Future targets for migraine treatment beyond CGRP.

BACKGROUND: Migraine is a disabling and chronic neurovascular headache disorder. Trigeminal vascular activation and release of calcitonin gene-related peptide (CGRP) play a pivotal role in the pathogenesis of migraine. This knowledge has led to the development of CGRP(-receptor) therapies. Yet, a substantial proportion of patients do not respond to these treatments. Therefore, alternative targets for future therapies are warranted. The current narrative review provides a comprehensive overview of the pathophysiological role of these possible non-CGRP targets in migraine. FINDINGS: We covered targets of the metabotropic receptors (pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal peptide (VIP), amylin, and adrenomedullin), intracellular targets (nitric oxide (NO), phosphodiesterase-3 (PDE3) and -5 (PDE5)), and ion channels (potassium, calcium, transient receptor potential (TRP), and acid-sensing ion channels (ASIC)). The majority of non-CGRP targets were able to induce migraine-like attacks, except for (i) calcium channels, as it is not yet possible to directly target channels to elucidate their precise involvement in migraine; (ii) TRP channels, activation of which can induce non-migraine headache; and (iii) ASICs, as their potential in inducing migraine attacks has not been investigated thus far. Drugs that target its receptors exist for PACAP, NO, and the potassium, TRP, and ASIC channels. No selective drugs exist for the other targets, however, some existing (migraine) treatments appear to indirectly antagonize responses to amylin, adrenomedullin, and calcium channels. Drugs against PACAP, NO, potassium channels, TRP channels, and only a PAC1 antibody have been tested for migraine treatment, albeit with ambiguous results. CONCLUSION: While current research on these non-CGRP drug targets has not yet led to the development of efficacious therapies, human provocation studies using these targets have provided valuable insight into underlying mechanisms of migraine headaches and auras. Further studies are needed on these alternative therapies in non-responders of CGRP(-receptor) targeted therapies with the ultimate aim to pave the way towards a headache-free future for all migraine patients.

Phenotype and imaging features associated with APP duplications.

BACKGROUND: APP duplication is a rare genetic cause of Alzheimer disease and cerebral amyloid angiopathy (CAA). We aimed to evaluate the phenotypes of APP duplications carriers. METHODS: Clinical, radiological, and neuropathological features of 43 APP duplication carriers from 24 French families were retrospectively analyzed, and MRI features and cerebrospinal fluid (CSF) biomarkers were compared to 40 APP-negative CAA controls. RESULTS: Major neurocognitive disorders were found in 90.2% symptomatic APP duplication carriers, with prominent behavioral impairment in 9.7%. Symptomatic intracerebral hemorrhages were reported in 29.2% and seizures in 51.2%. CSF Aß42 levels were abnormal in 18/19 patients and 14/19 patients fulfilled MRI radiological criteria for CAA, while only 5 displayed no hemorrhagic features. We found no correlation between CAA radiological signs and duplication size. Compared to CAA controls, APP duplication carriers showed less disseminated cortical superficial siderosis (0% vs 37.5%, p = 0.004 adjusted for the delay between symptoms onset and MRI). Deep microbleeds were found in two APP duplication carriers. In addition to neurofibrillary tangles and senile plaques, CAA was diffuse and severe with thickening of leptomeningeal vessels in all 9 autopsies. Lewy bodies were found in substantia nigra, locus coeruleus, and cortical structures of 2/9 patients, and one presented vascular amyloid deposits in basal ganglia. DISCUSSION: Phenotypes associated with APP duplications were heterogeneous with different clinical presentations including dementia, hemorrhage, and seizure and different radiological presentations, even within families. No apparent correlation with duplication size was found. Amyloid burden was severe and widely extended to cerebral vessels as suggested by hemorrhagic features on MRI and neuropathological data, making APP duplication an interesting model of CAA.

Genetics of migraine: where are we now?

Migraine is a complex brain disorder explained by the interaction of genetic and environmental factors. In monogenic migraines, including familial hemiplegic migraine and migraine with aura associated with hereditary small-vessel disorders, the identified genes code for proteins expressed in neurons, glial cells, or vessels, all of which increase susceptibility to cortical spreading depression. The study of monogenic migraines has shown that the neurovascular unit plays a prominent role in migraine. Genome-wide association studies have identified numerous susceptibility variants that each result in only a small increase in overall migraine risk. The more than 180 known variants belong to several complex networks of "pro-migraine" molecular abnormalities, which are mainly neuronal or vascular. Genetics has also highlighted the importance of shared genetic factors between migraine and its major co-morbidities, including depression and high blood pressure. Further studies are still needed to map all of the susceptibility loci for migraine and then to understand how these genomic variants lead to migraine cell phenotypes.

