Primary Ciliary Dyskinesia with Identical Genotype but Distinct Phenotypes in Two Siblings

In this study, we report two cases of siblings diagnosed with primary ciliary dyskinesia (PCD) sharing an identical genotype yet exhibiting distinct phenotypes. A 13-year-old girl with acute pneumonia was admitted to our hospital. Chest and sinus radiography revealed situs inversus and bilateral maxillary sinusitis. Chest computed tomography revealed bronchiectasis. Her 6-year-old brother with acute bronchitis was admitted and was diagnosed with bronchial asthma due to recurrent wheezing. Unlike his sister, he did not have situs inversus. Both patients had a chronic wet cough and were diagnosed with bronchial asthma by their family doctor. The mean PCD rule (PICADAR) scores were 9 and 7, respectively. Genetic analysis confirmed the presence of the same homozygous mutation (c.546C > A,pTyr182Ter) in DNAI2. To date, there have been four reports of the same pathogenic variants but different PCD phenotypes. Pathological variants of DNAI2 cause the loss of the outer dynein arm, the absence of which results in a lack of primary ciliary movement involved in the left-right axis formation during the embryonic period. A lack of functional cilia results in randomized visceral asymmetry; hence, the same pathogenic variant may exhibit different phenotypes. PCD is often overlooked and is sometimes managed as bronchial asthma, as in these siblings. In our case, the PICADAR score was useful in predicting the clinical diagnosis of PCD.