Megalencephaly-Capillary Malformation-Polymicrogyria Syndrome (MCAP)

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OMIM® 57 602501 KEGG 36 H02153 MeSH 44 D013684 D017445 D058627 ICD10 via Orphanet 33 Q87.3 UMLS via Orphanet 71 C1865285

Orphanet 58 ORPHA60040 MedGen 41 C1865285 SNOMED-CT via HPO 68 102594003 124975008 128613002 129154003 15253005 194021007 19410003 204108000 22006008 224958001 228156007 230745008 234141001 24551003 246545002 246800008 246923005 247578003 249769001 25081006 253184003 253549006 254211001 268251006 269475001 27911000 287731003 298203008 302849000 30288003 313307000 32113001 34048007 36440009 367506006 373413006 389100007 398151007 398152000 40159009 414403008 416377005 432788009 44808001 4945003 52515009 61142002 62218008 698247007 76976005 80093006 81793007 84757009 87163000 90145001 91138005 91175000 93143009 more UMLS 70 C1865285

GARD : ²⁰ The following summary is from Orphanet, a European reference portal for information on rare diseases and orphan drugs. Orpha Number: 60040 Definition A rare developmental defect during embryogenesis that is characterized by growth dysregulation with overgrowth of the brain and multiple somatic tissues, with capillary skin malformations, megalencephaly (MEG) or hemimegalencephaly (HMEG), cortical brain abnormalities (in particular polymicrogyria), typical facial dysmorphisms, abnormalities of somatic growth with asymmetry of the body and brain, developmental delay and digital anomalies. Epidemiology Over 200 patients have been reported without sex predominance. Clinical description Symptoms are usually recognizable at birth. Their severity varies widely among patients. Megalencephaly is a major clinical feature (MEG: occipitofrontal circumference [OFC] greater than or equal to 3 SD above the mean), which sometimes progresses to hydrocephaly, malformations of cortical development with polymicrogyria and Chiari malformation. Cutaneous capillary anomalies are often scattered over the limbs, palms, soles and trunk, are frequently pink/red and are aggravated by crying and emotions. Facial dysmorphism is observed with frontal bossing, full cheeks, prominent lips and nevus flammeus of the nose and/or philtrum and upper lip. There is a delay in speech and motor skills. Patients may present neurological symptoms, mainly neonatal hypotonia, and, less frequently, seizures. Additional clinical manifestations include prenatal overgrowth, limb asymmetry, joint laxity, soft skin and thick, ''doughy'' subcutaneous tissue, postaxial polydactyly and/or syndactyly of toes 2-3 or fingers 3-4. Some patients develop neoplasias (risk of tumor development estimated at 2-3%). There is a slight increased risk for congenital heart defects and/or cardiac rhythm abnormalities. Adult OFCs range from +2 to +10 SDs above the mean. Etiology Somatic mutations of the PIK3CA gene (3q26), with evidence of postzygotic mosaicism, were found in several patients. Two individuals had a de novo germline pathogenic variant in PIK3CA. The gene PIK3CA encodes the alpha catalytic subunit of phosphatidylinositol-4,5-bisphosphate 3-kinase. PIK3CA mutations are found in several benign overgrowth syndromes, collectively known as PIK3CA -related overgrowth spectrum (PROS). The mutational spectrum in children with the disorder is broader than other PIK3CA -related overgrowth disorders. Diagnostic methods The disorder can be diagnosed based on clinical findings in individuals with classic features of MEG or HMEG (major finding 1) associated with neurologic findings of hypotonia, seizures, and mild to severe intellectual disability and characteristic capillary malformations (major finding 2) with focal or generalized somatic overgrowth.. Mosaic mutations of the PIK3CA gene were mainly identified with the advent of massively parallel or next-generation sequencing (NGS) methods. that facilitate detection of low-frequency variation. The level of mosaicism is often lowest in blood-derived DNA, and higher in saliva and fibroblast -derived DNA: multiple tissue samples should be tested, prioritizing samples other than blood. Differential diagnosis Differential diagnoses include Hemimegalencephaly (HMEG), Megalencephaly - polymicrogyria - post-axial polydactyly - hydrocephalus (MPPH), Klippel-Trenaunay syndrome (KTS), Beckwith-Wiedemann syndrome (BWS), PTEN-related overgrowth disorders. Antenatal diagnosis Findings of prenatal ultrasound include marked fetal overgrowth and progressive macrocephaly in the absence of maternal hyperglycemia or fetal hyperinsulinemia, ventriculomegaly, hydrocephalus, frontal bossing, polydactyly, limb asymmetry, polyhydramnios, hydrops fetalis and pleural effusions. Genetic counseling The risk to sibs of a proband with somatic mosaicism for a pathogenic variant in PIK3CA would be expected to be the same as in the general population. However, low-level germline mosaicism may theoretically be present in a parent of a very rare child with a germline PIK3CA pathogenic variant. Management and treatment Management requires a multidisciplinary approach (involving pediatrician, neurologist, ophthalmologist, cardiologist, orthopedist, physiatrist, ENT, and dermatologist ). Neurologic complications (obstructive hydrocephalus, increased intracranial pressure, cerebellar tonsillar ectopia or Chiari malformation; epilepsy in those with HMEG) may warrant neurosurgical intervention. Regular surveillance is recommended (brain MRI in the first 8 years of life, kidney ultrasound for Wilms tumor screening in the first 8 years of life). However, tumor risk in the disorder appears to be lower than in BWS. Prognosis Prognosis depends on the severity of symptoms. Early death, due to complex cardiac heart disease and arrhythmia, has been reported in rare occasions.

