Rhizomelic Chondrodysplasia Punctata types 1, 2 & 3

What else is it called?

  • Chondrodysplasia Punctata, Rhizomelic 
  • RCDP 
  • RCP 

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What causes it?

Rhizomelic chondrodysplasia punctata (RCP) is caused by mutations (changes) in one of three genes. RCP type 1 which is the most common form, is caused by mutations in the PEX7 gene. RCP type 2 is caused by mutations in the GNPAT gene and RCP type 3 is caused by mutations in the AGPS gene.  

These genes are involved in the construction and function of structures called peroxisomes.  Peroxisomes are sac-like compartments within cells that hold the enzymes needed to break down substances such as fatty acids and certain toxic compounds. They also play a big role in the production of fats used in digestion and in the nervous system.  

Inside the peroxisomes, the proteins that are produced by the PEX7, GNPAT and AGPS genes play a part in the formation of lipid molecules also known as plasmalogens. Plasmalogens are found in cell membranes in the body but little is known about their function. Changes in these genes stop peroxisomes from making plasmalogens. This causes the symptoms associated with this condition; however it is still unclear how this leads to the specific symptoms of the disorder.

How common is it?

Rhizomelic Chondrodysplasia Punctatais a rare inherited condition that affects fewer than 1 in 100,000 people worldwide. RCP type 1 is more common than RCP type 2 or RCP type 3.  

What are the signs and symptoms?

This condition affects the normal development of many areas in the body. The main symptoms include: 

  • Skeletal (bone) abnormalities  
  • Distinctive facial features  
  • Intellectual disability  
  • Respiratory problems and infections 

Specific bone abnormalities associated with this condition include: 

  • Rhizomelia (shortening of the bones in the upper arms and thighs) 
  • Chondrodysplasia (a bone abnormality that affects the growth of the long bones and can be seen on x-rays) 
  • Contractures (joint deformities that make the joints stiff and painful) 

Specific distinctive facial features seen in individuals with RCP include: 

  • Prominent forehead 
  • Hypertelorism (widely set eyes) 
  • Midface hypoplasia (a sunken appearance of the middle of the face)  
  • Small nose with upturned nostrils  
  • Full cheeks  
  • Cataracts (clouding of the lenses of the eyes) – This is apparent at birth or early infancy 

Signs and symptoms associated with developmental delays and intellectual disability in individuals with RCP include: 

  • Missing developmental milestones (such as sitting up without support, feeding themselves or speaking in phrases) 
  • Much slower growth compared to children of the same age 
  • Seizures 

Recurrent respiratory infections and breathing problems that may be life threatening are also common in individuals with RCP. Due to these severe health problems, patients with this condition usually do not survive past childhood. Most affected children do not live past the age of 10 years. However, there are a few individuals with the condition who had milder symptoms and lived into early adulthood.  

The three types of RCP (type 1, 2 and 3) have similar features but are distinguished by their genetic causes.  

How is it diagnosed?

A diagnosis of RCP is based on a physical examination of the individual, identifying symptoms that are characteristic to this condition and radiography (such as x-rays) results. Molecular genetic testing will confirm the diagnosis of RCP.  

Can it be treated?

There is no specific treatment for RCP. Management of this condition can include physical therapy and orthopaedic (branch of medicine dealing with bones or muscles) procedures may improve function in affected individuals. However, the prognosis of this condition is poor, and patients usually do not live past the first decade (10 years) of life. This is mainly due to respiratory complications.  

Do my family need to be tested?

RCP is an inherited condition. Humans have chromosomes made up of DNA. Genes are pieces of DNA that carry the genetic information. Each chromosome may have several thousand genes. We inherit chromosomes from the egg of the mother and sperm of the father. The genes on those chromosomes carry the instructions that determine a person’s characteristics, which are a combination of the parents. 

The pattern of inheritance of RCP is autosomal recessive. This means that carriers of the condition do not have the disorder because the other gene of this pair is working normally. Parents of children with RCP are carriers.  

When both parents are carriers, the risk to the baby in each pregnancy is 

  • 25% chance (1 in 4) of developing the condition 
  • 50% chance (1 in 2) for the baby to be a carrier of the condition 
  • 25% chance (1 in 4) for the baby to have two working genes and neither have the condition nor be a carrier 

Genetic counselling can be requested to get a full explanation.  

Relevant Organisations

References

References are available on request. Please contact Helen Morris by phoning 0845 241 2173 or emailing helen@metabolicsupportuk.org [Resource Library No: AAP002]. 

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