Prekallikrein (PK) Tokushima: PK deficiency caused by a Gly401-->Glu mutation

A Rare Cause of Isolated Prolonged Activated Partial Thromboplastin Time: An Overview of Prekallikrein Deficiency and the Contact System

Prekallikrein (PK) deficiency, also known as Fletcher factor deficiency, is a very rare disorder inherited as an autosomal recessive trait. It is usually identified incidentally in asymptomatic patients with a prolonged activated partial thromboplastin time (aPTT). In this article, we present the case of a 52-year-old woman, with no prior personal or family history of thrombotic or hemorrhagic disorders, who was noted to have substantial protracted aPTT through the routine coagulation assessment before a kidney biopsy. The patient had an uneventful biopsy course after receiving fresh frozen plasma (FFP). Laboratory investigations performed before the biopsy indicated normal activity for factors VIII, IX, XI, XII, and von Willebrand factor (vWF) as well as negative lupus anticoagulant (LA) screen. The plasma PK assay revealed low activity at 15% consistent with mild PK deficiency. The deficit of PK is characterized by a severely prolonged aPTT and normal prothrombin time (PT) in the absence of bleeding tendency. PK plays a role in the contact-activated coagulation pathway and the inflammatory response. Thus, other differential diagnoses of isolated prolonged aPTT include intrinsic pathway factor deficiencies and nonspecific inhibitors such as LA. We concluded that the initial evaluation of a prolonged aPTT with normal PT should appraise the measurement of contact activation factors and factor inhibitors. PK deficiency should be considered in asymptomatic patients with isolated aPTT prolongation, which corrects on incubation, with normal levels of the contact activation factors and factor inhibitors.

Severe plasma prekallikrein deficiency: Clinical characteristics, novel KLKB1 mutations, and estimated prevalence

BACKGROUND

Severe plasma prekallikrein (PK) deficiency is an autosomal-recessive defect characterized by isolated activated partial thromboplastin time prolongation. To date, no comprehensive methodologically firm analysis has investigated the diagnostic, clinical, and genetic characteristics of PK deficiency, and its prevalence remains unknown.

PATIENTS/METHODS

We described new families with PK deficiency, retrieved clinical and laboratory information of cases systematically searched in the (gray) literature, and collected blood of these cases for complementary analyses. The Genome Aggregation Database (gnomAD) and the population-based Gutenberg Health Study served to study the prevalence of mutations and relevant genetic variants.

RESULTS

We assembled a cohort of 111 cases from 89 families and performed new genetic analyses in eight families (three unpublished). We identified new KLKB1 mutations, excluded the pathogenicity of some of the previously described ones, and estimated a prevalence of severe PK deficiency of 1/155 668 overall and 1/4725 among Africans. One individual reported with PK deficiency had, in fact, congenital kininogen deficiency associated with decreased PK activity. One quarter of individuals had factor XII clotting activity below the reference range. Four major bleeding events were described in 96 individuals, of which 3 were provoked, for a prevalence of 4% and an annualized rate of 0.1%. The prevalence of cardiovascular events was 15% (6% <40 years; 21% 40-65 years; 33% >65 years) for an annualized rate of 0.4%.

CONCLUSIONS

We characterized the genetic background of severe PK deficiency, critically appraised mutations, and provided prevalence estimates. Our data on laboratory characteristics and clinical course of severe PK deficiency may have clinical implications.

Genetics of equine bleeding disorders

Genetic bleeding disorders can have a profound impact on a horse's health and athletic career. As such, it is important to understand the mechanisms of these diseases and how they are diagnosed. These diseases include haemophilia A, von Willebrand disease, prekallikrein deficiency, Glanzmann's Thrombasthenia and Atypical Equine Thrombasthenia. Exercise-induced pulmonary haemorrhage also has a proposed genetic component. Genetic mutations have been identified for haemophilia A and Glanzmann's Thrombasthenia in the horse. Mutations are known for von Willebrand disease and prekallikrein deficiency in other species. In the absence of genetic tests, bleeding disorders are typically diagnosed by measuring platelet function, von Willebrand factor, and other coagulation protein levels and activities. For autosomal recessive diseases, genetic testing can prevent the breeding of two carriers.

