Reply to the Letter: “Diagnosis of Peroxisomal Disorders”
04 April 2019
21 April 2019
29 May 2019 (online)
We completely agree with the concern raised by Joob et al that the peroxisomal biogenesis disorders (PBDs) have wide spectrum. The most common disorders found in a Japanese study were X-linked adrenoleukodystrophy (X-ALD) and Zellweger syndrome (ZS). X-ALD is suspected in children usually in the first decade with neuroregression. The magnetic resonance imaging findings suggest leukodystrophy initially involving the dentate nuclei and superior cerebellar peduncles, later involving the whole brain. ZS is a severe form of the disorder presenting in infancy with severe neurologic dysfunction, growth retardation, and chondral calcification or epiphyseal stippling on X-rays.
In the present series, we have described 6 classical cases of PBD (3 ZS, 2 rhizomelic chondrodysplasia punctata, and 1 X-ALD) and highlighted the clinical characteristics and radiological features pointing toward the diagnosis supported by biochemical investigations. Recently, several milder and newer phenotypes associated with the PEX gene are identified with over 14 PEX gene mutations.   The diagnosis of milder ZS and single peroxisomal enzyme disorders require high clinical suspicion, extensive biochemical testing, and DNA analysis. The constellation of features includes intellectual disability, epilepsy, cerebellar ataxia, peripheral neuropathy, retinal degeneration, and late-onset leukoencephalopathy in cases with PEX gene mutations.  Molecular diagnosis definitely helps in confirming the diagnosis in unusual or atypical cases and helps in the further expansion of the PBD spectrum.
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