Macrocephaly | |
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Specialty | Medical genetics |
Macrocephaly is a condition in which circumference of the human head is abnormally large. [1] It may be pathological or harmless, and can be a familial genetic characteristic. People diagnosed with macrocephaly will receive further medical tests to determine whether the syndrome is accompanied by particular disorders. Those with benign or familial macrocephaly are considered to have megalencephaly.
Many people with abnormally large heads or large skulls are healthy, but macrocephaly may be pathological. Pathologic macrocephaly may be due to megalencephaly (enlarged brain), hydrocephalus (abnormally increased cerebrospinal fluid), cranial hyperostosis (bone overgrowth), and other conditions. Pathologic macrocephaly is called "syndromic", when it is associated with any other noteworthy condition, and "nonsyndromic" otherwise. Pathologic macrocephaly may be caused by congenital anatomic abnormalities, genetic conditions, or by environmental events. [2]
Many genetic conditions are associated with macrocephaly, including familial macrocephaly related to the holgate gene, autism, PTEN mutations such as Cowden disease, neurofibromatosis type 1, and tuberous sclerosis; overgrowth syndromes such as Sotos syndrome (cerebral gigantism), Weaver syndrome, Simpson–Golabi–Behmel syndrome (bulldog syndrome), and macrocephaly-capillary malformation (M-CMTC) syndrome; neurocardiofacial-cutaneous syndromes such as Noonan syndrome, Costello syndrome, Gorlin syndrome, [3] (also known as basal cell nevus syndrome) and cardiofaciocutaneous syndrome; Fragile X syndrome; leukodystrophies (brain white matter degeneration) such as Alexander disease, Canavan disease, and megalencephalic leukoencephalopathy with subcortical cysts; and glutaric aciduria type 1 and D-2-hydroxyglutaric aciduria. [2]
At one end of the genetic spectrum, duplications of chromosomes have been found to be related to autism and macrocephaly; at the other end, deletions of chromosomes have been found to be related to schizophrenia and microcephaly. [4] [5] [6]
Environmental events associated with macrocephaly include infection, neonatal intraventricular hemorrhage (bleeding within the infant brain), subdural hematoma (bleeding beneath the outer lining of the brain), subdural effusion (collection of fluid beneath the outer lining of the brain), and arachnoid cysts (cysts on the brain surface). [2]
In research, cranial height or brain imaging may be used to determine intracranial volume more accurately. [2]
Below is a list of conditions featuring macrocephaly from NCBI's MedGen: [7]
Macrocephaly is customarily diagnosed if head circumference is greater than two standard deviations (SDs) above the mean. [8] Relative macrocephaly occurs if the measure is less than two SDs above the mean, but is disproportionately above that when ethnicity and stature are considered. Diagnosis can be determined in utero or can be determined within 18–24 months after birth in some cases where head circumference tends to stabilize in infants. [9] Diagnosis in infants includes measuring the circumference of the child's head and comparing how significant it falls above the 97.5 percentile of children similar to their demographic. If falling above the 97.5th percentile then the patient will be checked to determine whether there is any intracranial pressure present and whether or not immediate surgery is needed. [10] If immediate surgery is not needed then further testing will be done to determine whether the patient has either macrocephaly or benign macrocephaly.
Diagnosis for macrocephaly involves the comparison of the infant's head circumference to that of other infants of the same age and ethnicity. If a patient is suspected of having macrocephaly molecular testing will be used to confirm diagnosis. Symptoms vary on the cause of macrocephaly on the child and if the child has any other accompanying syndromes which will be determined through molecular testing.
Benign macrocephaly can occur without reason or be inherited by one or both parents (in which it is considered benign familial macrocephaly and is considered a megalencephaly form of macrocephaly). Diagnosis for familial macrocephaly is determined by measuring the head circumference of both parents and comparing it to the child's. Benign and familial macrocephaly is not associated with neurological disorders. [10] While benign and familial macrocephaly do not result in neurological disorders, neurodevelopment will still need to be assessed.[ citation needed ]
Although neurological disorders do not occur, temporary symptoms of benign and familial macrocephaly include: developmental delay, epilepsy, and mild hypotonia. [10]
Neurodevelopment is assessed for all cases and suspected cases of macrocephaly to determine whether and what treatments may be needed, and whether any other syndrome/s may be present or likely to develop.[ citation needed ]
Other forms of macrocephaly include:
Treatment varies depending on whether or not it occurs with other medical conditions in the child and where cerebrospinal fluid is present. [9] If benign and found between the brain and skull then no surgery is needed. [9] [15] If excess fluid is found between the ventricle spaces in the brain then surgery will be needed. [15]
Below is a list of syndromes associated with macrocephaly that are noted in Signs and Symptoms of Genetic Conditions: A Handbook. [10]
Megalencephaly 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.
Brachycephaly is the shape of a skull shorter than average in its species. It is perceived as a cosmetically desirable trait in some domesticated dog and cat breeds, notably the pug and Persian, and can be normal or abnormal in other animal species.
Turricephaly is a type of cephalic disorder where the head appears tall with a small length and width. It is due to premature closure of the coronal suture plus any other suture, like the lambdoid, or it may be used to describe the premature fusion of all sutures. It should be differentiated from Crouzon syndrome. Oxycephaly is a form of turricephaly where the head is cone-shaped, and is the most severe of the craniosynostoses.
Sabinas brittle hair syndrome, also called Sabinas syndrome or brittle hair-mental deficit syndrome, is an autosomal recessive congenital disorder affecting the integumentary system.
A unibrow is a single eyebrow created when the two eyebrows meet in the middle above the bridge of the nose. The hair above the bridge of the nose is of the same color and thickness as the eyebrows, such that they converge to form one uninterrupted line of hair.
Glutaric acidemia type 1 (GA1) is an inherited disorder in which the body is unable to completely break down the amino acids lysine, hydroxylysine and tryptophan. Excessive levels of their intermediate breakdown products can accumulate and cause damage to the brain, but particularly the basal ganglia, which are regions that help regulate movement. GA1 causes secondary carnitine deficiency, as glutaric acid, like other organic acids, is detoxified by carnitine. Mental retardation may occur.
Legius syndrome (LS) is an autosomal dominant condition characterized by cafe au lait spots. It was first described in 2007 and is often mistaken for neurofibromatosis type I. It is caused by mutations in the SPRED1 gene. It is also known as neurofibromatosis type 1-like syndrome.
Thoracic dysplasia-hydrocephalus syndrome is a rare autosomal recessive genetic disorder characterized by shortening of the ribs, narrowing of the chest, mild shortening of the limbs (rhizomelia), hydrocephalus, and variable developmental delays. It has been described in two siblings born to consanguineous Pakistani parents.
Buttien-Fryns syndrome is a congenital genetic disorder that causes severe oligodactyly and micrognathia. It is caused by a change in the structure of the 10q gene. The condition has been reported in four patients, two of which were siblings.
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