The floppy infant: evaluation of hypotonia

Nemaline Myopathy in a Hypotonic Neonate: Diagnostic Approach for Early Detection and Management

Neonatal hypotonia presents with low muscle tone and an array of symptoms that vary depending on the etiology. The differential diagnosis for this condition is complex. It is crucial to exclude life-threatening causes before following a diagnostic algorithm and performing additional tests. Given the wide range of clinical symptoms and etiologies for neonatal hypotonia, rapid genetic testing has the potential to expedite diagnosis, reduce invasive testing such as muscle biopsy, reduce hospital stays, and guide condition management.  A four-week-old girl was admitted to the emergency department (ED) with a one-day history of lethargy, poor feeding, congestion, cough, and hypoxemia. Given positive rhino-enterovirus testing and high inflammatory markers, antibiotics were administered. Imaging, venous blood gas, and blood cultures were negative, and the patient was admitted to the pediatric intensive care unit (PICU) for hypoxemia. After speech-language pathology (SLP) and occupational therapy (OT) evaluation, weak orofacial muscles and feeding issues resulted in a nasogastric tube placement. A swallow study revealed decreased pharyngeal contraction and post-swallow liquid residue. Laryngoscopy showed mild laryngomalacia and dysphagia with aspiration. Genetic testing identified an ACTA1 mutation and confirmed nemaline myopathy (NM). The patient's oxygen levels dropped further during sleep, resulting in diagnoses of severe obstructive and moderate-severe central sleep apnea. Treatment included oxygen therapy, SLP, physical therapy, albuterol, and cough assists. After discharge, the patient was frequently re-admitted with chronic respiratory failure and bronchiolitis and later had gastrostomy and tracheostomy tubes inserted.  This specific case highlights the importance of implementing a diagnostic algorithm for neonatal hypotonia. It is also important for physicians, especially emergency medicine (EM) providers, to first exclude infection, sepsis, and cardiac and respiratory organ failure before looking into other tests. Then, physicians should evaluate for more rare etiologies. In this patient's case, the hypotonia was due to a rare genetic disease, nemaline myopathy, and a multidisciplinary approach was used for this patient's care.

Developmentally delayed children with different muscle tone have different muscle activity and acceleration during sit-to-stand

Developmental delays cover a wide range, with different movement characteristics occurring depending on differences in muscle tone. We aimed to investigate muscle activity and acceleration during sit-to-stand in developmentally delayed (DD) children with different muscle tones. Forty participants were divided into three groups: typically developing (TD) children (n=18), DD children with hypertonia (n=12), and DD children with hypotonia (n=10). Electromyography was used to measure muscle activity and BTS G-Walk was used to measure acceleration. As a result, the activities of the rectus abdominal muscle and quadriceps muscle were lower in DD children with hypertonia than in TD children (P<0.05). The activity of the tibialis anterior muscle was higher in DD children with hypotonia than in TD children (P<0.05). The trunk angle was greater in DD children with hypotonia than in TD children (P<0.05), and vertical acceleration was lower in DD children with hypertonia than in TD children (P<0.05). Based on these differences, we will be able to provide intervention programs appropriate for the characteristics of DD children with different muscle tone.

High-Yield, Case-Based, Interactive Workshop on Telehealth and Teleneurology With Pediatric Resident Physicians

Introduction

Increasing prevalence of neurologic disorders with an aging global population and limited availability of neurologists may lead to worse patient outcomes. As a result of the COVID-19 pandemic, telehealth services surged, and despite easing public health measures, the demand has remained. Telehealth technology has the potential to close the physical gaps in expanding the reach of care. This academic half-day workshop sought to provide a learning opportunity in response to these concerns.

Methods

The workshop consisted of small- and large-group case discussions among pediatric resident physicians (PGY 1-PGY 3) moderated by two child neurology faculty physicians over Zoom. Participants received a learner document with prereading articles and questions for each case. PowerPoint presentations with video demonstrations were used to introduce the cases and guide discussions.

Results

Of the 25 attendees, 14 (56% response rate) answered a nonmandatory postsession survey. Eighty-six percent of the respondents were very or extremely satisfied with the content covered and were similarly satisfied with the effectiveness of content delivery. Seventy-nine percent of the respondents found the content helpful or very helpful in preparation for the board, and 93% anticipated applying the content covered occasionally or frequently in their clinical practice.

