Familial variability of cerebrotendinous xanthomatosis lacking typical biochemical findings

Rare genetic cerebrotendinous xanthomatosis (CTX) cases without cholestanol elevation but with prominent cholesterol-rich tendon xanthomas

Cerebrotendinous xanthomatosis (CTX) is a rare inherited metabolic disease attributed to the mutation of the gene CYP27A1, resulting in sterol 27-hydroxylase deficiency characterized by deposition of cholestanol and cholesterol in several tissues, like the central nervous system and tendons. Furthermore, cataracts, gallstones, diarrhea and premature atherosclerosis have been reported. Nonetheless, clinical development is extremely heterogeneous in CTX. We report here two cases of CTX genetic alteration in the absence of cholestanol elevation in plasma and tendons but with prominent xanthomas. We propose that CTX may not be characteized by increased plasma cholestanol concentration due to alteration in the sterol 27-hydroxylase gene, but is a more complex pathology where there is significant genetic heterogeneity caused by various CYP27A1 mutations.

Genetically and clinically confirmed atypical cerebrotendinous xanthomatosis with normal cholestanol and marked elevations of bile acid precursors and bile alcohols

BACKGROUND

Cerebrotendinous xanthomatosis (CTX) is a rare autosomal recessive lipid disorder. Affected patients often remain undiagnosed until the age of 20-30 years, when they have already developed significant neurologic disease that may not be reversible. An elevated plasma cholestanol concentration has been accepted as a diagnostic criterion for CTX for decades.

OBJECTIVE

Full biochemical characterization was performed for three genetically and clinically confirmed atypical CTX cases with normal plasma cholestanol levels.

METHODS

Clinical assessment and genetic/biochemical testing for patients with CTX was performed by their physician providing routine standard of care.

RESULTS

We report three new atypical CTX cases with large extensor tendon xanthomas but normal plasma cholestanol levels. All three cases had marked elevations of bile acid precursors and bile alcohols in plasma and urine that decreased on treatment with chenodeoxycholic acid. We also review eight published cases of atypical CTX with normal/near normal circulating cholestanol levels.

CONCLUSION

The atypical biochemical presentation of these cases provides a diagnostic challenge for CTX, a disorder for which cholestanol has been believed to be a sensitive biomarker. These cases demonstrate measurements of plasma cholestanol alone are insufficient to exclude a diagnosis of CTX. The data presented is consistent with the concept that bile acid precursors and bile alcohols are sensitive biomarkers for atypical CTX with normal cholestanol, and that such testing is indicated, along with CYP27A1 gene analyses, in patients presenting with significant tendon and/or tuberous xanthomas and/or neurologic disease in early adulthood despite normal or near normal cholesterol and cholestanol levels.

Disorders with prominent posterior fossa involvement

Inherited white matter disorders include a wide range of disorders of various origins with distinct genetic, pathophysiologic, and metabolic backgrounds. Although most of these diseases have nonspecific clinical and radiologic features, some display distinct clinical and/or imaging (magnetic resonance imaging, MRI) characteristics that might suggest the causative gene. Recent advances in genetic testing allow assessing gene panels that include several hundred genes; however, an MRI-based diagnostic approach is important to narrow the choice of candidate genes, particularly in countries where these techniques are not available. Indeed, white matter disorders with prominent posterior fossa involvement present specific MRI (and clinical) phenotypes that can directly orient the diagnosis. This chapter describes the main genetic disorders with posterior fossa involvement and discusses diagnostic strategies.

Case Report: a novel CYP27A1 gene variant in a patient with cerebrotendinous xanthomatosis with unusual clinical findings

PURPOSE/AIM OF THE STUDY

Cerebrotendinous xanthomatosis is a disease with important clinical and molecular heterogeneity. CYP27A1 gene was described as the cause of these defects, with more than 50 mutations involved in the disease. The objective of this study was to carry out a genetic study and a clinical description of a patient with unusual clinical manifestation of the disease.

MATERIALS AND METHODS

DNA sequencing was used for the evaluation of CYP27A1 exon sequences and their intron/exon boundaries. Copy number variants were calculated using a method based on depth of sequencing coverage. In addition, the potential effects of the missense variants were analyzed, and an in-silico protein modeling tool was used. Finally, a patient case description was performed in order to evaluate patient phenotype according to genetic results.

