DPM2-congenital disorder of glycosylation

I have enough primary-source material now to compile the full report.

Comprehensive Research Report: DPM2-Congenital Disorder of Glycosylation (DPM2-CDG)

1. Disease Information

Overview. DPM2-CDG (also designated CDG type Iu, CDG1U) is an autosomal recessive congenital disorder of glycosylation caused by biallelic pathogenic variants in DPM2, which encodes the regulatory subunit of the heterotrimeric dolichol-phosphate-mannose (Dol-P-Man/DPM) synthase complex. Because Dol-P-Man is the mannose donor for N-linked glycosylation, O-mannosylation of α-dystroglycan, protein C-mannosylation, and GPI-anchor biosynthesis, DPM2 deficiency produces a combined glycosylation defect that bridges the classic CDGs with the secondary dystroglycanopathies (congenital muscular dystrophies caused by hypoglycosylation of α-dystroglycan). It was the first disorder shown to link CDG-I biochemistry directly to a dystroglycanopathy phenotype, following earlier descriptions of DPM1-CDG and DPM3-CDG (Barone et al., Ann Neurol 2012, PMID:23109149).

Key identifiers: - OMIM (phenotype): #615042 — Congenital Disorder of Glycosylation, Type Iu (CDG1U) - OMIM (gene): 603564 — DOLICHYL-PHOSPHATE MANNOSYLTRANSFERASE 2, REGULATORY SUBUNIT; DPM2 - Gene: DPM2; HGNC: HGNC:3006; Cytogenetic location: 9q34.11 - Orphanet: ORPHA:329178 — "Congenital muscular dystrophy with intellectual disability and severe epilepsy" (the DPM2-CDG Orphanet entry) - Inheritance: Autosomal recessive - Suggested MONDO term:* a DPM2-CDG-specific MONDO ID should be confirmed directly via the Monarch/MONDO API before curation (not independently verified in this research pass — flag for OAK lookup, e.g., uv run runoak -i sqlite:obo:mondo search "DPM2-CDG").

Synonyms/alternative names: CDG1U; CDG-Iu; DPM2-CDG; Dolichyl-phosphate mannosyltransferase subunit 2 deficiency; Congenital disorder of glycosylation, type Iu; (historically grouped clinically with) muscular dystrophy-dystroglycanopathy.

Evidence basis. Essentially all available information derives from individual published patient case reports/case series (n≈6–8 patients worldwide across 4 publications spanning 2012–2023) rather than aggregated registries — this is one of the rarest known CDGs, so curation should rely on primary case reports rather than population-level resources.

2. Etiology

Disease causal factor: Biallelic (homozygous or compound heterozygous) loss-of-function/hypomorphic variants in DPM2 (9q34.11), encoding the 84-amino-acid regulatory/stabilizing subunit of the ER-membrane-embedded DPM synthase complex. This is a purely monogenic, autosomal recessive Mendelian disease — no environmental or infectious causal factors are described.

Genetic risk factors — reported pathogenic variants: | Variant(s) | Zygosity | Family/Patients | Reference | |---|---|---|---| | c.68A>G, p.Tyr23Cys (missense, TM domain 1) | Homozygous | 2 unrelated Italian patients (P4, P5) | Barone 2012, PMID:23109149 | | c.68A>G (p.Tyr23Cys) + c.4-1G>C (splice) | Compound heterozygous | 1 Italian patient (P3) | Barone 2012, PMID:23109149 | | c.139C>T, p.Arg47Ter (nonsense) + c.173G>A, p.Gly58Asp (missense) | Compound heterozygous | 1 Indian, 23-year-old male | Radenkovic et al. 2021, PMID:33129689 | | c.197G>A, p.Gly66Glu (missense, TM domain 2) | Homozygous | 2 Chinese siblings | PMID:37152991 (PMC10154465) |

Genotype–phenotype correlation: Variants localizing to the first transmembrane/domain region (e.g., p.Tyr23Cys) associate with the severe, early-lethal phenotype; variants in the second domain region (p.Gly66Glu) or the Arg47Ter/Gly58Asp combination associate with a milder, longer-surviving phenotype — "patients with variants within the region encoding the first domain had more severe clinical symptoms than those with variants within the second domain" (PMC10154465).

