Testing and Diagnosis: Solving the Puzzle of Missing Cilia

Diagnosing nasal acilia (ciliary aplasia) is a complex process because there is no single “gold standard” test that provides a simple yes or no answer ^[1]. Instead, doctors must put together a puzzle using several different types of evidence to prove that your cilia are truly missing because of a genetic blueprint error, rather than just temporary damage ^[2][3].

The Screening Step: Nasal Nitric Oxide (nNO)

For most patients over the age of five, the first step is a nasal nitric oxide test. Nitric oxide is a gas naturally produced in healthy sinuses. In people with missing or non-functioning cilia, the levels of this gas are typically extremely low ^[3][4].

• The Threshold: A result below 77 nL/min is a strong screening clue in appropriately cooperative patients, not a stand-alone diagnosis. This cutoff depends on standardized technique, equipment, and an experienced laboratory. A normal result does not completely exclude every PCD-spectrum disorder ^[4][5].
• The Catch: Your levels can drop temporarily if you have a cold, a sinus infection, or even if your nose is very “stuffy” ^[6][7]. Because of this, a single low reading is not enough for a diagnosis. It should ideally be repeated on a separate day according to the testing center’s protocol ^[4][8].

Looking at the Tissue: Microscopy

If screening suggests a problem, the next step is a nasal brushing or biopsy. A tiny sample of the lining of your nose is taken and examined in two ways:

1. High-Speed Video Microscopy (HSVM): Scientists use a specialized camera to record the cilia in slow motion. In cases of ciliary aplasia (also called RGMC), the technician will find that most cells simply have no “hairs” at all ^[2]. Any cilia that are present may actually move in a normal, healthy pattern—there just aren’t enough of them to clear mucus ^[2][9].
2. Transmission Electron Microscopy (TEM): This is a powerful microscope that looks at the internal structure of a single cilium (the axoneme) ^[2]. In classic Primary Ciliary Dyskinesia (PCD), the cilia look “broken” inside. In RGMC, the few cilia that exist often look structurally perfect, which can lead to a confusing “normal” report if the pathologist isn’t looking for the number of cilia instead of their shape. Normal-looking remaining cilia or a normal TEM report do not by themselves exclude PCD ^[2][3].

Ruling Out Damage: Cell Culture (ALI)

One of the most common reasons a test shows “no cilia” is secondary damage from a past infection or environmental irritant ^[10]. To rule this out, specialized centers use Air-Liquid Interface (ALI) culture ^[11].

In this test, your nasal cells are grown in a lab for several weeks. In a controlled environment, away from pollution and germs, healthy cells will eventually sprout new, normal cilia. If the cells still fail to grow cilia in the lab, it supports the possibility that the problem is “primary” (built into your genetics) rather than “secondary” (caused by your environment). However, failure of cells to reciliate in ALI can also reflect technical culture problems, so it is supportive rather than absolute proof ^[10][11].

Genetic Testing

A definitive diagnosis of RGMC (Reduced Generation of Multiple Motile Cilia) is often supported by finding appropriate pathogenic or likely pathogenic variants in specific genes ^[12][3]. The two most common genes involved are:

• CCNO: Mutations here often cause a near-complete absence of cilia ^[13].
• MCIDAS: This gene is essential for the cell to build the “anchors” (basal bodies) that hold cilia in place ^[13][14].

A variant of uncertain significance (VUS) should not be treated as confirmation, and a negative panel does not strictly exclude the disease.

Completeness Checklist

Because these conditions are rare, ask your doctor whether these evaluations are appropriate for you:

• [ ] Clinical History: Does your history include chronic congestion or a daily wet cough since childhood? ^[15]
• [ ] Repeat nNO: Has repeat testing been considered if a result was unclear? ^[4]
• [ ] High-Speed Video: Did the lab quantify the number of cilia, or just check their movement? ^[2]
• [ ] Pathology Review: Does the report mention oligocilia (the presence of very few cilia)? ^[3]
• [ ] Genetic Panel: Did the testing include a comprehensive panel (including CCNO and MCIDAS)? ^[12]
• [ ] Follow-up: If tests were unclear, has a repeat sample or ALI culture been discussed? ^[10]

How to Read Your Report

If you see these terms on your pathology or microscopy report, here is what they generally mean:

• Aplasia/Acilia: No cilia were seen in the sample ^[2].
• Oligocilia: A significantly reduced number of cilia were found ^[3].
• Normal Ultrastructure: The cilia that were found look healthy inside. In the context of acilia, this can actually be a sign of RGMC ^[2][16].
• Secondary Changes: Evidence of inflammation or damage (like swelling or “blebbing”) which suggests the missing cilia might be due to a temporary cause like a recent cold ^[10].