RESULTS

Patient clinical features indicate the possible presence of a disease milder phenotype. When analyzing the CYP27A1 gene, patient presents a pathogenic variant (p.Arg474Trp) and a variant of unknown significance (p.Met130Ile) that causes a slight modification of the protein functional structure. This variant in homozygosis or double or compound heterozygosis together with other biallelic pathological mutations may be the cause of the clinical phenotype observed in the reported patient.

CONCLUSIONS

Clinical manifestations of cerebrotendinous xanthomatosis are heterogeneous, and sometimes wrongly suggest the presence of other diseases. Some patients seem to present an "incomplete" phenotype, which could be redefined as a variant of the disease with further studies. The evaluation of new mutations allows for earlier diagnosis and greater effectiveness in its treatment.

A case of cerebrotendinous xanthomatosis with massive xanthomas but without a considerable increase in serum cholestanol levels

Cerebrotendinous xanthomatosis (CTX) is a rare autosomal recessive disorder caused by mutations in the sterol 27-hydroxylase gene (CYP27A1). Due to the deficiency of 27-hydroxylase, the synthesis of bile acids from cholesterol is impaired and excessive cholestanol accumulates in various tissues, such as the central nervous system, tendons, and lenses. Patients with CTX typically manifest intellectual decline, pyramidal tract symptoms, cerebellar symptoms, tendon xanthomas, juvenile cataracts, neonatal jaundice, chronic diarrhea, osteoporosis, and premature cardiovascular disease. Here, we report the atypical case of a 35-year-old female with CTX having massive xanthomas but without a considerable increase in serum cholestanol levels (3.9 µg/mL). In the differential diagnosis of xanthoma, CTX should not be ruled out even if the serum levels of cholestanol are not high, and genetic testing is necessary to make the appropriate diagnosis.

Pathophysiology and Treatment of Lipid Abnormalities in Cerebrotendinous Xanthomatosis: An Integrative Review

Cerebrotendinous xanthomatosis (CTX) is an autosomal recessive disorder caused by pathogenic variants in CYP27A1, leading to a deficiency in sterol 27-hydroxylase. This defect results in the accumulation of cholestanol and bile alcohols in various tissues, including the brain, tendons and peripheral nerves. We conducted this review to evaluate lipid profile abnormalities in patients with CTX. A search was conducted in PubMed, Embase and the Virtual Health Library in January 2023 to evaluate studies reporting the lipid profiles of CTX patients, including the levels of cholestanol, cholesterol and other lipids. Elevated levels of cholestanol were consistently observed. Most patients presented normal or low serum cholesterol levels. A decrease in chenodeoxycholic acid (CDCA) leads to increased synthesis of cholesterol metabolites, such as bile alcohols 23S-pentol and 25-tetrol 3-glucuronide, which may serve as surrogate follow-up markers in patients with CTX. Lipid abnormalities in CTX have clinical implications. Cholestanol deposition in tissues contributes to clinical manifestations, including neurological symptoms and tendon xanthomas. Dyslipidemia and abnormal cholesterol metabolism may also contribute to the increased risk of atherosclerosis and cardiovascular complications observed in some CTX patients.

Allelic prevalence and geographic distribution of cerebrotendinous xanthomatosis

BACKGROUND

Cerebrotendinous xanthomatosis (CTX) is a rare recessive genetic disease characterized by disruption of bile acid synthesis due to inactivation of the CYP27A1 gene. Treatment is available in the form of bile acid replacement. CTX is likely underdiagnosed, and prevalence estimates based on case diagnosis are probably inaccurate. Large population-based genomic databases are a valuable resource to estimate prevalence of rare recessive diseases as an orthogonal unbiased approach building upon traditional epidemiological studies.

METHODS

We leveraged the Hardy-Weinberg principle and allele frequencies from gnomAD to calculate CTX prevalence. ClinVar and HGMD were used to identify high-confidence pathogenic missense variants and to calculate a disease-specific cutoff. Variant pathogenicity was also assessed by the VarSome implementation of the ACMG/AMP algorithm and the REVEL in silico predictor.

