Frequency and characteristics of emphysema in adults with FLNA variants: a single-center study

TL;DR

This study finds that adults with FLNA gene variants often develop emphysema, a lung condition typically linked to smoking or other risk factors.

Contribution

The study is one of the first to investigate emphysema frequency and characteristics in adults with FLNA pathogenic variants.

Findings

70% of the studied adults with FLNA variants had emphysema, mostly centrilobular and in upper lobes.

57.1% of emphysema cases were unexplained, lacking typical risk factors like smoking.

Pulmonary tests showed airflow limitation and reduced lung function in emphysema patients.

Abstract

FLNA pathogenic variants lead to various congenital malformations. Pulmonary manifestations were reported in early age. In adults, few cases of emphysema were published. We aimed to assess the frequency and characteristics of emphysema in adults with a pathogenic or probably pathogenic variant in FLNA.

We conducted a transversal single-center study. Adults with FLNA pathogenic variant followed in Lille University Hospital were identified among the French rare disease database BaMaRa®. They attended medical examination, non-contrast chest CT-scan and pulmonary function tests (PFT). We collected medical history, tobacco smoking status, occupational and domestic exposures. When emphysema was identified, the PTPN6 gene was sequenced and alpha1antitrypsin deficiency searched. The primary objective of the study was to assess the frequency of emphysema. Secondary objectives were to evaluate emphysema type, distribution and extension, lung function in case of emphysema and the frequency of unexplained emphysema.

Among the 29 patients identified, 10 met non-inclusion criteria, 4 declined, 5 could not be reached and so 10 patients were included. The frequency of emphysema was 70%. It was most often centrilobular and located in upper lobes (n = 4) with a median volume of 8.8% (IQR: 3.0–18.0%) of the total lung volume. The frequency of unexplained emphysema was estimated to be 57.1% of emphysema cases. PFT revealed airflow limitation (n = 3), reduced DLCO (n = 5) and small airway disease on IOS (n = 5).

These preliminary results suggest that adults with FLNA pathogenic variant frequently develop emphysema, allowing for a larger study to be considered.

ClinicalTrials.gov, NCT05550844, Registered 19 September 2022 https://clinicaltrials.gov/study/NCT05550844?cond=FLNA&rank=1.

Full text

To the Editor,

The X-linked filamin A gene (FLNA) encodes for filamin-A, an actin-binding protein playing a key role in the cytoskeleton organization. Loss-of-function pathogenic variants lead to periventricular nodular heterotopia (PVNH) and various gastro-intestinal, cardiovascular and connective tissue disorders while gain-of-function pathogenic variants result in otopalatodigital syndrome spectrum disorders. A range of pulmonary manifestations including neonatal respiratory failure, congenital emphysema, interstitial lung disease, atelectasis and recurrent infections have been reported in early age [1]. In adults, only few cases of emphysema have since been published [2–4]. We recently described two cases of emphysema within the same family unexplained by environmental exposure in adult women with FLNA loss-of-function pathogenic variants [5]. Since, three additional cases were described in women [3]. However, the link between FLNA-pathogenic variants and emphysema is unknown. In this preliminary study, we aimed to assess the frequency and characteristics of emphysema in adults with a pathogenic variant in FLNA.

We conducted a transversal single-center prospective study. All adults (≥ 18 years) with FLNA pathogenic or probably pathogenic variants followed in Lille University Hospital were identified in the French rare diseases database BaMaRa^®^ and proposed to participate in the study. We excluded patients unable to give consent or under guardianship and pregnant or breastfeeding women. All participants provided written informed consent. The study was approved by the Institutional Review Board Ouest II of Angers University Hospital (2022-A00972-41) and was declared to the National Commission on Informatics and Liberty.

Participants attended medical examination, non-contrast chest CT-scan and pulmonary function tests (PFT). We collected socio-demographic data, medical history, tobacco smoking status, occupational and domestic exposures with a focus on wood dust, fumes and pollution defined as a high traffic road at less than 500 m from home. Passive smoking was defined as the presence of a smoker within the home. A chest radiologist performed qualitative and quantitative analysis of emphysema by visual and automatized computed quantification of the number of voxels with density less than − 950HU (Syngo.via^®^, Siemens HealthinnersⓇ). PFT included spirometry, plethysmography, diffusion capacity for carbon monoxide (DLCO) and impulse oscillometry (IOS^®^, Jaeger). Global lung Initiative (GLI) predicted values were used for spirometry, volumes and DLCO and those from Oostveen et al. for IOS [6]. Forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), FEV1/FVC, forced expiratory flow between 25 and 75% of FVC (FEF25-75) and DLCO values were considered abnormal when the z-score was below − 1.64. Residual volume (RV), total lung capacity (TLC), RV/TLC, resistance at 5 Hz (R5), reactance at 5 Hz (X5) and integrated area of low frequency reactance (AX) values were considered abnormal when the z-score was over 1.64. Airflow limitation was defined by a FEV1/FVC < lower limit normal and lung hyperinflation by a RV/TLC >upper limit normal. The difference R5-R20 was considered abnormal when higher than 0.07 kPa/L/s, then defining small airway dysfunction (SAD).

