New ATP-binding cassette A3 mutation causing surfactant metabolism dysfunction pulmonary type 3

ABCA3 Deficiency-Variant-Specific Response to Hydroxychloroquine

Biallelic variants in ABCA3, the gene encoding the lipid transporter ATP-binding cassette subfamily A member 3 (ABCA3) that is predominantly expressed in alveolar type II cells, may cause interstitial lung diseases in children (chILD) and adults. Currently, there is no proven therapy, but, frequently, hydroxychloroquine (HCQ) is used empirically. We hypothesized that the in vitro responsiveness to HCQ might correlate to patients' clinical outcomes from receiving HCQ therapy. The clinical data of the subjects with chILD due to ABCA3 deficiency and treated with HCQ were retrieved from the literature and the Kids Lung Register data base. The in vitro experiments were conducted on wild type (WT) and 16 mutant ABCA3-HA-transfected A549 cells. The responses of the functional read out were assessed as the extent of deviation from the untreated WT. With HCQ treatment, 19 patients had improved or unchanged respiratory conditions, and 20 had respiratory deteriorations, 5 of whom transiently improved then deteriorated. The in vitro ABCA3 functional assays identified two variants with complete response, five with partial response, and nine with no response to HCQ. The variant-specific HCQ effects in vivo closely correlated to the in vitro data. An ABCA3⁺ vesicle volume above 60% of the WT volume was linked to responsiveness to HCQ; the HCQ treatment response was concentration dependent and differed for variants in vitro. We generated evidence for an ABCA3 variant-dependent impact of the HCQ in vitro. This may also apply for HCQ treatment in vivo, as supported by the retrospective and uncontrolled data from the treatment of chILD due to ABCA3 deficiency.

Systematic review of drug effects in humans and models with surfactant-processing disease

Fibrotic interstitial pneumonias are a group of rare diseases characterised by distortion of lung interstitium. Patients with mutations in surfactant-processing genes, such as surfactant protein C (SFTPC), surfactant protein A1 and A2 (SFTPA1 and A2), ATP binding cassette A3 (ABCA3) and Hermansky-Pudlak syndrome (HPS1, 2 and 4), develop progressive pulmonary fibrosis, often culminating in fatal respiratory insufficiency. Although many mutations have been described, little is known about the optimal treatment strategy for fibrotic interstitial pneumonia patients with surfactant-processing mutations.We performed a systematic literature review of studies that described a drug effect in patients, cell or mouse models with a surfactant-processing mutation. In total, 73 articles were selected, consisting of 55 interstitial lung disease case reports/series, two clinical trials and 16 cell or mouse studies. Clinical effect parameters included lung function, radiological characteristics and clinical symptoms, while experimental outcome parameters included chemokine/cytokine expression, surfactant trafficking, necrosis and apoptosis. SP600125, a c-jun N-terminal kinase (JNK) inhibitor, hydroxychloroquine and 4-phenylbutyric acid were most frequently studied in disease models and lead to variable outcomes, suggesting that outcome is mutation dependent.This systematic review summarises effect parameters for future studies on surfactant-processing disorders in disease models and provides directions for future trials in affected patients.

Lung disease caused by ABCA3 mutations

BACKGROUND

Knowledge about the clinical spectrum of lung disease caused by variations in the ATP binding cassette subfamily A member 3 (ABCA3) gene is limited. Here we describe genotype-phenotype correlations in a European cohort.

METHODS

We retrospectively analysed baseline and outcome characteristics of 40 patients with two disease-causing ABCA3 mutations collected between 2001 and 2015.

RESULTS

Of 22 homozygous (15 male) and 18 compound heterozygous patients (3 male), 37 presented with neonatal respiratory distress syndrome as term babies. At follow-up, two major phenotypes are documented: patients with (1) early lethal mutations subdivided into (1a) dying within the first 6 months or (1b) before the age of 5 years, and (2) patients with prolonged survival into childhood, adolescence or adulthood. Patients with null/null mutations predicting complete ABCA3 deficiency died within the 1st weeks to months of life, while those with null/other or other/other mutations had a more variable presentation and outcome. Treatment with exogenous surfactant, systemic steroids, hydroxychloroquine and whole lung lavages had apparent but many times transient effects in individual subjects.

CONCLUSIONS

Overall long-term (>5 years) survival of subjects with two disease-causing ABCA3 mutations was <20%. Response to therapies needs to be ascertained in randomised controlled trials.