Rare diseases · Sign or symptom
Flat occiput
HP:0005469
What it means
Reduced convexity of the occiput (posterior part of skull).
Reduced convexity of the occiput gives an appearance of flattening. There are no objective measures for convexity of the occiput, and evaluation depends heavily on the experience of the observer. This finding may or may not be accompanied by Brachycephaly (which should be coded separately), and may be observed more frequently when an infant is placed to sleep on his/her back. Occipital plagiocephaly can result from fusion or sclerosis of the lambdoid suture. If unilateral, this is accompanied by unilateral occipital flattening and bulging of the ispilateral frontal bone.
Rare diseases that can present with this32
Very common80–99%
11- Adenylosuccinate lyase deficiency
- Cleft lip/palate-intestinal malrotation-cardiopathy syndrome
- Hypertelorism-hypospadias-polysyndactyly syndrome
- Hypocalcemic vitamin D-dependent rickets
- Kleefstra syndrome due to 9q34 microdeletion
- Microbrachycephaly-ptosis-cleft lip syndrome
- Microcephaly-brachydactyly-kyphoscoliosis syndrome
- Müllerian derivatives-lymphangiectasia-polydactyly syndrome
- Myalgia-eosinophilia syndrome associated with tryptophan
- Oculocerebrofacial syndrome, Kaufman type
- Primary hypergonadotropic hypogonadism-partial alopecia syndrome
Common30–79%
9- 48,XXYY syndrome
- Angelman syndrome due to maternal 15q11q13 deletion
- Distal deletion 15q syndrome
- Early-onset seizures-distal limb anomalies-facial dysmorphism-global developmental delay syndrome
- Opsismodysplasia
- Osteopathia striata-cranial sclerosis syndrome
- Short ulna-dysmorphism-hypotonia-intellectual disability syndrome
- X-linked intellectual disability-plagiocephaly syndrome
- Zellweger syndrome
Sometimes5–29%
11- Angelman syndrome
- Angelman syndrome due to a point mutation
- Autosomal recessive myogenic arthrogryposis multiplex congenita
- Cortical dysgenesis with pontocerebellar hypoplasia due to TUBB3 mutation
- Distal 17p13.1 microdeletion syndrome
- DPM1-CDG
- Holoprosencephaly
- Intellectual disability-balding-patella luxation-acromicria syndrome
and 3 more in this range
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. A sign on this page is a conversation to have with a clinician, not a conclusion.
Part of the broader category
Also called: Flat back of skull · Flat back of the head · Flat back of the skull · Flat posterior cranium · Flat posterior head · Posterior flattening of the skull
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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.