| Domain | Established finding | Quantitative/detail | Evidence type | Certainty/limitation |
|---|---|---|---|---|
| Identifiers | Platelet-type bleeding disorder 19 (BDPLT19) is PRKACG-related severe autosomal-recessive macrothrombocytopenia. | OMIM 616176; MONDO:0014518; associated gene **PRKACG**. (pqac-00000000, pqac-00000009) | Aggregated disease resource plus primary human report | Disease–gene association is based principally on one family reported in 2014. |
| Human cases | Two affected West Indian siblings were described in a consanguineous family. | Proband II-1 was diagnosed at age 4; brother II-2 at age 2. Both lacked reported syndromic features. (pqac-00000011, pqac-00000012) | Human clinical—single pedigree | Extremely small evidence base; phenotype frequencies cannot be generalized beyond 2/2 reported affected individuals. |
| Genetic cause and inheritance | Homozygous germline **PRKACG c.222C>G**, causing **p.Ile74Met** in the PKA catalytic γ subunit, cosegregated with disease under an autosomal-recessive model. | Both affected siblings were homozygous; mother I-1 and relative III-1 were unaffected heterozygotes; II-3 was homozygous wild type. The variant was absent from databases queried in 2014, affected a conserved residue, and was predicted damaging by PolyPhen-2. (pqac-00000012, pqac-00000013) | Human genetic segregation plus computational prediction | Strong segregation and functional support within one pedigree, but no independent-family replication or current population-frequency estimate was identified. |
| Thrombocytopenia | Affected siblings had severe, persistent thrombocytopenia. | Platelet counts were **5 × 10⁹/L** in II-1 and **8 × 10⁹/L** in II-2. (pqac-00000011, pqac-00000012) | Human laboratory | Direct measurements in two patients; automated MPV was unavailable for either affected sibling. |
| Platelet size | Macrothrombocytopenia with predominantly giant or macrocytic platelets was demonstrated by smear and electron microscopy. | Approximately **90%** of platelets were giant or macrocytic; mean diameters were **4.86 μm** and **4.98 μm**, versus **2.84 μm** in an external control and **2.97 μm** in a heterozygous relative. (pqac-00000012) | Human cytology and ultrastructure | Demonstrated in both affected siblings, but no independent cohort exists. |
| Bleeding phenotype | Bleeding was mucocutaneous and gynecologic, ranging from moderate to life-threatening. | II-1 had epistaxis, spontaneous hematomas, menorrhagia with anemia, and three hemorrhagic ovarian-cyst ruptures requiring platelet and red-cell transfusion; WHO bleeding score **4**. II-2 had lifelong epistaxis and cutaneous hematomas; narrative WHO score **3**. (pqac-00000012, pqac-00000014) | Human clinical | Disease-specific treatment experience is limited to transfusion support; the table and narrative differ for II-2’s score. |
| Platelet dysfunction | Patient platelets showed defective agonist-induced activation, secretion, calcium signaling, receptor trafficking, and VWF-associated actin polymerization. | After stimulation, GPIb internalization was **18%** of resting level versus **44.2%** in control; control αIIbβ3 surface expression rose to **193%**, whereas patient platelets showed no increase; P-selectin externalization was absent; the VWF-associated F-actin/G-actin ratio was **44% of control**. (pqac-00000012, pqac-00000015) | Ex vivo human platelet assays | Directly demonstrated with patient samples; reproducibility across unrelated cases is unknown. |
| Megakaryocytes and marrow | Bone marrow contained megakaryocyte clusters, while cultured megakaryocyte differentiation and ploidization were preserved; the principal production defect occurred during proplatelet formation. | Mature CD41⁺CD42⁺ cell proportions and ploidy were comparable with controls, but homozygous patient megakaryocytes had a **2.5-fold lower** proportion of proplatelet-bearing cells. (pqac-00000012, pqac-00000013) | Human marrow morphology and patient-derived CD34⁺ culture | Supports a late thrombopoiesis defect rather than impaired megakaryocyte differentiation; based on one family. |