MalaCards based summary : Megalencephaly-Capillary Malformation-Polymicrogyria Syndrome, also known as megalencephaly-capillary malformation syndrome, is related to megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome 1 and polymicrogyria, and has symptoms including seizures An important gene associated with Megalencephaly-Capillary Malformation-Polymicrogyria Syndrome is PIK3CA (Phosphatidylinositol-4,5-Bisphosphate 3-Kinase Catalytic Subunit Alpha), and among its related pathways/superpathways are mTOR signaling pathway and Pathways of neurodegeneration - multiple diseases. Affiliated tissues include brain, skin and heart, and related phenotypes are macrocephaly and arteriovenous malformation

MedlinePlus Genetics : ⁴³ Megalencephaly-capillary malformation syndrome (MCAP) is a disorder characterized by overgrowth of several tissues in the body. Its primary features are a large brain (megalencephaly) and abnormalities of small blood vessels in the skin called capillaries (capillary malformations).In individuals with MCAP, megalencephaly leads to an unusually large head size (macrocephaly), which is typically evident at birth. After birth, the brain and head continue to grow at a fast rate for the first few years of life; then, the growth slows to a normal rate, although the head remains larger than average. Additional brain abnormalities are common in people with MCAP; these can include excess fluid within the brain (hydrocephalus) and abnormalities in the brain's structure, such as those known as Chiari malformation and polymicrogyria. Abnormal brain development leads to intellectual disability in most affected individuals and can also cause seizures or weak muscle tone (hypotonia). In particular, polymicrogyria is associated with speech delays and difficulty chewing and swallowing.The capillary malformations characteristic of MCAP are composed of enlarged capillaries that increase blood flow near the surface of the skin. These malformations usually look like pink or red spots on the skin. In most affected individuals, capillary malformations occur on the face, particularly the nose, the upper lip, and the area between the nose and upper lip (the philtrum). In other people with MCAP, the malformations appear as patches spread over the body or as a reddish net-like pattern on the skin (cutis marmorata).In some people with MCAP, excessive growth affects not only the brain but other individual parts of the body, which is known as segmental overgrowth. This can lead to one arm or leg that is bigger or longer than the other or a few oversized fingers or toes. Some affected individuals have fusion of the skin between two or more fingers or toes (cutaneous syndactyly).Additional features of MCAP can include flexible joints and skin that stretches easily. Some affected individuals are said to have doughy skin because the tissue under the skin is unusually thick and soft.The gene involved in MCAP is also associated with several types of cancer. Only a small number of individuals with MCAP have developed tumors (in particular, a childhood form of kidney cancer known as Wilms tumor and noncancerous tumors in the nervous system known as meningiomas).

OMIM® : ⁵⁷ Megalencephaly-capillary malformation-polymicrogyria syndrome (MCAP) is characterized by a spectrum of anomalies including primary megalencephaly, prenatal overgrowth, brain and body asymmetry, cutaneous vascular malformations, digital anomalies consisting of syndactyly with or without postaxial polydactyly, connective tissue dysplasia involving the skin, subcutaneous tissue, and joints, and cortical brain malformations, most distinctively polymicrogyria (summary by Mirzaa et al., 2012). This disorder is also known as the macrocephaly-capillary malformation (MCM) syndrome (Conway et al., 2007). Mirzaa et al. (2012) suggested use of the term MCAP rather than MCM to reflect the very large brain size, rather than simply large head size, that characterizes this syndrome, and the importance and high frequency of perisylvian polymicrogyria. (602501) (Updated 05-Apr-2021)

KEGG : ³⁶ Megalencephaly-capillary malformation (MCAP) syndrome is a rare overgrowth syndrome. The main symptoms are progressive megalencephaly, polymicrogyria, capillary malformations, syndactyly, and connective tissue dysplasia. Mutations in PIK3CA have been reported in MCAP patients.

UniProtKB/Swiss-Prot : ⁷² Megalencephaly-capillary malformation-polymicrogyria syndrome: A syndrome characterized by a spectrum of anomalies including primary megalencephaly, prenatal overgrowth, brain and body asymmetry, cutaneous vascular malformations, digital anomalies consisting of syndactyly with or without postaxial polydactyly, connective tissue dysplasia involving the skin, subcutaneous tissue, and joints, and cortical brain malformations, most distinctively polymicrogyria.

Wikipedia : ⁷³ Macrocephaly-capillary malformation (M-CM) is a multiple malformation syndrome causing abnormal body and... more...

Clinical features from OMIM®:

602501 (Updated 05-Apr-2021)

#	Description	GenomeRNAi Source Accession	Score	Top Affiliating Genes
1	Decreased viability	GR00055-A-1	10.11	PIK3CA
2	Decreased viability	GR00055-A-2	10.11	PIK3CA
3	Decreased viability	GR00173-A	10.11	PIK3R2
4	Decreased viability	GR00221-A-1	10.11	AKT3 PIK3R2 PIK3CA
5	Decreased viability	GR00221-A-2	10.11	AKT3 PIK3R2 PIK3CA
6	Decreased viability	GR00221-A-3	10.11	AKT3
7	Decreased viability	GR00221-A-4	10.11	AKT3 PIK3R2 PIK3CA
8	Decreased viability	GR00249-S	10.11	PIK3R2
9	Decreased viability	GR00301-A	10.11	AKT3 PIK3R2
10	Decreased viability	GR00402-S-2	10.11	PIK3CA
11	Decreased cell migration	GR00055-A-1	9.13	AKT3 PIK3R2
12	Decreased cell migration	GR00055-A-3	9.13	PIK3CA

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