Trait

Decreased head circumference

An abnormally reduced head circumference in a growing child. Head circumference is measured with a nonelastic tape and comprises the distance from above the eyebrows and ears and around the back of the head. The measured HC is then plotted on an appropriate growth chart. Microcephaly is defined as a head circumference (HC) that is great than two standard deviations below the mean of age- and gender-matched population based samples. Severe microcephaly is defined with an HC that is three standard deviations below the mean.

HPO HP:0040195

Body system: Abnormality of head or neck Abnormality of the musculoskeletal system

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12 condition reports read genes linked to this trait

Dante Labs condition reports look at the genes behind groups of inherited conditions, read from one whole-genome test. Each page says which conditions and genes a report covers, how it is read and what it cannot tell you.

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15 genes linked to Decreased head circumference

Changes in these genes cause rare conditions in which Decreased head circumference is seen. Most people with this trait have none of those conditions, and a gene on this list says nothing about anyone's own genome.

Gene	How often it is seen	Conditions
BLMBLM RecQ like helicase	Often (30–79%)	In 1 condition
SIN3ASIN3 transcription regulator family member A	Often (30–79%)	In 1 condition
SIN3BSIN3 transcription regulator family member B	Often (30–79%)	In 1 condition
GALCgalactosylceramidase	Sometimes (5–29%)	In 1 condition
IGFALSinsulin like growth factor binding protein acid labile subunit	Sometimes (5–29%)	In 1 condition
PGAP2post-GPI attachment to proteins 2	Sometimes (5–29%)	In 1 condition
PGAP3post-GPI attachment to proteins phospholipase 3	Sometimes (5–29%)	In 1 condition
PIGLphosphatidylinositol glycan anchor biosynthesis class L	Sometimes (5–29%)	In 1 condition
PIGOphosphatidylinositol glycan anchor biosynthesis class O	Sometimes (5–29%)	In 1 condition
PIGVphosphatidylinositol glycan anchor biosynthesis class V	Sometimes (5–29%)	In 1 condition
PIGWphosphatidylinositol glycan anchor biosynthesis class W	Sometimes (5–29%)	In 1 condition
PIGYphosphatidylinositol glycan anchor biosynthesis class Y	Sometimes (5–29%)	In 1 condition
PSAPprosaposin	Sometimes (5–29%)	In 1 condition
CDK10cyclin dependent kinase 10	Not recorded	In 1 condition
PIGPphosphatidylinositol glycan anchor biosynthesis class P	Not recorded	In 1 condition

How often is among people with one of the gene's conditions, the most often across them, as the Human Phenotype Ontology records it. These pages describe traits and the research behind them; they are not a diagnosis, and a doctor or genetic counsellor is the person to ask about symptoms.

Narrower traits

Broader traits

Abnormality of skull size

Where this comes from

The Human Phenotype Ontology, release 2026-09-01: the trait, its names, its definition and the genes linked to it. Find out more at hpo.jax.org.
Data release 2026.10.19-9814e911.

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