Failure to demonstrate the fifth middle phalanx (late calcification of the middle
phalanx of the fifth finger)
|
|
|
Types and clinical signs
|
Each of the fingers apart from the thumb has 3 sections, called phalanges. Sometimes
ultrasound examination
of the fifth finger fails to demonstrate the middle phalanx - this is a result of
delayed ossification, i.e. delay in the deposition of calcium in the bone of the
middle phalanx. This does not constitute a defect, and it will always develop into
a normal fifth finger.
In some cases the middle phalanx can be seen, but appears to be smaller than usual.
This condition manifests as a slight inward curvature of the little finger - this
is called clinodactyly and is of no clinical importance. Clinodactyly can be hereditary
and be present in one of the parents. In another group of cases, the bone is completely
normal.
The delayed ossification of the phalanx in this digit has no clinical significance
and no adverse effects. It constitutes an ultrasonographic sign that may slightly
raise the statistical risk for Down
syndrome, although this is under dispute. This correlation is considered
less statistically significant nowadays. The exact degree of increased risk for
Down syndrome, if any, is not precisely known but is estimated to be up to approximately
3 times.
|
The finding in the fifth finger as part of an aggregate of parameters estimating
the statistical risk for chromosome disorders
|
There are several parameters that establish the statistical probability for Down syndrome, and the presence
of delayed ossification of the phalanx in this digit can be considered as part of
the aggregate of these parameters. Normal nuchal translucency, young maternal age,
absence of other signs or defects on ultrasonography, and a normal biochemical screening
result are all factors that indicate a significantly reduced risk for Down syndrome.
|
What should be done once this is diagnosed?
|
|
|
Opinions vary.
Amniocentesis
(or chorionic
villus sampling) is undoubtedly the only test that can categorically rule
out chromosome
disorders.
However, it is neither medically indicated nor recommended that every pregnant woman
should undergo amniocentesis - only those who are at high risk of having a specific
problem that can be examined by this test (see information sheet titled: Why is there no medical recommendation
for amniocentesis in all cases?).
Most opinions hold that in the great majority of the cases in which middle fifth
phalanx ossification delay is the sole finding, and taking into account the other
parameters mentioned above, which do not raise the risk for a chromosome disorder,
the weighted risk is not in the high-risk range for which amniocentesis is indicated.
|
|
For practical purposes
|
The -gold-standard- threshold for recommendation of amniocentesis is a risk of Down syndrome greater than 1:386 based on the
results of the biochemical marker screening tests,
and when the weighted risk is equal to or higher than this amniocentesis is generally
recommended. However, the presence of middle fifth phalanx ossification delay in
the fetus may statistically increase the risk of Down syndrome. Therefore in these
cases some physicians suggest that this should be integrated with the results of
the biochemical screening tests and the new threshold for recommending amniocentesis
is a risk for Down syndrome of greater than 1:1000 in the biochemical marker screening tests. If other abnormal
findings are also present, these guidelines are insufficiently established and the
woman should be referred for genetic counseling. In genetic counseling, the necessity for amniocentesis
can be assessed.
|
Inheritance pattern
|
Not yet known - this will be ascertained in the future.
Clindodactyly is transmitted by
autosomal recessive inheritance.
|
Penetrance
|
Not known
|
Associated features that can be demonstrated in tests performed during pregnancy
|
It is important to look for other ultrasonic signs associated with Down syndrome
and other chromosomal syndromes.
It is also important to refer the couple for genetic counseling within which the
significance of the finding and the advisability of undergoing amniocentesis will
be discussed. All data, including the results of other tests performed during the
pregnancy such as alpha-fetoprotein, nuchal translucency, etc., should be brought
to this counseling.
|
What is the risk of recurrence in a subsequent pregnancy?
|
Not known
|
Molecular genetic information
|
The gene for the disease
Not known
Location
Not known
|
Genetic testing
|
Diagnostic testing
Not available
Carrier testing
Not available
Fetal testing
Ultrasound examination only
|