Encephalocraniocutaneous lipomatosis (ECCL) comprises a spectrum of predominantly congenital anomalies. In its typical form, ECCL is characterized by congenital anomalies of the skin (nevus psiloliparus, patchy or streaky non-scarring alopecia, subcutaneous lipomas in the frontotemporal region, focal skin aplasia or hypoplasia on the scalp, and/or small nodular skin tags on the eyelids or between the outer canthus and tragus), eye (choristoma), and brain (in particular intracranial and spinal lipomas). To a much lesser degree, the bones and the heart can be affected. About 40% of affected individuals have bilateral abnormalities of the skin or the eyes. About one third of affected individuals have normal cognitive development, another one third have mild developmental delay (DD) or intellectual disability (ID), and the final one third have severe or unspecified DD/ID. Half of individuals have seizures. Affected individuals are at an increased (i.e., above the general population) risk of developing brain tumors, particularly low-grade gliomas such as pilocytic astrocytomas. There is evidence that oculoectodermal syndrome (OES) may constitute a clinical spectrum with ECCL, with OES on the mild end and ECCL on the more severe end of the spectrum.

Heterotaxy Heterotaxy ('heter' meaning 'other' and 'taxy' meaning 'arrangement'), or situs ambiguus, is a developmental condition characterized by randomization of the placement of visceral organs, including the heart, lungs, liver, spleen, and stomach. The organs are oriented randomly with respect to the left-right axis and with respect to one another (Srivastava, 1997). Heterotaxy is a clinically and genetically heterogeneous disorder. Multiple Types of Congenital Heart Defects Congenital heart defects (CHTD) are among the most common congenital defects, occurring with an incidence of 8/1,000 live births. The etiology of CHTD is complex, with contributions from environmental exposure, chromosomal abnormalities, and gene defects. Some patients with CHTD also have cardiac arrhythmias, which may be due to the anatomic defect itself or to surgical interventions (summary by van de Meerakker et al., 2011). Reviews Obler et al. (2008) reviewed published cases of double-outlet right ventricle and discussed etiology and associations. Genetic Heterogeneity of Visceral Heterotaxy See also HTX2 (605376), caused by mutation in the CFC1 gene (605194) on chromosome 2q21; HTX3 (606325), which maps to chromosome 6q21; HTX4 (613751), caused by mutation in the ACVR2B gene (602730) on chromosome 3p22; HTX5 (270100), caused by mutation in the NODAL gene (601265) on chromosome 10q22; HTX6 (614779), caused by mutation in the CCDC11 gene (614759) on chromosome 18q21; HTX7 (616749), caused by mutation in the MMP21 gene (608416) on chromosome 10q26; HTX8 (617205), caused by mutation in the PKD1L1 gene (609721) on chromosome 7p12; HTX9 (618948), caused by mutation in the MNS1 gene (610766) on chromosome 15q21; HTX10 (619607), caused by mutation in the CFAP52 gene (609804) on chromosome 17p13; HTX11 (619608), caused by mutation in the CFAP45 gene (605152) on chromosome 1q23; and HTX12 (619702), caused by mutation in the CIROP gene (619703) on chromosome 14q11. Genetic Heterogeneity of Multiple Types of Congenital Heart Defects An X-linked form of CHTD, CHTD1, is caused by mutation in the ZIC3 gene on chromosome Xq26. CHTD2 (614980) is caused by mutation in the TAB2 gene (605101) on chromosome 6q25. A form of nonsyndromic congenital heart defects associated with cardiac rhythm and conduction disturbances (CHTD3; 614954) has been mapped to chromosome 9q31. CHTD4 (615779) is caused by mutation in the NR2F2 gene (107773) on chromosome 15q26. CHTD5 (617912) is caused by mutation in the GATA5 gene (611496) on chromosome 20q13. CHTD6 (613854) is caused by mutation in the GDF1 gene (602880) on chromosome 19p13. CHTD7 (618780) is caused by mutation in the FLT4 gene (136352) on chromosome 5q35. CHTD8 (619657) is caused by mutation in the SMAD2 gene (601366) on chromosome 18q21. CHTD9 (620294) is caused by mutation in the PLXND1 gene (604282) on chromosome 3q22.

CHIME syndrome, also known as Zunich neuroectodermal syndrome, is an extremely rare autosomal recessive multisystem disorder clinically characterized by colobomas, congenital heart defects, migratory ichthyosiform dermatosis, mental retardation, and ear anomalies (CHIME). Other clinical features include distinctive facial features, abnormal growth, genitourinary abnormalities, seizures, and feeding difficulties (summary by Ng et al., 2012). The disorder is caused by a defect in glycosylphosphatidylinositol (GPI) biosynthesis. For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293).

