that usually appears in adulthood. ARVC is a disorder of the myocardium, which is the muscular wall of the heart. This condition causes part of the myocardium to break down over time, increasing the risk of an abnormal heartbeat (arrhythmia) and sudden death.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a form of heart disease that usually appears in adulthood. ARVC is a disorder of the myocardium, which is the muscular wall of the heart. This condition causes part of the myocardium to break down over time, increasing the risk of an abnormal heartbeat (arrhythmia) and sudden death.\n\nARVC may not cause any symptoms in its early stages. However, affected individuals may still be at risk of sudden death, especially during strenuous exercise. When symptoms occur, they most commonly include a sensation of fluttering or pounding in the chest (palpitations), light-headedness, and fainting (syncope). Over time, ARVC can also cause shortness of breath and abnormal swelling in the legs or abdomen. If the myocardium becomes severely damaged in the later stages of the disease, it can lead to heart failure.

Brugada syndrome is characterized by cardiac conduction abnormalities (ST segment abnormalities in leads V1-V3 on EKG and a high risk for ventricular arrhythmias) that can result in sudden death. Brugada syndrome presents primarily during adulthood, although age at diagnosis may range from infancy to late adulthood. The mean age of sudden death is approximately 40 years. Clinical presentations may also include sudden infant death syndrome (SIDS; death of a child during the first year of life without an identifiable cause) and sudden unexpected nocturnal death syndrome (SUNDS), a typical presentation in individuals from Southeast Asia. Other conduction defects can include first-degree AV block, intraventricular conduction delay, right bundle branch block, and sick sinus syndrome.

Congenital long QT syndrome is electrocardiographically characterized by a prolonged QT interval and polymorphic ventricular arrhythmias (torsade de pointes). These cardiac arrhythmias may result in recurrent syncope, seizure, or sudden death (Jongbloed et al., 1999). For a discussion of genetic heterogeneity of long QT syndrome, see LQT1 (192500).

Any familial isolated dilated cardiomyopathy in which the cause of the disease is a mutation in the ACTC1 gene.

Multiple congenital anomalies-hypotonia-seizures syndrome-2 (MCAHS2) is an X-linked recessive neurodevelopmental disorder characterized by dysmorphic features, neonatal hypotonia, early-onset myoclonic seizures, and variable congenital anomalies involving the central nervous, cardiac, and urinary systems. Some affected individuals die in infancy (summary by Johnston et al., 2012). The phenotype shows clinical variability with regard to severity and extraneurologic features. However, most patients present in infancy with early-onset epileptic encephalopathy associated with developmental arrest and subsequent severe neurologic disability; these features are consistent with a form of developmental and epileptic encephalopathy (DEE) (summary by Belet et al., 2014, Kato et al., 2014). The disorder is caused by a defect in glycosylphosphatidylinositol (GPI) biosynthesis. For a discussion of genetic heterogeneity of MCAHS, see MCAHS1 (614080). For a discussion of nomenclature and genetic heterogeneity of DEE, see 308350. For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

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

A dilated cardiomyopathy that has material basis in variation in the chromosome region 9q13.

Thrombocytopenia-8 with dysmorphic features and developmental delay (THC8) is an autosomal dominant syndromic disorder characterized by early-childhood onset of chronic thrombocytopenia with anisotropy and immature enlarged platelets, usually without spontaneous bleeding episodes. Affected individuals have dysmorphic facial features and variable developmental delay with speech delay and mildly impaired intellectual development (Latham et al., 2018). For a discussion of genetic heterogeneity of thrombocytopenia, see 313900.