What Is Achondrogenesis?
Achondrogenesis refers to the group of severe disorders that affect the cartilage and the development of bone. The term was first given by Italian pathologist Marco Fraccaro. This term is derived from a Greek word meaning "not producing cartilage." Children with this disorder have a small body, short limbs, and other skeletal abnormalities.
Achondrogenesis is a serious health problem. Infants with achondrogenesis typically die before birth or die soon after birth from respiratory failure; however, some infants have survived for a short duration of time with the right intensive medical support. It is otherwise known as achondrogenesis syndrome.
What Are the Different Types of Achondrogenesis?
Achondrogenesis is classified into three different types. Their characteristics, inheritance pattern, and genetic causes differ accordingly. Here are the types of achondrogenesis:
-
Type 1A.
-
Type 1B.
-
Type 2.
Type 1A:
Type 1A is the least understood among the three forms of achondrogenesis. Achondrogenesis type 1A is otherwise known as the Houston-Harris type. The infants affected with this type have the following characteristics:
-
Extremely short limbs.
-
Narrow chest.
-
Short ribs that can fracture easily.
-
Lack of bone formation in the skull, spine, and pelvis.
Type 1B:
Type 1B is otherwise known as the Parenti-Fraccaro type. This type shows the following features:
-
Extremely short limbs.
-
Narrow chest.
-
Prominent and rounded abdomen.
-
Short fingers and toes.
-
Clubfeet (fingers may turn inward and upward).
Type 1A and type 1B are hard to diagnose without genetic testing.
Type 2:
Achondrogenesis type 2 is otherwise known as the Langer-Saldino type. Infants affected by this type 2 have the following features:
-
Short arms and legs.
-
Narrow chest with short ribs.
-
Underdeveloped lungs.
-
Lack of bone development in the spine and pelvis.
-
Prominent forehead.
-
Small chin.
The affected infants often have a condition known as hydrops fetalis, in which excess fluid builds up in the body before birth, and their abdomen is enlarged.
What Are the Causes for Achondrogenesis?
Typically achondrogenesis is a genetic condition. So parents can do nothing to cause it or to prevent it. Infants develop this condition due to abnormalities in the genes. Among the distinct types of achondrogenesis, type 1A and type 1B are autosomal recessive disorders. Infants develop this type when their parents copy an abnormal copy of a specific gene. A change (mutation) in the TRIP11 gene causes type 1A achondrogenesis, and a change in the SLC26A2 gene causes type 1B achondrogenesis.
Achondrogenesis is most often seen in parents who are closely related, as it is more likely that close relatives have the same genetic mutation.
In most cases, type 2 achondrogenesis is caused due to a de novo mutation and not something that is passed down from the parents. It is considered an autosomal dominant disorder as one copy of the mutated gene in each cell is sufficient. Mutation in the COL2A1 gene is responsible for causing type 2 achondrogenesis. Mutations in these particular genes cause the production of proteins that are not able to perform their functions properly within the body. Though it is clear that mutation in particular genes is the causative factor for achondrogenesis, scientists are not clear about what is causing these mutations (changes) and if anything can prevent them from occurring.
What Happens When Both the Parents Carry the Mutation in the Genes?
When both parents carry a mutation in the genes linked with achondrogenesis, then the child is likely to have:
-
25 % probability of having achondrogenesis.
-
50 % probability of carrying the mutation but not having the disorder.
-
25 % chance of neither having the disorder nor carrying the mutated gene.
How Is Achondrogenesis Diagnosed?
Screening during pregnancy helps determine achondrogenesis. When diagnosed with this condition, genetic counseling is given to the parents to weigh the risks and benefits of pregnancy.
Ultrasound:
The ultrasound taken between the 12th and 14th week of pregnancy helps determine the condition. Achondrogenesis can resemble other conditions as well. To confirm the diagnosis, the doctor may recommend additional tests such as amniocentesis.
Genetic Testing:
Genetic testing is suggested for parents who have a higher chance of passing down the disorder, such as people with a family history of achondrogenesis or parents being closely related. Genetic testing can also help determine the type of achondrogenesis.
X-Ray:
After birth, it can be diagnosed when the infant has extremely short arms and legs, short ribs, short chest, and short trunk. X-ray findings help determine the underdeveloped skull, vertebrae, and rib cage.
Is Achondrogenesis a Common Condition?
Achondrogenesis is a rare condition. Among the different types of achondrogenesis, type 1A and type 1B are so rare that their prevalence has not been estimated yet. Type 2 achondrogenesis is seen in around 1 in 40,000 to 1 in 60,000 infants. If both parents carry the mutated gene, then around 1 in 4 infants have the chance of developing the disorder. Having family members affected with this disorder, then there is an increased likelihood of the child being a carrier.
Can Achondrogenesis Be Treated?
There is no cure found yet for achondrogenesis. With the results that come out from 12 weeks to 14 weeks screening, parents are guided with genetic counseling and about the risks of the condition. Some parents decide to terminate, whereas there are parents who are willing to continue their pregnancy. Most frequently, babies die before birth or soon after birth. So when the baby is born, treatment mainly focuses on alleviating the symptoms and giving support to both parents.
What Kind of Support Do Parents Require During Pregnancy or After Loss of the Baby?
The infants affected with achondrogenesis do not survive long after birth. So when the parents choose to terminate the pregnancy, they tend to experience painful emotions. They may have a fear of facing societal judgment and stigma. There are a lot of organizations to give mental support to the parents before or after the loss of the baby.
In instances when the infant dies in later pregnancy or immediately after birth, the woman is more likely to develop postpartum depression. Offering appropriate psychological and medical care to those women helps improve their well-being.
The parents who lost their child require maximum support from relatives and friends. It is good if relatives and friends could acknowledge the parents' decision as reasonable and right. Do not judge or insult the parents when they have decided to terminate the pregnancy. Give them moral and physical support.
What Is the Prognosis for Children Born With Achondrogenesis?
The affected infants usually die before birth or shortly after birth. When born with achondrogenesis, they may have underdeveloped lungs that may lead to serious breathing issues leading to lung failure. Eventually, they die.
Conclusion
There is no cure for achondrogenesis, so parents should be offered genetic counseling to weigh the risks and benefits of the subsequent pregnancies. Infant loss gives absolute distress, and parents should know that they are not alone. There are various organizations and social forums to help them with mental support for overall well-being.