Applicability of the Edinburgh CT Criteria for Lobar Intracerebral Hemorrhage Associated with Cerebral Amyloid Angiopathy.

OBJECTIVE: Based on histopathology, Edinburgh diagnostic criteria were proposed to consider a nontraumatic intracerebral lobar hemorrhage (ICH) as related to cerebral amyloid angiopathy (CAA) using the initial computed tomography (CT) scan and the APOE genetic status. We aimed to externally validate the Edinburgh prediction model, excluding the APOE genotyping and based on the modified Boston criteria on the MRI for CAA diagnosis METHODS: We included patients admitted for spontaneous lobar ICH in the emergency department between 2016 and 2019 who underwent noncontrast CT scan and MRI. According to the MRI, patients were classified into the CAA group or into the non-CAA group in the case of other causes of ICH. Two neuroradiologists, blinded to the final retained diagnosis, rated each radiological feature on initial CT scan described in the Edinburgh study on initial CT scan RESULTS: A total of 102 patients were included, of whom 36 were classified in the CAA group, 46 in the non-CAA causes group and 20 of undetermined cause (excluded from the primary analysis). The Edinburgh prediction model, including finger-like projections and subarachnoid extension showed an area under receiver operating characteristic curves (AUC) of 0.760 (95% confidence interval, CI: 0.660-0.859) for the diagnosis of CAA. The AUC reached 0.808 (95% CI: 0.714-0.901) in a new prediction model integrating a third radiologic variable: the ICH cortical involvement. CONCLUSION: Using the Boston MRI criteria as a final assessment, we provided a new external confirmation of the radiological Edinburgh CT criteria, which are directly applicable in acute settings of spontaneous lobar ICH and further proposed an original 3­set model considering finger-like projections, subarachnoid extension, and cortical involvement that may achieve a high discrimination performance.

Cerebrospinal Fluid Profile of Tau, Phosphorylated Tau, Aß42, and Aß40 in Probable Cerebral Amyloid Angiopathy.

BACKGROUND: There is no consensus regarding the diagnostic value of cerebrospinal fluid (CSF) Alzheimer's disease (AD) biomarkers in cerebral amyloid angiopathy (CAA). OBJECTIVE: To describe the CSF levels of Aß42, Aß40, total protein Tau, and phosphorylated-Tau (p-Tau) in a large series of probable CAA patients and to compare with AD patients in order to identify a specific pattern in CAA but also to look for correlations with the neuroimaging profile. METHODS: We retrospectively included from 2 French centers probable CAA patients according to modified Boston criteria who underwent lumbar puncture (LP) with CSF AD biomarker quantifications. Two neurologists independently analyzed all MRI sequences. A logistic regression and Spearman's correlation coefficient were used to identify correlation between MRI and CSF biomarkers in CAA. RESULTS: We included 63 probable CAA and 27 AD patients. Among CAA 50.8% presented with decreased Aß42 level associated with elevated p-Tau and/or Tau, 34.9% with isolated decreased Aß42 level and 14.3% patients with normal Aß42 level. Compared to AD, CAA showed lower levels of Tau (p = 0.008), p-Tau (p = 0.004), and Aß40 (p = 0.001) but similar Aß42 level (p = 0.07). No correlation between Aß42 or Aß40 levels and neuroimaging was found. CONCLUSION: CSF biomarkers may improve the accuracy of the modified Boston criteria with altered profile in 85% of the patients fulfilling revised Boston criteria for probable CAA. Aß40 appears as an interesting selective biomarker in differential diagnosis.

The clinical characteristics of familial cluster headache.

