Connective tissue presentation in two families expands the phenotypic spectrum of PYROXD1 disorders.

Recessive variants in the oxidoreductase PYROXD1 are reported to cause a myopathy in 22 affected individuals from 15 families. Here, we describe two female probands from unrelated families presenting with features of a congenital connective tissue disorder including osteopenia, blue sclera, soft skin, joint hypermobility and neuromuscular junction dysfunction in addition to known features of PYROXD1 myopathy including respiratory difficulties, weakness, hypotonia and oromotor dysfunction. Proband AII:1 is compound heterozygous for the recurrent PYROXD1 variant Chr12(GRCh38):g.21452130A>G;NM_024854.5:c.464A>G;p.(N155S) and Chr12(GRCh38):g.21462019_21462022del;NM_024854.5:c.892_895del;p.(V298Mfs*4) and proband BII:1 is compound heterozygous for Chr12(GRCh38):g.21468739-21468741del;NM_024854.5:c.1488_1490del;p.(E496del) and Chr12(GRCh38):g.21467619del;NM_024854.5:c.1254+1del. RNA studies demonstrate c.892_895del;p.(V298Mfs*4) is targeted by nonsense mediated decay and c.1254+1delG elicits in-frame skipping of exon-11. Western blot from cultured fibroblasts shows reduced PYROXD1 protein levels in both probands. Testing urine from BII:1 and six individuals with PYROXD1 myopathy showed elevated levels of deoxypyridinoline, a mature collagen crosslink, correlating with PYROXD1-disorder severity. Urine and serum amino acid testing of the same individuals revealed no reportable changes. In contrast to PYROXD1 knock-out, we find no evidence for disrupted tRNA ligase activity, as measured via XBP1 splicing, in fibroblasts expressing PYROXD1 variants. In summary, we expand the clinical spectrum of PYROXD1-related disorders to include an overlapping connective tissue and myopathy presentation, identify three novel, pathogenic PYROXD1 variants, and provide preliminary evidence that elevated urine DPD crosslinks may provide a clinical biomarker for PYROXD1 disorders. Our results advocate consideration of PYROXD1 variants in the differential diagnosis for undiagnosed individuals presenting with a connective tissue disorder and myopathy.

Delandistrogene Moxeparvovec Gene Therapy in Ambulatory Patients (Aged ≥4 to <8 Years) with Duchenne Muscular Dystrophy: 1-Year Interim Results from Study SRP-9001-103 (ENDEAVOR).

OBJECTIVE: Delandistrogene moxeparvovec is approved in the USA for the treatment of ambulatory patients (4-5 years) with Duchenne muscular dystrophy. ENDEAVOR (SRP-9001-103; NCT04626674) is a single-arm, open-label study to evaluate delandistrogene moxeparvovec micro-dystrophin expression, safety, and functional outcomes following administration of commercial process delandistrogene moxeparvovec. METHODS: In cohort 1 of ENDEAVOR (N = 20), eligible ambulatory males, aged ≥4 to <8 years, received a single intravenous infusion of delandistrogene moxeparvovec (1.33 × 1014 vg/kg). The primary endpoint was change from baseline (CFBL) to week 12 in delandistrogene moxeparvovec micro-dystrophin by western blot. Additional endpoints evaluated included: safety; vector genome copies; CFBL to week 12 in muscle fiber-localized micro-dystrophin by immunofluorescence; and functional assessments, including North Star Ambulatory Assessment, with comparison with a propensity score-weighted external natural history control. RESULTS: The 1-year safety profile of commercial process delandistrogene moxeparvovec in ENDEAVOR was consistent with safety data reported in other delandistrogene moxeparvovec trials (NCT03375164 and NCT03769116). Delandistrogene moxeparvovec micro-dystrophin expression was robust, with sarcolemmal localization at week 12; mean (SD) CFBL in western blot, 54.2% (42.6); p < 0.0001. At 1 year, patients demonstrated stabilized or improved North Star Ambulatory Assessment total scores; mean (SD) CFBL, +4.0 (3.5). Treatment versus a propensity score-weighted external natural history control demonstrated a statistically significant difference in least squares mean (standard error) CFBL in North Star Ambulatory Assessment, +3.2 (0.6) points; p < 0.0001. INTERPRETATION: Results confirm efficient transduction of muscle by delandistrogene moxeparvovec. One-year post-treatment, delandistrogene moxeparvovec was well tolerated, and demonstrated stabilized or improved motor function, suggesting a clinical benefit for patients with Duchenne muscular dystrophy. ANN NEUROL 2023;94:955-968.

