U01.01.030 Primary ciliary dyskinesia

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Learning Objective: By the end of this session, medical students should be able to describe the genetic basis, pathophysiology, clinical features, and diagnostic findings of Primary Ciliary Dyskinesia, and correlate them with clinical presentations relevant to USMLE Step 1.

Overview

Feature	Description
Inheritance	Autosomal recessive
Defect	Dynein arm defect → immotile cilia
Result	Dysfunctional ciliated epithelia
Most common form	Kartagener syndrome = PCD + Situs inversus

Pathophysiology

The dynein arm provides the ATPase-driven force for ciliary movement.
Loss or defect leads to immotile or dyskinetic cilia, impairing mucociliary clearance and embryonic nodal flow.
Consequences:
- Impaired mucociliary clearance → recurrent respiratory infections
- Defective embryonic rotation → situs inversus
- Impaired sperm/fallopian tube cilia → infertility

Clinical Manifestations

System Affected	Clinical Features	Mechanism
Respiratory	Chronic sinusitis, otitis media, bronchiectasis	Impaired ciliary clearance
Reproductive	Infertility, ↑ risk of ectopic pregnancy	Immotile sperm, impaired ovum transport
Developmental	Situs inversus (Kartagener), hearing loss	Abnormal embryonic rotation; dysfunctional eustachian cilia

Laboratory Findings

Investigation	Finding	Comment
Nasal nitric oxide test	↓ Nitric oxide levels	Screening tool for PCD
Electron microscopy	Absence of dynein arms	Confirms diagnosis
Genetic testing	DNAH5 or DNAI1 mutations	Confirms molecular cause

Key Points for USMLE

Inheritance: Autosomal recessive
Triad (Kartagener): Situs inversus + chronic sinusitis + bronchiectasis
Infertility: Seen in both sexes due to immotile sperm or an oocyte transport defect
Screening: ↓ Nasal nitric oxide