A range of 30%-62% of functioning multiciliated airway cells is sufficient to maintain ciliary airway clearance.

BACKGROUND: Primary ciliary dyskinesia (PCD) is a genetic disorder caused by aberrant motile cilia function that results in defective ciliary airway clearance and subsequently to recurrent airway infections and bronchiectasis. QUESTION: How many functional multiciliated airway cells are sufficient to maintain ciliary airway clearance? METHODS: To answer this question we exploited the molecular defects of the X-linked recessive PCD variant caused by pathogenic variants in DNAAF6 (PIH1D3), characterized by immotile cilia in the affected males. We carefully analyzed the clinical phenotype, molecular defect (immunofluorescence and transmission-electron microscopy) and performed in vitro (particle tracking in air-liquid interface cultures) and in vivo (radiolabeled tracer studies) studies to assess ciliary clearance of respiratory cells from females with heterozygous and males with hemizygous pathogenic DNAAF6 variants. RESULTS: PCD males with hemizygous pathogenic DNAAF6 variants displayed exclusively immotile cilia, absence of ciliary clearance and severe PCD symptoms. Due to random or skewed X-chromosome inactivation in six females with heterozygous pathogenic DNAAF6 variants, 54.3%±10 (range 38%-70%) of multiciliated cells were defective. Nevertheless, in vitro and in vivo assessment of the ciliary airway clearance was normal or slightly abnormal. Consistently, heterozygous female individuals showed no or only mild respiratory symptoms. CONCLUSIONS: Our findings indicate that 30%-62% of functioning multiciliated respiratory cells are able to generate either normal or slightly reduced ciliary clearance. Because heterozygous females displayed either no or subtle respiratory symptoms, complete correction of 30% of cells by precision medicine might be able to improve ciliary airway clearance in PCD individuals as well as clinical symptoms.

TMEM16A deficiency: a potentially fatal neonatal disease resulting from impaired chloride currents.

INTRODUCTION: TMEM16A is a calcium-activated chloride channel expressed in various secretory epithelia. Two siblings presented in early infancy with reduced intestinal peristalsis and recurrent episodes of haemorrhagic diarrhoea. In one of them, the episodes were characterised by hepatic pneumatosis with gas bubbles in the portal vein similar to necrotising enterocolitis of the newborn. METHODS: Exome sequencing identified a homozygous truncating pathogenic variant in ANO1. Expression analysis was performed using reverse transcription PCR, western blot and immunohistochemistry. Electrophysiological and cell biological studies were employed to characterise the effects on ion transport both in patient respiratory epithelial cells and in transfected HEK293 cells. RESULTS: The identified variant led to TMEM16A dysfunction, which resulted in abolished calcium-activated Cl- currents. Secondarily, CFTR function is affected due to the close interplay between both channels without inducing cystic fibrosis (CF). CONCLUSION: TMEM16A deficiency is a potentially fatal disorder caused by abolished calcium-activated Cl- currents in secretory epithelia. Secondary impairment of CFTR function did not cause a CF phenotyp, which may have implications for CF treatment.

Limitations of Nasal Nitric Oxide Measurement for Diagnosis of Primary Ciliary Dyskinesia with Normal Ultrastructure.

Rationale: Primary ciliary dyskinesia (PCD) is a heterogeneous, multisystem disorder characterized by defective ciliary beating. Diagnostic guidelines of the American Thoracic Society and European Respiratory Society recommend measurement of nasal nitric oxide (nNO) for PCD diagnosis. Several studies demonstrated low nNO production rates in PCD individuals, but underlying causes remain elusive. Objectives: To determine nNO production rates in a well-characterized PCD cohort, including subgroup analyses with regard to ultrastructural and ciliary beating phenotypes. Methods: This study included 301 individuals assessed according to European Respiratory Society guidelines. Diagnostic cutoffs for nNO production rates for this study cohort and subgroups with normal and abnormal ultrastructure were determined. Diagnostic accuracy was also tested for the widely used 77 nl/min cutoff in this study cohort. The relationship between nNO production rates and ciliary beat frequencies (CBFs) was evaluated. Results: The study cohort comprised 180 individuals with definite PCD diagnosis, including 160 individuals with genetic diagnosis, 16 individuals with probable PCD diagnosis, and 105 disease controls. The 77 nl/min nNO cutoff showed a test sensitivity of 0.92 and specificity of 0.86. Test sensitivity was lower (0.85) in the subgroup of 47 PCD individuals with normal ultrastructure compared with 133 PCD individuals with abnormal ultrastructure (0.95). The optimal diagnostic cutoff for the nNO production rate for the whole study cohort was 69.8 nl/min (sensitivity, 0.92; specificity, 0.89); however, it was 107.8 nl/min (sensitivity, 0.89; specificity, 0.78) for the subgroup of PCD with normal ultrastructure. PCD individuals with normal ultrastructure compared with abnormal ultrastructure showed higher ciliary motility. Consistently, PCD individuals with higher CBFs showed higher nNO production rates. In addition, laterality defects occurred less frequently in PCD with normal ultrastructure. Conclusions: Measurements of nNO below the widely used 77 nl/min cutoff are less sensitive in detecting PCD individuals with normal ultrastructure. Our findings indicate that higher nNO production in this subgroup with a higher cutoff for the nNO production rate (107.8 nl/min) and higher residual ciliary motility is dependent on the underlying molecular PCD defect. Higher nNO production rates, higher residual CBFs, and the lower prevalence of laterality defects hamper diagnosis of PCD with normal ultrastructure. Adjusting the cutoff of nNO production rate to 107.8 nl/min might promote diagnosing PCD with normal ultrastructure.

A bumpy road to the diagnosis of a Kytococcus schroeteri shunt infection.

We report a ventriculoperitoneal shunt infection associated with Kytococcus schroeteri, a Gram-positive bacterium from the family Dermacoccaceae. While the biochemical identification systems do not reliably identify this potential pathogen, sequence-based identification is recommended to guide the antibiotic treatment of this intrinsically meticillin-resistant species, which is susceptible to vancomycin, gentamicin and/or rifampicin.