The first genetically confirmed cohort of Facioscapulohumeral Muscular Dystrophy from Northern India.

Facioscapulohumeral muscular dystrophy (FSHD) is the third most common form of hereditary myopathy. Sixty per cent of the world's population lives in Asia, so a significant percentage of the world's FSHD participants is expected to live there. To date, most FSHD studies have involved individuals of European descent, yet small-scale studies of East-Asian populations suggest that the likelihood of developing FSHD may vary. Here, we present the first genetically confirmed FSHD cohort of Indian ancestry, which suggests a pathogenic FSHD1 allele size distribution intermediate between European and North-East Asian populations and more asymptomatic carriers of 4 unit and 5 unit FSHD1 alleles than observed in European populations. Our data provides important evidence of differences relevant to clinical diagnostics and underscores the need for global FSHD participation in research and trial-ready Indian FSHD cohorts.

Best practice guidelines on genetic diagnostics of facioscapulohumeral muscular dystrophy: Update of the 2012 guidelines.

The gold standard for facioscapulohumeral muscular dystrophy (FSHD) genetic diagnostic procedures was published in 2012. With the increasing complexity of the genetics of FSHD1 and 2, the increase of genetic testing centers, and the start of clinical trials for FSHD, it is crucial to provide an update on our knowledge of the genetic features of the FSHD loci and renew the international consensus on the molecular testing recommendations. To this end, members of the FSHD European Trial Network summarized the evidence presented during the 2022 ENMC meeting on Genetic diagnosis, clinical outcome measures, and biomarkers. The working group additionally invited genetic and clinical experts from the USA, India, Japan, Australia, South-Africa, and Brazil to provide a global perspective. Six virtual meetings were organized to reach consensus on the minimal requirements for genetic confirmation of FSHD1 and FSHD2. Here, we present the clinical and genetic features of FSHD, specific features of FSHD1 and FSHD2, pros and cons of established and new technologies (Southern blot in combination with either linear or pulsed-field gel electrophoresis, molecular combing, optical genome mapping, FSHD2 methylation analysis and FSHD2 genotyping), the possibilities and challenges of prenatal testing, including pre-implantation genetic testing, and the minimal requirements and recommendations for genetic confirmation of FSHD1 and FSHD2. This consensus is expected to contribute to current clinical management and trial-readiness for FSHD.

Autosomal dominant in cis D4Z4 repeat array duplication alleles in facioscapulohumeral dystrophy.

Facioscapulohumeral dystrophy (FSHD) has a unique genetic aetiology resulting in partial chromatin relaxation of the D4Z4 macrosatellite repeat array on 4qter. This D4Z4 chromatin relaxation facilitates inappropriate expression of the transcription factor DUX4 in skeletal muscle. DUX4 is encoded by a retrogene that is embedded within the distal region of the D4Z4 repeat array. In the European population, the D4Z4 repeat array is usually organized in a single array that ranges between 8 and 100 units. D4Z4 chromatin relaxation and DUX4 derepression in FSHD is most often caused by repeat array contraction to 1-10 units (FSHD1) or by a digenic mechanism requiring pathogenic variants in a D4Z4 chromatin repressor like SMCHD1, combined with a repeat array between 8 and 20 units (FSHD2). With a prevalence of 1.5% in the European population, in cis duplications of the D4Z4 repeat array, where two adjacent D4Z4 arrays are interrupted by a spacer sequence, are relatively common but their relationship to FSHD is not well understood. In cis duplication alleles were shown to be pathogenic in FSHD2 patients; however, there is inconsistent evidence for the necessity of an SMCHD1 mutation for disease development. To explore the pathogenic nature of these alleles we compared in cis duplication alleles in FSHD patients with or without pathogenic SMCHD1 variant. For both groups we showed duplication-allele-specific DUX4 expression. We studied these alleles in detail using pulsed-field gel electrophoresis-based Southern blotting and molecular combing, emphasizing the challenges in the characterization of these rearrangements. Nanopore sequencing was instrumental to study the composition and methylation of the duplicated D4Z4 repeat arrays and to identify the breakpoints and the spacer sequence between the arrays. By comparing the composition of the D4Z4 repeat array of in cis duplication alleles in both groups, we found that specific combinations of proximal and distal repeat array sizes determine their pathogenicity. Supported by our algorithm to predict pathogenicity, diagnostic laboratories should now be furnished to accurately interpret these in cis D4Z4 repeat array duplications, alleles that can easily be missed in routine settings.