When emphysema was identified, the PTPN6 gene [7] was sequenced using Sanger method (ABI Prism 3730XL Genetic Analyzer; Applied Biosystems^®^) and alpha-1-antitrypsin (AAT) deficiency was searched (serum level, isoelectric focusing and gene sequencing).

The primary objective was to assess the frequency of emphysema, defined as the presence of focal areas or regions of low attenuation, usually without visible walls. Secondary objectives were to evaluate (1) emphysema type (centrilobular, panlobular or paraseptal), distribution (upper, lower lobes, or no predominance) and extension, (2) lung function in the whole population and in participants with emphysema and (3) the frequency of unexplained emphysema, defined as low tobacco exposure (active smoking < 5 pack-years and no significant passive smoking), no exposure to noxious particles, no AAT deficiency and no pathogenic variant in PTPN6 gene. Our approach was specifically designed based on the study by Bossé et al. [7], which identified a heterozygous missense variant (Ala455Thr) within a critical functional site of the PTPN6 protein. Accordingly, we focused our investigation on point mutations within this functionally important region, particularly residues 453 to 459, using targeted Sanger sequencing.

Twenty-eight patients with FLNA pathogenic or probably pathogenic variants and one patient with a variant of unknown significance were identified in BaMaRa^®^ of whom 10 met non-inclusion criteria (8 underaged, 1 breastfeeding, 1 under guardianship), 4 declined and 5 could not be reached. Finally, we analyzed 10 women with a median age of 40.5 years (IQR: 33.0-49.5). Patients’ characteristics are reported in Table 1 with genetic data detailed in Table 2.

Table 1. Characteristics of patients in the whole population and in patients with emphysemaWhole population (n = 10)With emphysema (n = 7) Demographic features Female10 (100%)7 (100%)Age, years40.5 (33.0;49.5)42.0 (31.0;52.0)BMI, kg/m^2^27.6 (22.4;30.6)27.1 (20.8;28.1) Medical history Neonatal acute respiratory failure2 (20%)1 (14%)Previously known emphysema*3 (30%)3 (43%)Asthma2 (20%)0 (0.0%)Pulmonary embolism1 (10%)1 (14%)Hypertension1 (10%)1 (14%)Supraventricular arrhythmia2 (20%)1 (14%)Aortic root dilatation3 (30%)2 (29%)Pulmonary hypertension2 (20%)2 (29%)Congenital cardiopathy2 (20%)1 (14%)Valvular disease3 (30%)1 (14%)PVNH5 (50%)4 (57%)Melnick-Needles syndrom1 (10%)1 (14%) Environmental exposure Tobacco smoker > 5 pack-years0 (0%)0 (0%)Tobacco passive smoker4 (40%)3 (43%)Cannabis smoker0 (0%)0 (0%)Household0 (0%)0 (0%)Occupational0 (0%)0 (0%)Air pollution0 (0%)0 (0%) Respiratory symptoms Chronic cough2 (20%)0 (0%)Exertional dyspnea8 (80%)5 (71%)mMRC01 (10%)0 (0%)mMRC13 (30%)1 (14%)mMRC22 (20%)2 (29%)mMRC31 (10%)1 (14%)mMRC41 (10%)1 (14%)Chronic bronchitis1 (10%)0 (0%) CT scan Centrilobular-4.0 (57%)Panlobular-2.0 (29%)Paraseptal-2.0 (29%)Upper predominance-4.0 (57%)No predominance-3.0 (43%)Volume of emphysema, %-8.8 (3.0;18.0) Pulmonary function tests FEV1, Z-score-2.40 (-3.37;-1.44)-1.78 (-3.51;-0.70)FEV1 < LLN7 (70%)4 (57%)FEV1/FVC, Z-score-1.96 (-2.76;-1.14)-1,29 (-2.39;-0.79)FEV/FVC < LLN6 (60%)3 (43%)FEF25-75, Z-score-2.10 (-3.28;-0.32)-1.28 (-2.44;0.32)FEF25-75 < LLN5 (50%)2 (29%)RV/TLC2.01 (1.40;2.26)2.00 (0.80;2.50)RV/TLC > ULN7 (70%)4 (57%)DLCO, Z-score-1.56 (-2.68;-0.03)-2.41 (-3.49;-1.41)DLCO < LLN5 (50%)5 (71%)R5, Z-score1.43 (0.64;2.02)0.77 (0.60;1.83)R5 > ULN4 (40%)2 (29%)X5, Z-score1.57 (-0.13;2.47)0.12 (-0.22;2.13)X5 > ULN3 (30%)1 (14%)AX, Z-score1.72 (0.62;2.86)0.97 (0.51;2.8)AX > ULN5 (50%)2 (29%)R5-R20, kPa/L/s0.11 (0.08;0.20)0.09 (0.08;0.17)R5-R20 > 0.077 (70%)5 (71%)Values reported as n (%) for qualitative variables and median (IQR) for quantitative variables; IOS values (R5, R5-R20, X5, AX) were not available in 2 patients with emphysemaAX: integrated area of low frequency reactance; BMI: body mass index; DLCO: diffusion capacity for carbon monoxide; FEF25-75 : forced expired flow between 25 and 75% of FVC; FEV1 : forced expiratory volume 1 s; FLNA : filamin A; FVC : forced vital capacity; LLN: lower limit of normal; mMRC: modified Medical Research Council; PVNH: periventricular nodular heterotopia; R5: resistance at 5 Hz; RV: residual volume; TLC: total lung capacity; ULN: upper limit of normal; X5: reactance at 5 Hz; * : In all these cases, emphysema was diagnosed in adulthood

