Rare diseases · Sign or symptom
Microcephaly
Abnormally small skull
HP:0000252
What it means
Head circumference below 2 standard deviations below the mean for age and gender.
Head circumference is measured from just above the glabella (the most prominent point on the frontal bone above the root of the nose) to the most posterior prominent point of the occipital bone using a tape measure. Some standard charts are organized by centiles, others by standard deviations. It is important to add an indication of how far below the normal standard the head circumference is if an accurate assessment of this can be made. Microcephaly is an absolute term. The term relative microcephaly can be used when the head size centile is less than the centile for height, for example, head size at the 3rd centile with height at the 75% for age and sex. On prenatal ultrasound, microcephaly is diagnosed if the head circumference or the biparietal diameter is more than three standard deviations below the mean. Microcephaly is divided into primary microcephaly, which is present at birth, and secondary microcephaly, which develops postnatally. The crucial difference between these groupings is that primary microcephaly is usually a static developmental anomaly, whereas secondary microcephaly indicates a progressive neurodegenerative condition
Rare diseases that can present with this607
Always100%
7Very common80–99%
73- 16p11.2p12.2microduplication syndrome
- 19p13.3microduplication syndrome
- 19q13.11microdeletion syndrome
- 2p15p16.1microdeletion syndrome
- 5q35microduplication syndrome
- 6q25.2q25.3microdeletion syndrome
- Achalasia-microcephaly syndrome
- Acrofacial dysostosis, Catania type
- Adenylosuccinate lyase deficiency
- Alopecia-intellectual disability syndrome
- Amish lethal microcephaly
- Angelman syndrome
- Aphalangy-syndactyly-microcephaly syndrome
- Atrioventricular defect-blepharophimosis-radial and anal defect syndrome
- Autosomal dominant primary microcephaly
- Autosomal recessive chorioretinopathy-microcephaly syndrome
- Autosomal recessive primary microcephaly
- Bangstad syndrome
- Bartsocas-Papas syndrome
- Blepharophimosis-intellectual disability syndrome, Ohdo type
- Bonnemann-Meinecke-Reich syndrome
- Bowen-Conradi syndrome
- Brachymorphism-onychodysplasia-dysphalangism syndrome
- Branchioskeletogenital syndrome
- BRESEK syndrome
- CAMOS syndrome
- Camptodactyly syndrome, Guadalajara type 2
- Cataract-intellectual disability-hypogonadism syndrome
- CEDNIK syndrome
- Cerebellar-facial-dental syndrome
- Cernunnos-XLF deficiency
- Chondrodysplasia-difference of sex development syndrome
- CK syndrome
- Cleft palate-large ears-small head syndrome
- COFS syndrome
- Cohen syndrome
- Congenital ichthyosis-microcephalus-tetraplegia syndrome
- Congenital osteogenesis imperfecta-microcephaly-cataracts syndrome
- Cornelia de Lange syndrome
- Corpus callosum agenesis-abnormal genitalia syndrome
- Corpus callosum agenesis-neuronopathy syndrome
- Craniofacial dysostosis-diaphyseal hyperplasia syndrome
- C syndrome
- Cutaneous mastocytosis-deafness-microtia syndrome
- Desmosterolosis
- Diabetic embryopathy
- Dihydropteridine reductase deficiency
- Distal deletion 17q syndrome
- Distal deletion 1q syndrome
- Distal duplication 5q syndrome
- Distal monosomy 7q36 syndrome
- Distal Xq28 microduplication syndrome
- Dubowitz syndrome
- Duplication of the pituitary gland
- DYRK1A-related intellectual disability syndrome
- Dysplastic cortical hyperostosis, Kozlowski-Tsuruta type
- Ear-patella-short stature syndrome
- Epilepsy-microcephaly-skeletal dysplasia syndrome
- Erythrokeratodermia variabilis
- Feingold syndrome
- Feingold syndrome type 1
- Feingold syndrome type 2
- Fetal alcohol syndrome
- Fetal methylmercury syndrome
- Filippi syndrome
- FOXG1 syndrome due to 14q12 microdeletion
- Fryns-Smeets-Thiry syndrome
- Galloway-Mowat syndrome
- Genitopatellar syndrome
- GMS syndrome
- Goldberg-Shprintzen megacolon syndrome
- Growth delay due to insulin-like growth factor type 1 deficiency
- Hall-Riggs syndrome
The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions, and Orphanet separately records 2 diseases where this sign is specifically absent. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
Also called: Abnormally small cranium · Abnormally small head · Decreased circumference of cranium · Decreased size of cranium · Decreased size of head · Decreased size of skull · Reduced head circumference · small calvarium
Tracking symptoms like this for someone? Eleplan keeps symptoms, diagnoses, medications and every specialist in one plan.
Start free with EleplanThis page uses the Human Phenotype Ontology (2026-06-23) — Human Phenotype Ontology Consortium, hpo.jax.org. Disease associations from Orphanet (INSERM), CC BY 4.0. Content is educational and is not medical advice.