Population/allele-frequency risk factors: No specific ClinVar/gnomAD population enrichment or founder-effect data were identified for DPM2 variants; the G66E and Y23C alleles are absent from gnomAD/1000 Genomes/ClinVar, consistent with extreme rarity rather than population-specific founder alleles. No consanguinity data beyond standard AR expectation were specifically reported in the search results retrieved.

Protective factors: None identified — no protective variant or environmental modifier literature exists for this ultra-rare monogenic disorder.

Gene-environment interactions: Not applicable/not reported; this is a fully genetically determined enzymatic deficiency with no known environmental modifiers.

3. Phenotypes

DPM2-CDG spans a severe, early-lethal end (Barone et al. 2012) and a mild, long-survival end (Radenkovic et al. 2021; the Chinese sibling report) — genuine phenotypic heterogeneity rather than a single stereotyped presentation.

Severe end-of-spectrum (3 patients, 2 Italian families; onset at birth): - Profound/severe developmental delay, absent psychomotor development — HP:0012758 (Motor delay), HP:0001263 (Global developmental delay) - Intractable/treatment-resistant epilepsy, described as "severe epilepsy" — HP:0001250 (Seizure), HP:0002373 (Febrile/other- consider HP:0011097 for epileptic spasms if applicable) - Progressive microcephaly — HP:0000252 - Severe hypotonia — HP:0001252 - Elevated blood creatine kinase — HP:0003236 (Elevated CK) - Mild cerebellar hypoplasia in one patient — HP:0007360 - Early fatal outcome: deaths at 3 years, 16 months, and 7 months of age - Muscle biopsy: deficient O-mannosylation of α-dystroglycan on immunohistochemistry, consistent with dystroglycanopathy-type congenital muscular dystrophy — HP:0003198 (Myopathy), HP:0009046 (Diffusely decreased α-dystroglycan immunostaining, if precise term available)

Mild end-of-spectrum (23-year-old Indian male, PMID:33129689): - Truncal hypotonia and hypertonicity (mixed tone abnormality) — HP:0001252 / HP:0001276 - Congenital heart defects — HP:0001627 - Intellectual disability (mild-moderate) — HP:0001249 - Generalized muscle wasting — HP:0003202 - Alive at 23 years — markedly better survival than the severe cohort

Mild end-of-spectrum (2 Chinese sisters, PMID:37152991, ages 11 and 20 years): - Motor and language developmental delay (delayed head control to 4 months, walking at 3 years in one) — HP:0001270 - Mild intellectual disability — HP:0001256 - Hypotonia (elder sibling) / hypertonia (younger sibling) — mixed tone findings - Strabismus — HP:0000486 - Recurrent infections in preschool years — HP:0002719 - Exercise intolerance — HP:0003546 - Markedly elevated CK (2097 and 2022 U/L; reference 20–250) and CK-MB elevation — HP:0003236 - Peripheral nerve involvement: slowed motor nerve conduction velocity, prolonged motor latency — HP:0003431 - Brain MRI: demyelinating lesions in bilateral parietal white matter — HP:0002500 (or HP:0032131) - EEG: mildly slowed occipital background — HP:0011182 - Orthopedic sequela requiring Achilles tendon lengthening (contracture) — HP:0001371

Severity/progression: Bimodal — either a rapidly progressive, fatal infantile neuromuscular/epileptic encephalopathy, or a stable/slowly progressive congenital myopathy-intellectual disability phenotype persisting into adulthood. No formal QOL instrument (EQ-5D/SF-36) data were located for this disorder given its extreme rarity; QOL impact can be inferred as substantial in the severe form (early death, no psychomotor development) and moderate in the mild form (chronic disability, preserved survival to adulthood).

4. Genetic/Molecular Information

Causal gene: DPM2 (HGNC:3006; OMIM *603564; chr9q34.11). Encodes an 84-amino-acid, two-transmembrane-domain ER integral membrane protein.

Variant classes reported: missense (p.Tyr23Cys, p.Gly58Asp, p.Gly66Glu), nonsense (p.Arg47Ter), and a canonical splice-acceptor variant (c.4-1G>C). All are germline, biallelic, loss-of-function or hypomorphic — no somatic DPM2 variants are described (not a cancer-associated gene in this context).

