Hereditary defect of the intrinsic coagulation pathway due to prekallikrein (Fletcher factor) deficiency. It produces prolongation of activated partial thromboplastin time (aPTT) without, in general, any clinically relevant bleeding tendency. It is usually an incidental laboratory finding. It is inherited in a recessive manner.

Shih tzu, according to the breed attribution recorded in OMIA000819-9615. No reliable carrier frequencies are published in the general population; it is a poorly studied defect and data are limited. Note: the primary article by Okawa et al. (2011) describes the mutation, but its accessible abstract does not specify the dog's breed.

- Prolonged aPTT as an incidental finding
- Generally asymptomatic
- Mild or absent bleeding after surgery or trauma in most cases
- Possible prolongation of bleeding time in some individuals

Prekallikrein deficiency (Fletcher factor) was recognised in the dog from findings of prolonged aPTT in animals without a relevant bleeding tendency. Okawa et al. (2011) first described a point mutation in the canine prekallikrein gene: a change in exon 8 that produces an amino acid substitution in the fourth apple domain of the protein, corresponding to KLKB1 c.988T>A (p.F330I). The benign nature of the defect means its clinical impact is limited, but its detection prevents erroneous interpretation of aPTT.

- Test before surgery or bleeding procedures rather than for breeding selection
- Do not mate two carriers when status is known: 25 % risk of homozygotes
- A carrier can be mated to a clear dog without clinically relevant bleeding risk
- Prioritise the transmission of other traits above this benign defect, without disregarding testing

Differential diagnosis with other causes of prolonged aPTT (factor VIII, IX, XI, XII deficiency) and with circulating anticoagulants. Prekallikrein deficiency does not usually produce clinically significant bleeding, but it should be known before surgery so as not to erroneously attribute the prolongation to a more serious defect.

1. Okawa T et al. (2011) Prekallikrein deficiency in a dog. J Vet Med Sci 73(1):107-111. PMID: 20736516
2. OMIA:000819-9615. Prekallikrein deficiency in Canis lupus familiaris. https://omia.org/OMIA000819/9615/