Intron mutations and early transcription termination in Duchenne and Becker muscular dystrophy.

DMD pathogenic variants for Duchenne and Becker muscular dystrophy are detectable with high sensitivity by standard clinical exome analyses of genomic DNA. However, up to 7% of DMD mutations are deep intronic and analysis of muscle-derived RNA is an important diagnostic step for patients who have negative genomic testing but abnormal dystrophin expression in muscle. In this study, muscle biopsies were evaluated from 19 patients with clinical features of a dystrophinopathy, but negative clinical DMD mutation analysis. Reverse transcription-polymerase chain reaction or high-throughput RNA sequencing methods identified 19 mutations with one of three pathogenic pseudoexon types: deep intronic point mutations, deletions or insertions, and translocations. In association with point mutations creating intronic splice acceptor sites, we observed the first examples of DMD pseudo 3'-terminal exon mutations causing high efficiency transcription termination within introns. This connection between splicing and premature transcription termination is reminiscent of U1 snRNP-mediating telescripting in sustaining RNA polymerase II elongation across large genes, such as DMD. We propose a novel classification of three distinct types of mutations identifiable by muscle RNA analysis, each of which differ in potential treatment approaches. Recognition and appropriate characterization may lead to therapies directed toward full-length dystrophin expression for some patients.

Thrombotic Microangiopathy Following Onasemnogene Abeparvovec for Spinal Muscular Atrophy: A Case Series.

Spinal muscular atrophy is treated with onasemnogene abeparvovec, which replaces the missing survival motor neuron 1 gene via an adeno-associated virus vector. As of July 1, 2020, we had identified 3 infants who developed thrombotic microangiopathy following onasemnogene abeparvovec. Early recognition and treatment of drug-induced thrombotic microangiopathy may lessen mortality and morbidity.

Laboratory monitoring of nusinersen safety.

INTRODUCTION: This retrospective study reports our tertiary care center's experience with intrathecal nusinersen administration in children and adults with spinal muscular atrophy (SMA). METHODS: We reviewed safety monitoring laboratory results and need for procedural sedation and fluoroscopy-guidance in all SMA patients receiving nusinersen between February 2017 and March 2020. RESULTS: Fifty-eight patients ages 1 mo- 56 y received 494 nusinersen doses. There were 166 laboratory abnormalities in 45 patients. Most were either mild (145 [87.3%]) or were transient proteinuria (18 [10.8%]). None altered nusinersen treatment. Twenty-eight patients required either general anesthesia (75 doses) or anxiolysis with oral midazolam (133 doses, including 6 patients [23 doses] with SMA type I). Eight patients with complicated spines (45 doses) required fluoroscopic guidance. One treatment-related serious adverse event (emesis leading to intubation) occurred during general anesthesia. Two children had asymptomatic increased intracranial pressure. No patients discontinued treatment due to adverse events. DISCUSSION: Intrathecal nusinersen is generally safe and well-tolerated, including in patients requiring oral anxiolysis, general sedation, and fluoroscopic guidance. Frequent serial laboratory monitoring did not identify any persistent significantly abnormal findings or alter treatment.

The Spinal Muscular Atrophy Health Index: A novel outcome for measuring how a patient feels and functions.

INTRODUCTION: The Spinal Muscular Atrophy Health Index (SMA-HI) is a multifaceted, disease-specific, patient-reported outcome to measure an SMA patient's perception of their disease burden. In preparation for upcoming therapeutic trials, we examine the validity, reliability, and usability of the SMA-HI in adults, teenagers, and children with SMA. METHODS: Using data from a cross-sectional study of 359 international adult patients with SMA, we identified the most relevant symptoms to include in the SMA-HI. We utilized factor analysis, patient interviews with adults and minors (age 8-15 years), known-group validity testing, and test-retest reliability assessments to evaluate and refine the SMA-HI. RESULTS: The SMA-HI measures overall disease burden and 15 areas of SMA health. Fifteen adult patients and five patients, age 8 to 15 years, participated in semistructured qualitative interviews and found the SMA-HI to be comprehensive, easily completed, and to have clear meaning. The final SMA-HI and its subscales demonstrated good internal consistency (Cronbach α = 0.77-0.96), high test-retest reliability (intraclass correlation coefficient = 0.60-0.96), and an ability to differentiate between SMA groups with different disease severities affecting areas such as employment and ambulation (P < .0001 for both). DISCUSSION: This research provides evidence that the SMA-HI is a valid, relevant, and reliable outcome measure to assess multifaceted patient-reported disease burden in older children, teenagers, and adults with SMA. The SMA-HI provides an opportunity for researchers and clinicians to measure a SMA patient's perception of their health and determine relevant changes in response to therapeutic intervention or disease progression.