BACKGROUND: A positive family history predisposes to the development of cluster headache. The distinct characteristics of familial cluster headache have yet to be confirmed, however, evidence suggests a younger age of onset and higher proportion of females in this subgroup. OBJECTIVES: To assess the rate and mode of inheritance of familial cluster headache in a tertiary referral centre for headache. To describe the clinical features of familial cluster headache. METHODS: A retrospective study conducted between 2007 and 2017. Cluster headache was confirmed in probands and affected relatives. Differences in demographics, clinical characteristics, and response-to-treatment in familial cluster headache were delineated through multivariate analysis using a control cohort of 597 patients with sporadic cluster headache. RESULTS: Familial cluster headache was confirmed in 48 (7.44%) patients and predominantly reflected an autosomal dominant mode of inheritance with reduced penetrance. Familial cases were more likely to report nasal blockage (OR 4.06, 95% CI; 2.600-6.494, p < 0.001) during an attack and a higher rate of concurrent short-lasting unilateral neuralgiform headache with conjunctival injection and tearing (OR 3.76, 95% CI; 1.572-9.953, p = 0.004). CONCLUSION: These findings add to evidence suggesting a genetic component to cluster headache. Here, we demonstrated prominent nasal blockage, and a higher occurrence of concomitant short-lasting unilateral neuralgiform headache with conjunctival injection and tearing in this subgroup, further delineating the phenotype.

Early-Onset Cerebral Amyloid Angiopathy and Alzheimer Disease Related to an APP Locus Triplication.

BACKGROUND AND OBJECTIVE: To report a triplication of the amyloid-ß precursor protein (APP) locus along with relative messenger RNA (mRNA) expression in a family with autosomal dominant early-onset cerebral amyloid angiopathy (CAA) and Alzheimer disease (AD). METHODS: Four copies of the APP gene were identified by quantitative multiplex PCR of short fluorescent fragments, fluorescent in situ hybridization (FISH), and array comparative genomic hybridization. APP mRNA levels were assessed using reverse-transcription-digital droplet PCR in the proband's whole blood and compared with 10 controls and 9 APP duplication carriers. RESULTS: Beginning at age 39 years, the proband developed severe episodic memory deficits with a CSF biomarker profile typical of AD and multiple lobar microbleeds in the posterior regions on brain MRI. His father had seizures and recurrent cerebral hemorrhage since the age of 37 years. His cerebral biopsy showed abundant perivascular amyloid deposits, leading to a diagnosis of CAA. In the proband, we identified 4 copies of a 506-kb region located on chromosome 21q21.3 and encompassing the whole APP gene without any other gene. FISH suggested that the genotype of the proband was 3 copies/1 copy corresponding to an APP locus triplication, which was consistent with the presence of 2 APP copies in the healthy mother and with the paternal medical history. Analysis of the APP mRNA level showed a 2-fold increase in the proband and a 1.8 fold increase in APP duplication carriers compared with controls. DISCUSSION: Increased copy number of APP is sufficient to cause AD and CAA, with likely earlier onset in case of triplication compared with duplication.

Genome-Wide Association Study Identifies Risk Loci for Cluster Headache.

OBJECTIVE: This study was undertaken to identify susceptibility loci for cluster headache and obtain insights into relevant disease pathways. METHODS: We carried out a genome-wide association study, where 852 UK and 591 Swedish cluster headache cases were compared with 5,614 and 1,134 controls, respectively. Following quality control and imputation, single variant association testing was conducted using a logistic mixed model for each cohort. The 2 cohorts were subsequently combined in a merged analysis. Downstream analyses, such as gene-set enrichment, functional variant annotation, prediction and pathway analyses, were performed. RESULTS: Initial independent analysis identified 2 replicable cluster headache susceptibility loci on chromosome 2. A merged analysis identified an additional locus on chromosome 1 and confirmed a locus significant in the UK analysis on chromosome 6, which overlaps with a previously known migraine locus. The lead single nucleotide polymorphisms were rs113658130 (p = 1.92 × 10-17 , odds ratio [OR] = 1.51, 95% confidence interval [CI] = 1.37-1.66) and rs4519530 (p = 6.98 × 10-17 , OR = 1.47, 95% CI = 1.34-1.61) on chromosome 2, rs12121134 on chromosome 1 (p = 1.66 × 10-8 , OR = 1.36, 95% CI = 1.22-1.52), and rs11153082 (p = 1.85 × 10-8 , OR = 1.30, 95% CI = 1.19-1.42) on chromosome 6. Downstream analyses implicated immunological processes in the pathogenesis of cluster headache. INTERPRETATION: We identified and replicated several genome-wide significant associations supporting a genetic predisposition in cluster headache in a genome-wide association study involving 1,443 cases. Replication in larger independent cohorts combined with comprehensive phenotyping, in relation to, for example, treatment response and cluster headache subtypes, could provide unprecedented insights into genotype-phenotype correlations and the pathophysiological pathways underlying cluster headache. ANN NEUROL 2021;90:193-202.

