Skeletal dysplasias are a heterogeneous group of
congenital anomalies which affect cartilage and/or
bone growth. There are many specific syndromes which
are often very precisely characterised, down to knowledge
of the specific gene defect in many cases, with only
subtle differences between classifications. Individually
these syndromes have a low birth prevalence.
Skeletal dysplasias are generally caused by a single
gene defect and most are autosomal recessive, however
some types are autosomal dominant (e.g. achondroplasia)
or caused by teratogens (e.g. warfarin). The syndromes
in this group have certain features in common, and
allow for a general overview of these conditions.
The long bones of the limbs and the ribs are the
structures most often affected, and many of the syndromes
in this group have additional features which help
to make the diagnosis.
The shortening of the long bones may primarily
affect the proximal bones (the femur and humerus),
called rhizomelic shortening or primarily affect
the distal bones (the tibia/fibula and radius/ulna),
called mesomelic. The long bones may be curved or
so weak that multiple fractures occur, leading to
angulation within the long bones.
Top of Page
The diagnosis of skeletal dysplasia is usually first
suspected by ultrasound measurement of the long bones.
The femur is traditionally measured, although once
a suspicion of an abnormality has been raised all
the long bones and the foot length are helpful in
establishing a diagnosis. The appearances of the
chest are crucial to the outcome and the thoracic
circumference should be measured and compared to
standard charts and the abdominal circumference.
The chest has a distinctive picture on longitudinal
section with the fetal head, chest and abdomen together
resembling a champagne
with the chest being narrow and the abdomen relatively
much larger. The heart, although normal sized, will
appear large in the chest and this may be the first
Once a diagnosis of skeletal dysplasia has been
made the outcome must be discussed frankly with the
parents. Many will opt for termination of pregnancy,
and following delivery a careful inspection of the
fetus, X-rays of the whole baby and postmortem examination
by an experienced perinatal pathologist will be necessary
to establish the diagnosis. If possible fetal blood
or amniocytes should be cultures to allow DNA extraction
to take place so that a genetic diagnosis can be
made where possible. This will give the option of
early prenatal diagnosis in a future pregnancy using
chorion villus sampling at 11 weeks gestation. If
DNA diagnosis is not possible the diagnosis may not
be clearly established until 20 weeks, or even later
in some cases.
Top of Page
In the majority of skeletal dysplasias
the outcome for the baby is governed by the length
of the ribs. Most types will cause severe shortening
of the ribs leading to a narrow malformed chest
which causes the lung development to be so restricted
that the baby will die immediately after birth.
This pulmonary hypoplasia rather than the severity
of the limb malformations makes the majority of
these conditions lethal.
Whilst most skeletal dysplasias
are evident at birth some cases of milder dysplasia
present later in childhood (hypochondroplasia,
mesomelic dwarfism). It is important to establish
a diagnosis by clinical examination and radiological
Top of Page
To be added
Top of Page