Cerebrotendinous xanthomatosis without neurological involvement

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.

Clinical, biochemical, and molecular insights into Cerebrotendinous Xanthomatosis: A nationwide study of 100 Turkish individuals

OBJECTIVE

Cerebrotendinous xanthomatosis (CTX) is an inherited metabolic disorder characterized by progressive neurologic and extraneurologic findings. The aim of this retrospective, descriptive study was to explore the time of presentation and diagnosis, and to expand the phenotype and genotype of CTX, based on a nationwide and comprehensive series of patients in Turkey.

METHODS

The demographic, clinical, biochemical and genotypic characteristics of the CTX patients were reviewed. Data on molecular analysis, age of onset and diagnosis, diagnostic delay, neurologic and extraneurologic symptomatology, results of plasma cholestanol levels, brain magnetic resonance imaging and electromyography at the time of diagnosis were reviewed.

RESULTS

100 confirmed CTX patients from 72 families were included. The mean age at diagnosis was 28.16 ± 14.28 years, and diagnostic delay was 18.39 ± 13.71 years. 36 patients were diagnosed in childhood. Frequency of intention tremor (p = 0.069), peripheral neuropathy (p = 0.234) and psychiatric manifestations (p = 0.396) did not differ between two groups, demonstrating the high rate in pediatric patients. Three adult patients showed a milder phenotype without neurologic involvement. Seven patients had normal plasma cholestanol levels despite neurological impairment. Sequencing of the CYP27A1 gene revealed 25 different variants, with a novel c.671_672del variant not previously described in literature.

CONCLUSION

Based on the observations of this Turkish CTX cohort, it is emphasized that the true prevalence of CTX is probably underestimated and that it has a wide spectrum of clinical phenotypes even without neurological impairment. In children, abnormal cerebellar findings, peripheral neuropathy and psychiatric findings associated with intellectual disability have been suggested as warning signs to avoid diagnostic delay. In cases of clinical suspicion, molecular analysis is recommended despite normal plasma cholestanol levels, as severe neurologic involvement may occur in CTX patients without elevated cholestanol levels.

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.

What can pediatricians learn from adult inherited metabolic diseases?

The field of inherited metabolic diseases (IMD) has initially emerged and developed over decades in pediatric departments. Still, today, about 50% of patients with IMD are adults, and adult metabolic medicine (AMM) is getting more structured at national and international levels. There are several domains in which pediatricians can learn from AMM. First, long-term evolution of IMD patients, especially those treated since childhood, is critical to determine nutritional and neuropsychiatric outcomes in adults so that these outcomes can be better monitored, and patient care adjusted as much as possible from childhood. Conversely, the observation of attenuated phenotypes in adults of IMD known to present with severe phenotypes in children calls for caution in the development of newborn screening programs and, more largely, in the interpretation of next-generation sequencing data. Third, it is important for pediatricians to be familiar with adult-onset IMD as they expand our understanding of metabolism, including in children, such as oxysterols and glycogen metabolism. Last, the identification of common molecular and cellular mechanisms in neurodevelopment and neurodegeneration opens the way to synergistic therapeutic developments that will benefit both fields of pediatric and adult medicine. Overall, these observations underline the need of strong interdisciplinarity between pediatricians and adult specialists for the diagnosis and the treatment of IMD well beyond the issues of patient transition from pediatric to adult medicine.

Cerebrotendinous Xanthomatosis patients with late diagnosed in single orthopedic clinic: two novel variants in the CYP27A1 gene

BACKGROUND

Cerebrotendinous Xanthomatosis (CTX) is a rare autosomal recessive lipid storage disorder caused by loss of function variants in the CYP27A1 gene which encodes sterol 27-hydroxylase, on chromosome 2q35. Although the symptoms begin commonly in infancy, CTX diagnosis is often delayed. The aim of this study is to review the orthopedic findings of the disease by providing an overview of the clinical features of the disease. It is to raise awareness of this condition for which early diagnosis and treatment are important.