Functional consequences: - Reduced DPM2 protein expression in patient fibroblasts (compound heterozygous R47X/G58D case), with secondary reduction of DPM1 protein — loss-of-function/destabilization of the complex. - Conversely, the G66E variant, when overexpressed in HCT116 cells, showed increased DPM2 mRNA and protein but still produced a functional glycosylation defect (significant decrease in ICAM1, "a universal biomarker for hypoglycosylation in patients with CDG") — indicating the pathogenic mechanism is not simply reduced protein abundance but impaired function/regulatory activity, without altering ER subcellular localization. - Net biochemical consequence in all cases: reduced Dol-P-Man synthesis → defective N-glycan precursor assembly (CDG type I biochemical pattern), deficient O-mannosylation of α-dystroglycan, and (mechanistically expected, per GPI-pathway biology) defective GPI-anchor mannosylation.

Allele frequency: All reported pathogenic DPM2 alleles are absent or near-absent from gnomAD/1000 Genomes/ClinVar population databases, consistent with an ultra-rare AR disease.

Modifier genes: None specifically documented; genotype-driven severity (TM domain 1 vs. domain 2 location) functions as the main documented "modifier" of phenotype, as above.

Chromosomal abnormalities: None reported; DPM2-CDG is due to sequence-level variants, not structural/copy-number changes.

Epigenetic information: No DPM2-CDG-specific methylation/histone data were identified.

Suggested HGNC/ontology binding for curation: hgnc:3006 (lowercase per dismech convention), gene symbol DPM2.

5. Environmental Information

No environmental, lifestyle, or infectious contributing factors are described for DPM2-CDG — it is a purely monogenic enzymatic-deficiency disorder. (Infections were reported as a consequence — "recurrent infections during preschool years" in one sibling case — rather than a cause, plausibly reflecting immune-glycoprotein hypoglycosylation, a recognized theme across CDGs broadly; see immunological-involvement-in-CDG literature, PMC7408855, for the general mechanism, though not DPM2-specific.)

6. Mechanism / Pathophysiology

Causal chain (upstream → downstream):

1. Molecular lesion: Biallelic DPM2 variants (missense/nonsense/splice) → loss or dysfunction of the DPM2 regulatory subunit.
2. Complex destabilization: DPM synthase is a heterotrimer — DPM1 (catalytic, cytoplasmic-facing), DPM2 (ER membrane, stabilizes DPM1's correct ER localization and enhances dolichol-phosphate binding to DPM1), and DPM3 (tethers/stabilizes DPM1 at the ER membrane). Loss of DPM2 function destabilizes DPM1 localization/expression and impairs dolichol-phosphate binding.
3. Enzymatic consequence: Reduced synthesis of dolichol-phosphate-mannose (Dol-P-Man) from GDP-mannose + dolichol-phosphate in the ER membrane (GO:0004582, dolichyl-phosphate beta-D-mannosyltransferase activity; the complex itself localizes to GO:0005789, endoplasmic reticulum membrane).
4. Multi-pathway mannose-donor deficiency (Dol-P-Man is required by four distinct downstream pathways):
5. N-linked glycosylation: impaired mannosylation of the dolichol-linked oligosaccharide (LLO) precursor in the ER lumen → truncated/hypoglycosylated LLO → hypoglycosylated glycoproteins (CDG type I biochemical signature). Lipid-linked oligosaccharide analysis in patient fibroblasts showed accumulation of the truncated intermediate Dol-PP-GlcNAc₂Man₅ (Barone et al. 2012), diagnostic of a defect at/after the Dol-P-Man-dependent mannosylation steps of LLO assembly.
6. O-mannosylation of α-dystroglycan: loss of Dol-P-Man-dependent O-mannosyl transfer onto α-dystroglycan (POMT1/POMT2-catalyzed step) → hypoglycosylated α-dystroglycan → loss of its laminin-binding function in the extracellular matrix → secondary dystroglycanopathy with muscular dystrophy features (confirmed by reduced α-dystroglycan immunostaining on muscle biopsy in the Barone cohort).
7. Protein C-mannosylation (e.g., of thrombospondin repeats) — also Dol-P-Man-dependent, mechanistically implicated though not specifically assayed in these patients.
8. GPI-anchor biosynthesis: Dol-P-Man is required for mannosylation steps of the GPI-anchor precursor in the ER; DPM2-deficient cells accumulate GPI intermediates lacking mannose, and GPI-anchored proteins such as alkaline phosphatase are degraded/mis-processed rather than properly surface-expressed — mechanistically linking DPM2-CDG to the broader GPI-anchor-deficiency (CDG type II/IV) disease class.
9. Cellular/tissue consequence: Combined N-glycan and O-mannosylation/GPI defects → skeletal muscle membrane fragility and impaired laminin-dystroglycan-ECM linkage (myopathy/elevated CK), CNS glycoprotein/glycolipid dysfunction (developmental delay, seizures, white-matter/demyelinating change, cerebellar hypoplasia), and generalized hypoglycosylation of serum glycoproteins (abnormal transferrin isoelectric focusing pattern, CDG type I).
10. Downstream systemic consequence: In the Radenkovic et al. (2021) glycomics/lipidomics study, secondary alterations in phospholipid and sphingolipid metabolism were identified, suggesting broader downstream metabolic perturbation beyond glycoprotein synthesis alone.

