Rhizomelic chondrodysplasia punctata

Rhizomelic chondrodysplasia punctata
Low levels of plasmalogens is a characteristic of rhizomelic chondrodysplasia punctata.
Specialty	Medical genetics
Symptoms	Alopecia, flat face[1]
Causes	PEX7 gene, GNPAT gene and AGPS gene mutations[2]
Diagnostic method	Clinical and radiologic finding[3]
Treatment	Physical therapy[4]

Rhizomelic chondrodysplasia punctata is a rare developmental brain disorder characterized by abnormally short arms and legs (rhizomelia), seizures, recurrent respiratory tract infections and congenital cataracts.

The cause is a genetic mutation that results in low levels of plasmalogens, which are a type of lipid found in cell membranes throughout the body, but whose function is not known.^[2]

Rhizomelic chondrodysplasia punctata has the following symptoms:^[4][1]

• Bilateral shortening of the femur, resulting in short legs
• Post-natal growth problems (deficiency)
• Cataracts
• Intellectual disability
• Possible seizures
• Possible infections of respiratory tract

This condition is a consequence of mutations in the PEX7 gene, the GNPAT gene (which is located on chromosome 1) or the AGPS gene. The condition is acquired in an autosomal recessive manner.^[2]

The mechanism of rhizomelic chondrodysplasia punctata in the case of type 1 of this condition involves a defect in PEX7, whose product is involved in peroxisome assembly. There are 3 pathways that depend on peroxisomal biogenesis factor 7 activities, including:^{[4][5][verification needed]}

• AGPS (catalyzes plasmalogen biosynthesis)
• PhYH (catalyzes catabolism of phytanic acid)
• ACAA1 (catalyzes beta-oxidation of VLCFA - straight)

The diagnosis of rhizomelic chondrodysplasia punctata can be based on genetic testing^[6] as well as radiography results, plus a physical examination of the individual.^[3]

• Type 1 (RCDP1) is associated with PEX7 mutations; these are peroxisome biogenesis disorders where proper assembly of peroxisomes is impaired.^[4]
• Type 2 (RCDP2) is associated with DHAPAT mutations.^[7]
• Type 3 (RCDP3) is associated with AGPS mutations.^[8]

Management of rhizomelic chondrodysplasia punctata can include physical therapy; additionally orthopedic procedures improved function sometimes in affected people.^[4]

The prognosis is poor in this condition,^[3] and most children die before the age of 10.^[4] However, some survive to adulthood, especially if they have a non-classical (mild) form of RCDP.^[4]

Children with classical, or severe, RCDP1 have severe developmental disabilities. Most of them achieve early developmental skills, such as smiling, but they will not develop skills expected from a baby older than six months (such as feeding themselves or walking).^[4] By contrast, children with non-classical mild RCDP1 often learn to walk and talk.^[4]

• Plasmalogen
• Peroxisomal disorder

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