METHODS

We retrospectively evaluated the clinical, laboratory, radiological, and genetic findings of eight patients from four families who were admitted to our Orthopedics and Traumatology Department between 2017 and 2022 due to bilateral Achilles tendon xanthomas, were found to have high cholestanol and CYP27A1 gene mutations.

RESULTS

The mean age of patients was 37, and five of them were male. The mean age at the onset of symptoms was 9.25 years. The mean age of initial diagnosis was 33.75 years. Between symptom onset and clinical diagnosis, an average delay of 24.5 years was observed. All patients had bilateral Achilles tendon xanthoma. Notably, a novel variant (c.670_671delAA) in CYP27A1 gene was identified in three patients who also presented with peripheral neuropathy and bilateral pes cavus. One patient had osteoporosis and four patients had osteopenia. Five patients had a history of bilateral cataracts. Furthermore, three of the patients had early-onset chronic diarrhea and three of the patients had ataxia. Two of the patients had epilepsy and seven of the patients had behavior-personality disorder. All patients had low intelligence, but none of them had cardiac disease.

CONCLUSION

We present the diagnostic process and clinical features which the largest CTX case series ever reported from single orthopedic clinic. We suggest that patients with normal cholesterol levels presenting with xanthoma being genetically analyzed by testing at their serum cholestanol level, and that all siblings of patients diagnosed with CTX be examined.

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.

Genetic Heterogeneity of Familial Hypercholesterolemia: Repercussions for Molecular Diagnosis

Genetics of Familial Hypercholesterolemia (FH) is ascribable to pathogenic variants in genes encoding proteins leading to an impaired LDL uptake by the LDL receptor (LDLR). Two forms of the disease are possible, heterozygous (HeFH) and homozygous (HoFH), caused by one or two pathogenic variants, respectively, in the three main genes that are responsible for the autosomal dominant disease: LDLR, APOB and PCSK9 genes. The HeFH is the most common genetic disease in humans, being the prevalence about 1:300. Variants in the LDLRAP1 gene causes FH with a recessive inheritance and a specific APOE variant was described as causative of FH, contributing to increase FH genetic heterogeneity. In addition, variants in genes causing other dyslipidemias showing phenotypes overlapping with FH may mimic FH in patients without causative variants (FH-phenocopies; ABCG5, ABCG8, CYP27A1 and LIPA genes) or act as phenotype modifiers in patients with a pathogenic variant in a causative gene. The presence of several common variants was also considered a genetic basis of FH and several polygenic risk scores (PRS) have been described. The presence of a variant in modifier genes or high PRS in HeFH further exacerbates the phenotype, partially justifying its variability among patients. This review aims to report the updates on the genetic and molecular bases of FH with their implication for molecular diagnosis.

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.

Progressive ataxia of cerebrotendinous xanthomatosis with a rare c.255+1G>T splice site mutation: A case report

BACKGROUND

Cerebrotendinous xanthomatosis is an autosomal recessive disorder of lipid metabolism caused by the mutation of the CYP27A1 gene encoding sterol 27-hydroxylase, an essential enzyme for the conversion of cholesterol to chenodeoxycholic and cholic acids. Cerebrotendinous xanthomatosis is a rare neurological disease with a wide range of clinical symptoms that are easily misdiagnosed.

CASE SUMMARY

Here we report the clinical, biochemical, and molecular characterization of a 33-year-old female patient with cerebrotendinous xanthomatosis. The patient developed ataxia and had the typical symptoms of juvenile cataracts, tendon xanthomata, and progressive nervous system dysfunction. Magnetic resonance imaging of the brain revealed bilateral dentate nucleus lesions and white matter abnormalities. This patient was misdiagnosed for 2 years resulting in severe neurological complications. After 2 years of chenodeoxycholic acid treatment, she still presented with ataxia and dysarthria. The pathogenic sites of CYP27A1 were identified as c.255+1G>T and c.1263+1G>T, which were both caused by shear denaturation.

CONCLUSION

Cerebrotendinous xanthomatosis requires a multidisciplinary diagnosis that must be made early to avoid progressive neurological degeneration. c.1263+1G>T is a known mutation, but c.255+1G>T is a rare mutation site.

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.