Suggested ontology terms for pathophysiology nodes: - GO (molecular function): GO:0004582 (dolichyl-phosphate beta-D-mannosyltransferase activity) - GO (biological process): GO:0006486 (protein glycosylation), GO:0035269 (protein O-linked mannosylation), GO:0006506 (GPI anchor biosynthetic process), GO:0009101 (glycoprotein biosynthetic process) - GO (cellular component): GO:0005789 (endoplasmic reticulum membrane), GO:0033185 (dolichol-phosphate-mannose synthase complex, if present in current GO) - CL (cell types): CL:0000188 (skeletal muscle cell/myocyte), CL:0000540 (neuron) — reflecting the two principal affected tissues - UBERON: UBERON:0001134 (skeletal muscle tissue), UBERON:0000955 (brain)

Molecular/omics profiling available: Lipid-linked oligosaccharide (LLO) profiling (Barone 2012); glycomics + lipidomics (phospholipid/sphingolipid) profiling (Radenkovic 2021); targeted transcript/protein overexpression functional assay with ICAM1 as a glycosylation reporter (PMC10154465). No published single-cell, spatial transcriptomic, or CRISPR functional-genomics screen specific to DPM2-CDG was identified.

7. Anatomical Structures Affected

Organ level: - Primary: Skeletal muscle (dystroglycanopathy-type myopathy), central nervous system (developmental delay, epilepsy, structural brain abnormality) - Secondary/variable: Cardiovascular system (congenital heart defects in the mild-phenotype adult patient), peripheral nervous system (demyelinating peripheral neuropathy in the Chinese sibling case), craniofacial (dysmorphic features, micrognathia, malocclusion in the severe Barone cohort), musculoskeletal (congenital joint contractures, scoliosis, strabismus/ocular findings) - Body systems involved: musculoskeletal, nervous (central and peripheral), cardiovascular, ophthalmologic

Tissue/cell level: - Skeletal myofibers (CL:0000188/CL:0000737) — dystrophic changes, hypoglycosylated α-dystroglycan on the sarcolemma - Neurons and white-matter oligodendrocyte-myelin unit (demyelinating lesions reported) — CL:0000128 (oligodendrocyte) - Cerebellar tissue (hypoplasia in one Italian patient)

Subcellular level: - Endoplasmic reticulum (site of DPM synthase complex and Dol-P-Man synthesis) — GO:0005789 - ER lumen (site of LLO assembly and N-glycan precursor mannosylation) - Plasma membrane (site of hypoglycosylated α-dystroglycan and deficient GPI-anchored protein display)

Localization/laterality: Bilateral/symmetric involvement is described (e.g., bilateral parietal white-matter demyelination); no lateralized/asymmetric pattern reported.

8. Temporal Development

Onset: Congenital in essentially all reported cases — severe cases present at birth (hypotonia, dysmorphism, joint contractures); milder cases present in early childhood with developmental/motor/language delay (walking delayed to 3 years in one sibling), later diagnosed retrospectively in adulthood.

Onset pattern: Insidious/chronic developmental presentation in the mild phenotype; acute/severe neonatal presentation with rapid multisystem involvement in the severe phenotype.

Progression: - Severe phenotype: Rapidly progressive, fatal — deaths at 7 months, 16 months, and 3 years of age; intractable epilepsy and progressive microcephaly documented. - Mild phenotype: Stable-to-slowly progressive chronic course; patients survive into the third decade of life (23-year-old male; 20-year-old sibling) with persistent but non-fatal disability (intellectual disability, myopathy, exercise intolerance).

Disease duration: Lifelong/chronic in survivors; the disease is not self-limited.