The category of 3-methylglutaconic aciduria type IV (MGCA4) represents a heterogeneous unclassified group of patients who share mild or intermittent urinary excretion of 3-methylglutaconic acid. MGCA excretion is a nonspecific finding observed in many other disorders caused by defects in mitochondrial energy metabolism (Gunay-Aygun, 2005). For a general phenotypic description and a discussion of genetic heterogeneity of 3-methylglutaconic aciduria, see MGCA1 (250950)

A rare, genetic, multiple congenital anomalies syndrome characterized by congenital heart defects (e.g. coarctation of the aorta with or without atrioventricular canal and subaortic stenosis), associated with tongue hamartomas, postaxial hand polydactyly and toe syndactyly.

Secundum atrial septal defect (ASD) is a common congenital heart malformation that occurs as an isolated anomaly in 10% of individuals with congenital heart disease. Uncorrected ASD can cause pulmonary overcirculation, right heart volume overload, and premature death (summary by Benson et al., 1998). Genetic Heterogeneity of Atrial Septal Defect The ASD1 locus has been mapped to chromosome 5p. Other forms of atrial septal defect that are associated with other congenital heart disease but no conduction defects or noncardiac abnormalities include ASD2 (607941), caused by mutation in the GATA4 gene (600576), and ASD4 (611363), caused by mutation in the TBX20 gene (606061). ASD3 (614089) and ASD5 (612794), in which atrial septal defect is not associated with other cardiac abnormalities, are caused by mutation in the MYH6 (160710) and ACTC1 (102540) genes, respectively. ASD6 (613087), in which atrial septal defect may be associated with aneurysm of the interatrial septum and cardiac arrhythmias, is caused by mutation in the TLL1 gene (606742). ASD7 (108900), in which ASD is often associated with atrioventricular conduction defects, is caused by mutation in the NKX2-5 gene (600584). ASD8 (614433), in which ASD may be associated with other cardiac anomalies, is caused by mutation in the CITED2 gene (602937). ASD9 (614475) is caused by mutation in the GATA6 gene (601656). Somatic mutations in the HAND1 gene (602406) have been identified in tissue samples from patients with ASDs.

Patients with chromosome 2q37 deletion syndrome show highly variable clinical manifestations likely resulting from different deletion sizes and deletions of different genes. Variable clinical features included brachydactyly type E (BDE), affecting the metacarpals and metatarsals (in about 50% of patients), short stature, mild to moderate intellectual disability, behavioral abnormalities, and dysmorphic facial features. However, many individuals with deletions do not show cognitive deficits (summary by Villavicencio-Lorini et al., 2013, Wheeler et al., 2014, Jean-Marcais et al., 2015).

An extremely rare genetic congenital heart disease characterized by the presence of atrial septal defect, mostly of the ostium secundum type, associated with conduction anomalies like atrioventricular block, atrial fibrillation or right bundle branch block.

Mosaic variegated aneuploidy syndrome is an autosomal recessive disorder characterized by poor growth and variable phenotypic manifestations, such as facial dysmorphism and congenital heart defects, associated with mosaic aneuploidies resulting from defects in cell division (summary by Snape et al., 2011). See also MVA1 (257300), caused by mutation in the BUB1B gene (602860) on chromosome 15q15.

Hypertrophic cardiomyopathy (HCM) is typically defined by the presence of unexplained left ventricular hypertrophy (LVH). Such LVH occurs in a non-dilated ventricle in the absence of other cardiac or systemic disease capable of producing the observed magnitude of increased LV wall thickness, such as pressure overload (e.g., long-standing hypertension, aortic stenosis) or storage/infiltrative disorders (e.g., Fabry disease, amyloidosis). The clinical manifestations of HCM range from asymptomatic LVH to progressive heart failure to sudden cardiac death (SCD), and vary from individual to individual even within the same family. Common symptoms include shortness of breath (particularly with exertion), chest pain, palpitations, orthostasis, presyncope, and syncope. Most often the LVH of HCM becomes apparent during adolescence or young adulthood, although it may also develop late in life, in infancy, or in childhood.

Multiple types of congenital heart defects-2 (CHTD2) is characterized by variable congenital heart defects, primarily involving the valves, but also including septal defects or aneurysms, and complex defects such as tetralogy of Fallot. Dilated cardiomyopathy and myocardial noncompaction have been reported in some patients. In addition, some affected individuals exhibit facial dysmorphism and features of connective tissue disease (Thienpont et al., 2010; Ackerman et al., 2016; Ritelli et al., 2018). For a discussion of genetic heterogeneity of CHTD, see 306955.