Is pituitary MRI screening necessary in cluster headache?

OBJECTIVE: To determine the prevalence and clinical predictors of pituitary adenomas in cluster headache patients, in order to determine the necessity of performing dedicated pituitary magnetic resonance imaging in patients with cluster headache. METHODS: A retrospective study was conducted of all consecutive patients diagnosed with cluster headache and with available brain magnetic resonance imaging between 2007 and 2017 in a tertiary headache center. Data including demographics, attack characteristics, response to treatments, results of neuroimaging, and routine pituitary function tests were recorded. RESULTS: Seven hundred and eighteen cluster headache patients attended the headache clinic; 643 underwent a standard magnetic resonance imaging scan, of whom 376 also underwent dedicated pituitary magnetic resonance imaging. Pituitary adenomas occurred in 17 of 376 patients (4.52%). Non-functioning microadenomas (n = 14) were the most common abnormality reported. Two patients, one of whom lacked the symptoms of pituitary disease, required treatment for their pituitary lesion. No clinical predictors of those adenomas were identified after multivariate analysis using random forests. Systematic pituitary magnetic resonance imaging scanning did not benefit even a single patient in the entire cohort. CONCLUSION: The prevalence of pituitary adenomas in cluster headache is similar to that reported in the general population, thereby precluding an over-representation of pituitary lesions in cluster headache. We conclude that the diagnostic assessment of cluster headache patients should not include specific pituitary screening. Only patients with standard brain magnetic resonance imaging findings or symptoms suggestive of a pituitary disorder require brain magnetic resonance imaging with dedicated pituitary views.

Machine phenotyping of cluster headache and its response to verapamil.

Cluster headache is characterized by recurrent, unilateral attacks of excruciating pain associated with ipsilateral cranial autonomic symptoms. Although a wide array of clinical, anatomical, physiological, and genetic data have informed multiple theories about the underlying pathophysiology, the lack of a comprehensive mechanistic understanding has inhibited, on the one hand, the development of new treatments and, on the other, the identification of features predictive of response to established ones. The first-line drug, verapamil, is found to be effective in only half of all patients, and after several weeks of dose escalation, rendering therapeutic selection both uncertain and slow. Here we use high-dimensional modelling of routinely acquired phenotypic and MRI data to quantify the predictability of verapamil responsiveness and to illuminate its neural dependants, across a cohort of 708 patients evaluated for cluster headache at the National Hospital for Neurology and Neurosurgery between 2007 and 2017. We derive a succinct latent representation of cluster headache from non-linear dimensionality reduction of structured clinical features, revealing novel phenotypic clusters. In a subset of patients, we show that individually predictive models based on gradient boosting machines can predict verapamil responsiveness from clinical (410 patients) and imaging (194 patients) features. Models combining clinical and imaging data establish the first benchmark for predicting verapamil responsiveness, with an area under the receiver operating characteristic curve of 0.689 on cross-validation (95% confidence interval: 0.651 to 0.710) and 0.621 on held-out data. In the imaged patients, voxel-based morphometry revealed a grey matter cluster in lobule VI of the cerebellum (-4, -66, -20) exhibiting enhanced grey matter concentrations in verapamil non-responders compared with responders (familywise error-corrected P = 0.008, 29 voxels). We propose a mechanism for the therapeutic effect of verapamil that draws on the neuroanatomy and neurochemistry of the identified region. Our results reveal previously unrecognized high-dimensional structure within the phenotypic landscape of cluster headache that enables prediction of treatment response with modest fidelity. An analogous approach applied to larger, globally representative datasets could facilitate data-driven redefinition of diagnostic criteria and stronger, more generalizable predictive models of treatment responsiveness.

New insights in post-traumatic headache with cluster headache phenotype: a cohort study.

