Microcephaly

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Microcephaly is a neurological disorder in which the circumference of the head is at least three standard deviations smaller than average for the person's age and sex. Microcephaly may be congenital or it may develop in the first few years of life.

Pathophysiology

The disorder may stem from a wide variety of conditions that cause abnormal growth of the brain, or from syndromes associated with chromosomal abnormalities. Two copies of a loss-of-function mutation in one of the microcephalin genes causes primary microcephaly.

Microcephaly is a disorder characterized by a small brain and may be caused by a disturbance in the proliferation of nerve cells. Microcephaly may also be associated with maternal problems such as alcoholism (which can result in the Fetal alcohol syndrome disability), diabetes, or rubella (German measles). A genetic factor may play a role in causing some cases of microcephaly. Affected newborns generally have striking neurological defects and seizures. Severely impaired intellectual development is common, but disturbances in motor functions may not appear until later in life.

Causes

Common Causes

1. Anencephaly
2. Cerebral atrophy; perinatal brain damage from hypoxia
3. Congenital transplacental infection
   • Congenital toxoplasmosis
   • Congenital rubella syndrome
   • Congenital cytomegalovirus infection
   • Neonatal herpes
   • Congenital syphilis
4. Craniosynostosis (total)
5. Encephalocele
6. Micrencephaly (idiopathic small brain)

Uncommon Causes

Aicardi Goutieres syndrome Allan-Herndon-Dudley syndrome Aminopterin fetopathy Anencephaly Angelman syndrome Aspartylglucosaminuria Beckwith-Wiedemann syndrome Børjeson-Forssman-Lehman syndrome Brachmann-de Lange syndrome (de Lange syndrome) CAMFAK syndrome Cantu syndrome Cayler cardiofacial syndrome Cephalo skeletal dysplasia (Taybi Linder syndrome) Cerebrocostomandibular syndrome Ceroid lipofuscinosis, neuronal 1, infantile CHARGE syndrome Chondrodysplasia punctata (rhizomelic type) Christian syndrome (adducted thumbs syndrome) Chromosomal abnormalities Chromosome 14q deletion syndrome Chromosome 4 ring syndrome Chromosome 6 ring syndrome Chromosome 9 trisomy syndrome Chromosome syndromes Cocaine abuse Cockayne syndrome Coffin-Siris syndrome Cohen syndrome Cornelia de Lange syndrome Corpus callosum agenesis type 2 Craniosynostosis(total) Cri du chat syndromeCutis verticis gyrat Drug or poison ingestion Dubowitz syndrome Dyggve-Melchior-Clausen dysplasia Encephalocele Familial microcephaly Fanconi anaemia Feingold syndrome Fetal alcohol syndrome Fetal hydantoin syndrome(Dilantin embryopathy) Fetal trimethadione syndrome Fraser syndrome (cryptophthalmia syndrome)

Freeman-Sheldon syndrome (whistling face syndrome) Fumarase deficiency Galloway-Mowat syndrome Goltz syndrome (focal dermal hypoplasia) GOMBO syndrome Hischsprung disease-microcephaly-mental retardation syndrome Holoprosencephaly Homocystinuria Hoyeraal-Hreidarsson syndrome Incontinentia pigmenti Infantile Spasms - Microcephaly Johanson-Blizzard syndrome Juberg-Hayward syndrome Kearns-Sayre syndrome Krabbe disease (globoid cell leukodystrophy) Langer-Giedion syndrome Lathosterolosis Lenz microphthalmia syndrome Leprechaunism Lison syndrome Lissencephaly syndromes (congenital agyria) Lowry-Wood syndrome Malformations in neuronal migration - microcephaly Marinesco-Sjögren syndrome Gestational diabetes Maternal phenylketonuria Meckel syndrome Menkes syndrome (kinky-hair syndrome) Methylenetetrahydrofolate reductase deficiency Mevalonate kinase deficiency Micrencephaly (idiopathic small brain) Microcephalic osteodysplastic dysplasia Microcephaly-lymphedema syndrome Mirhosseini-Holmes-Walton syndrome Neu-Laxova syndrome Nijmegen chromosome breakage syndrome Noonan syndrome Normal variant Norman-Roberts syndrome Oculo-auriculo-vertebral spectrum (Goldenhar-Gorlin syndrome) Opitz trigonocephaly syndrome (C syndrome) Osteoporosis-pseudoglioma syndrome Otopalatodigital syndrome type 2 Pelizaeus-Merzbacher disease Phosphoehanolaminuria Pitt-Rogers-Danks syndrome Prader-Willi syndrome Prenatal radiation

