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INHERITED MONOGENIC DISEASES

           

Refsum disease

Refsum disease belongs to the group of leukodystrophic diseases and is characterized biochemically by an accumulation of phytanic acid. The accumulation of phytanic acid (3,7,11,15-tetramethylhezadecanoic acid) causes damage to the retina, brain and peripheral nervous system. In most cases, the etiology involves mutations in the PHYN gene (PAXH, located at 10p13) that codes for the peroxisome enzyme fitanoyl-CoA hydroxylase (PhyH), which oxidizes the phytanic acid in alpha, placing it in the first step of its degradation. Another mutation has recently been described in the PEX7 gene, located at 6q23.3. This gene codes for the peroxin 7 receptor, which allows the entry of PhyH to the peroxisomes.

It presents an autosomal recessive inheritance and the prevalence of the disease is 1/1.000.000 individuals, without distinction between men and women.

Initial symptoms usually appear in adolescence, although they have also been described in infancy and adults of 30 and 40 years of age. The first symptom is hemeralopathy (loss of vision in the dark), followed by episodes of chronic distal motor polyneuropathy. Other associated clinical signs include: perceptual deafness, anosmia, cerebellar ataxia and sometimes severe intellectual deficit.

Over time, cutaneous symptoms (ichthyosis) appear, along with poliphyseal dysplasia, cardiomyopathy, elevated protein content in the cerebrospinal fluid, and retinitis pigmentosa that may lead to blindness.

Phytanic acid comes exclusively from the diet (vegetables and herbivorous animals), a strict diet helps the partial regression of symptoms.

GENE OR REGION STUDIED


  • PEX7
  • PHYH

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