Raphael Schiffmann M.D.

Choquet, K., D. Forget, E. Meloche, M. J. Dicaire, G. Bernard, A. Vanderver, R. Schiffmann, M. R. Fabian, M. Teichmann, B. Coulombe, B. Brais and C. L. Kleinman (2019). “Leukodystrophy-associated POLR3A mutations down-regulate the RNA polymerase III transcript and important regulatory RNA BC200.” J Biol Chem 294(18): 7445-7459.

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RNA polymerase III (Pol III) is an essential enzyme responsible for the synthesis of several small noncoding RNAs, a number of which are involved in mRNA translation. Recessive mutations in POLR3A, encoding the largest subunit of Pol III, cause POLR3-related hypomyelinating leukodystrophy (POLR3-HLD), characterized by deficient central nervous system myelination. Identification of the downstream effectors of pathogenic POLR3A mutations has so far been elusive. Here, we used CRISPR-Cas9 to introduce the POLR3A mutation c.2554A–>G (p.M852V) into human cell lines and assessed its impact on Pol III biogenesis, nuclear import, DNA occupancy, transcription, and protein levels. Transcriptomic profiling uncovered a subset of transcripts vulnerable to Pol III hypofunction, including a global reduction in tRNA levels. The brain cytoplasmic BC200 RNA (BCYRN1), involved in translation regulation, was consistently affected in all our cellular models, including patient-derived fibroblasts. Genomic BC200 deletion in an oligodendroglial cell line led to major transcriptomic and proteomic changes, having a larger impact than those of POLR3A mutations. Upon differentiation, mRNA levels of the MBP gene, encoding myelin basic protein, were significantly decreased in POLR3A-mutant cells. Our findings provide the first evidence for impaired Pol III transcription in cellular models of POLR3-HLD and identify several candidate effectors, including BC200 RNA, having a potential role in oligodendrocyte biology and involvement in the disease.

van der Knaap, M. S., A. Fogli, O. Boespflug-Tanguy, T. E. M. Abbink and R. Schiffmann (2019). “Childhood Ataxia with Central Nervous System Hypomyelination / Vanishing White Matter.” GeneReviews((R)) Available online 04 April 2019.

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CLINICAL CHARACTERISTICS: Childhood ataxia with central nervous system hypomyelination / vanishing white matter (CACH/VWM) is characterized by ataxia, spasticity, and variable optic atrophy. The phenotypic range includes a prenatal/congenital form, a subacute infantile form (onset age <1 year), an early childhood-onset form (onset age 1 to <4 years), a late childhood-/juvenile-onset form (onset age 4 to <18 years), and an adult-onset form (onset >/=18 years). The prenatal/congenital form is characterized by severe encephalopathy. In the later-onset forms initial motor and intellectual development is normal or mildly delayed, followed by neurologic deterioration with a chronic progressive or subacute course. While in childhood-onset forms motor deterioration dominates, in adult-onset forms cognitive decline and personality changes dominate. Chronic progressive decline can be exacerbated by rapid deterioration during febrile illnesses or following head trauma or major surgical procedures, or by acute and extreme fright. DIAGNOSIS/TESTING: The diagnosis of CACH/VWM can be established in an individual with typical clinical findings, characteristic abnormalities on cranial MRI, and identification of biallelic pathogenic variants in one of five genes (EIF2B1, EIF2B2, EIF2B3, EIF2B4, EIF2B5), which encode the five subunits of the eukaryotic translation initiation factor 2B (eIF2B). MANAGEMENT: Treatment of manifestations: Physical therapy and rehabilitation for motor dysfunction (mainly spasticity and ataxia); antiepileptic drugs for seizures. Prevention of secondary complications: Prevention of infections and fever when possible through the use of vaccinations, low-dose maintenance antibiotics during winter, antibiotics for minor infections, and antipyretics for fever. For children, wearing a helmet when outside helps minimize the effects of head trauma. Surveillance: Close monitoring of neurologic status for several days during febrile infections and following head trauma or surgical procedures with anesthesia. Agents/circumstances to avoid: Contact sports, head trauma, infections, high body temperature and, if possible, major surgery. GENETIC COUNSELING: CACH/VWM is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Prenatal diagnosis for pregnancies at increased risk is possible if the pathogenic variants in an affected relative have been identified.

Hughes, D. A., K. Nicholls, G. Sunder-Plassmann, A. Jovanovic, U. Feldt-Rasmussen, R. Schiffmann, R. Giugliani, V. Jain, C. Viereck, J. P. Castelli, N. Skuban, J. A. Barth and D. G. Bichet (2019). “Safety of switching to Migalastat from enzyme replacement therapy in Fabry disease: Experience from the Phase 3 ATTRACT study.” Am J Med Genet A Mar 28. [Epub ahead of print].