Optical Genome Mapping for the Molecular Diagnosis of Facioscapulohumeral Muscular Dystrophy: Advancement and Challenges.

Facioscapulohumeral muscular dystrophy (FSHD) is the second most common muscular dystrophy in adults, and it is associated with local D4Z4 chromatin relaxation, mostly via the contraction of the D4Z4 macrosatellite repeat array on chromosome 4q35. In this study, we aimed to investigate the use of Optical Genome Mapping (OGM) as a diagnostic tool for testing FSHD cases from the UK and India and to compare OGM performance with that of traditional techniques such as linear gel (LGE) and Pulsed-field gel electrophoresis (PFGE) Southern blotting (SB). A total of 6 confirmed and 19 suspected FSHD samples were processed with LGE and PFGE, respectively. The same samples were run using a Saphyr Genome-Imaging Instrument (1-color), and the data were analysed using custom EnFocus FSHD analysis. OGM was able to confirm the diagnosis of FSHD1 in all FSHD1 cases positive for SB (n = 17), and D4Z4 sizing highly correlated with PFGE-SB (p < 0.001). OGM correctly identified cases with mosaicism for the repeat array contraction (n = 2) and with a duplication of the D4Z4 repeat array. OGM is a promising new technology able to unravel structural variants in the genome and seems to be a valid tool for diagnosing FSHD1.

DUX4 expression in cancer induces a metastable early embryonic totipotent program.

The transcription factor DUX4 regulates a portion of the zygotic gene activation (ZGA) program in the early embryo. Many cancers express DUX4 but it is unknown whether this generates cells similar to early embryonic stem cells. Here we identified cancer cell lines that express DUX4 and showed that DUX4 is transiently expressed in a small subset of the cells. DUX4 expression activates the DUX4-regulated ZGA transcriptional program, the subsequent 8C-like program, and markers of early embryonic lineages, while suppressing steady-state and interferon-induced MHC class I expression. Although DUX4 was expressed in a small number of cells under standard culture conditions, DNA damage or changes in growth conditions increased the fraction of cells expressing DUX4 and its downstream programs. Our demonstration that transient expression of endogenous DUX4 in cancer cells induces a metastable early embryonic stem cell program and suppresses antigen presentation has implications for cancer growth, progression, and immune evasion.

Neuromuscular disease genetics in under-represented populations: increasing data diversity.

Neuromuscular diseases (NMDs) affect ∼15 million people globally. In high income settings DNA-based diagnosis has transformed care pathways and led to gene-specific therapies. However, most affected families are in low-to-middle income countries (LMICs) with limited access to DNA-based diagnosis. Most (86%) published genetic data is derived from European ancestry. This marked genetic data inequality hampers understanding of genetic diversity and hinders accurate genetic diagnosis in all income settings. We developed a cloud-based transcontinental partnership to build diverse, deeply-phenotyped and genetically characterized cohorts to improve genetic architecture knowledge, and potentially advance diagnosis and clinical management. We connected 18 centres in Brazil, India, South Africa, Turkey, Zambia, Netherlands and the UK. We co-developed a cloud-based data solution and trained 17 international neurology fellows in clinical genomic data interpretation. Single gene and whole exome data were analysed via a bespoke bioinformatics pipeline and reviewed alongside clinical and phenotypic data in global webinars to inform genetic outcome decisions. We recruited 6001 participants in the first 43 months. Initial genetic analyses 'solved' or 'possibly solved' ∼56% probands overall. In-depth genetic data review of the four commonest clinical categories (limb girdle muscular dystrophy, inherited peripheral neuropathies, congenital myopathy/muscular dystrophies and Duchenne/Becker muscular dystrophy) delivered a ∼59% 'solved' and ∼13% 'possibly solved' outcome. Almost 29% of disease causing variants were novel, increasing diverse pathogenic variant knowledge. Unsolved participants represent a new discovery cohort. The dataset provides a large resource from under-represented populations for genetic and translational research. In conclusion, we established a remote transcontinental partnership to assess genetic architecture of NMDs across diverse populations. It supported DNA-based diagnosis, potentially enabling genetic counselling, care pathways and eligibility for gene-specific trials. Similar virtual partnerships could be adopted by other areas of global genomic neurological practice to reduce genetic data inequality and benefit patients globally.