Patterns: No remission pattern is described (this is a structural enzymatic deficiency, not an episodic/relapsing-remitting disease). No specific "critical period" intervention window has been established given the absence of disease-modifying therapy.

9. Inheritance and Population

Epidemiology: DPM2-CDG is ultra-rare — only approximately 6–8 patients have been reported in the peer-reviewed literature worldwide as of the most recent identified report (2023): 3 from 2 Italian families (Barone 2012), 1 Indian adult male (Radenkovic 2021), and 2 Chinese sisters (2023). No formal prevalence/incidence rate (cases per 100,000) has been established or published; combined N-linked CDG prevalence across ~27 disorders has been estimated around 1 in 22,000 in European populations, but DPM2-CDG specifically is far rarer than the more common subtypes (e.g., PMM2-CDG).

Inheritance pattern: Autosomal recessive (biallelic variants required in all reported cases — either homozygous or compound heterozygous).

Penetrance: Full penetrance is implied by all reported biallelic carriers being clinically affected (no unaffected biallelic carriers reported), though the sample size is too small for formal penetrance estimation.

Expressivity: Markedly variable expressivity — this is the disease's most notable population-genetics feature, spanning neonatal-lethal to adult-viable mild phenotypes, correlating with variant location (TM domain 1 vs domain 2/other).

Genetic anticipation: Not applicable (not a repeat-expansion disorder).

Founder effects/consanguinity: Not explicitly documented in the retrieved literature; the 2 Italian families with the same p.Tyr23Cys variant (one homozygous in 2 patients) could suggest a possible regional founder allele, but this has not been formally established.

Carrier frequency: Not established; consistent with allele absence from gnomAD.

Population demographics: Cases reported from Italy, India, and China — no evidence of a specific ethnic/geographic predisposition; likely reflects ascertainment/publication bias rather than a true geographic pattern for an ultra-rare AR disease.

Sex ratio: Reported cases include both sexes — 2 males + 1 female of unspecified sex noted in the severe Italian cohort description ("affected boys" is mentioned for 2 of the 3 severe patients), 1 male (Indian adult), 2 females (Chinese siblings) — no clear sex bias is apparent, consistent with autosomal inheritance.

Age distribution: Bimodal — infantile deaths (7–36 months) in the severe subgroup vs. surviving pediatric/adult patients (11, 20, 23 years) in the mild subgroup.

10. Diagnostics

Laboratory tests: - Serum creatine kinase (CK): Markedly elevated in all reported patients (up to ~2000 U/L; reference range 20–250 U/L) — reflects the myopathic/dystroglycanopathy component. - Transferrin isoelectric focusing (IEF): Shows a CDG type I pattern (cathodic shift due to under-sialylated, hypoglycosylated N-glycans from incomplete LLO assembly) — the classic first-line CDG screening test (gold standard per general CDG diagnostic literature). - Lipid-linked oligosaccharide (LLO) analysis in cultured fibroblasts: Diagnostic biochemical signature — accumulation of the truncated intermediate Dol-PP-GlcNAc₂Man₅, localizing the biosynthetic block to the Dol-P-Man-dependent mannosylation steps. - ICAM1 expression assay: Used as a functional glycosylation biomarker in one functional-variant study (decreased with pathogenic DPM2 variant expression).

Biomarkers: Elevated CK (muscle-specific); abnormal transferrin glycoform pattern (glycosylation-specific); reduced ICAM1 as an experimental hypoglycosylation reporter.

Imaging: Brain MRI — cerebellar hypoplasia (severe cases); demyelinating white-matter lesions, bilateral parietal distribution (mild case).

Electrophysiology: EEG — epileptiform/slowed background activity; nerve conduction studies — slowed motor conduction velocity and prolonged motor latency (peripheral neuropathy component in at least one mild-phenotype patient).

Biopsy/histopathology findings: Skeletal muscle biopsy immunohistochemistry demonstrating deficient O-mannosylation of α-dystroglycan — the confirmatory tissue-level test linking the biochemical CDG-I finding to the dystroglycanopathy phenotype.

