Миға шамадан тыс үлкейіп өсу және оның түрлері

Megalencephaly (or macrencephaly; abbreviated MEG) is a growth development disorder in which the brain is abnormally large. It is characterized by a brain with an average weight that is 2.5 standard deviations above the mean of the general population. Approximately 1 out of 50 children (2%) are said to have the characteristics of megalencephaly in the general population. A mutation in the PI3K AKT pathway is believed to be the primary cause of brain proliferation and ultimately the root cause of megalencephaly. This mutation has produced a classification of brain overdevelopment that consists of two syndromes including megalencephaly capillary malformation (MCAP) and megalencephaly polydactyly polymicrogyria hydrocephalus (MPPH). Megalencephaly is usually diagnosed at birth and is confirmed with an MRI. There are several neuropsychiatric disorders linked with megalencephaly; however, studies have shown that autism is the most prevalent association with the malformation of MEG. Although no treatment currently exists for megalencephaly, management methods are focused at reducing deficits linked with autism. Most recent research is targeted at creating inhibitors to reduce the mutational pathway that causes megalencephaly. A person with macrocephaly does not necessarily indicate that megalencephaly is also present. Large skulls usually exhibit no neurodevelopment conditions at all, meaning most individuals with macrocephaly are healthy.

Hemimegalencephaly is an extremely rare form of macrocephaly and is characterized by uneven development of brain hemispheres (one half of the brain is larger than the other). It can present by itself or in association with phakomatosis or hemigigantism. Additionally, hemimegalencephaly will frequently cause severe epilepsy, focal neuro logical deficits, macrocrania, and mild to severe intellectual disability.

Megalencephaly capillary (MCAP) is one of the two major syndromes of megalencephaly. Typically, MCAP and MPPH can be distinguished by somatic features. MCAP includes many characteristics that are observed at birth including: cutaneous vascular malformations, especially capillary malformations of the face and cutis marmorata, polydactyly, connective tissue dysplasia, and focal or segmental body overgrowth. Furthermore, MCAP can occasionally be linked with asymmetric brain overgrowth (hemimegalencephaly) as well as segmental overgrowth of the body (hemihypertrophy). People who present both megalencephaly and autistic characteristics usually also show signs of hyperactivity as a major symptom. However, there is no definitive evidence that autism is the primary cause/result of megalencephaly. Since most children with megalencephaly also have autism, the goal of treatment for MEG is focused on managing the signs and symptoms associated with autism.

Although very little is still known as to the direct cause of megalencephaly, recent studies have begun to provide early indications of possible sources for its formation. Recent research has shown that there is a strong link between genetic pathways that cause brain develop and mutations in that pathway that result in brain overgrowth.

Recent studies have shown that mutations in phosphoinositide 3 kinase (PI3K) and AKT (also known as protein kinase B) pathway have been identified in MCAP and MPPH. This pathway has proven to be an integral part of brain growth and development and is an area of interest to many researchers who study the cause of megalencephaly. Mutations in this pathway have been shown to cause a gain of function in the activation of the PI3K AKT pathway. This cellular pathway is critical in the regulation of diverse cell functions including, cell growth, proliferation, metabolism, survival, apoptosis, angiogenesis, tumorigenesis and most importantly in regards to megalencephaly, brain development. AKT is a crucial signaling molecule part of the PI3K pathway and is also involved in many cellular functions. These functions include, brain development, synaptic plasticity and neurodevelopment. Loss of function in AKT can cause microcephaly in humans while inactivation of the pathway can cause hemimegalencephaly.

Pur alpha (purα) is a sequence specific single stranded DNA and RNA binding protein. Studies have shown that the protein is primarily active during early development and is believed to have a role in brain enlargement. Although the exact function is still controversial, it is believed that pur alpha is responsible for neuronal proliferation during neurogenesis as well as the maturation of dendrites. Thus, pur alpha is also considered a potential root cause of megalencephaly and brain overgrowth.

One impact of megalencephaly is the complete lack of motor development. One medical study assessed three patients presenting megalencephaly who showed severely impaired motor and speech development as well as distinct facial abnormalities including skull bossing, a low nasal bridge and large eyes.

Diagnosis of megalencephaly has changed over the years, however, with the development of more advanced equipment, physicians have been able to confirm the disorder with better accuracy. Usually, a physical exam is first performed when characteristics of megalencephaly have appeared. This typically occurs at birth or during early child development. A physician will then take head measurements in order to determine the circumference. This is known as the head circumference.

The prognosis of megalencephaly depends heavily on the underlying cause and associated neurological disorders. Because the majority of megalencephaly cases are linked with autism, the prognosis is equivalent to the corresponding condition. Since hemimegalencephaly is associated with severe seizures, hemiparesis and intellectual disability, the result is a poor prognosis. In most cases, those diagnosed with this type of megalencephaly usually do not survive through adulthood.

Approximately one out of every 50 (2%) children in the general population are said to have megalencephaly.