Pulse oral corticosteroids in pediatric chronic inflammatory demyelinating polyneuropathy.

Childhood onset chronic inflammatory demyelinating polyneuropathy (CIDP) often requires long-term immunomodulatory therapy. We report a comprehensive review of our treatment of pediatric CIDP with a focus on high-dose weekly corticosteroids ("pulse oral corticosteroids"), a treatment method that is not commonly reported. We retrospectively reviewed medical records of pediatric patients with CIDP treated at our center between 2000 and 2018 for whom we had at least 12 mo follow-up. Here, we describe the demographics, disease course, treatment regimens, and long-term outcomes of these patients. Twenty-five patients were identified for analysis. Pulse oral corticosteroid monotherapy was the predominant maintenance treatment in 56% of patients. Patients were followed for a median of 4 y. Side effects were seen in a minority of patients. The probability of a normal exam or being off treatment at last follow-up was similar regardless of predominant maintenance therapy. Pulse oral corticosteroid therapy is a safe and effective long-term treatment option in children with CIDP.

Evaluation for Late Nerve Transfer Surgery in Spinal Cord Injury: Predicting the Degree of Lower Motor Neuron Injury.

PURPOSE: Nerve transfer surgery is used to restore upper extremity function following cervical spinal cord injury (SCI) with substantial variation in outcomes. The injury pattern in SCI is complex and can include isolated upper motor neuron (UMN) and combined UMN/lower motor neuron (LMN) dysfunction. The purpose of the study was to determine the most effective diagnostic technique for determining suitable candidates for nerve transfer surgery in SCI. METHODS: Medical records were reviewed of patients who had nerve transfers to restore upper extremity function in SCI. Data collected included (1) preoperative clinical examination and electrodiagnostic testing; (2) intraoperative neuromuscular stimulation (NMS); and (3) nerve histopathology. Preoperative, intraoperative, and postoperative data were compared to identify predictors of isolated UMN versus combined UMN/LMN injury patterns. RESULTS: The study sample included 22 patients with 50 nerve transfer surgeries and included patients ranging from less than 1 year to over a decade post-SCI. Normal recipient nerve conduction studies (NCS) before surgery corresponded to the intraoperative presence of recipient NMS and postoperative histopathology that showed normal nerve architecture. Conversely, abnormal recipient NCS before surgery corresponded with the absence of recipient NMS during surgery and patterns of denervation on postoperative histopathology. Normal donor preoperative manual muscle testing corresponded with the presence of donor NMS during surgery and normal nerve architecture on postoperative histopathology. An EMG of corresponding musculature did not correspond with intraoperative donor or recipient NMS or histopathological findings. CONCLUSIONS: NCS better predict patterns of injury in SCI than EMG. This is important information for clinicians evaluating people for late nerve transfer surgery even years post-SCI. TYPE OF STUDY/LEVEL OF EVIDENCE: Diagnostic II.

Reliability of bedside ultrasound of limb and diaphragm muscle thickness in critically ill children.

INTRODUCTION: We evaluated the reliability of measuring muscle thickness with ultrasound in limbs and diaphragms of critically ill children and determined the sensitivity of these measures to quantitate muscle atrophy over time. METHODS: An expert and trained novice sonographers prospectively measured limb and diaphragm muscle thickness in 33 critically ill children. RESULTS: Expert and novice intrarater and interrater reliability were similar. Intraclass correlations (ICC) and coefficients of variation (CoV) were better in limbs (ICC > 0.9; CoV 3.57%-5.40%) than in diaphragm (ICC > 0.8; CoV novice 11.88%, expert, 12.28%). Mean relative difference in all muscles was small (1%-8%). Limits of agreement of the relative difference were smaller in limb (<13%-18%) than in diaphragm (<38%) muscles. DISCUSSION: Muscle thickness is reliably measured with ultrasound by trained examiners in critically ill children. Our approach detects atrophy >13% in limb and >38% in diaphragm muscles. The smaller detectable change in limb muscles is likely due to their greater thickness. Muscle Nerve 59:88-94, 2019.

