Full (complete) situs inversus
- the heart and abdominal organs are completely reversed, i.e. the apex of the heart
and the stomach are on the right.
Partial (incomplete) situs inversus
- the heart is on the right but the liver is usually in the center of the body.
There are two main types:
These are called respectively left and right isomerism sequence.
- One where both sides of the body resemble the left side.
- One where both sides of the body resemble the right side.
Limited situs inversus with an inversion of the stomach only
Situs inversus as part of Kartagener
syndrome - approximately 20% of cases of full situs inversus are Kartagener
Full situs inversus - the
heart and abdominal organs are completely reversed, i.e. the apex of the heart and
the stomach are on the right. This condition is not usually associated with accompanying
defects, although some studies have reported associated heart defects that are evident
on ultrasound examination.
In the absence of a heart defect, there are usually no other problems, but a few
cases of blockage of the biliary tract have been described. This is apparently the
more common type, occurring in 1 out of every 6,000 births. It is estimated that
up to about 20% of these cases are Kartagener syndrome (see below).
Partial situs inversus -
the heart is on the right but the liver is usually in the center of the body. There
are two main types:
Limited situs inversus in which there
is inversion of only the stomach
- Both sides of the body resemble the left side (left isomerism sequence). Here there
are bilateral long bronchi and bilateral bilobed lungs, i.e. each lung has two lobes
whereas in a healthy individual this is only the case in the left lung. This condition
is associated with congenital failure of development of part of the inferior vena
cava. Multiple spleens often develop. Some of the heart defects are associated with
increased blood flow to the lungs and the resultant engorging of the lungs with
blood. There are also defects in the digestive tract including incorrectly situated
intestines, intestinal blockages, etc., and blockages of the bile ducts in the liver.
- Both sides of the body resemble the right side (right isomerism sequence). Here
there are bilateral short bronchi and bilateral trilobed lungs, i.e. each lung has
three lobes whereas in a healthy individual this is only the case in the right lung.
This condition is also associated with agenesis of the spleen and many other defects.
Heart defects are associated with inadequate blood flow to the lungs and marked
absence of blood vessels in the lungs. There are also defects in the digestive tract
including incorrectly situated intestines, intestinal blockages, etc., and blockages
of the bile ducts in the liver.
Both these types may also involve additional defects, such as cleft palate, defects
in the closure of the spinal column, blockages of the airways in the nose, which
can, however, be opened immediately after birth, clubfeet, etc.
Situs inversus as part of Kartagener syndrome. Kartagener syndrome is a group of
diseases caused by lack of motility of the cilia on the cells of the lining of the
respiratory tract and a disorder in the motility of sperm cells.
In the airways the disease manifests as recurrent (chronic) sinusitis, recurrent
ear infections and chronic respiratory tract inflammation, including damage to the
walls of the lungs and chronic infection of the damaged region (bronchiectasis).
The defect in this condition is caused by a lack of the substance that provides
the cilia with the energy they need, called dynein.
Due to this, there is a reduction or absence of ciliary motility.
This leads to a severely reduced ability to evacuate phlegm, particles and infective
pathogens using the cilia, which in turn leads to an accumulation of bacteria, and
later to all the complications listed above. The frequency is 1 in 20,000. Diagnosis
is made by examining the cilia under an electron microscope in order to confirm
the absence of the characteristic dynein arms in the cilia, and to provide a quantitative
examination of the ciliary motility. The prognosis is significantly better than
that of diseases such as cystic
fibrosis, and if effectively treated, the subject's life expectancy is normal.
Recently, in vitro fertilization involving the injection of sperm cells into ova
has commenced- this ensures that Kartagener syndrome patients remain fertile.
Most cases of situs inversus, with the exception of Kartagener syndrome, are sporadic,
without a tendency for recurrence in subsequent pregnancies. In these cases, there
may be a spontaneous (new) mutation or involvement of a number of genes in conjunction
with environmental conditions that together determine whether the disease appears.
A number of different genes involved in the process of determining the normal direction
of intrauterine development have been found - damage in these can lead to situs
inversus. There are a few cases with autosomal dominant inheritance, and in these
the risk for recurrence is 50% in every pregnancy.
Kartagener syndrome has clear
autosomal recessive inheritance - the risk of recurrence in a couple who
has already had a child with this condition is 25% in every pregnancy.
In Kartagener syndrome patients, situs inversus occurs in only 50% of cases.
Associated features that can be demonstrated by imagery
Fetal ultrasound examination may reveal abnormalities in the locations of the heart,
stomach, and liver. It may also be possible to see heart defects and
polyhydramnios on ultrasound, and maybe failure to demonstrate a gallbladder.
and clubfeet, etc. may be seen.
What is the risk of recurrence in subsequent pregnancies?
The regular risk in the population is about 1 in every 6,000 pregnancies.
Parents who have had a child with this condition have a risk of up to 50%.
In Kartagener syndrome, the risk for recurrence of a couple with an affected child
is 25% in every pregnancy.
Molecular genetic information
The genes for the disease
Different and diverse genes associated with situs inversus of the various types
are known. It is difficult to identify them at the present time.
A gene known as DNAI1 that is responsible for about 15% of cases of Kartagener syndrome
has recently been found. There are apparently other genes that can also cause this
syndrome. The mutations in the gene that have been found up to now in Kartagener
syndrome patients are all in the same region of the gene, so it is relatively easy
to test for them.
The gene DNAI1 is situated on chromosome 9p13.
There are to date no clinical genetic tests for diagnosing this condition. Only
in families with multiple cases is it possible to carry out investigations that
may lead to the possibility of performing practical tests in some families in the
future, initially by indirect tests (linkage analysis), and in the more distant
future, once the gene itself has been found, by identifying the mutation or mutations.
This will be done in cooperation with a genetic institute. See information sheet:
Indirect testing for genetic markers in a family
that has one or several patients - when there are a number of different genes that
can each cause the disease - the gene, or most of the genes not having been located
/ identified / mapped - multifactorial diseases
In Kartagener syndrome it is possible to look for mutations in the gene that has
been found, DNAI1. A normal test, however, does not rule out this condition, as
the gene is responsible for only 15% of cases - in the others, a different gene
This cannot usually be performed. See above under diagnostic testing.
This cannot usually be performed. See above under diagnostic testing. Ultrasound
detection as stated above is possible.