Genetic testing: Confirmatory diagnosis requires DPM2 sequencing (single-gene test, CDG gene panel, or exome/genome sequencing given the extreme rarity and phenotypic overlap with other CDG-I subtypes and dystroglycanopathies). Given the phenotypic and biochemical overlap with DPM1-CDG and DPM3-CDG, a CDG/dystroglycanopathy gene panel approach (covering DPM1, DPM2, DPM3, POMT1/2, POMGNT1/2, FKTN, FKRP, LARGE1, B3GALNT2, etc.) is the pragmatic first-tier test; single-gene DPM2 testing is appropriate when biochemical/biopsy findings (combined CDG-I pattern + dystroglycan hypoglycosylation) point specifically to the DPM synthase complex.

Differential diagnosis: Other DPM-synthase-complex CDGs (DPM1-CDG, DPM3-CDG — allelic-complex disorders with overlapping combined CDG-I/dystroglycanopathy biochemistry); other secondary dystroglycanopathies (POMT1/2-, POMGNT1/2-, FKTN-, FKRP-, LARGE1-, B3GALNT2-related congenital muscular dystrophies, e.g., Walker-Warburg syndrome/muscle-eye-brain disease spectrum); other CDG type I disorders (PMM2-CDG, ALG-family CDGs) presenting with elevated CK and developmental delay; GPI-anchor-deficiency disorders (PIGA, PIGV, PIGO, etc.) given the shared GPI-mannosylation defect.

Screening: No population/newborn screening program exists for this ultra-rare disorder; diagnosis is case-by-case, typically prompted by a combination of unexplained developmental delay/epilepsy/hypotonia with elevated CK, triggering CDG biochemical screening (transferrin IEF) followed by molecular confirmation.

11. Outcome/Prognosis

Survival/mortality: Bimodal, variant-dependent: - Severe phenotype (TM-domain-1 variants, e.g., p.Tyr23Cys): Uniformly fatal in infancy/early childhood — reported deaths at 7 months, 16 months, and 3 years. - Mild phenotype (other variants): Survival into adulthood documented (23-year-old male alive at report; siblings aged 11 and 20 alive at report) — no mortality reported in this subgroup.

No formal actuarial life-expectancy or population-level mortality-rate data exist given the rarity of the disease.

Morbidity/function: In survivors — chronic intellectual disability (mild-moderate), myopathy/generalized muscle wasting, exercise intolerance, orthopedic complications (contractures requiring surgical correction), and in one case peripheral neuropathy. No standardized QOL instrument data identified.

Complications: Intractable epilepsy (severe form); congenital heart defects (mild-form adult patient); recurrent infections (childhood, mild-form siblings) — plausibly reflecting broader hypoglycosylation of immune glycoproteins, consistent with general CDG immunological literature, though not specifically studied in DPM2-CDG.

Prognostic factors: The single most important documented prognostic factor is variant location within the DPM2 protein — first transmembrane-domain variants (p.Tyr23Cys) predict a severe/lethal course, while variants outside this region (p.Gly66Glu; p.Arg47Ter/p.Gly58Asp) predict a milder, longer-surviving course. No molecular biomarker (beyond genotype) has been validated as prognostic.

Recovery potential: None — this is a fixed enzymatic/structural deficiency with a progressive-to-stable neuromuscular course; there is no disease-modifying treatment altering the underlying trajectory.

12. Treatment

Pharmacotherapy: No DPM2-CDG-specific or DPM-synthase-complex-targeted pharmacological therapy exists. Unlike PMM2-CDG (where oral D-mannose and D-galactose supplementation have shown biochemical/clinical benefit in some patients — Ligezka et al., PMC8359111; PMC7510076) or MPI-CDG (mannose-responsive) and SLC35C1-CDG/PIGM-CDG/PGM1-CDG (which have specific targeted therapies per the general CDG treatment literature), DPM2-CDG has no established substrate-supplementation or targeted therapy — the defect is upstream at the level of Dol-P-Man synthesis itself (regulatory subunit dysfunction), not substrate availability, so simple mannose supplementation would not be expected to bypass the enzymatic block. This is an important curation distinction from PMM2-CDG. - NCIT suggestion for generic management: NCIT:C15747 (Supportive Care)

Symptomatic/supportive management (documented in case reports): - Anti-seizure medication for intractable epilepsy in the severe phenotype (specific agents not detailed in retrieved abstracts) — NCIT:C15986 (Pharmacotherapy) - Orthopedic surgical correction — Achilles tendon lengthening for contracture in one sibling — NCIT:C15329 (Surgical Procedure) / NCIT:C16186 (Orthopedic Surgical Procedure) - Physical therapy / rehabilitative management for hypotonia/motor delay — NCIT:C15302 (Physical Therapy) - Nutritional/growth support (implied for failure to thrive in severe neonatal presentations) — NCIT:C15447 (Dietary Intervention) - Cardiac management for congenital heart defects in the mild adult phenotype — cardiology follow-up/surgical repair as indicated

Advanced/experimental therapeutics: No gene therapy, cell therapy, RNA-based therapy, or clinical trial specific to DPM2-CDG was identified (no ClinicalTrials.gov entries located in this search). Given the extreme rarity (<10 published patients), a dedicated interventional trial is unlikely to exist.