Congenital prekallikrein deficiency

The congenital deficiency of prekallikrein (PK) is a rare condition in which there is a peculiar discrepancy between a severe in vitro defect and absence of bleeding. The gene controlling PK synthesis is located on chromosome 4 and consists of 14 exons and 15 introns. Only approximately 80 cases of PK deficiency have been described in the literature. Owing to the lack of bleeding, most cases go undetected or, if detected, go unreported. Occasional bleeding or thrombosis have been reported in a few patients but this was only due to the presence of associated risk factors. It is certain that the defect does not protect from thrombosis. Diagnosis is based on the presence of a great prolongation of partial thromboplastin time and normal prothrombin time and thrombin time. The long partial thromboplastin time is fully corrected by the addition of normal plasma or normal serum and presents the unusual feature of shortening on long incubation times. Platelet and vascular tests are normal. Immunological studies allow differentiation into two types, namely cases of true deficiency, which are approximately 70% of the total, and cases with abnormal forms. PK is a glycoprotein synthesized in the liver as a single-chain peptide of 88000 Da. It mostly circulates (∼75%) as a complex with high-molecular-weight kininogen. It is cleaved by FXIIa into a heavy chain and a light chain (catalytic domain), held together by disulfide bonds. Molecular biology techniques have so far only been applied to eleven families, and these studies do not yet allow definite phenotype/genotype conclusions. The exons involved are 5, 8, 11, 14 and 15. The noncoagulative effects of PK, mainly based on the effect of kallikrein, have been studied less, since they appear to be the result of the involvement of other components of the contact phase. Kallikrein can mainly affect the formation of bradykinin from high-molecular-weight kininogen and the activation of pro-urokinase to urokinase. Bradykinin causes inflammation, vasodilatation and an increase in vessel permeability. The activation of pro-urokinase results in enhanced fibrinolysis. However, fibrinolysis has been reported to be normal or defective in these patients.

[An elderly case of congenital prekallikrein deficiency]

The proband is a 69-year-old woman with purpura and subcutaneous hematoma.We investigated this patient with prekallikrein (PK) deficiency, using both standard coagulation study and molecular genetic analysis of the PK gene. In a coagulation study, the prothrombin time (PT) was normal but the activated partial thromboplastin time (APTT) was prolonged. Preincubation of normal plasma with APTT reagent caused shortening of abnormal clotting time. Plasma PK activity was <1%. Her parents were cousins. Molecular genetic analysis showed a homozygous Gly401Glu substitution in exon 11 in the PK gene. This mutation has already been reported in a Japanese patient as PK Tokushima. Gly401 is positioned in PK light chain, which encodes the serine protease domain. The disulfide binding is formed between Cys400 and Cys416, thus Gly401 is located next to His415, which is one of the activation peptides and is important in supporting the correct conformation of proteins. Therefore, we suggest that this mutation may prevent formation of disulfide binding and reduce enzyme activity. In conclusion, in the elderly case with prolonged APTT, we should consider the contact factor deficiency and determine PK activity apart from the abnormality of coagulation factor VIII, IX, XI and XII activities.

A new type of plasma prekallikrein deficiency associated with homozygosity for Gly104Arg and Asn124Ser in apple domain 2 of the heavy-chain region

Three Japanese patients demonstrated plasma prekallikrein (PK) deficiency (PKD) after an examination of the proband family line named 'PKD Seki'. A molecular genetic analysis of these PK genes showed homozygous amino acid substitutions Gly104Arg and Asn124Ser in exon 5, which encodes part of the apple domain 2 (A2) of the heavy chain. This is the first case involving substitutions in the heavy chain of the PK gene which affected blood coagulation. Because the apple domains of PK bind to the C-terminal domain (D6(H)) of high-molecular weight kininogen (HMWK), the two substitutions in A2 may therefore be the main cause of PKD Seki. We subsequently investigated the effects of amino acid substitutions in A2 to elucidate the binding activity of PK to HMWK using mutant A2 proteins produced in Escherichia coli. We clearly demonstrated that the Gly104Arg-substitution with the Asn124Ser-substitution in A2 reduce the binding activity of A2 to HMWK. PKD Seki is the first significant case to show the amino acid substitutions in the A2 affecting the binding capacity of PK with HMWK. Our findings therefore suggest that the binding of PK to HMWK may play a crucial role in the first step of blood coagulation.

Severe prekallikrein deficiencies due to homozygous C529Y mutations

Two consecutive severe prekallikrein deficiencies were investigated. The first was identified in a 63-year-old patient admitted for ischemic stroke. The second deficiency was identified in a 38-year-old patient admitted for a second-trimester pregnancy loss. A homozygous C529Y mutation was identified for both cases, whereas they are unrelated and no consanguineous marriage is known from the patients. These data point to a possible high frequency of this mutation as a cause of prekallikrein deficiency.

Severe prekallikrein deficiency associated with homozygosity for an Arg94Stop nonsense mutation

An elderly patient with no abnormal bleeding presented with prolongation of the activated partial thromboplastin time (aPTT). Preincubation of plasma with aPTT reagent caused shortening of the abnormal clotting time. Plasma prekallikrein (PK) activity and antigen were <5 u/dL. Molecular analysis showed a homozygous Arg94Stop substitution in the PK gene, predicted to prevent expression of the mutant allele. The five heterozygous offspring of the proband each showed a normal aPTT but reduced PK activity and antigen. This is the first description of a kindred in which absence of expression of one or both PK alleles has been confirmed by genotype.