PB1117 - Congenital Thrombotic Thrombocytopenic Purpura: identification of two heterozygous mutations in splice sites through NGS sequencing

Tuesday, June 27, 2023

18:30 – 19:30 ET

Room: Exhibition

Presenting Author(s)

DL

Dolors Llobet, PhD

Biologist.PhD
Unitat d'Hemostàsia i Trombosi. Hospital de la Santa Creu i Sant Pau
Barcelona, Catalonia, Spain

Co-Author(s)

GR

Guillermo Ramil

Doctor
Unitat d'Hemostàsia i Trombosi. Hospital de la Santa Creu i Sant Pau
Barcelona, Catalonia, Spain
IT

Isabel Tirado

Pharmacist
Unitat d'Hemostàsia i Trombosi. Hospital de la Santa Creu i Sant Pau
Barcelona, Catalonia, Spain
NV

Noèlia Vilalta

Doctor
Unitat d'Hemostàsia i Trombosi. Hospital de la Santa Creu i Sant Pau
Barcelona, Catalonia, Spain
LR

Lidia Romero

Technician
Unitat d'Hemostàsia i Trombosi. Hospital de la Santa Creu i Sant Pau
Barcelona, Catalonia, Spain
Marina Carrasco, PHD (she/her/hers)

Doctor
Unitat d'Hemostàsia i Trombosi. Hospital de la Santa Creu i Sant Pau
Barcelona, Catalonia, Spain
MS

Marta Simón

Technician
Unitat d'Hemostàsia i Trombosi. Hospital de la Santa Creu i Sant Pau
Barcelona, Catalonia, Spain
SQ

Susana Quero

Technician
Unitat d'Hemostàsia i Trombosi. Hospital de la Santa Creu i Sant Pau
Barcelona, Catalonia, Spain
Rubén Berrueco, PhD

Head of Department. Pediatric Hematology
Hospital Sant Joan de Déu
Esplugues Llobregat, Catalonia, Spain
JM

José Mateo

Doctor
Unitat d'Hemostàsia i Trombosi. Hospital de la Santa Creu i Sant Pau
Barcelona, Catalonia, Spain

Background: Congenital Thrombotic Thrombocytopenic Purpura (cTTP), also known as Upshaw-Schulman syndrome, is an ultra-rare hereditary condition caused by ADAMTS13 mutations leading to severe deficiency of ADAMTS13. cTTP has an autosomal recessive inheritance and to date, over 150 different mutations on ADAMTS13 have been reported, frequently presenting as compound heterozygous.

Aims: To confirm the diagnosis of cTTP through next-generation sequencing (NGS) in a patient with congenital deficiency of ADAMTS13 and only one heterozygous mutation detected.

Methods: We report a 19-year-old male diagnosed with a probable cTTP at 7 months old after presenting with microangiopathic anemia and thrombocytopenia, undetectable ADAMTS13 levels and absence of inhibitory antibodies.
At diagnosis, genetic analysis confirmed that patient had a deletion on ADAMTS13 gene (c.334delG). The same mutation was found on his mother. Only with RNA sequencing, we detected a large deletion between exon 7 and exon 11. The same large deletion was found in his father. With these results, we considered the patient as a probable carrier of two heterozygous mutations on ADAMTS13 gene. Using NGS technologies, a custom panel that includes ADAMTS13 gene was performed to the patient (Table 1). The panel covers the full coding region of ADAMTS13 as well as splicing sites and 5’UTR and 3’UTR regions (reference sequence NM_139025.4).

Results: Two pathogenic variants on ADAMTS13 were confirmed: a single-nucleotide frameshift deletion (c.334delG) affecting the splice site between intron 3 and exon 4, and a large deletion of 188 base pairs at the splice site between intron 8 and exon 9 (Figure 1).

Conclusion(s): 1. NGS is a useful tool for genetic characterization of rare inherited coagulopathies.
2. Disease-causing mutations of ADAMTS13 in cTTP usually present as compound heterozygous whilst homomozygous mutations are rare. This could explain the differences in age of onset and severity among affected individuals.