Genetic counseling: Recommended given autosomal recessive inheritance and 25% recurrence risk per pregnancy for carrier parents — NCIT:C15240 (Genetic Counseling).

Treatment strategy: Management is multidisciplinary and purely supportive/symptom-directed (neurology for seizures, orthopedics for contractures/scoliosis, cardiology as needed, physical/occupational therapy, nutritional support) — no disease-modifying or curative approach currently exists.

13. Prevention

Primary prevention: None available (no environmental risk factor to modify; a purely genetic AR disease).

Secondary prevention/screening: No population or newborn screening program exists. In families with a known proband, carrier testing and prenatal/preimplantation genetic diagnosis are the applicable prevention strategies once the familial DPM2 variants are identified — standard for any AR Mendelian disorder with 25% recurrence risk.

Genetic counseling: Central preventive/family-planning tool — informing carrier parents of recurrence risk and reproductive options (prenatal diagnosis, PGD/IVF) — NCIT:C15240.

Tertiary prevention: Anticipatory multidisciplinary surveillance (seizure monitoring/management, orthopedic monitoring for contractures/scoliosis, cardiac surveillance, developmental/rehabilitative support) to reduce complications in affected individuals, particularly in the milder, longer-surviving phenotype.

Immunization/public health/prophylaxis: No disease-specific vaccination, public-health, or prophylactic-medication strategy is described.

14. Other Species / Natural Disease

Taxonomy: No naturally occurring DPM2-deficient disease has been reported in non-human species (companion animals, wildlife) — this appears to be a human-only reported clinical entity; no OMIA (Online Mendelian Inheritance in Animals) entry was identified in this search.

Orthologous gene: Mouse Dpm2 (MGI:1330238) is the confirmed ortholog; used exclusively for laboratory knockout modeling (see Model Organisms below), not for natural/spontaneous veterinary disease.

Comparative biology: The DPM synthase complex (DPM1/DPM2/DPM3) is evolutionarily conserved from yeast to humans — a functional DPM2 homolog exists in Saccharomyces cerevisiae (Yil102c-A, PMC7728079), underscoring deep conservation of Dol-P-Man biosynthesis machinery across eukaryotes and validating yeast as a tool for functional variant characterization (as used for the related PMM2-CDG disorder, though not yet specifically published for DPM2 variants in the retrieved literature).

Zoonotic potential/transmission: Not applicable — this is a non-infectious, purely genetic disorder.

15. Model Organisms

Mouse: - Constitutive Dpm2 knockout is homozygous embryonic/perinatal lethal — "Knockout of the mouse homolog of human DPM2 is homozygous-lethal (defined as absence of homozygous mice after screening of at least 28 pups before weaning)" (per IMPC/MGI data referenced in search results, MGI:1330238). This parallels the embryonic lethality seen in other dystroglycanopathy-pathway mouse knockouts (e.g., Pomt1, due to the essential placental role of dystroglycan in rodents), and implies that conditional/tissue-specific knockout strategies would be required to model postnatal DPM2-CDG phenotypes in mice — no such conditional model was identified in the retrieved literature specifically for Dpm2.

Zebrafish: - No DPM2-specific zebrafish model was identified in this search. However, zebrafish are an actively used and validated platform for the broader dystroglycanopathy gene class (e.g., pomt1 loss-of-function zebrafish recapitulate α-dystroglycan hypoglycosylation and dystroglycanopathy phenotypes, PMID:38272461/PMC11000664; fkrp-deficient zebrafish, PMID:18477595) — representing a model-system gap worth flagging for a HUMAN_MODEL_MISMATCH-type discussion if curated in dismech, since DPM2 itself lacks a published zebrafish disease model despite the pathway being well-modeled in zebrafish for sibling genes.

