Cerebrotendinous xanthomatosis: clinical and biochemical evaluation of eight patients and review of the literature

Cholesterol and cataracts

Inherited defects in enzymes of cholesterol metabolism and use of drugs which inhibit lens cholesterol biosynthesis can be associated with cataracts in animals and man. The basis of this relationship apparently lies in the need of the lens to satisfy its sustained requirement for cholesterol by on-site synthesis, and impairing this synthesis can lead to alteration of lens membrane structure. Lens membrane contains the highest cholesterol content of any known membrane. The Smith-Lemli-Opitz syndrome, mevalonic aciduria, and cerebrotendinous xanthomatosis all involve mutations in enzymes of cholesterol metabolism, and affected patients can develop cataracts. Two established models of rodent cataracts are based on treatment with inhibitors of cholesterol biosynthesis. The long-term ocular safety of the very widely used vastatin class of hypocholesterolemic drugs is controversial. Some vastatins are potent inhibitors of cholesterol biosynthesis by animal lenses, can block cholesterol accumulation by these lenses and can produce cataracts in dogs. Whether these drugs inhibit cholesterol biosynthesis in human lenses at therapeutic doses is unknown. Results of clinical trials of 1-5 years duration in older patient populations indicate high ocular safety. However, considering the slow life-long growth of the lens and its continuing need for cholesterol, longterm safety of the vastatins should perhaps be viewed in units of 10 or 20 years, particularly with younger patients.

Ocular and systemic manifestations of cerebrotendinous xanthomatosis

PURPOSE

Cerebrotendinous xanthomatosis is a storage disease that usually leads to severe mental and neurologic deterioration before the diagnosis and start of treatment are established. We identified major ocular and systemic characteristics that may enable a diagnosis to be made earlier.

METHODS

Ten patients (group 1) of the University Hospital Nijmegen, with a diagnosis of cerebrotendinous xanthomatosis, were re-examined for detailed ocular and major clinical manifestations. Meanwhile, we looked for similar but undiagnosed cases in patients (group 2) who visited the Institute of Ophthalmology during a 12-month period.

RESULTS

A diagnosis of cerebrotendinous xanthomatosis had been made in the patients of group 1 at an average age of 40 years (range, 33 to 48 years). Subsequently, six new cases (group 2) were diagnosed in patients 7 to 37 years old (average age, 18 years). Bilateral cataract was the major ocular manifestation in all 16 patients. Small irregular corticonuclear opacities, anterior polar cataracts, and dense posterior subcapsular cataracts were diagnosed at various ages (mean, 18 years; range, 4 to 40 years). Four patients showed clinical signs of optic neuropathy, whereas retinal function was normal in all patients. Other major clinical signs included a history of chronic diarrhea (since childhood), mental deterioration (mean age, 23 years), neurologic deterioration (mean age, 31 years), and tendon xanthomas (mean age, 37 years).

CONCLUSIONS

Appropriate biochemical investigations for cerebrotendinous xanthomatosis should be performed in patients with unexplained juvenile or early-onset adult cataracts, especially if these cataracts are associated with chronic diarrhea since infancy, mental retardation or deterioration, neurologic dysfunction, or xanthomas.

The neuropathology of cerebrotendinous xanthomatosis revisited: a case report and review of the literature

Cerebrotendinous xanthomatosis (CTX), a rare autosomal-recessive lipid storage disease, has been well characterized clinically and biochemically, and recently also from the molecular biological aspect. However, only a very few publications deal with its neuropathology, and views on its pathogenesis vary. Based on a recently examined case, we propose that central-peripheral distal axonopathy is the major pathogenetic mechanism of nervous system injury in CTX. The latter is characterized by white matter pathology, typically in form of long tract involvement with the more distal parts of the tract more severely affected. Most severely affected are the cerebellar white matter, the optic pathways and the long tracts of the brain stem and spinal cord, particularly the pyramidal tracts, although there is hardly a CNS region which does not display some form of pathology. Lesions are characterized by loss of myelinated fibers and accumulation of lipid products in form of foamy macrophages, clear oil-red-O-positive spaces and crystalline clefts, accompanied by gliosis, occasional axonal spheroids, and in the cerebellum--the most severely affected structure--also by multi-nucleated foreign body giant cells. Demyelination is not seen, and ultrastructurally myelin sheaths are normally structured. Signs of axonal degeneration are also present in the spinal roots. We hypothesize that the basic enzymatic defect in CTX leads to accumulation of metabolites in the brain which may be neurotoxic and may impair the metabolic apparatus of neurons with resultant axonopathy and subsequent nonspecific lipid deposition in the injured tracts.

