Cause: Genetic, autosomal recessive
Pathophys:Phytanic acid (simple lipid with branches, 16 carbons) pile up in serum; can drop to normal in a year on no-chlorophyll diet. Phytolic acid, a fatty side chain of chlorophyll, is major source of phytanic acid in man. There is no endogenous source. Block is in initial decarboxylation to pristanic acid. Heterozygous relatives metabolize by half normal rate; diseased patients at 3% of normal by cultured fibroblasts
Sx:Nightblindness (100%), often 1st sx; sensorineural deafness (88%), begins in early adult life; anosmia (75%); muscular hypertrophy in some cases
Si:Cerebellar ataxia (100%); retinitis pigmentosa (100%), r/o syphilis and a-beta lipoproteinemia; tunnel vision, narrow fields (95%); lenticular opacities (cataracts) (82%); epiphyseal dysplasia (53%); ichthyosis (67%); muscular atrophy, esp of peroneal and intrinsic hand and foot muscles
Appears in childhood, earliest onset at age 3 yr; may be precipitated by acute illness; relapses and remits
Cardiac arrhythmias and block are the most frequent cause of death
Lab:
Chem:Serum phytanic acid >2 µgm/cc
CSF:Protein increased as high as 450 mg %
Noninv:EKG abnormal (57%)
Path:Nerve and brain biopsies show 15% of fatty acids in myelin are phytanic acid