Targeted long-read sequencing identifies and characterizes structural variants in cases of inherited platelet disorders

BACKGROUND

Genetic diagnosis of inherited platelet disorders (IPDs) is mainly performed by high-throughput sequencing (HTS). These short-read-based sequencing methods sometimes fail to characterize the genetics of the disease.

OBJECTIVES

To evaluate nanopore long-read DNA sequencing for characterization of structural variants (SVs) in patients with IPDs.

METHODS

Four patients with a clinical and laboratory diagnosis of Glanzmann thrombasthenia (GT) (P1 and P2) and Hermansky-Pudlak syndrome (HPS) (P3 and P4) in whom HTS missed the underlying molecular cause were included. DNA was analyzed by both standard HTS and nanopore sequencing on a MinION device (Oxford Nanopore Technologies) after enrichment of DNA spanning regions covering GT and HPS genes.

RESULTS

In patients with GT, HTS identified only 1 heterozygous ITGB3 splice variant c.2301+1G>C in P2. In patients with HPS, a homozygous deletion in HPS5 was suspected in P3, and 2 heterozygous HPS3 variants, c.2464C>T (p.Arg822∗) and a deletion affecting 2 exons, were reported in P4. Nanopore sequencing revealed a complex SV affecting exons 2 to 6 in ITGB3 (deletion-inversion-duplication) in homozygosity in P1 and compound heterozygosity with the splice variant in P2. In the 2 patients with HPS, nanopore defined the length of the SVs, which were characterized at nucleotide resolution. This allowed the identification of repetitive Alu elements at the breakpoints and the design of specific polymerase chain reactions for family screening.

CONCLUSION

The nanopore technology overcomes the limitations of standard short-read sequencing techniques in SV characterization. Using nanopore, we characterized novel defects in ITGB3, HPS5, and HPS3, highlighting the utility of long-read sequencing as an additional diagnostic tool in IPDs.

Adherence to prophylaxis in adult patients with severe haemophilia A

INTRODUCTION

Adherence is a cornerstone of factor VIII prophylactic treatment. Information regarding the factors with potential influence on adherence is limited, particularly in adult patients.

AIM

To assess adherence in adult patients with severe haemophilia A receiving prophylactic treatment in a real-life setting, and investigate the factors influencing adherence.

METHODS

Observational, prospective study including adult patients receiving factor VIII therapy in 15 Spanish centres. Patients recorded infusion doses on a logbook and answered various questionnaires to assess their health beliefs. Adherence rate was the percentage of infused doses over the prescribed ones. Self-perceived adherence was assessed using the VERITAS-Pro questionnaire, the psychometric properties of which were validated in the Spanish population. The relationship between adherence rate and treatment, clinical and demographic characteristics, health beliefs and perceived self-efficacy was investigated.

RESULTS

A total of 66 patients were followed up for 12 months. Mean adherence rate at the end of follow-up was 82.5%. Most of the study patients (n = 53, 80.3%) showed a moderate-to-high adherence rate (>70%). The VERITAS-Pro revealed a high perception of adherence. Multivariate analyses to predict treatment adherence identified the knee as a target joint and longer treatment duration as variables with significant (negative) influence on adherence. Adherence rate was not influenced by the patient's health beliefs or perceived self-efficacy.

CONCLUSION

Most adult patients receiving factor VIII prophylactic treatment in Spain have moderate-to-high treatment adherence. Treatment duration and the knee as a target joint are factors with a moderate negative influence on treatment adherence.