RESULTS

CTX prevalence estimates were highest in Asians (1:44,407-93,084) and lowest in the Finnish population (1:3,388,767). Intermediate estimates were found in Europeans, Americans, and Africans/African Americans (1:70,795-233,597). The REVEL-predicted pathogenic variants accounted for a greater increase in prevalence estimates for Europeans, Americans, and Africans/African Americans compared with Asians. We identified the most frequent alleles designated pathogenic in ClinVar (p.Gly472Ala, p.Arg395Cys), labeled pathogenic based on sequence consequence (p.Met1?), and predicted to be pathogenic by REVEL (p.Met383Lys, p.Arg448His) across populations. Also, we provide a prospective geographic map of estimated disease distribution based on CYP27A1 variation queries performed by healthcare providers from selected specialties.

CONCLUSIONS

Prevalence estimates calculated herein support and expand upon existing evidence indicating underdiagnosis of CTX, suggesting that improved detection strategies are needed. Increased awareness of CTX is important for early diagnosis, which is essential for patients as early treatment significantly slows or prevents disease progression.

First case series of Polish patients with cerebrotendinous xanthomatosis and systematic review of cases from the 21st century

Cerebrotendinous xanthomatosis (CTX) is an inborn error of metabolism caused by recessive variants in the cytochrome P450 CYP27A1 gene. CTX is said to manifest with childhood-onset chronic diarrhea and the classic triad of juvenile-onset cataracts, Achilles tendons xanthomas, and progressive ataxia. It is currently one of the few inherited neurometabolic disorders amenable to a specific treatment. The diagnosis may be significantly delayed resulting in permanent neurological impairment. A retrospective review of the clinical characteristics and diagnostic findings in case series of six Polish patients with CTX. Additional retrospective review of symptoms and pathogenic variants of 568 CTX available cases and case series from the past 20 years. To the best of our knowledge, this is the widest review of CTX cases reported in years 2000-2021. We report the largest cohort of Polish patients ever published, with the identification of two hot-spot mutations. During the review of available 568 cases, we found significant differences in the clinical phenotypes and the localization of variants within the gene between Asian and non-Asian populations. These findings may facilitate molecular testing in the Polish and Asian populations. Invariably better screening for CTX and wider awareness is needed.

Expert opinion on diagnosing, treating and managing patients with cerebrotendinous xanthomatosis (CTX): a modified Delphi study

Background

Cerebrotendinous xanthomatosis (CTX) is a rare, chronic, progressive, neurodegenerative disorder requiring life-long care. Patients with CTX often experience a diagnostic delay. Although early diagnosis and treatment initiation can improve symptoms and prognosis, a standardised approach to diagnosis, treatment and management of patients is not yet established.

Aim

To assess expert opinion on best care practices for patients with CTX using a modified Delphi method.

Methods

A multidisciplinary group of healthcare professionals with expertise in CTX responded to a 3-round online questionnaire (n = 10 in Rounds 1 and 2; n = 9 in Round 3), containing questions relating to the diagnosis, treatment, monitoring, multidisciplinary care and prognosis of patients with CTX. Determination of consensus achievement was based on a pre-defined statistical threshold of ≥ 70% Delphi panellists selecting 1–2 (disagreement) or 5–6 (agreement) for 6-point Likert scale questions, or ≥ 70% Delphi panellists choosing the same option for ranking and proportion questions.

Results

Of the Round 1 (n = 22), Round 2 (n = 32) and Round 3 (n = 26) questions for which consensus was assessed, 59.1%, 21.9% and 3.8% reached consensus, respectively. Consensus agreement that genetic analyses and/or determination of serum cholestanol levels should be used to diagnose CTX, and dried bloodspot testing should facilitate detection in newborns, was reached. Age at diagnosis and early treatment initiation (at birth, where possible) were considered to have the biggest impact on treatment outcomes. All panellists agreed that chenodeoxycholic acid (CDCA) is a lifetime replacement therapy which, if initiated early, can considerably improve prognosis as it may be capable of reversing the pathophysiological process in CTX. No consensus was reached on the value of cholic acid therapy alone. Monitoring patients through testing plasma cholestanol levels and neurologic examination was recommended, although further research regarding monitoring treatment and progression of the disease is required. Neurologists and paediatricians/metabolic specialists were highlighted as key clinicians that should be included in the multidisciplinary team involved in patients’ care.

Conclusions

The results of this study provide a basis for standardisation of care and highlight key areas where further research is needed to inform best practices for the diagnosis, treatment and management of patients with CTX.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01980-5.