Progressive encephalopathy-edema-hypsarrhythmia-optic atrophy syndrome Pseudoprogeria syndrome Pseudotoxoplasmosis syndrome Pyruvate dehydrogenase deficiency Riley-Day syndrome (familial dysautonomia) Rubinstein-Taybi syndrome Schizencephaly - microcephaly Seckel syndrome (bird-headed dwarfism) Seemanova syndrome 1 Severe maternal malnutrition Smith-Lemli-Opitz syndrome Smith-McCort dysplasia Sutherland-Haan syndrome Syphilis Taybi-Linder syndrome Toluene Trichorhinophalangeal dysplasia, type II (Langer-Giedion syndrome) and III (Ruvalcaba syndrom) Trisomy 13 syndrome(Patau syndrome) Trisomy 18 syndrome(Edwards syndrome) Trisomy 21 syndrome (Down syndrome) Trisomy 22 syndrome Trisomy 9 syndrome Upton Young syndrome Van Maldergem Wetzburger Verloes syndrome Velocardiofacial syndrome Viljone Kallis Voges syndrome Waardenburg syndrome type 3 Warburton Anyane Yeboa syndrome Weaver Williams syndrome Willems De vries syndrome Winship Viljoen Leary syndrome Wolf-Hirschhorn syndrome Worster-Drought syndrome Wrinkly skin syndrome X chromosome, duplication Xq13 1 q21 1 - Microcephaly X chromosome, trisomy Xp3 - Microcephaly X chromosome, trisomy Xq25 - Microcephaly X-linked mental retardation-hypotonic facies syndrome XXXXX syndrome Yunis-Varon syndrome Zerres Rietschel Majewski syndrome 18: del 18q syndrome 4: del 4p syndrome (Wolf-Hirschhorn syndrome) 49,XXXXX syndrome 7: del 7q syndrome 9: dup 9p syndrome

Natural History, Complications, Prognosis

Microcephaly may be congenital or it may develop in the first few years of life. Infants with microcephaly are born with either a normal or reduced head size. Subsequently the head fails to grow while the face continues to develop at a normal rate, producing a child with a small head and a receding forehead, and a loose, often wrinkled scalp. As the child grows older, the smallness of the skull becomes more obvious, although the entire body also is often underweight and dwarfed. Development of motor functions and speech may be delayed. Hyperactivity and mental retardation are common occurrences, although the degree of each varies. Convulsions may also occur. Motor ability varies, ranging from clumsiness in some to spastic quadriplegia in others. Some children will only have mild disability. Others, especially if they are otherwise growing and developing normally, will have normal intelligence and continue to develop and meet regular age-appropriate milestones.

Prognosis

In general, life expectancy for individuals with microcephaly is reduced. The prognosis varies depending on the presence of associated abnormalities.

Diagnosis

Physical Examination

Head

THe circumference of the head is smaller than 3 standard deviations below that of age sex matched individuals.

• 
  Diagram of microcephaly
• 
  Microcephaly. Primer cause unknown

Treatment

Generally there is no specific treatment for microcephaly. Treatment is symptomatic and supportive.

Related Chapters

• Hydrocephaly
• Macrocephaly
• Seckel syndrome
• Anencephaly

External links

• NINDS Microcephaly Information Page
• NINDS Overview