OBJECTIVES: To define the characteristics of post-traumatic headache with cluster headache phenotype (PTH-CH) and to compare these characteristics with primary CH. METHODS: A retrospective study was conducted of patients seen between 2007 and 2017 in a headache centre and diagnosed with PTH-CH that developed within 7 days of head trauma. A control cohort included 553 patients with primary CH without any history of trauma who attended the headache clinic during the same period. Data including demographics, attack characteristics and response to treatments were recorded. RESULTS: Twenty-six patients with PTH-CH were identified. Multivariate analysis revealed significant associations between PTH-CH and family history of CH (OR 3.32, 95% CI 1.31 to 8.63), chronic form (OR 3.29, 95% CI 1.70 to 6.49), parietal (OR 14.82, 95% CI 6.32 to 37.39) or temporal (OR 2.04, 95% CI 1.10 to 3.84) location of pain, and presence of prominent cranial autonomic features during attacks (miosis OR 11.24, 95% CI 3.21 to 41.34; eyelid oedema OR 5.79, 95% CI 2.57 to 13.82; rhinorrhoea OR 2.65, 95% CI 1.26 to 5.86; facial sweating OR 2.53, 95% CI 1.33 to 4.93). Patients with PTH-CH were at a higher risk of being intractable to acute (OR 12.34, 95% CI 2.51 to 64.73) and preventive (OR 16.98, 95% CI 6.88 to 45.52) treatments and of suffering from associated chronic migraine (OR 10.35, 95% CI 3.96 to 28.82). CONCLUSION: This largest series of PTH-CH defines it as a unique entity with specific evolutive profile. Patients with PTH-CH are more likely to suffer from the chronic variant, have marked autonomic features, be intractable to treatment and have associated chronic migraine compared with primary CH.

Is there a timing for sensitivity to acute cerebral ischemia in migraine patients?

BACKGROUND: Migraine may be a factor of increased cerebral sensitivity to ischemia. Previous studies were conducted within 6 to 72 after stroke onset. We aimed to determine if an accelerated infarct growth exists in migraine patients within the first 4.5 h. METHOD: A retrospective case-control study was conducted where all patients admitted for acute stroke started <4.5 h before and who underwent perfusion CT were assessed. The hypoperfusion and necrosis volumes on initial CT perfusion were analyzed, as well as the final infarct volume on MRI performed within 72 h after admission. A no-mismatch pattern was defined as a ratio necrosis/hypoperfusion volume > 83%. RESULTS: 24 patients with personal history of migraine were identified, 8 of them with aura. The control cohort included 51 patients. No difference was found between groups in terms of demographics, initial severity or outcome or presumed cause of stroke. Mean time to CT scan was 125 min in migraine patients and 127 min in the control group. A no-mismatch pattern was equally found in migraine patients and controls, even after adjustment for age, sex and presence of proximal occlusion (p = .22). The final infarct volume was also similar in both groups. CONCLUSIONS: Migraine patients did not display more no-mismatch pattern than controls within the 4.5 h of stroke onset. This deviates from previous studies and may be due to our earlier time from stroke onset to CT scan. A history of migraine may lead to malignant progression of ischemia but occurring only after several hours.

Trigeminal Neuralgia and Charcot-Marie-Tooth Disease: An Intriguing Association. Lessons From a Large Family Case Report and Review of Literature.

We report a case of familial trigeminal neuralgia (TN) and Charcot-Marie-Tooth disease (CMT) caused by an identified MPZ mutation with a review of previous cases described in the literature. BACKGROUND: The association of TN in CMT patients has previously been reported in a few cases. The pathophysiological link can be detailed with recent use of genetic analysis in CMT. METHODS: We report a large family including 7 members affected by CMT, 4 of whom also presented with TN. We then performed a literature review of literature by search of Pubmed from 1950 to September 2018, using the search terms "trigeminal neuralgia" and "Charcot-Marie-Tooth" and the references of relevant articles. RESULTS: Overall, we found 29 previously published TN cases in 12 CMT families. Among them, only 7 families (69%) included several affected members, suggesting that not all mutations involved in CMT predispose to TN. TN in this context seems to present with specific characteristics, including earlier age of onset, bilateral presentation, and poor tolerance to preventive treatments with gait disturbance exacerbated by the underlying neuropathy. CONCLUSION: This report of familial TN in CMT with identified MPZ mutation highlighted specific characteristics of this association. Considered as a rare association in the literature, it may be underestimated and the clinician should be aware of its specific pattern, including earlier age of onset, bilateral presentation, and poor tolerance to preventive treatments.

Moyamoya angiopathy in PHACE syndrome not associated with RNF213 variants.