Diagnostic capabilities of nanopore long-read sequencing in muscular dystrophy.

Many individuals with muscular dystrophies remain genetically undiagnosed despite clinical diagnostic testing, including exome sequencing. Some may harbor previously undetected structural variants (SVs) or cryptic splice sites. We enrolled 10 unrelated families: nine had muscular dystrophy but lacked complete genetic diagnoses and one had an asymptomatic DMD duplication. Nanopore genomic long-read sequencing identified previously undetected pathogenic variants in four individuals: an SV in DMD, an SV in LAMA2, and two single nucleotide variants in DMD that alter splicing. The DMD duplication in the asymptomatic individual was in tandem. Nanopore sequencing may help streamline genetic diagnostic approaches for muscular dystrophy.

Chromosome 10q-linked FSHD identifies DUX4 as principal disease gene.

BACKGROUND: Facioscapulohumeral dystrophy (FSHD) is an inherited muscular dystrophy clinically characterised by muscle weakness starting with the facial and upper extremity muscles. A disease model has been developed that postulates that failure in somatic repression of the transcription factor DUX4 embedded in the D4Z4 repeat on chromosome 4q causes FSHD. However, due to the position of the D4Z4 repeat close to the telomere and the complex genetic and epigenetic aetiology of FSHD, there is ongoing debate about the transcriptional deregulation of closely linked genes and their involvement in FSHD. METHOD: Detailed genetic characterisation and gene expression analysis of patients with clinically confirmed FSHD and control individuals. RESULTS: Identification of two FSHD families in which the disease is caused by repeat contraction and DUX4 expression from chromosome 10 due to a de novo D4Z4 repeat exchange between chromosomes 4 and 10. We show that the genetic lesion causal to FSHD in these families is physically separated from other candidate genes on chromosome 4. We demonstrate that muscle cell cultures from affected family members exhibit the characteristic molecular features of FSHD, including DUX4 and DUX4 target gene expression, without showing evidence for transcriptional deregulation of other chromosome 4-specific candidate genes. CONCLUSION: This study shows that in rare situations, FSHD can occur on chromosome 10 due to an interchromosomal rearrangement with the FSHD locus on chromosome 4q. These findings provide further evidence that DUX4 derepression is the dominant disease pathway for FSHD. Hence, therapeutic strategies should focus on DUX4 as the primary target.

High-resolution breakpoint junction mapping of proximally extended D4Z4 deletions in FSHD1 reveals evidence for a founder effect.

Facioscapulohumeral muscular dystrophy (FSHD) is an inherited myopathy clinically characterized by weakness in the facial, shoulder girdle and upper a muscles. FSHD is caused by chromatin relaxation of the D4Z4 macrosatellite repeat, mostly by a repeat contraction, facilitating ectopic expression of DUX4 in skeletal muscle. Genetic diagnosis for FSHD is generally based on the sizing and haplotyping of the D4Z4 repeat on chromosome 4 by Southern blotting (SB), molecular combing or single-molecule optical mapping, which is usually straight forward but can be complicated by atypical rearrangements of the D4Z4 repeat. One of these rearrangements is a D4Z4 proximally extended deletion (DPED) allele, where not only the D4Z4 repeat is partially deleted, but also sequences immediately proximal to the repeat are lost, which can impede accurate diagnosis in all genetic methods. Previously, we identified several DPED alleles in FSHD and estimated the size of the proximal deletions by a complex pulsed-field gel electrophoresis and SB strategy. Here, using the next-generation sequencing, we have defined the breakpoint junctions of these DPED alleles at the base pair resolution in 12 FSHD families and 4 control individuals facilitating a PCR-based diagnosis of these DPED alleles. Our resultsshow that half of the DPED alleles are derivates of an ancient founder allele. For some DPED alleles, we found that genetic elements are deleted such as DUX4c, FRG2, DBE-T and myogenic enhancers necessitating re-evaluation of their role in FSHD pathogenesis.