| PKA–FLNA mechanism | Mutant PRKACG protein was not degraded, but PKA dysfunction was associated with markedly reduced filamin A and elevated platelet cAMP. Loss of PKA-mediated FLNA Ser2152 phosphorylation and consequent proteolysis was proposed. | FLNA was almost absent from mature patient megakaryocytes and platelets; platelet cAMP was **3- to 5-fold higher** than in controls or a heterozygous relative. GPIbβ Ser166 phosphorylation was normal. (pqac-00000013, pqac-00000014) | Human biochemical assays plus mechanistic inference | FLNA loss and cAMP elevation were demonstrated; defective FLNA Ser2152 phosphorylation and proteolytic causality were inferred rather than directly measured. |
| Functional rescue | Wild-type PRKACG rescued abnormal proplatelet formation in patient-derived megakaryocytes; mutant PRKACG did not. | Wild-type lentiviral expression significantly increased proplatelet formation and reduced platelet-like structure diameter from **3.67 to 1.68 μm** in II-1 and **4.17 to 2.01 μm** in II-2. (pqac-00000014) | In vitro patient-cell rescue | Strong disease-gene functional evidence, but not a clinical gene-therapy result or evidence of in vivo safety or efficacy. |
| Diagnosis | Diagnosis requires recognition of congenital giant-platelet thrombocytopenia with platelet dysfunction, exclusion of phenocopies, and molecular confirmation. | The original study excluded **GP1BA/GP1BB/GP9** defects and neutrophil inclusions suggestive of MYH9-related disease, then used exome sequencing and Sanger segregation. General IPD evaluation includes bleeding and family history, CBC and smear, platelet-function testing, flow cytometry or electron microscopy, and panel, WES, or WGS testing. (pqac-00000013, pqac-00000018, pqac-00000020) | Disease-specific workup plus expert-review guidance | No validated BDPLT19-specific diagnostic criteria, biomarker, or standalone functional assay exists. |
| Management | No PRKACG-specific standard therapy or response-rate evidence exists. Supportive inherited-platelet-disorder care is the current practical framework. | General expert guidance favors local hemostasis, trauma and antiplatelet-drug avoidance, antifibrinolytics or desmopressin for selected bleeding or procedures, and platelet transfusion for major bleeding or critical sites, while minimizing exposure and using HLA-compatible products when needed. (pqac-00000019, pqac-00000021) | Expert review extrapolated from other inherited platelet disorders | Not validated specifically in BDPLT19; no disease-specific evidence supports thrombopoietin-receptor agonists, HSCT, splenectomy, rFVIIa, pharmacogenomics, or targeted therapy. |
| Epidemiology | BDPLT19 is ultra-rare, with no population prevalence, incidence, carrier-frequency, sex-ratio, or mortality estimate. | The established literature identified **2 affected siblings in 1 pedigree**; reviews historically described only one PRKACG variant from a single pedigree. (pqac-00000024, pqac-00000025) | Literature ascertainment | Two published cases are not a prevalence estimate; underdiagnosis is plausible but unquantified. |
| 2023–2024 update | No disease-specific 2023–2024 cohort, independently confirmed family or pathogenic variant, natural-history study, animal model, omics or single-cell study, clinical trial, or targeted treatment was identified. | Recent literature primarily provides general inherited platelet-disorder diagnostic context rather than new BDPLT19 evidence. (pqac-00000022, pqac-00000027) | Evidence-gap assessment | Absence from retrieved literature does not prove that unpublished cases or database submissions do not exist; the 2014 report remains the principal direct evidence. |


*Table: Concise summary of the established clinical, genetic, mechanistic, diagnostic, and management evidence for PRKACG-related BDPLT19. The table emphasizes that direct evidence remains limited to one family and identifies major recent-research gaps.*