Megalencephaly-capillary malformation syndrome


The main characteristics of megalencephaly-capillary malformation (MCAP) syndrome are megalencephaly (large brain size) and a marbled appearance of the skin (called cutis marmorata), which is present at birth and is due to problem with small blood vessels called capillaries.


Medical text written February 2002 by Dr Jill Clayton-Smith. Last updated December 2012 by Professor Jill Clayton-Smith, Consultant Clinical Geneticist, St Mary’s Hospital, Manchester, UK.

What are the symptoms?

In addition to a marbled appearance to the skin, individuals may have pink/red birth marks (see entry Vascular Birthmarks), particularly over the upper lip. Macrocephaly (large head size) is usually present along with webbing between the second and third toes and sometimes between the fingers. Occasionally, extra fingers or toes may be present. It is also common to have one side of the body which is slightly larger than the other (hemihypertrophy).

Whilst cutis marmorata can occur on its own, only individuals with the other, additional features can be said to have MCAP syndrome.

Babies with MCAP syndrome often have a high birth weight. It is common for children with this condition to have low muscle tone and so there may be initial difficulties with feeding. Children with MCAP syndrome are often slow to learn to sit and walk because they have low muscle tone and very mobile joints. Many children with MCAP syndrome learn at a slower rate than normal, but the condition is extremely variable and some affected individuals have normal development.

There are other rarer complications of MCAP syndrome which include heart problems, seizures, internal blood vessel malformations and developmental abnormalities of the brain. Many children, however, have good general health.

What are the causes?

Individuals with MCAP syndrome have a change in the genetic code of a gene called PIK3CA in some, but not all of the cells in the body. When disorders arise in this way they are referred to as ‘mosaic’ disorders.

How is it diagnosed?

Diagnosis will be based on the typical features of the syndrome being observed in a child. A magnetic resonance imaging (MRI) scan may reveal characteristic appearances including a difference in the appearance of the two halves of the brain and polymicrogyria (where the folds of the brain are unusual in appearance). Genetic testing, where available, may also confirm the diagnosis but is difficult as the gene change may not be present in blood cells and it may be necessary to test other types of cell.

How is it treated?

Treatment of MCAP syndrome involves managing the various symptoms. All children with the condition should have regular check-ups by a paediatrician. Recent studies have suggested that every child should have a heart scan, an ECG, a check for thrombophilia (abnormal blood clotting) and an MRI scan of the brain and spinal cord at diagnosis. Occasionally surgery will be recommended to drain fluid or relieve pressure within the brain. In many children, although the head is larger than average, head growth stabilises and no treatment is needed. The marbled appearance of the skin tends to get less obvious with time. Children may need physiotherapy to improve muscle tone and aid mobility.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
MCAP occurs sporadically (with no previous family history), and usually affects only one member of a family. Affected families should be referred to a genetics centre for information and advice.

Prenatal diagnosis
Ultrasound scan abnormalities including increased amniotic fluid, large head size and signs of increased fluid around the baby have been observed in some affected pregnancies. To date, specific genetic testing has not been undertaken in pregnancy.

Is there support?



The Group was established in 2015. Their aims are to support families with an M-CM/MCAP diagnosis, provide a strong patient voice in policy and research and to raise awareness of M-CM/MCAP.

Group details added December 2016.

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