Homozygous nonsense variant in LRIF1 associated with facioscapulohumeral muscular dystrophy.

OBJECTIVE: Facioscapulohumeral muscular dystrophy (FSHD) is a heterogenetic disorder predominantly characterized by progressive facial and scapular muscle weakness. Patients with FSHD either have a contraction of the D4Z4 repeat on chromosome 4q35 or mutations in D4Z4 chromatin modifiers SMCHD1 and DNMT3B, both causing D4Z4 chromatin relaxation and inappropriate expression of the D4Z4-encoded DUX4 gene in skeletal muscle. In this study, we tested the hypothesis whether LRIF1, a known SMCHD1 protein interactor, is a disease gene for idiopathic FSHD2. METHODS: Clinical examination of a patient with idiopathic FSHD2 was combined with pathologic muscle biopsy examination and with genetic, epigenetic, and molecular studies. RESULTS: A homozygous LRIF1 mutation was identified in a patient with a clinical phenotype consistent with FSHD. This mutation resulted in the absence of the long isoform of LRIF1 protein, D4Z4 chromatin relaxation, and DUX4 and DUX4 target gene expression in myonuclei, all molecular and epigenetic hallmarks of FSHD. In concordance, LRIF1 was shown to bind to the D4Z4 repeat, and knockdown of the LRIF1 long isoform in muscle cells results in DUX4 and DUX4 target gene expression. CONCLUSION: LRIF1 is a bona fide disease gene for FSHD2. This study further reinforces the unifying genetic mechanism, which postulates that FSHD is caused by D4Z4 chromatin relaxation, resulting in inappropriate DUX4 expression in skeletal muscle.

Intronic SMCHD1 variants in FSHD: testing the potential for CRISPR-Cas9 genome editing.

BACKGROUND: Facioscapulohumeral dystrophy (FSHD) is associated with partial chromatin relaxation of the DUX4 retrogene containing D4Z4 macrosatellite repeats on chromosome 4, and transcriptional de-repression of DUX4 in skeletal muscle. The common form of FSHD, FSHD1, is caused by a D4Z4 repeat array contraction. The less common form, FSHD2, is generally caused by heterozygous variants in SMCHD1. METHODS: We employed whole exome sequencing combined with Sanger sequencing to screen uncharacterised FSHD2 patients for extra-exonic SMCHD1 mutations. We also used CRISPR-Cas9 genome editing to repair a pathogenic intronic SMCHD1 variant from patient myoblasts. RESULTS: We identified intronic SMCHD1 variants in two FSHD families. In the first family, an intronic variant resulted in partial intron retention and inclusion of the distal 14 nucleotides of intron 13 into the transcript. In the second family, a deep intronic variant in intron 34 resulted in exonisation of 53 nucleotides of intron 34. In both families, the aberrant transcripts are predicted to be non-functional. Deleting the pseudo-exon by CRISPR-Cas9 mediated genome editing in primary and immortalised myoblasts from the index case of the second family restored wild-type SMCHD1 expression to a level that resulted in efficient suppression of DUX4. CONCLUSIONS: The estimated intronic mutation frequency of almost 2% in FSHD2, as exemplified by the two novel intronic SMCHD1 variants identified here, emphasises the importance of screening for intronic variants in SMCHD1. Furthermore, the efficient suppression of DUX4 after restoring SMCHD1 levels by genome editing of the mutant allele provides further guidance for therapeutic strategies.

