SNP Shot: Genomic Insights

Primary ciliary dyskinesia (PCD) is a genetic disorder marked by persistent respiratory infections, misplaced internal organs, and infertility. These issues stem from defects in cilia and flagella. Cilia are tiny, finger-like projections on cell surfaces, present in the airways, reproductive system, and other tissues. Flagella, similar to cilia, are tail-like structures that enable sperm to move.

In the respiratory system, cilia beat in a coordinated fashion to move mucus toward the throat, clearing fluid, bacteria, and particles from the lungs. Newborns with PCD often have breathing difficulties, highlighting cilia's role in clearing fetal lung fluid. From early childhood, individuals with PCD experience frequent respiratory infections. Defective cilia in the airways allow bacteria to linger, causing these infections. Chronic nasal congestion and cough are also common. These recurrent infections can lead to bronchiectasis, a condition that damages the bronchi (air passages to the lungs), potentially causing life-threatening respiratory problems.

Some people with PCD have organs positioned abnormally within their chest and abdomen. This occurs during early embryonic development when the body establishes left and right sides. Roughly half of PCD patients exhibit situs inversus totalis, a complete mirror-image reversal of internal organs. For example, the heart is on the right side instead of the left. Situs inversus totalis usually doesn't cause health issues. PCD patients with situs inversus totalis are often diagnosed with Kartagener syndrome.

About 12% of PCD patients have heterotaxy syndrome (situs ambiguus), characterized by heart, liver, intestinal, or spleen abnormalities. These organs might be malformed or incorrectly positioned. Individuals may also lack a spleen (asplenia) or have multiple spleens (polysplenia). Heterotaxy syndrome arises from problems establishing left-right body asymmetry during embryonic development. The severity of heterotaxy varies significantly.

PCD can cause infertility. Flagella movements are essential for sperm to reach the egg. Males with PCD often cannot father children because their sperm do not move correctly. Some affected females are infertile, likely due to defective cilia in the fallopian tubes.

Recurrent ear infections (otitis media), particularly in young children, are another symptom of PCD. Untreated otitis media can result in permanent hearing loss. These infections are likely related to cilia abnormalities within the inner ear.

In rare cases, PCD patients develop hydrocephalus (fluid buildup in the brain), possibly due to abnormal brain cilia.

Inheritance:

PCD follows an autosomal recessive inheritance pattern. This means that an affected individual must inherit a mutated copy of the relevant gene from each parent. Parents carrying one copy of the mutated gene usually do not exhibit symptoms of the condition.