Twice-weekly glucocorticosteroids in infants and young boys with Duchenne muscular dystrophy.

INTRODUCTION: Glucocorticosteroids (GC) are effective in slowing weakness in boys with Duchenne muscular dystrophy (DMD). METHODS: This is a multisite, 1-year, open-label trial of twice-weekly prednisolone (5 mg/kg/dose) in infants/young boys (0.4-2.4 years) with DMD. We compared changes in Bayley III Scales of Infant Development (Bayley-III) with untreated boys followed for 1 year (historical control cohort [HCC]). Twenty-three of 25 participants completed the study. RESULTS: Treated boys gained an average of 0.5 points on the Bayley-III gross motor scaled score (GMSS) compared with the HCC who, on average, declined 1.3 points (P = 0.03). All boys maintained linear growth, and none developed Cushingoid features. Excessive weight gain occurred in 13 of 23 (56%) boys. DISCUSSION: This study provides evidence that twice-weekly GC is well tolerated in infants and young boys with DMD and improves GMSS. Excessive weight gain is a potential risk. Longer follow-up is required to determine whether early GC initiation is feasible in most infants/boys with DMD. Muscle Nerve 59:650-657, 2019.

Quantitative muscle ultrasound detects disease progression in Duchenne muscular dystrophy.

OBJECTIVE: We assessed changes in quantitative muscle ultrasound data in boys with Duchenne muscular dystrophy (DMD) and healthy controls to determine whether ultrasound can serve as a biomarker of disease progression. Two approaches were used: gray scale level (GSL), measured from the ultrasound image, and quantitative backscatter analysis (QBA), measured directly from the received echoes. METHODS: GSL and QBA were obtained from 6 unilateral arm/leg muscles in 36 boys with DMD and 28 healthy boys (age = 2-14 years) for up to 2 years. We used a linear mixed effects model with random intercept and slope terms to compare trajectories of GSL, QBA, and functional assessments. We analyzed separately a subset of boys who initiated corticosteroids. RESULTS: Compared to healthy boys, increasing GSL in DMD boys >7.0 years old was first identified at 6 months (eg, anterior forearm slope difference of 1.16 arbitrary units/mo, p = 0.004, 95% confidence interval [CI] = 0.38-1.94); in boys ≤ 7 years old, differences in GSL first appeared at 12 months (0.82 arbitrary units/mo, p = 0.04, 95% CI = 0.075-1.565, in rectus femoris). QBA performed similarly to GSL (eg, DMD boys > 7 years old: 0.41dB/mo, p = 0.01, 95% CI = 0.096-0.72, in anterior forearm at 6 months). Ultrasound identified differences earlier than functional measures including 6-minute walk and supine-to-stand tests. However, neither QBA nor GSL showed an effect of corticosteroid initiation. INTERPRETATION: QBA performs similarly to GSL, and both appear more sensitive than functional assessments for detecting muscle deterioration in DMD. Additional studies will be required to determine whether quantitative muscle ultrasound can detect therapeutic efficacy. Ann Neurol 2017;81:633-640.

Electrical impedance myography for assessment of Duchenne muscular dystrophy.

OBJECTIVE: Sensitive, objective, and easily applied methods for evaluating disease progression and response to therapy are needed for clinical trials in Duchenne muscular dystrophy (DMD). In this study, we evaluated whether electrical impedance myography (EIM) could serve this purpose. METHODS: In this nonblinded study, 36 boys with DMD and 29 age-similar healthy boys underwent multifrequency EIM measurements for up to 2 years on 6 muscles unilaterally along with functional assessments. A linear mixed-effects model with random intercept and slope terms was used for the analysis of multifrequency EIM values and functional measures. Seven DMD boys were initiated on corticosteroids; these data were analyzed using a piecewise linear mixed-effects model. RESULTS: In boys > 7.0 years old, a significant difference in the slope of EIM phase ratio trajectories in the upper extremity was observed by 6 months of -0.074/month, p = 0.023, 95% confidence interval (CI) = -0.013, -0.14; at 2 years, this difference was -0.048/month, p < 0.0001, 95% CI = -0.028, -0.068. In boys ≤ 7.0 years old, differences appeared at 6 months in gastrocnemius (EIM phase slope = -0.83 °/kHz/mo, p = 0.007, 95% CI = -0.26, -1.40). EIM outcomes showed significant differences earlier than functional tests. Initiation of corticosteroids significantly improved the slope of EIM phase ratio (0.057/mo, p = 0.00019, 95% CI = 0.028, 0.086) and EIM phase slope (0.14 °/kHz/mo, p = 0.013, 95% CI = 0.028, 0.25), consistent with corticosteroids' known clinical benefit. INTERPRETATION: EIM detects deterioration in muscles of both younger and older boys by 6 months; it also identifies the therapeutic effect of corticosteroid initiation. Because EIM is rapid to apply, painless, and requires minimal operator training, the technique deserves to be further evaluated as a biomarker in DMD clinical therapeutic trials. Ann Neurol 2017;81:622-632.