Generation of genetically matched hiPSC lines from two mosaic facioscapulohumeral dystrophy type 1 patients.

Facioscapulohumeral dystrophy type 1 (FSHD1) is caused by contraction of the D4Z4 repeat array on chromosome 4q resulting in sporadic misexpression of the transcription factor DUX4 in skeletal muscle tissue. In ~4% of families, de novo D4Z4 contractions occur after fertilization resulting in somatic mosaicism with control and FSHD1 cell populations present within the same patient. Reprogramming of mosaic fibroblasts from two FSHD1 patients into human induced pluripotent stem cells (hiPSCs) generated genetically matched control and FSHD1 hiPSC lines. All hiPSC lines contained a normal karyotype, expressed pluripotency genes and differentiated into cells from the three germ layers.

SMCHD1 mutation spectrum for facioscapulohumeral muscular dystrophy type 2 (FSHD2) and Bosma arhinia microphthalmia syndrome (BAMS) reveals disease-specific localisation of variants in the ATPase domain.

BACKGROUND: Variants in the Structural Maintenance of Chromosomes flexible Hinge Domain-containing protein 1 (SMCHD1) can cause facioscapulohumeral muscular dystrophy type 2 (FSHD2) and the unrelated Bosma arhinia microphthalmia syndrome (BAMS). In FSHD2, pathogenic variants are found anywhere in SMCHD1 while in BAMS, pathogenic variants are restricted to the extended ATPase domain. Irrespective of the phenotypic outcome, both FSHD2-associated and BAMS-associated SMCHD1 variants result in quantifiable local DNA hypomethylation. We compared FSHD2, BAMS and non-pathogenic SMCHD1 variants to derive genotype-phenotype relationships. METHODS: Examination of SMCHD1 variants and methylation of the SMCHD1-sensitive FSHD locus DUX4 in 187 FSHD2 families, 41 patients with BAMS and in control individuals. Analysis of variants in a three-dimensional model of the ATPase domain of SMCHD1. RESULTS: DUX4 methylation analysis is essential to establish pathogenicity of SMCHD1 variants. Although the FSHD2 mutation spectrum includes all types of variants covering the entire SMCHD1 locus, missense variants are significantly enriched in the extended ATPase domain. Identification of recurrent variants suggests disease-specific residues for FSHD2 and in BAMS, consistent with a largely disease-specific localisation of variants in SMCHD1. CONCLUSIONS: The localisation of missense variants within the ATPase domain of SMCHD1 may contribute to the differences in phenotypic outcome.

FSHD1 and FSHD2 form a disease continuum.

OBJECTIVE: To compare the clinical features of patients showing a classical phenotype of facioscapulohumeral muscular dystrophy (FSHD) with genetic and epigenetic characteristics of the FSHD1 and FSHD2 loci D4Z4 and SMCHD1. METHODS: This is a national multicenter cohort study. We measured motor strength, motor function, and disease severity by manual muscle testing sumscore, Brooke and Vignos scores, clinical severity score (CSS), and age-corrected CSS, respectively. We correlated these scores with genetic (D4Z4 repeat size and haplotype; SMCHD1 variant status) and epigenetic (D4Z4 methylation) parameters. RESULTS: We included 103 patients: 54 men and 49 women. Among them, we identified 64 patients with FSHD1 and 20 patients with FSHD2. Seven patients had genetic and epigenetic characteristics of FSHD1 and FSHD2, all carrying repeats of 9-10 D4Z4 repeat units (RU) and a pathogenic SMCHD1 variant. In the remaining patients, FSHD was genetically excluded or remained unconfirmed. All clinically affected SMCHD1 mutation carriers had a D4Z4 repeat of 9-16 RU on a disease permissive 4qA haplotype. These patients are significantly more severely affected by all clinical scales when compared to patients with FSHD1 with upper-sized FSHD1 alleles (8-10 RU). CONCLUSION: The overlap between FSHD1 and FSHD2 patients in the 9-10 D4Z4 RU range suggests that FSHD1 and FSHD2 form a disease continuum. The previously established repeat size threshold for FSHD1 (1-10 RU) and FSHD2 (11-20 RU) needs to be reconsidered. CLINICALTRIALSGOV IDENTIFIER: NCT01970735.