Table 2 Description of FLNA variants and related clinical features n HGVS DNA on transcriptHGVS ProteinZygosityACMG classTypeFLNA related features With emphysema 1^+^c.730 C > Tp.(Pro244Ser)Heterozygous4MissenseMelnick-Needles syndrome2c.134 A > Gp.(Gln45Arg)Heterozygous4MissensePVNH, aortic root dilatation, valvular disease3^F^c.7898_7900delp.(Gly2633del)Heterozygous4Inframe4^− F^c.7609delp.(Ser2537LeufsTer2)Heterozygous5Frameshift5c.(?1)(2022_?)delN.AN.A4DeletionPVNH, joint hypermobility, congenital heart disease, pulmonary hypertension, neonatal acute respiratory failure6c.992_993delp.Lys331SerfsTer5Heterozygous5FrameshiftPVNH, dilatation of thoracic aorta7*c.992_993delp.Lys331SerfsTer5Heterozygous5FrameshiftPVNH, pulmonary hypertension Without emphysema 8^−^c.7306G > Ap.(Gly2436Arg)Heterozygous3MissensePVNH, valvular disease, patent ductus arteriosus, neonatal acute respiratory failure, congenital cardiopathy9^−^c.1966 C > Tp.(Leu656Phe)Heterozygous4MissenseDilatation of thoracic aorta, valvular disease10^− F^c.7941_7942delp.(Ter2648SerextTer100)Heterozygous4Stop-lossACMG : American College of Medical Genetics and Genomics. HGVS : Human Genome Variation Society. N.A : not available. PVNH : periventricular nodular heterotopia. Function of the protein : * : loss of function; + : gain of function; - : not available. ^F^ : genetic testing performed because of family history. These patients did not have clinical involvement suggestive of a FLNA mutation. All patients reported in Table 2 are women

The frequency of emphysema was 70.0%. It was most often centrilobular and located in upper lobes (n = 4) with a median volume of 8.8% (IQR: 3.0–18.0%) of the total lung volume. Among patients with emphysema, PFT showed airflow limitation in 3 cases, lung hyperinflation in 4 cases, reduced DLCO in 5 cases and SAD in all 5 emphysema patients who performed IOS, together with an increased AX in 2 of them (Table 1). Two patients without emphysema had asthma and presented reduced FEV1/FVC and FEV1, and SAD.

In the emphysema group, three patients reported significant passive tobacco smoking, and four met the criteria of unexplained emphysema. The frequency of unexplained emphysema was therefore estimated to be 57.1% of emphysema cases.

In this preliminary study, we found a significant frequency of emphysema estimated at 70% in patients with FLNA pathogenic or probably pathogenic variants among which 57.1% are unexplained. The volume of emphysema was clinically relevant as it represented 8.8% (IQR: 3.0–18.0%) of the total lung volume while it was reported to represent 1.2% (IQR: 0,5–2,5%) of the total lung volume in healthy non-smoker people [8]. The only patient with a gain-of-function mutation had minimal emphysema (0.2%) without exposure to tobacco. These data suggest that FLNA pathogenic variants, particularly those associated with loss-of-function may be associated with emphysema. This is supported by experimental data reporting emphysema in mice with loss-of-function FLNA pathogenic variants [9], possibly due to abnormal endothelial adherens junctions.

PFT revealed abnormalities usually found in patients with emphysema, the most frequent being reduced DLCO [2, 3]. They also revealed SAD in all emphysema patients who performed IOS, consistently with a previous study reporting a good diagnosis accuracy of IOS-diagnosed SAD for the detection of emphysema [10].

The main limit of this study is the small sample size, due to the scarcity of FLNA pathogenic variants and the monocentric design. We decided to carry out this pilot study on a limited number of patients to assess the relevance of our hypothesis, given the irradiating nature of chest CT.

In conclusion, our results suggest that adult women with loss-of-function FLNA pathogenic variants develop emphysema. They encourage focusing on measures for lung protection and paying particular attention on respiratory symptoms in this condition.