The most common clinical problems encountered in PCD are related to the upper (ears and sinuses) and lower (lungs) respiratory system. However, people with PCD may experience problems related to laterality/situs (organ placement) issues or, in rare cases, malformation of the abdominal and thoracic (chest) organs.
Situs Inversus & Organ Orientation
‘Laterality’ is a term describing the dominance or difference between the sides of the body. The body is not identical on both sides (called ‘asymmetry’), and the process by which the body knows how to organize laterality/asymmetry is very complex. One important factor appears to be the motion of unique cilia on the embryonic node (called ‘nodal cilia’) which only appear once in our life. The activity of these unique motile cilia plays an important role in determining the placement of organs within the thoracic and abdominal cavities. In the absence of this ciliary motion, organ placement becomes a random event, giving each affected embryo a 50/50 chance of having typical placement (known as situs solitus), mirror-image placement with reversed organs (known as situs inversus) or an unusual pattern of unique organ development or placement (situs ambiguous or heterotaxy). Many PCD genetic mutations also impact the motility of the nodal cilia. With these mutations, approximately 50% of PCD patients present with situs solitus and the remaining patient population having either situs inversus or situs ambiguus (‘ambiguous’)/heterotaxy.
‘Kartagener syndrome,’ is an older term commonly used to describe PCD with situs inversus. Since this presentation of PCD is just one of three possible organ placements, the term ‘Kartagener’s’ is somewhat limiting. Nevertheless, it persists because it has been in the medical literature for over a century. Individuals with PCD and situs solitus or PCD with situs ambiguus do not have ‘Kartagener syndrome’ as the term is only used for PCD with situs inversus. For more information on the terms used to describe PCD, please check out ‘What’s in a Name? A Brief History of PCD Terminology.’
Situs ambiguus/heterotaxy syndromes can result in very serious clinical complications, including complex congenital heart defects and defects of the spleen.
Polysplenia literally means “many spleens” (or, more accurately, partial spleens called ‘splenules’). Asplenia indicates the congenital absence of a spleen. The spleen plays an important role filtering and storing blood and helping to clear bacteria from the blood stream. An increased incidence of asplenia and polysplenia (frequently associated with cardiac defects) has been reported in patients with PCD and situs ambiguus/heterotaxy. Typically, splenic function is preserved in polysplenia. In rare cases, however, there is not enough functioning splenic tissue in the ‘splenules,’ resulting in a condition known as ‘functional asplenia.’ Splenic function can be assessed with a blood test that looks for Howell-Jolly bodies. In extreme cases of splenic dysfunction, surgical repair or removal of the spleen may be required.
Congenital Heart Defects
Congenital malformations of the heart can be associated with PCD, especially in the presence of situs ambiguus/heterotaxy. Defects in the wall (septum) separating the atria or ventricles (chambers of the heart) have also been reported, as well as multiple complex cardiac malformations. At times, these can be life-threatening and require immediate surgical attention.
There is evidence to suggest that hydrocephalus may be a rare complication in individuals with PCD. Hydro (meaning ‘water’) and ‘cephalus’ (meaning related to the brain or head) is a condition where excess cerebrospinal fluid collects in the ventricles of the brain and causes them to become enlarged. If not corrected, brain damage can result. Ventriculomegaly, where the ventricles are enlarged, but there is no excess fluid, has also been reported rarely in PCD.
The ventricles of the brain are openings in the center of the brain that are lined with ciliated tissue. In animal models of PCD, hydrocephalus is quite common and often very severe. It is believed that failure of ciliary activity in the ventricles contributes to faulty drainage, allowing excess fluid to build up. These more severe cases of hydrocephalus are rarely seen in humans with PCD, possibly because as upright walkers (bipeds), gravity provides us with drainage assistance that quadrupeds (animals that walk on four legs) do not have.
Infertility and sub-fertility are common manifestations of PCD. Male infertility used to be considered universal, but there are reports of male PCD patients with normal reproductive capabilities. Females may experience sub-fertility and/or an increased risk for ectopic (tubal) pregnancy. Many women with PCD have achieved pregnancy naturally, however. For family planning purposes, it is important not to assume you will be infertile just because you have PCD!
Subfertility in PCD is a mechanical issue—a matter of being unable to get the necessary reproductive components where they need to be. This should be distinguished from ‘sterility,’ which implies that the components themselves are not viable. Because most people with PCD have sperm and egg cells that are perfectly fine, just unable to travel due to ciliary inactivity, IVF, ICSI and other assisted reproductive services have been used with a high level of success in PCD.
Syndromic Associated Conditions
PCD is inherited as a recessive genetic disorder, meaning both parents of an affected person carried a mutated copy of a PCD gene (the same gene) and both passed on their mutated, rather than good copy to the affected offspring. In very rare instances, PCD can be passed as an x-linked trait or can occur in the presence of disorders associated with chromosomal deletions. When this happens, the affected individual has PCD in addition to the other underlying syndrome. Examples of this include Cri du Chat syndrome (deletion on chromosome 5 in the same location as PCD gene DNAH5); Oral-Facial-Digital syndrome and retinitis pigmentosa (x-linked defects). These forms of PCD inheritance are very rare.
As we continue to learn more about the genes associated with PCD, it is likely that additional associated or overlapping conditions will be identified. These will likely be tied to specific genetic defects and not affect the entire patient population.