Early onset as a marker for disease severity in facioscapulohumeral muscular dystrophy.

OBJECTIVE: To assess the relation between age at onset and disease severity in facioscapulohumeral muscular dystrophy (FSHD). METHODS: In this prospective cross-sectional study, we matched adult patients with FSHD with an early disease onset with 2 sex-matched FSHD control groups with a classic onset; the first group was age matched, and the second group was disease duration matched. Genetic characteristics, muscle performance, respiratory functioning, hearing loss, vision loss, epilepsy, educational level, and work status were compared with the 2 control groups. RESULTS: Twenty-eight patients with early-onset FSHD were age (n = 28) or duration (n = 27) matched with classic-onset patients. Patients with early-onset FSHD had more severe muscle weakness (mean FSHD clinical score 11 vs 5 in the age-matched and 9 in the duration-matched group, p < 0.05) and a higher frequency of wheelchair dependency (57%, 0%, and 30%, respectively, p < 0.05). In addition, systemic features were more frequent in early-onset FSHD, most important, hearing loss, decreased respiratory function and spinal deformities. There was no difference in work status. Genetically, the shortest D4Z4 repeat arrays (2-3 units) were found exclusively in the early-onset group, and the largest repeat arrays (8-9 units) were found only in the classic-onset groups. De novo mutations were more frequent in early-onset patients (46% vs 4%). CONCLUSIONS: Patients with early-onset FSHD more often have severe muscle weakness and systemic features. The disease severity is greater than in patients with classic-onset FSHD who are matched for disease duration, suggesting that the progression is faster in early-onset patients.

Cis D4Z4 repeat duplications associated with facioscapulohumeral muscular dystrophy type 2.

Facioscapulohumeral muscular dystrophy, known in genetic forms FSHD1 and FSHD2, is associated with D4Z4 repeat array chromatin relaxation and somatic derepression of DUX4 located in D4Z4. A complete copy of DUX4 is present on 4qA chromosomes, but not on the D4Z4-like repeats of chromosomes 4qB or 10. Normally, the D4Z4 repeat varies between 8 and 100 units, while in FSHD1 it is only 1-10 units. In the rare genetic form FSHD2, a combination of a 4qA allele with a D4Z4 repeat size of 8-20 units and heterozygous pathogenic variants in the chromatin modifier SMCHD1 causes DUX4 derepression and disease. In this study, we identified 11/79 (14%) FSHD2 patients with unusually large 4qA alleles of 21-70 D4Z4 units. By a combination of Southern blotting and molecular combing, we show that 8/11 (73%) of these unusually large 4qA alleles represent duplication alleles in which the long D4Z4 repeat arrays are followed by a small FSHD-sized D4Z4 repeat array duplication. We also show that these duplication alleles are associated with DUX4 expression. This duplication allele frequency is significantly higher than in controls (2.9%), FSHD1 patients (1.4%) and in FSHD2 patients with typical 4qA alleles of 8-20 D4Z4 units (1.5%). Segregation analysis shows that, similar to typical 8-20 units FSHD2 alleles, duplication alleles only cause FSHD in combination with a pathogenic variant in SMCHD1. We conclude that cis duplications of D4Z4 repeats explain DUX4 expression and disease presentation in FSHD2 families with unusual long D4Z4 repeats on 4qA chromosomes.

Phenotype-genotype relations in facioscapulohumeral muscular dystrophy type 1.