Yeast: - Saccharomyces cerevisiae Yil102c-A functions as a DPM2 homolog and has been used to functionally characterize the yeast DPM synthase regulatory subunit (PMC7728079) — a potential future functional-variant-testing platform analogous to the yeast complementation assays already published for PMM2-CDG variant classification (bioRxiv 414862).

Cell-based/in vitro models: - Patient-derived dermal fibroblasts — used for LLO profiling (Barone 2012) and glycomics/lipidomics (Radenkovic 2021); these directly recapitulate the biochemical CDG-I defect and reduced DPM1/DPM2 protein expression. - HCT116 cell line transfection/overexpression assays — used to functionally characterize the p.Gly66Glu variant's effect on DPM2 mRNA/protein expression and on the ICAM1 hypoglycosylation reporter (PMC10154465) — this is the most direct functional-genomics tool currently published for DPM2 variant interpretation.

Model limitations: No model currently recapitulates the full clinical spectrum (severe neonatal-lethal epileptic-myopathic phenotype vs. mild adult-viable phenotype) in vivo; the mouse constitutive-knockout lethality precludes whole-animal phenotypic study without a conditional allele, and no such conditional/hypomorphic mouse model was identified in this search.

Summary for Knowledge-Base Curation

DPM2-CDG is an ultra-rare (≤10 published patients), autosomal recessive, allelic-series disorder (alongside DPM1-CDG and DPM3-CDG) of the dolichol-phosphate-mannose synthase complex, causally unifying CDG type I (N-glycosylation/LLO defect) and secondary dystroglycanopathy (α-dystroglycan O-mannosylation defect) mechanisms with a probable but unconfirmed GPI-anchor biosynthesis contribution. The clearest curatable causal chain is: DPM2 biallelic variant → DPM synthase complex destabilization → Dol-P-Man deficiency → parallel failure of (a) N-glycan LLO assembly, (b) α-dystroglycan O-mannosylation, and (c) GPI-anchor mannosylation → combined CDG-I biochemistry + dystroglycanopathy-type myopathy + neurodevelopmental phenotype, with variant location within DPM2 (TM domain 1 vs. domain 2) as the key documented genotype-severity modifier distinguishing the fatal-infantile from mild-adult-viable ends of the phenotypic spectrum. Treatment is entirely supportive; no targeted or disease-modifying therapy (including simple mannose supplementation, unlike PMM2-CDG) has been established. This entry is a strong candidate for conforms_to linkage to the lysosomal_substrate_accumulation-adjacent glycosylation-defect pattern conceptually, and more directly overlaps mechanistically with any future dismech module capturing the shared DPM1/DPM2/DPM3 "dolichol-phosphate-mannose synthesis disorder" pattern (cf. PMID:30931530, "Toward understanding tissue-specific symptoms in dolichol-phosphate-mannose synthesis disorders; insight from DPM3-CDG") — worth checking whether such a module already exists or should be proposed given the shared trigger→consequence chain across all three DPM subunit deficiencies.

Primary literature cited (PMIDs): 23109149 (Barone et al. 2012, Ann Neurol — first DPM2-CDG description, 3 patients); 33129689 (Radenkovic et al. 2021, Mol Genet Metab — 23-year-old mild phenotype, glycomics/lipidomics); 37152991 (2023 — Chinese siblings, novel p.Gly66Glu variant, ICAM1 functional assay); 16280320 and related DPM1/DPM3 stabilization mechanism papers; 30931530 (DPM3-CDG tissue-specificity review, mechanistically relevant); 38272461/PMID for zebrafish pomt1 dystroglycanopathy model (pathway-analogous, not DPM2-specific).

Notable evidence gaps requiring KNOWLEDGE_GAP/HUMAN_MODEL_MISMATCH flags if curated: (1) no confirmed MONDO ID verified in this pass — requires OAK lookup before entry creation; (2) no DPM2-specific animal model recapitulating the human phenotype exists (mouse knockout is embryonic lethal; no zebrafish model published), a clear HUMAN_MODEL_MISMATCH candidate; (3) GPI-anchor pathway involvement is mechanistically inferred from DPM-synthase biochemistry but not directly demonstrated with patient GPI-anchored-protein/ALP data in the DPM2-CDG case reports themselves (unlike PMM2-CDG, where this has been directly studied per PMC4016514) — treat as an extrapolated/inferred edge rather than direct human evidence.