| Domain | DEE81 evidence snapshot | Evidence status |
|---|---|---|
| Identity | Developmental and epileptic encephalopathy 81 (DEE81); OMIM **618663**; severe progressive Ohtahara/early-infantile DEE phenotype. A disease-specific MONDO, Orphanet, ICD-10/11, or MeSH identifier was not established in the retrieved evidence. | Human disease-level evidence (pqac-00000002, pqac-00000009) |
| Causal gene / inheritance | **DMXL2** (Dmx-like 2; rabconnectin-3α); biallelic loss-of-function or severe hypomorphic variants; **autosomal recessive**. Parents in the three foundational families were heterozygous and clinically unaffected. | Human segregation and functional evidence (pqac-00000005, pqac-00000007) |
| Known DEE81 variants | Family 1: compound heterozygous **c.5135C>T (p.Ala1712Val)** and **c.4478C>G (p.Ser1493\*)**; Family 2: homozygous **c.4478C>A (p.Ser1493\*)**; Family 3: homozygous **c.7518-1G>A**, causing exon-31 skipping and **p.Trp2507Argfs\*4** (also rendered p.Trp2508Argfs\*4 in one passage). All were absent from gnomAD in the original report. | Human molecular evidence (pqac-00000002, pqac-00000005, pqac-00000006) |
| Foundational cohort size | **6 affected children**, comprising **3 sibling pairs from 3 unrelated families**. No sufficiently large DEE81-specific natural-history cohort was identified. | Human case series (pqac-00000002) |
| Onset, EEG, and seizures | Manifestation began on the **first day or first days of life**. All six had persistent/continuous **suppression-burst EEG** consistent with Ohtahara syndrome. Seizures were predominantly tonic, less often myoclonic, with occasional focal seizures; epilepsy was described as intractable. Exact patient-level seizure frequencies and treatment-response rates are unknown. | Human clinical evidence (pqac-00000002, pqac-00000006, pqac-00000010) |
| Development and motor function | **6/6** had profound developmental impairment, hypotonia, and quadriparesis; **0/6** acquired developmental, communicative, or motor skills after birth. | Human clinical evidence (pqac-00000002, pqac-00000006) |
| Brain MRI | Early MRI showed **thin/hypoplastic corpus callosum and hypomyelination in 6/6**. Two children had a simplified gyral pattern. Serial MRI in **3 patients**, performed **9–21 months** later, showed progressive grey- and white-matter volume loss/brain shrinkage with leukoencephalopathy. | Human imaging evidence (pqac-00000003, pqac-00000010) |
| Extra-neurologic findings | Sensorineural hearing loss and dysmorphic features occurred in **6/6**. Mild peripheral polyneuropathy occurred in **4/4 evaluated children** from Families 1 and 2; nerve-conduction testing was not reported for Family 3. Respiratory/systemic complications contributed to deaths. Detailed organ-specific frequencies and standardized quality-of-life measurements are unknown. | Human clinical evidence (pqac-00000006, pqac-00000010) |
| Mortality / prognosis | **5/6 (83%)** died before age 9; one child was alive at 15 months at reporting. Cause-specific survival curves, median survival, and treated-versus-untreated life expectancy are unknown. | Human case-series evidence (pqac-00000002, pqac-00000010) |
| Mechanism | DMXL2 deficiency disrupts V-ATPase regulation and endolysosomal homeostasis, producing defective degradation and autophagy: reduced LC3/LC3-II, p62 and polyubiquitinated-protein accumulation, and abnormal autolysosomes. Patient fibroblast abnormalities were rescued by wild-type DMXL2. Dmxl2-silenced mouse hippocampal neurons showed impaired neurite growth and synaptic loss; the link from these cellular defects to seizures is strongly supported but partly inferential. | Human cells, rescue experiments, and mouse-neuron model (pqac-00000005, pqac-00000008, pqac-00000020, pqac-00000026) |
| Diagnostics | Molecular confirmation requires identification of pathogenic/likely pathogenic variants on both **DMXL2** alleles with parental phasing. Exome/genome sequencing or a comprehensive epilepsy/DEE panel with copy-number analysis is appropriate; EEG, brain MRI, hearing assessment, developmental evaluation, and neuropathy surveillance define extent. No validated DEE81-specific biochemical biomarker or formal diagnostic criteria are known. | Disease-specific discovery plus general epilepsy-genomics evidence (pqac-00000002, pqac-00000014, pqac-00000018) |
| Treatment / trials | No disease-modifying therapy, genotype-specific drug, or relevant registered DMXL2/DEE81 interventional trial was identified. Care is supportive and phenotype-directed; no reproducible DEE81-specific antiseizure-drug response rate is available. V-ATPase, lysosomal-acidification, and autophagy modulation remain preclinical therapeutic concepts. | Evidence gap and mechanistic review (pqac-00000013, pqac-00000020) |
| Epidemiology | Population prevalence, incidence, carrier frequency, sex ratio, founder effects, and geographic-risk estimates are **unknown**. Published evidence is limited principally to three families, including consanguineous Israeli-Arab and Turkish families and a non-consanguineous Italian-Brazilian family; this does not establish population enrichment. | Very limited human case-series evidence (pqac-00000006) |


*Table: A compact evidence map of DMXL2-related DEE81, separating quantified observations from currently unknown epidemiologic, diagnostic, and therapeutic information.*