Nerve ultrasound in polyneuropathies.

Ultrasound can be used to visualize pathology in the peripheral nerves of patients with polyneuropathy. Nerve enlargement is the most frequent pathology, but other abnormalities, including abnormal nerve echogenicity and vascularity, are also encountered. This monograph presents an overview of the role of nerve ultrasound in the evaluation and management of both inherited and acquired polyneuropathies. A description of the sonographic techniques and common abnormalities is provided, followed by a presentation of typical findings in different neuropathies. Scoring systems for characterizing the presence and pattern of nerve abnormalities as they relate to different polyneuropathies are presented. Muscle Nerve 57: 716-728, 2018.

Nerve ultrasound reliability of upper limbs: Effects of examiner training.

INTRODUCTION: Duration of training to reliably measure nerve cross-sectional area with ultrasound is unknown. METHODS: A retrospective review was performed of ultrasound data, acquired and recorded by 2 examiners-an expert and either a trainee with 2 months (novice) or a trainee with 12 months (experienced) of experience. Data on median, ulnar, and radial nerves were reviewed for 42 patients. RESULTS: Interrater reliability was good and varied most with nerve site but little with experience. Coefficient of variation (CoV) range was 9.33%-22.5%. Intraclass correlation coefficient (ICC) was good to excellent (0.65-95) except ulnar nerve-wrist/forearm and radial nerve-humerus (ICC = 0.39-0.59). Interrater differences did not vary with nerve size or body mass index. Expert-novice and expert-experienced interrater differences and CoV were similar. The ulnar nerve-wrist expert-novice interrater difference decreased with time (rs = -0.68, P = 0.001). DISCUSSION: A trainee with at least 2 months of experience can reliably measure upper limb nerves. Reliability varies by nerve and location and slightly improves with time. Muscle Nerve 57: 189-192, 2018.

Intramuscular blood flow quantification with power doppler ultrasonography.

INTRODUCTION: Quantification of blood flow to muscle using ultrasound is limited to large vessels. Small vessel intramuscular blood flow cannot be quantified using ultrasound without specialized methods or intravenous contrast. METHODS: We describe a technique using power Doppler to quantify postcontraction hyperemia in intramuscular vessels that can be used at the bedside. RESULTS: In 11 healthy subjects, postcontraction intramuscular blood flow in the forearm flexors and tibialis anterior muscles increased with stronger and repeated contractions. Intravascular blood flow measured by pulsed Doppler in the brachial artery similarly increased. Three patients with muscular dystrophies showed a negligible increase of postcontraction intramuscular blood flow. CONCLUSIONS: Intramuscular blood flow can be quantified using power Doppler ultrasonography; it increases following contraction and may be reduced in patients with muscular dystrophies. This quantitative, noninvasive technique can be applied at the bedside and may facilitate studies of disease impact on intramuscular blood flow. Muscle Nerve 54: 872-878, 2016.

Nerve ultrasound identifies abnormalities in the posterior interosseous nerve in patients with proximal radial neuropathies.

INTRODUCTION: The radial nerve and posterior interosseous nerve (PIN) are prone to injury at multiple sites. Electrodiagnostic (EDx) studies may only identify the most proximal lesion. Nerve ultrasound could augment EDx by visualizing additional pathology. METHODS: This investigation was a retrospective examination of ultrasound and EDx from 26 patients evaluated for posterior cord/radial/PIN lesions. RESULTS: Eighteen of 26 patients had abnormalities on EDx (15 radial, 2 PIN, 1 posterior cord). Ultrasound identified 15 of 18 (83%) of the EDx abnormalities and provided additional diagnostic information. In 6 of 15 (40%) patients with EDx evidence of radial neuropathy, ultrasound identified both radial nerve enlargement and additional, unsuspected PIN enlargement (53% to 339% enlarged vs. unaffected side). Ultrasound also identified: nerve (dis)continuity at the trauma site (n = 8); and nerve tumor (n = 2; 1 with normal EDx). CONCLUSION: In radial neuropathy, ultrasound often augments EDx studies and identifies a second lesion in the PIN. Further studies are required to determine the etiology and significance of this additional distal pathology.

