The radial spoke head protein 4 homolog A (RSPH4A) gene is one of more than 50 genes that cause Primary ciliary dyskinesia (PCD), a rare genetic ciliopathy. Genetic mutations in the RSPH4A gene alter an important protein structure involved in ciliary pathogenesis. Radial spoke proteins, such as RSPH4A, have been conserved across multiple species. In humans, ciliary function deficiency caused by RSPH4A pathogenic variants results in a clinical phenotype characterized by recurrent oto-sino-pulmonary infections. More than 30 pathogenic RSPH4A genetic variants have been associated with PCD. In Puerto Rican Hispanics, a founder mutation (RSPH4A (c.921+3_921+6delAAGT (intronic)) has been described. The spectrum of the RSPH4A PCD phenotype does not include laterality defects, which results in a challenging diagnosis. PCD diagnostic tools can combine transmission electron microscopy (TEM), nasal nitric oxide (nNO), High-Speed Video microscopy Analysis (HSVA), and immunofluorescence. The purpose of this review article is to provide a comprehensive overview of current knowledge about the RSPH4A gene in PCD, ranging from basic science to human clinical phenotype.

Primary ciliary dyskinesia (PCD) is a rare, heterogeneous ciliopathy resulting in chronic oto-sino-pulmonary disease, bronchiectasis, newborn respiratory distress, and laterality defects. PCD diagnosis can be achieved by following diagnostic algorithms that include electron microscopy, genetics, and ancillary testing. Genetic mutations in more than 45 genes, including RSPH4A, can lead to PCD. RSPH4A mutations located on chromosome six, affect radial spokes and results in central complex apparatus abnormalities. The RSPH4A [c.921 + 3_6delAAGT] founder mutation was described as one cause of PCD without laterality defects in Puerto Rico. Additionally, there are further diagnostic challenges present in the Puerto Rican population to diagnose PCD. We describe the demographics, clinical features, and RSPH4A genetic variants in 13 patients with clinical PCD affecting 11 Puerto Ricans from unrelated families.

Primary ciliary dyskinesia (PCD) has been linked to more than 50 genes that cause a spectrum of clinical symptoms, including newborn respiratory distress, sinopulmonary infections, and laterality abnormalities. Although the RSPH4A (c.921+3_6delAAGT) pathogenic variant has been related to Hispanic groups with Puerto Rican ancestry, it is uncertain how frequently other PCD-implicated genes are present on the island. A retrospective chart review of n = 127 genetic reports from Puerto Rican subjects who underwent genetic screening for PCD variants was conducted from 2018 to 2022. Of 127 subjects, 29.1% subjects presented PCD pathogenic variants, and 13.4% were homozygous for the RSPH4A (c.921+3_6delAAGT) founder mutation. The most common pathogenic variants were in RSPH4A and ZMYND10 genes. A description of the frequency and geographic distribution of implicated PCD pathogenic variants in Puerto Rico is presented. Our findings reconfirm that the presence of PCD in Puerto Rico is predominantly due to a founder pathogenic variant in the RSPH4A (c.921+3_6delAAGT) splice site. Understanding the frequency of PCD genetic variants in Puerto Rico is essential to map a future genotype-phenotype PCD spectrum in Puerto Rican Hispanics with a heterogeneous ancestry.

Primary ciliary dyskinesia (PCD) is an inherited disorder that impairs motile cilia, essential for respiratory health, with a reported prevalence of 1 in 16,309 within Hispanic populations. Despite 70% of Puerto Rican patients having the RSPH4A [c.921+3_921+6del (intronic)] founder mutation, the characterization of the ciliary dysfunction remains unidentified due to the unavailability of advanced diagnostic modalities like High-Speed Video Microscopy Analysis (HSVA). Our study implemented HSVA for the first time on the island as a tool to better diagnose and characterize the RSPH4A [c.921+3_921+6del (intronic)] founder mutation in Puerto Rican patients. By applying HSVA, we analyzed the ciliary beat frequency (CBF) and pattern (CBP) in native Puerto Rican patients with PCD. Our results showed decreased CBF and a rotational CBP linked to the RSPH4A founder mutation in Puerto Ricans, presenting a novel diagnostic marker that could be implemented as an axillary test into the PCD diagnosis algorithm in Puerto Rico. The integration of HSVA technology in Puerto Rico substantially enhances the PCD evaluation and diagnosis framework, facilitating prompt detection and early intervention for improved disease management. This initiative, demonstrating the potential of HSVA as an adjunctive test within the PCD diagnostic algorithm, could serve as a blueprint for analogous developments throughout Latin America.

Primary ciliary dyskinesia (PCD) is an inherited disorder that impairs motile cilia, essential for respiratory health, with a reported prevalence of 1 in 16,309 within Hispanic populations. Despite having the RSPH4A [c.921+3_921+6del (intronic)] founder mutation in 70% of Puerto Rican patients, the characterization of the ciliary dysfunction remains unidentified due to the unavailability of advanced diagnostic modalities like High-Speed Video Microscopy Analysis (HSVA). Our study implemented HSVA for the first time on the island as a tool to better diagnose and characterize the RSPH4A [c.921+3_921+6del (intronic)] founder mutation in Puerto Rican patients. By applying HSVA, we analyzed the ciliary beat frequency (CBF) and pattern (CBP) in native Puerto Rican patients with PCD. Our results showed decreased CBF and a rotational CBP linked to the RSPH4A founder mutation in Puerto Ricans, presenting a novel diagnostic marker that could be implemented as an axillary test into the PCD diagnosis algorithm in Puerto Rico. The integration of HSVA technology in Puerto Rico substantially enhances the framework for PCD evaluation and diagnosis, facilitating prompt detection and early intervention for improved disease management. This initiative, demonstrating the potential of HSVA as an adjunctive test within the PCD diagnostic algorithm, could serve as a blueprint for analogous developments throughout Latin America.

Genetic mutations in >50 genes, including RSPH4A, can lead to primary ciliary dyskinesia (PCD). RSPH4A mutations affect radial spokes, which alter the configuration of the ciliary ultrastructure and lead to chronic oto-sinopulmonary disease. The RSPH4A [c.921+3_6delAAGT] founder mutation was described as one cause of PCD without laterality defects in Puerto Rico. The average Puerto Rican genetic composition includes 64% European, 21% African ancestral, and 15% Native-American or Taino, a native tribe in the Caribbean at the start of the European colonization, genes. Due to the relatively elevated Taino ancestry on the island, it might have contributed to the endemicity of the RSPH4A [c.921+3_6delAAGT] splice site mutation. However, the ancestry of this mutation is still not confirmed. This article describes the two pediatric PCD cases with the Puerto Rican founder mutation and reports an ancestral haplotype analysis of the RSPH4A [c.921+3_6delAAGT] splice site mutation. A median-joining haplotype network was constructed with the genome sequence data from 104 Puerto Rican subjects in the 1000 Genomes Project (1000GP). This study found that the RSPH4A [c.921+3_6delAAGT] splice site mutation was carried to Puerto Rico from Europe by conquistadors or shortly after the conquest and that it gained frequency on the island through genetic drift fueled by a subsequent population expansion.