Early onset or syndromic epilepsy

Gene: ATP6AP2

Green List (high evidence)

Comment on list classification: There are more than 3 unrelated families reported in literature where individuals harboured hemizygous ATP6AP2 splicing variants (causing exon skipping), and presented with intellectual disability and early-onset severe epilepsy. Hence, this gene should be promoted to Green at the next update.

Created: 8 Jul 2026, 12:44 p.m. | Last Modified: 8 Jul 2026, 12:44 p.m.

Panel Version: 9.32

PMID: 41131679 Raynor et al., 2026
Authors identified three males and one female from three families with ATP6AP2 splicing variants (confirmed splicing effects by RNA-seq) and ID/DD, severe epilepsy (3 male patients), axial hypotonia, axonal neuropathy and microcephaly; the heterozygous female has a milder phenotype (at 14yrs she had mild ID, autism, and progressive microcephaly). RNA-Seq in patient-derived fibroblasts validated defective splicing, correlated with lowered ATP6AP2 protein levels in fibroblasts alongside glycosylation abnormalities. No liver involvement in these 4 patients.

PMID: 38274877 Liang et al., 2024
Report of a male patient with developmental and epileptic encephalopathy (DEE) carrying an ATP6AP2 c.858G>A (p.Ala286=) variant. SpliceAI score = Splice-Altering / moderate (0.25). An in vitro splicing assay for the ATP6AP2 gene mRNA revealed that the variant caused a deletion in exon 8 and a corresponding protein truncation of p.Phe247_Ala286del. Patient presentation: tonic seizures at 3.5 months of age, MRI indicated impaired brain white matter development and reduced left hippocampal volume.

PMID: 30985297 Hirose et al., 2019
Study identified a de novo intronic ATP6AP2 variant c.301-11_301-10delTT in a boy with XLID and fulminant early postnatal neurodegeneration. He was diagnosed at the age of 2 weeks with seizures and mild facial dysmorphism, he developed intractable seizures and generalized limb spasticity. MRI showed rapidly decreasing cortical gray and white matter volumes, a thin, poorly developing corpus callosum, and myelination deficits. Variant is expected to increase exon 4 skipping - confirmed by RT-PCR (20% full-length ATP6AP2 (fl-ATP6AP2) and 80% ATP6AP2Δe4 transcripts).

Other reports not curated in detail:
PMID: 26467484 Gupta et al., 2015: 'A splice site mutation in ATP6AP2 causes X-linked intellectual disability, epilepsy, and parkinsonism'
PMID: 15746149 Ramser et al., 2005: 'A unique exonic splice enhancer mutation in a family with X-linked mental retardation and epilepsy points to a novel role of the renin receptor'
PMID: 11782983 Hedera et al., 2002: 'Novel mental retardation-epilepsy syndrome linked to Xp21.1-p11.4'

ATP6AP2 is associated with X-linked Congenital disorder of glycosylation, type IIr, OMIM:301045, Intellectual developmental disorder, X-linked syndromic, Hedera type, OMIM:300423, and ?Parkinsonism with spasticity, X-linked, OMIM:300911 (OMIM accessed 8th July 2026).

Created: 8 Jul 2026, 12:39 p.m. | Last Modified: 8 Jul 2026, 12:53 p.m.

Panel Version: 9.32

Mode of inheritance
X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)

Phenotypes
Intellectual developmental disorder, X-linked syndromic, Hedera type, OMIM:300423; syndromic X-linked intellectual disability Hedera type, MONDO:0010319

Publications

• 11782983
• 15746149
• 26467484
• 30985297
• 38274877
• 41131679

I don't know

Review and rating collated by Tracy Lester (Oxford Medical Genetics Laboratories Oxford University Hospitals NHS Foundation Trust, 2019_02_06) on behalf of Wessex and West Midlands GLH for GMS Neurology specialist test group, for Clinical Indication R59 'Early onset or syndromic epilepsy'. Review contributors: Alison Callaway and John Taylor. Suggested gene rating: Red.

Created: 6 Aug 2019, 8:38 p.m. | Last Modified: 6 Aug 2019, 8:38 p.m.

Panel Version: 1.189

Red List (low evidence)

Very few reports of epilepsy so far.

Created: 6 Aug 2019, 8:31 p.m. | Last Modified: 6 Aug 2019, 8:31 p.m.

Panel Version: 1.188

Mode of inheritance
X-LINKED: hemizygous mutation in males, biallelic mutations in females

Phenotypes
?Parkinsonism with spasticity X-linked 300911; Mental retardation X-linked syndromic Hedera type 300423

Publications

• 26467484
• 23595882
• 29127204

I don't know

Associated with phenotype in OMIM and as a possible G2P. At least 2 variants reported, (c.321C>T, p.D107D) affects normal splicing (PMID 15746149) and c.168+6T-A predicted to affect splicing (PMID 26467484). Seizures, generalised tonic-clonic reported as a clinical feature of this phenotype

Created: 14 Dec 2017, 2:31 p.m.

Mode of inheritance
X-LINKED: hemizygous mutation in males, biallelic mutations in females

Phenotypes
Mental retardation, X-linked, syndromic, Hedera type 300423

Publications

• 26467484
• 15746149