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Migalastat is the only oral treatment for Fabry disease, which provides a suitable alternative to once‐every‐2‐weeks intravenous enzyme replacement therapy (ERT) in patients with amenable mutations who are ERT‐experienced and can also be utilized as a first‐line therapy in ERT‐naive patients. Although there has not yet been a consensus among physicians who treat patients with Fabry disease on when to choose migalastat over ERT, we have developed some criteria in our clinical practices, which include: age 16 years and older (18 years and older in the United States and Canada), a confirmed amenable mutation, an eGFR > 30 mL/min/1.73 m2, compliance with every‐other‐day oral administration, and no intention by female patients to become pregnant. Patients’ preference and hypersensitivity to ERT are also factors in considering the best treatment option for patients. We suggest having a comprehensive counseling session with the patient to discuss the mechanism of action, clinical data, and approved indication for migalastat, as well as schedule of administration. For patients switching from ERT, migalastat is commonly initiated ~2 weeks after the last dose of ERT based on the infusion interval; however, other practical considerations may influence the exact duration between the last ERT infusion and first dose of migalastat. Migalastat may be safely initiated within days of the last ERT infusion. In conclusion, patients with amenable mutations who have been receiving ERT infusions can be safely switched to migalastat 150 mg QOD, and no special procedure is needed for the switch. (Excerpt from text, p. 3-4; no abstract available.)

Choquet, K., D. Forget, E. Meloche, M. J. Dicaire, G. Bernard, A. Vanderver, R. Schiffmann, M. R. Fabian, M. Teichmann, B. Coulombe, B. Brais and C. L. Kleinman (2019). “Leukodystrophy-associated POLR3A mutations down-regulate the RNA polymerase III transcript and important regulatory RNA BC200.” J Biol Chem Mar 21. [Epub ahead of print].

Full text of this article.

RNA polymerase III (Pol III) is an essential enzyme responsible for the synthesis of several small non-coding RNAs, a number of which are involved in mRNA translation. Recessive mutations in POLR3A, encoding the largest subunit of Pol III, cause POLR3-related hypomyelinating leukodystrophy (POLR3-HLD), characterized by deficient central nervous system myelination. Identification of the downstream effectors of pathogenic POLR3A mutations has been so far elusive. Here, we used CRISPR-Cas9 to introduce the POLR3A mutation c.2554A>G (p.M852V) into human cell lines and assessed its impact on Pol III biogenesis, nuclear import, DNA occupancy, transcription, and protein levels. Transcriptomic profiling uncovered a subset of transcripts vulnerable to Pol III hypofunction, including a global reduction in tRNA levels. The brain cytoplasmic BC200 RNA (BCYRN1), involved in translation regulation, was consistently affected in all our cellular models, including patient-derived fibroblasts. Genomic BC200 deletion in an oligodendroglial cell line led to major transcriptomic and proteomic changes, having a larger impact than those of POLR3A mutations. Upon differentiation, mRNA levels of the MBP gene, encoding myelin basic protein, were significantly decreased in POLR3A-mutant cells. Our findings provide the first evidence for impaired Pol III transcription in cellular models of POLR3-HLD and identify several candidate effectors, including BC200 RNA, having a potential role in oligodendrocyte biology and involvement in the disease.

Raymond, G. V. and R. Schiffmann (2019). “Cerebrotendinous xanthomatosis: The rare “treatable” disease you never consider.” Neurology 92(2): 61-62.

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Cerebrotendinous xanthomatosis (CTX; Online Mendelian Inheritance in Man No. 213700) is an autosomal recessive disorder due to pathogenic variant in the CYP27A1 gene resulting in a defect in the mitochondrial enzyme sterol 27-hydroxylase. The enzyme catalyzes multiple hydroxylation reactions involved in cholesterol metabolism and bile acid synthesis. When affected, it results in decreased synthesis of bile acids, with the resultant production of cholestanol and cholesterol affecting all tissues . . . In this issue of Neurology®, Stelten et al. examined whether early treatment could prevent the development of neurologic findings. They examined a Dutch cohort of 56 individuals with long-term follow-up and evaluated CDCA treatment in relation to the clinical neurologic outcomes. The mean age at diagnosis was 25.6 years, but the authors emphasize that, with the application of a clinical suspicion index, individuals could have been diagnosed 8 years earlier with a mean age of 17.3 years. They go on to demonstrate that those treated before 24 years of age had better outcomes and that neurologic deterioration was seen only in those treated after this age. While earlier treatment improved function, neurologic symptoms were seen before the age of 24 (25% vs 88%), with pyramidal and cerebellar symptoms being the most common. In this early treated group, these findings completely disappeared in those adherent to therapy, and none developed new neurologic symptoms. Some degree of intellectual impairment was seen in 50% of individuals diagnosed and treated before 24 years, but again, with early treatment, this stabilized. In those treated later in life, 61% worsened, with parkinsonism developing as a treatment-resistant feature of the disease. Experience in this large cohort of treated patients with CTX followed up for up to 35 years demonstrates that the age at diagnosis and initiation of CDCA therapy correlates with prognosis and that the routine delay in testing for the condition adversely affects the affected individual. Many questions will of course remain with a rare disorder, but it is clear that diagnosis and subsequent treatment are not occurring in a timely fashion. Faster, earlier diagnosis matters to these people in getting them treatment. Strategies to improve diagnosis with a clinical suspicion index, while admirable, have clearly not been effective. Most clinicians are not even aware that they should be suspicious. Improved detection is necessary, but this will most likely take a multiprong strategy to implement. Ordering cholestanol should become as routine, easy, and reflexive as ordering amino acids on any child seen in the clinic. It should become incorporated into all of the diagnostic DNA panels for cataracts, gastrointestinal disorders, and the multitude of neurologic and psychiatric diseases. We also need to imbue residents and fellows with the necessity of testing because they will ultimately change clinical practice. The proposed universal detection through newborn blood spots has challenges but may yet prove to be the most appropriate strategy. Until that time, however, it is imperative that we continue to improve detection and treatment. (Excerpt from text of this editorial, p. 61-62; abstract not available.)