To determine how much of the clinical variability in facioscapulohumeral muscular dystrophy type 1 (FSHD1) can be explained by the D4Z4 repeat array size, D4Z4 methylation and familial factors, we included 152 carriers of an FSHD1 allele (23 single cases, 129 familial cases from 37 families) and performed state-of-the-art genetic testing, extensive clinical evaluation and quantitative muscle MRI. Familial factors accounted for 50% of the variance in disease severity (FSHD clinical score). The explained variance by the D4Z4 repeat array size for disease severity was limited (approximately 10%), and varied per body region (facial muscles, upper and lower extremities approximately 30%, 15% and 3%, respectively). Unaffected gene carriers had longer repeat array sizes compared to symptomatic individuals (7.3 vs 6.0 units, P = 0.000) and slightly higher Delta1 methylation levels (D4Z4 methylation corrected for repeat size, 0.96 vs -2.46, P = 0.048). The D4Z4 repeat array size and D4Z4 methylation contribute to variability in disease severity and penetrance, but other disease modifying factors must be involved as well. The larger effect of the D4Z4 repeat array on facial muscle involvement suggests that these muscles are more sensitive to the influence of the FSHD1 locus itself, whereas leg muscle involvement seems highly dependent on modifying factors.

Facioscapulohumeral Dystrophy in Childhood: A Nationwide Natural History Study.

OBJECTIVE: Facioscapulohumeral dystrophy (FSHD) is one of the most frequent heritable muscular dystrophies, with a large variety in age at onset and disease severity. The natural history and molecular characteristics of FSHD in childhood are incompletely understood. Our objective is to clinically and genetically characterize FSHD in childhood. METHODS: We performed a nationwide, single-investigator, natural history study on FSHD in childhood. RESULTS: Multiple-source recruitment resulted in 32 patients with FSHD (0-17 years), leading to an estimated prevalence of 1 in 100,000 children in The Netherlands. This series of 32 children with FSHD revealed a heterogeneous phenotype and genotype in childhood. The phenotypic hallmarks of FSHD in childhood are: facial weakness with normal or only mildly affected motor performance, decreased functional exercise capacity (6-minute walk test), lumbar hyperlordosis, and increased echo intensity on muscle ultrasonography. In addition, pain and fatigue were frequent and patients experienced a lower quality of life compared to healthy peers. In contrast to the literature on early-onset FSHD, systemic features such as hearing loss and retinal and cardiac abnormalities were infrequent and subclinical, and epilepsy and intellectual disability were absent. Genotypically, patients had a mean D4Z4 repeat array of 5 units (range, 2-9), and 14% of the mutations were de novo. INTERPRETATION: FSHD in childhood is more prevalent than previously known and the genotype resembles classic FSHD. Importantly, FSHD mainly affects functional exercise capacity and quality of life in children. As such, these results are paramount for counseling, clinical management, and stratification in clinical research. Ann Neurol 2018;84:635-645.

FSHD type 2 and Bosma arhinia microphthalmia syndrome: Two faces of the same mutation.

OBJECTIVE: To determine whether congenital arhinia/Bosma arhinia microphthalmia syndrome (BAMS) and facioscapulohumeral muscular dystrophy type 2 (FSHD2), 2 seemingly unrelated disorders both caused by heterozygous pathogenic missense variants in the SMCHD1 gene, might represent different ends of a broad single phenotypic spectrum associated with SMCHD1 dysfunction. METHODS: We examined and/or interviewed 14 patients with FSHD2 and 4 unaffected family members with N-terminal SMCHD1 pathogenic missense variants to identify BAMS subphenotypes. RESULTS: None of the patients with FSHD2 or family members demonstrated any congenital defects or dysmorphic features commonly found in patients with BAMS. One patient became anosmic after nasal surgery and one patient was hyposmic; one man was infertile (unknown cause) but reported normal pubertal development. CONCLUSION: These data suggest that arhinia/BAMS and FSHD2 do not represent one phenotypic spectrum and that SMCHD1 pathogenic variants by themselves are insufficient to cause either of the 2 disorders. More likely, both arhinia/BAMS and FSHD2 are caused by complex oligogenic or multifactorial mechanisms that only partially overlap at the level of SMCHD1.