Treatment of cerebrotendinous xanthomatosis: effects of chenodeoxycholic acid, pravastatin, and combined use

Treatments by oral administration of chenodeoxycholic acid (CDCA) alone, 3-hydroxy-3-methylglutaryl (HMG) CoA reductase inhibitor (pravastatin) alone, and combination of the two drugs were attempted for 7 patients with cerebrotendinous xanthomatosis (CTX). CDCA treatment at a dose of 300 mg/day reduced serum cholestanol (67.3% reduction), lathosterol (50.8%), campesterol (61.7%) and sitosterol (12.7%). However, the sera of the patients changed to be "atherogenic"; total cholesterol, triglyceride and low-density lipoprotein (LDL)-cholesterol were increased, while high-density lipoprotein (HDL)-cholesterol was decreased. Contrarily, pravastatin at a dose of 10 mg/day improved the sera of the patients to be markedly "anti-atherogenic", but the reductions of cholestanol (30.4%), lathosterol (44.0%), campesterol (22.9%) and sitosterol (9.6%) were inadequate. Combined treatment with CDCA and pravastatin showed good overlapping of the effects of each drug alone. The sera of the patients were apparently more "anti-atherogenic" than those after CDCA treatment. Serum cholestanol concentration was still 2.7 times higher than in controls, but the serum lathosterol level was within the normal range, indicating that the enhancement of overall cholesterol synthesis in the patients was sufficiently suppressed. Plant sterol levels were also within the normal range. The combination of CDCA and pravastatin was a good treatment for CTX, based on the improvement of serum lipoprotein metabolism, the suppression of cholesterol synthesis, and reductions of cholestanol and plant sterol levels. In all of 7 patients, the progression of disease was arrested, but dramatic effects on clinical manifestations, xanthoma, and electrophysiological findings could not be found after the treatment of these drugs.

Treatment of cerebrotendinous xanthomatosis with low-density lipoprotein (LDL)-apheresis

We studied the effects of LDL-apheresis on the biochemical and clinical abnormalities of 5 patients with cerebrotendinous xanthomatosis (CTX). Levels of both cholestanol and cholesterol decreased to approximately 60% of those of pretreatment after one perfusion and gradually returned to their initial levels within 2 weeks. Improvement of clinical manifestations and regression of Achilles tendon xanthomas were detected after several perfusions, though dramatic changes could not be recognized. EEG abnormalities were improved immediately after LDL-apheresis in one patient. We conclude that LDL-apheresis may affect the serum cholestanol level and clinical manifestations in patients with CTX.

Somatosensory and motor evoked potentials in the assessment of cerebrotendinous xanthomatosis before and after treatment with chenodeoxycholic acid: a preliminary study

We studied two unrelated patients with cerebrotendinous xanthomatosis, in whom clinical examination revealed central nervous system long tract involvement. Brain and spinal cord magnetic resonance imaging showed no signs supporting the involvement of the long pathways. Somatosensory and motor evoked potentials demonstrated central sensory and motor conduction abnormalities, which suggested distal degeneration of longer fibers, rather than scattered focal lesions in the CNS. In one of the patients the neurophysiological study was repeated 6 and 12 months after the beginning of treatment with chenodeoxycholic acid, showing a progressive improvement. Therefore, our data suggest that central motor and sensory conduction studies may be useful in the assessment of the disease and in monitoring treatment.

Cerebrotendinous xanthomatosis: cranial CT and MRI studies in eight patients

We report the findings on cranial computed tomography (CT) and magnetic resonance imaging (MRI) and their correlation with the clinical manifestations, disease severity and biochemical abnormalities in eight patients with cerebrotendinous xanthomatosis. CT revealed cerebral atrophy in seven cases, cerebellar atrophy in four and focal low density lesions in the cerebral white matter in two. T2-weighted MRI showed high signal lesions in the cerebral white matter, focal in four cases and diffuse in one, and in the globus pallidus in three patients, two of whom also had lesions in the cerebellar white matter. While severely affected patients showed variable CT and MRI abnormalities, our cases did not show the dramatic findings expected from the neurological manifestations. Diffuse lesions in the cerebral and cerebellar white matter have been emphasized in previous reports, but in our study the focal lesions in the cerebral white matter were also present; the globus pallidus was frequently involved.

Cerebrotendinous xanthomatosis

Cerebrotendinous xanthomatosis (CTX) is a familial sterol storage disease based on an inborn error of metabolism involving bile acid synthesis. Predominant clinical features are a chronic progressive neurological syndrome, mental deterioration, bilateral cataract and xanthomas. The presence of xanthomas usually leads to the diagnosis, and the reverse is probably also true: without xanthomas the diagnosis will often not be made. CTX may therefore be less rare than commonly thought, and the incidence of xanthomas in CTX may be overestimated. Four cases without xanthomas among the presenting symptoms are described, and the relevance of xanthomas in CTX is discussed.

Atherogenic risk factors in cerebrotendinous xanthomatosis

In a study of coronary artery disease in patients with cerebrotendinous xanthomatosis (CTX), we documented the presence or absence of atherogenic risk factors and performed detailed analyses of serum lipid and lipoprotein profiles. Four of the seven patients examined had coronary arterial narrowing and/or obstruction, but multiple atherogenic risk factors were not found in any of these patients. Total cholesterol (T.ch) levels and low density lipoprotein-cholesterol (LDL-ch) levels were lower, and high density lipoprotein2-cholesterol (HDL2-ch) levels were higher in CTX patients than in controls. Triglyceride and very low density lipoprotein (VLDL) levels were significantly lower in the former. Indices correlating with the risk of atherosclerosis, such as the atherogenic index, and the ratios of apolipoprotein B/apolipoprotein AI, HDL2-ch/LDL-ch, HDL2-ch/HDL3-ch, indicated that CTX serum was, in fact, 'anti-atherogenic'. However, coronary artery disease is frequently seen in patients with CTX. This discrepancy suggests the existence of a unique mechanism by which atherosclerosis is induced in patients with CTX. We discuss a mechanism of disturbed lipoprotein metabolism which might be responsible for the deposition of sterols in the tissues of patients with CTX.