Clinical trial readiness in non-ambulatory boys and men with duchenne muscular dystrophy: MDA-DMD network follow-up.

INTRODUCTION: Outcomes sensitive to change over time in non-ambulatory boys/men with Duchenne muscular dystrophy (DMD) are not well-established. METHODS: Subjects (n = 91; 16.8 ± 4.5 years old) were assessed at baseline and 6-month intervals for 2 years. We analyzed all subjects using an intent-to-treat model and a subset of stronger subjects with Brooke Scale score ≤4, using repeated measures. RESULTS: Eight patients (12-33 years old) died during the study. Sixty-six completed 12-month follow-up, and 51 completed 24-month follow-up. Those taking corticosteroids performed better at baseline, but rates of decline were similar. Forced vital capacity percent predicted (FVC% predicted) declined significantly only after 2 years. However, Brooke and Egen Klassifikation (EK) Scale scores, elbow flexion, and grip strength declined significantly over both 1 and 2 years. CONCLUSION: Brooke and EK Scale scores, elbow flexion, and grip strength were outcomes most responsive to change. FVC% predicted was responsive to change over 2 years. Corticosteroids benefited non-ambulatory DMD subjects but did not affect decline rates of measures tested here. Muscle Nerve 54: 681-689, 2016.

Quantitative Ultrasound Assessment of Duchenne Muscular Dystrophy Using Edge Detection Analysis.

OBJECTIVES: The purpose of this study was to investigate the ability of quantitative ultrasound (US) using edge detection analysis to assess patients with Duchenne muscular dystrophy (DMD). METHODS: After Institutional Review Board approval, US examinations with fixed technical parameters were performed unilaterally in 6 muscles (biceps, deltoid, wrist flexors, quadriceps, medial gastrocnemius, and tibialis anterior) in 19 boys with DMD and 21 age-matched control participants. The muscles of interest were outlined by a tracing tool, and the upper third of the muscle was used for analysis. Edge detection values for each muscle were quantified by the Canny edge detection algorithm and then normalized to the number of edge pixels in the muscle region. The edge detection values were extracted at multiple sensitivity thresholds (0.01-0.99) to determine the optimal threshold for distinguishing DMD from normal. Area under the receiver operating curve values were generated for each muscle and averaged across the 6 muscles. RESULTS: The average age in the DMD group was 8.8 years (range, 3.0-14.3 years), and the average age in the control group was 8.7 years (range, 3.4-13.5 years). For edge detection, a Canny threshold of 0.05 provided the best discrimination between DMD and normal (area under the curve, 0.96; 95% confidence interval, 0.84-1.00). According to a Mann-Whitney test, edge detection values were significantly different between DMD and controls (P < .0001). CONCLUSIONS: Quantitative US imaging using edge detection can distinguish patients with DMD from healthy controls at low Canny thresholds, at which discrimination of small structures is best. Edge detection by itself or in combination with other tests can potentially serve as a useful biomarker of disease progression and effectiveness of therapy in muscle disorders.

Muscle ultrasound quantifies disease progression over time in infants and young boys with duchenne muscular dystrophy.

INTRODUCTION: Quantitative muscle ultrasound (QUS) in boys with Duchenne muscular dystrophy (DMD) shows increased echointensity as muscle is replaced with fat and fibrosis. Studies of quantitative ultrasound in infants/young boys with DMD over time have not been reported. METHODS: We used calibrated muscle backscatter (cMB), a reproducible measure of ultrasound echointensity, to quantify muscle pathology in 5 young boys with DMD (ages 0.5-2.8 years) over 17-29 months. We compared the results with repeated assessments of function (n = 4) and with muscle ultrasound images from a cross-section of 6 male controls (0.6-3.1 years). RESULTS: cMB in boys with DMD increased (worsened) over time (P < 0.001), whereas function improved. After age 2 years, cMB in most (4 of 5) boys with DMD was higher than in any control. CONCLUSIONS: QUS measures disease progression in young boys with DMD despite functional improvements. QUS could be employed as an outcome measure for serial assessment of young boys with DMD.