Iron is suggested to play a detrimental role in the progression of chronic kidney disease (CKD). The kidney recycles iron back into the circulation. However, the localization of proteins relevant for physiological tubular iron handling and their potential role in CKD remain unclear. We examined associations between iron deposition, expression of iron handling proteins and tubular injury in kidney biopsies from CKD patients and healthy controls using immunohistochemistry. Iron was deposited in proximal (PT) and distal tubules (DT) in 33% of CKD biopsies, predominantly in pathologies with glomerular dysfunction, but absent in controls. In healthy kidney, PT contained proteins required for iron recycling including putative iron importers ZIP8, ZIP14, DMT1, iron storage proteins L- and H-ferritin and iron exporter ferroportin, while DT only contained ZIP8, ZIP14, and DMT1. In CKD, iron deposition associated with increased intensity of iron importers (ZIP14, ZIP8), storage proteins (L-, H-ferritin), and/or decreased ferroportin abundance. This demonstrates that tubular iron accumulation may result from increased iron uptake and/or inadequate iron export. Iron deposition associated with oxidative injury as indicated by heme oxygenase-1 abundance. In conclusion, iron deposition is relatively common in CKD, and may result from altered molecular iron handling and may contribute to renal injury.

Background SELENON (SEPN1)-related myopathy (SELENON-RM) is a rare congenital myopathy characterized by slowly progressive proximal muscle weakness, early onset spine rigidity and respiratory insufficiency. A muscular dystrophy caused by mutations in the LAMA2 gene (LAMA2-related muscular dystrophy, LAMA2-MD) has a similar clinical phenotype, with either a severe, early-onset due to complete Laminin subunit α2 deficiency (merosin-deficient congenital muscular dystrophy type 1A (MDC1A)), or a mild, childhood- or adult-onset due to partial Laminin subunit α2 deficiency. For both muscle diseases, no curative treatment options exist, yet promising preclinical studies are ongoing. Currently, there is a paucity on natural history data and appropriate clinical and functional outcome measures are needed to reach trial readiness. Methods LAST STRONG is a natural history study in Dutch-speaking patients of all ages diagnosed with SELENON-RM or LAMA2-MD, starting August 2020. Patients have four visits at our hospital over a period of 1.5 year. At all visits, they undergo standardized neurological examination, hand-held dynamometry (age ≥ 5 years), functional measurements, questionnaires (patient report and/or parent proxy; age ≥ 2 years), muscle ultrasound including diaphragm, pulmonary function tests (spirometry, maximal inspiratory and expiratory pressure, sniff nasal inspiratory pressure; age ≥ 5 years), and accelerometry for 8 days (age ≥ 2 years); at visit one and three, they undergo cardiac evaluation (electrocardiogram, echocardiography; age ≥ 2 years), spine X-ray (age ≥ 2 years), dual-energy X-ray absorptiometry (DEXA-)scan (age ≥ 2 years) and full body magnetic resonance imaging (MRI) (age ≥ 10 years). All examinations are adapted to the patient’s age and functional abilities. Correlation between key parameters within and between subsequent visits will be assessed. Discussion Our study will describe the natural history of patients diagnosed with SELENON-RM or LAMA2-MD, enabling us to select relevant clinical and functional outcome measures for reaching clinical trial-readiness. Moreover, our detailed description (deep phenotyping) of the clinical features will optimize clinical management and will establish a well-characterized baseline cohort for prospective follow-up. Conclusion Our natural history study is an essential step for reaching trial readiness in SELENON-RM and LAMA2-MD. Trial registration This study has been approved by medical ethical reviewing committee Region Arnhem-Nijmegen (NL64269.091.17, 2017–3911) and is registered at ClinicalTrial.gov (NCT04478981).

In the original version of this Article, the name of author Marius C. van den Heuvel was incorrectly given as Marius van den Heuvel. In addition the authors Sanne van Raaij, Rachel van Swelm, Marius C. van den Heuvel and Harry van Goor were incorrectly indexed.

Centronuclear myopathy (CNM) is a genetically heterogeneous congenital myopathy characterized by muscle weakness, atrophy, and variable degrees of cardiorespiratory involvement. The clinical severity is largely explained by genotype (DNM2, MTM1, RYR1, BIN1, TTN, and other rarer genetic backgrounds), specific mutation(s), and age of the patient. The histopathological hallmark of CNM is the presence of internal centralized nuclei on muscle biopsy. Information on the phenotypical spectrum, subtype prevalence, and phenotype-genotype correlations is limited. To characterize CNM more comprehensively, we retrospectively assessed a national cohort of 48 CNM patients (mean age = 32 ± 24 years, range 0-80, 54% males) from the Netherlands clinically, histologically, and genetically. All information was extracted from entries in the patient's medical records, between 2000 and 2020. Frequent clinical features in addition to muscle weakness and hypotonia were fatigue and exercise intolerance in more mildly affected cases. Genetic analysis showed variants in four genes (18 DNM2, 14 MTM1, 9 RYR1, and 7 BIN1), including 16 novel variants. In addition to central nuclei, histologic examination revealed a large variability of myopathic

BackgroundX-linked myotubular myopathy (XL-MTM) is an early onset congenital myopathy characterized by mild to severe muscle weakness in males.ObjectiveTo characterize the clinical spectrum of neuromuscular features in X-linked myotubular myopathy (XL-MTM) carriers.MethodsWe performed a nationwide cross-sectional study focusing on neuromuscular features in an unselected cohort of Dutch XL-MTM carriers. Participants were recruited from neuromuscular centres in the Netherlands and through the Dutch and European patient associations. Genetic results were collected. Carriers were classified based on ambulatory status and muscle weakness. We used a questionnaire focussing on medical and family history and neuromuscular symptoms. Additionally, we performed a neurological examination including Manual Muscle Testing (MMT), Timed Up and Go test (TUG), and 6 Minutes Walking Test (6MWT).ResultsWe included 21 carriers (20 genetically confirmed and one obligate), of whom eleven (52%) carriers were classified as manifesting, with severe (non-ambulatory; n=2), moderate (minimal independent ambulation/assisted ambulation; n=2), mild (independent ambulation but with limb or axial muscle weakness; n=3) and minimal (only facial muscle weakness, n=4) phenotypes. Three of the manifesting carriers (two severe, one moderate) were from families without genetically confirmed male XL-MTM patients. Furthermore, seven manifesting carriers (one moderate; two mild; four minimal) were not classified as manifesting carriers before participation in our study. Three carriers reported a history of pneumothorax. The obstetric history revealed frequent polyhydramnios (50%) and reduced fetal movements (36%) in pregnancies of affected sons. Muscle weakness was most pronounced in proximal and limb girdle muscles. Other frequently reported sign included (asymmetric) facial weakness (73%), reduced or absent deep tendon reflexes (45%), scoliosis (40%), and ptosis (45%). Ten participants (48%) were classified as non-manifesting. Manifesting carriers had lower functional testing scores on 6MWT and TUG compared to non-manifesting carriers.DiscussionThis study showed that 52% of an unselected group of XL-MTM carriers has muscle weakness (three of whom previously unclassified as manifesting). This corresponds to findings of our recent questionnaire study on self-reported symptoms in XLMTM carriers. These observations should raise awareness of the neuromuscular manifestations of the XL-MTM carrier state, and provide important epidemiological information required for future clinical trials.