Singleton-Merten syndrome (SGMRT) is an uncommon autosomal dominant disorder characterized by abnormalities of blood vessels, teeth, and bone. Calcifications of the aorta and aortic and mitral valves occur in childhood or puberty and can lead to early death. Dental findings include delayed primary tooth exfoliation and permanent tooth eruption, truncated tooth root formation, early-onset periodontal disease, and severe root and alveolar bone resorption associated with dysregulated mineralization, leading to tooth loss. Osseous features consist of osteoporosis, either generalized or limited to distal extremities, distal limb osteolysis, widened medullary cavities, and easy tearing of tendons from bone. Less common features are mild facial dysmorphism (high anterior hair line, broad forehead, smooth philtrum, thin upper vermilion border), generalized muscle weakness, psoriasis, early-onset glaucoma, and recurrent infections. The disorder manifests with variable inter- and intrafamilial phenotypes (summary by Rutsch et al., 2015). Genetic Heterogeneity of Singleton-Merten Syndrome An atypical form of Singleton-Merten syndrome (SGMRT2; 616298) is caused by mutation in the DDX58 gene (609631) on chromosome 9p21.

Noonan syndrome with multiple lentigines (NSML) is a condition in which the cardinal features consist of lentigines, hypertrophic cardiomyopathy, short stature, pectus deformity, and dysmorphic facial features including widely spaced eyes and ptosis. Multiple lentigines present as dispersed flat, black-brown macules, mostly on the face, neck, and upper part of the trunk with sparing of the mucosa. In general, lentigines do not appear until age four to five years but then increase to the thousands by puberty. Some individuals with NSML do not exhibit lentigines. Approximately 85% of affected individuals have heart defects, including hypertrophic cardiomyopathy (typically appearing during infancy and sometimes progressive) and pulmonary valve stenosis. Postnatal growth restriction resulting in short stature occurs in fewer than 50% of affected persons, although most affected individuals have a height that is less than the 25th centile for age. Sensorineural hearing deficits, present in approximately 20% of affected individuals, are poorly characterized. Intellectual disability, typically mild, is observed in approximately 30% of persons with NSML.

Autosomal recessive presynaptic congenital myasthenic syndrome-7B (CMS7B) is characterized by severe generalized muscle weakness apparent from birth; decreased fetal movements may be apparent in utero. Affected infants have generalized hypotonia with poor cry and feeding, head lag, and facial muscle weakness with ptosis. Some patients may have respiratory involvement. Electrophysiologic studies show decreased compound muscle action potentials (CMAPs) and a decremental response to repetitive nerve stimulation. Treatment with 3,4-diaminopyridine and pyridostigmine may result in clinical improvement (summary by Bauche et al., 2020).

Neurodevelopmental disorder with hypotonia and dysmorphic facies (NEDHYDF) is characterized by global developmental delay and hypotonia apparent from birth. Affected individuals have variably impaired intellectual development, often with speech delay and delayed walking. Seizures are generally not observed, although some patients may have single seizures or late-onset epilepsy. Most patients have prominent dysmorphic facial features. Additional features may include congenital cardiac defects (without arrhythmia), nonspecific renal anomalies, joint contractures or joint hyperextensibility, dry skin, and cryptorchidism. There is significant phenotypic variability in both the neurologic and extraneurologic manifestations (summary by Tan et al., 2022).

Severe congenital liver disease (SCOLIV) is an autosomal recessive disorder characterized by the onset of progressive hepatic dysfunction usually in the first years of life. Affected individuals show feeding difficulties with failure to thrive and features such as jaundice, hepatomegaly, and abdominal distension. Laboratory workup is consistent with hepatic insufficiency and may also show coagulation defects, anemia, or metabolic disturbances. Cirrhosis and hypernodularity are commonly observed on liver biopsy. Many patients die of liver failure in early childhood (Moreno Traspas et al., 2022).

Cardiac valvular dysplasia-2 (CVDP2) is characterized primarily by congenital stenosis and insufficiency of the semilunar valves, although mild insufficiency of the atrioventricular valves has been observed as well. Other features include subaortic stenosis and dilation of the ascending aorta and/or pulmonary artery in some patients (Wunnemann et al., 2020; Massadeh et al., 2020). For a discussion of genetic heterogeneity of CVDP, see CVDP1 (212093).