Moyamoya angiopathy is a rare vasculopathy with stenosis and/or occlusion of bilateral intracranial parts of internal carotid arteries and/or proximal parts of middle and anterior cerebral arteries. PHACE syndrome is characterized by large segmental hemangiomas in the cervical-facial region. Both conditions are known to be associated in rare cases. Recently, it was discussed in the literature that RNF213 variants could be etiologically involved in this association. Here, we describe a childhood case with this rare co-occurrence in which we did not identify any rare RNF213 variant. The clinical and genetic backgrounds are discussed.

Biallelic MYORG mutation carriers exhibit primary brain calcification with a distinct phenotype.

Primary familial brain calcification (PFBC) is a rare neurogenetic disorder with diverse neuropsychiatric expression. Mutations in four genes cause autosomal dominant PFBC: SLC20A2, XPR1, PDGFB and PDGFRB. Recently, biallelic mutations in the MYORG gene have been reported to cause PFBC with an autosomal recessive pattern of inheritance. We screened MYORG in 29 unrelated probands negatively screened for the autosomal dominant PFBC genes and identified 11 families with a biallelic rare or novel predicted damaging variant. We studied the clinical and radiological features of 16 patients of these 11 families and compared them to that of 102 autosomal dominant PFBC patients carrying a mutation in one of the four known autosomal dominant PFBC genes. We found that MYORG patients exhibited a high clinical penetrance with a median age of onset of 52 years (range: 21-62) with motor impairment at the forefront. In particular, dysarthria was the presenting sign in 11/16 patients. In contrast to patients with autosomal dominant PFBC, 12/15 (80%) symptomatic patients eventually presented at least four of the following five symptoms: dysarthria, cerebellar syndrome, gait disorder of any origin, akinetic-hypertonic syndrome and pyramidal signs. In addition to the most severe clinical pattern, MYORG patients exhibited the most severe pattern of calcifications as compared to the patients from the four autosomal dominant PFBC gene categories. Strikingly, 12/15 presented with brainstem calcifications in addition to extensive calcifications in other brain areas (lenticular nuclei, thalamus, cerebellar hemispheres, vermis, ±cortex). Among them, eight patients exhibited pontine calcifications, which were observed in none of the autosomal dominant PFBC patients and hence appeared to be highly specific. Finally, all patients exhibited cerebellar atrophy with diverse degrees of severity on CT scans. We confirmed the existence of cerebellar atrophy by performing MRI voxel-based morphometry analyses of MYORG patients with autosomal dominant PFBC mutation carriers as a comparison group. Of note, in three families, the father carried small pallido-dentate calcifications while carrying the mutation at the heterozygous state, suggesting a putative phenotypic expression in some heterozygous carriers. In conclusion, we confirm that MYORG is a novel major PFBC causative gene and that the phenotype associated with such mutations may be recognized based on pedigree, clinical and radiological features.

Clinical and Molecular Features of 5 European Multigenerational Families With Moyamoya Angiopathy.

Background and Purpose Moyamoya angiopathy (MMA) is a rare cerebral vasculopathy outside of Asia. In Japanese patients, a vast majority of patients carry the founder p.R4810K variant in the RNF213 gene, and familial cases are around 10%. In European patients, data about familial occurrence are limited. The aim of this study was to characterize the clinical and molecular features of several European families with a parent-to-child transmission of MMA. Methods Out of 126 MMA probands referred, we identified 113 sporadic probands and 13 familial probands. Segregation analysis showed a vertical parent-to-child pattern of inheritance in the families of 5 of these probands. All 5 families were of German or Dutch ancestry. We investigated the clinical features of affected members and used whole-exome sequencing to screen RNF213 and 13 genes involved in Mendelian MMA and to identify genes recurrently mutated in these families. Results Twelve affected MMA patients were identified, including 9 females and 3 males. Age at clinical onset ranged from 11 to 65 years. In 3 of 5 families, associated livedo racemosa was found. We did not detect any deleterious variants in the 13 known MMA genes. RNF213 rare missense variants predicted to be pathogenic were detected in all affected members of 2 of these families, as well as 2 candidate variants of the PALD1 gene. Conclusions Nonsyndromic MMA was identified in 5 European families, including 2 to 3 clinically affected cases segregating with a parent-to-child pattern of inheritance in each family. Molecular screening detected rare deleterious variants within RNF213 and PALD1 in all affected members of 2 of these 5 families, as well as in some clinically unaffected members. Altogether these data raise the difficult and, to date unanswered, question of the medical indication of presymptomatic screening.