Hypochondrogenesis
Encyclopedia
Hypochondrogenesis is a severe genetic disorder
causing malformations of bone
growth. The condition is characterized by a short body and limbs and abnormal bone formation in the spine
and pelvis
.
Hypochondrogenesis is a subtype of collagenopathy, types II and XI
, and is similar to another skeletal disorder, achondrogenesis type 2
, although the spinal changes seen in hypochondrogenesis tend to be somewhat milder.
s. The spinal bones (vertebrae) in the neck and part of the pelvis (the sacrum) do not harden, or ossify
, properly. The face appears flat and oval-shaped, with widely spaced eyes, a small chin, and, in some cases, an opening in the roof of the mouth called a cleft palate. The abdomen is enlarged, and excess fluid may build up in the body before birth (a condition called hydrops fetalis
).
As a result of these serious health problems, infants are usually premature and stillborn or die shortly after birth from respiratory failure. Some infants have lived for a time, however, with intensive medical support. Babies who live past the newborn period are usually reclassified as having spondyloepiphyseal dysplasia congenita
, a related disorder on the spectrum of abnormal bone growth.
. The protein made by this gene forms type II collagen, a molecule found mostly in cartilage
and in the clear gel that fills the eyeball (the vitreous
). Type II collagen is essential for the normal development of bones and other connective tissues (tissues that form the body's supportive framework). Mutations in the COL2A1 gene interfere with the assembly of type II collagen molecules, which prevents bones from developing properly.
This condition is caused by new mutations in the COL2A1 gene. Hypochondrogenesis is considered an autosomal dominant disorder because the affected gene is located on an autosome
, and only one copy of the altered gene is necessary to cause the condition. The disorder is not passed on to the next generation, however, because affected individuals do not live long enough to have children.
Genetic disorder
A genetic disorder is an illness caused by abnormalities in genes or chromosomes, especially a condition that is present from before birth. Most genetic disorders are quite rare and affect one person in every several thousands or millions....
causing malformations of bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
growth. The condition is characterized by a short body and limbs and abnormal bone formation in the spine
Vertebral column
In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...
and pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
.
Hypochondrogenesis is a subtype of collagenopathy, types II and XI
Collagenopathy, types II and XI
The type II and XI collagenopathies are a group of disorders that affect connective tissue, the tissue that supports the body's joints and organs. These disorders are caused by defects in type II or type XI collagen. Collagens are complex molecules that provide structure, strength, and elasticity ...
, and is similar to another skeletal disorder, achondrogenesis type 2
Achondrogenesis type 2
Infants with achondrogenesis, type 2 have short arms and legs, a small chest with short ribs, and underdeveloped lungs. Achondrogenesis, type 2 is a subtype of collagenopathy, types II and XI. This condition is also associated with a lack of bone formation in the spine and pelvis...
, although the spinal changes seen in hypochondrogenesis tend to be somewhat milder.
Diagnosis
Affected infants have short arms and legs, a small chest with short ribs, and underdeveloped lungLung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s. The spinal bones (vertebrae) in the neck and part of the pelvis (the sacrum) do not harden, or ossify
Ossification
Ossification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...
, properly. The face appears flat and oval-shaped, with widely spaced eyes, a small chin, and, in some cases, an opening in the roof of the mouth called a cleft palate. The abdomen is enlarged, and excess fluid may build up in the body before birth (a condition called hydrops fetalis
Hydrops fetalis
Hydrops fetalis is a condition in the fetus characterized by an accumulation of fluid, or edema, in at least two fetal compartments. By comparison, hydrops allantois or hydrops amnion are an accumulation of excessive fluid in the allantoic or amniotic space respectively.-Presentation:Locations can...
).
As a result of these serious health problems, infants are usually premature and stillborn or die shortly after birth from respiratory failure. Some infants have lived for a time, however, with intensive medical support. Babies who live past the newborn period are usually reclassified as having spondyloepiphyseal dysplasia congenita
Spondyloepiphyseal dysplasia congenita
Spondyloepiphyseal dysplasia congenita is a rare disorder of bone growth that results in dwarfism, characteristic skeletal abnormalities, and occasionally problems with vision and hearing...
, a related disorder on the spectrum of abnormal bone growth.
Pathophysiology
Hypochondrogenesis is one of the most severe conditions in a spectrum of disorders caused by mutations in the COL2A1 geneGene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
. The protein made by this gene forms type II collagen, a molecule found mostly in cartilage
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
and in the clear gel that fills the eyeball (the vitreous
Vitreous humour
The vitreous humour or vitreous humor is the clear gel that fills the space between the lens and the retina of the eyeball of humans and other vertebrates...
). Type II collagen is essential for the normal development of bones and other connective tissues (tissues that form the body's supportive framework). Mutations in the COL2A1 gene interfere with the assembly of type II collagen molecules, which prevents bones from developing properly.
This condition is caused by new mutations in the COL2A1 gene. Hypochondrogenesis is considered an autosomal dominant disorder because the affected gene is located on an autosome
Autosome
An autosome is a chromosome that is not a sex chromosome, or allosome; that is to say, there is an equal number of copies of the chromosome in males and females. For example, in humans, there are 22 pairs of autosomes. In addition to autosomes, there are sex chromosomes, to be specific: X and Y...
, and only one copy of the altered gene is necessary to cause the condition. The disorder is not passed on to the next generation, however, because affected individuals do not live long enough to have children.