Type 1 rhizomelic chondrodysplasia punctata with a homozygous PEX7 mutation

Background: Rhizomelic chondrodysplasia punctata (RCDP) is a rare peroxisomal disease characterised by punctate calcifications of non-ossified cartilage epiphyseal centres. The main biochemical marker of all RCDP types is a decrease in the levels of plasmalogens. Additionally, the accumulation of phytanic acid can be used as a differential marker between types of RDCP. Due to the biochemical overlap between types 1 and 5 RCDP, a genetic analysis of these genes should be performed in patients to identify the type.

Case presentation: A 2-month-19-day-old male child presented with symptoms of limited movement and discomfort with movement in the extremities. His sister, who had similar clinical findings, was diagnosed with tetralogy of Fallot and died at 6 months of age. A physical examination revealed an atypical facial appearance, bilateral cataracts, sensitivity to touch in the extremities, shortness in the proximal segments of the long bones, limited movement in both knees and elbows and axial hypotonicity. Laboratory analyses revealed normal ammonia, lactate, plasma and urine amino acids, long chain fatty acids and phytanic acid levels. Rhizomelia, significant metaphyseal expansion, irregularities in the cortex, loss of ossification, fragmented appearance and punctate calcifications in both elbows, both knees and in the femoral epiphysis were seen on the skeletal survey. A homozygote p.L70W (c.209T>G) mutation was found in the PEX7 gene.

Conclusions: Plasma phytanic acid levels can be normal in a patient with type 1 RCDP that develops as a result of a PEX7 gene mutation, as in our case. A molecular genetic analysis and/or fibroblast culture must be conducted in clinically suspicious cases. While no cardiac pathology was found in our case, tetralogy of Fallot was present in his sister with similar clinical findings. The presence of different cardiological phenotypes in the sibling suggested that the genotype-phenotype correlation may not be complete in this disorder.