Discussion

Small-group discussions with video demonstrations are helpful in increasing proficiency with telehealth technology and in examining board-relevant cases on pediatric patients. There is strong interest in subsequent telehealth half-day workshops that incorporate teaching through group discussions on relevant patient case scenarios.

Griscelli syndrome type 1: a novel pathogenic variant, and review of literature

Griscelli syndrome type 1 (GS1) is a rare inherited autosomal recessive disease caused by a deleterious variant in the MYO5A gene and characterized by general hypopigmentation, neurological symptoms, motor disability, hypotonia, and vision abnormality. Only nine pathogenic variants in the MYO5A gene have been confirmed in association with the GS1. All of the reported pathogenic variants are truncating. Herein, two siblings from a consanguineous Iranian family with abnormal pigmentation and neurological symptoms were referred for genetic counseling. Whole-exome sequencing (WES) revealed a novel homozygous truncating variant c.1633_1634delAA (p.Asn545Glnfs*10) in the MYO5A gene, which was completely co-segregated with the phenotype in all affected and unaffected family members. Computational analysis and protein modeling demonstrated the deleterious effects of this variant on the structure and function of the protein. The variant, according to ACMG guidelines, was classified as pathogenic. Besides the novelty of the identified variant, our patients manifested more severe clinical symptoms and presented distal hyperlaxity in all four limbs, which was a new finding. In conclusion, we expanded the mutational and phenotypic spectrum of the GS1. Moreover, by studying clinical manifestations in all molecularly confirmed reported cases, provided a comprehensive overview of clinical presentation, and attempted to find a genotype-phenotype correlation.

Abdominal and lower extremity muscles activity and thickness in typically developing children and children with developmental delay

We investigated abdominal and lower extremity muscle activity and thickness in typically developing children and children with developmental delays. A total of 35 children participated: typically developing peers (n=13), children with hypotonia (n=10), and children with spasticity (n=12). Muscle activity and thickness were measured at rest and during activity. Electromyography was used to measure abdominal and lower extremity muscle activities, and abdominal muscle thickness was measured using ultrasonography. There was a significant difference between the groups in the activity of the rectus abdominis and quadriceps muscles at rest and during activity (P<0.05). There was a significant difference between the groups in the thickness of the external oblique and transversus abdominis muscles during activity (P<0.05). There was a significant difference between the groups in the thickness of the external oblique and internal oblique muscles in the sitting position (P<0.05). Therefore, the characteristics of muscle tone should be considered when applying interventions to children with developmental delay.

Vojta Approach Affects Neck Stability and Static Balance in Sitting Position of Children With Hypotonia

Purpose

In this study, the effect of the Vojta approach on neck stability and static balance in children with hypotonia was studied.

Methods

Seventeen children with hypotonia were randomly divided into the Vojta approach group (n=9) and the general physical therapy group (n=8). Each group was applied intervention for 30 minutes per session, 3 times a week, for a total of 4 weeks. Ultrasonography was used to measure deep neck flexor muscle thickness, craniovertebral angle (CVA) to measure neck alignment along the spine segment, and Balancia software program to measure static balance.

Results

In the Vojta approach group, the deep neck flexor muscle thickness was significantly increased (P<0.05), and the CVA was significantly improved (P<0.05). In addition, path area among static balance was significantly improved (P<0.05).

Conclusions

The Vojta approach can be suggested as an effective intervention method for improving neck stability and static balance in children with hypotonia.

Combination Therapy with Nusinersen and Onasemnogene Abeparvovec-xioi in Spinal Muscular Atrophy Type I

Background: Spinal muscular atrophy (SMA) is a neuromuscular progressive disease, characterized by decreased amounts of survival motor neuron (SMN) protein, due to an autosomal recessive genetic defect. Despite recent research, there is still no cure. Nusinersen, an antisense oligonucleotide acting on the SMN2 gene, is intrathecally administered all life long, while onasemnogene abeparvovec-xioi, a gene therapy, is administered intravenously only once. Both therapies have proven efficacy, with best outcomes obtained when administered presymptomatically. In recent years, disease-modifying therapies such as nusinersen and onasemnogene abeparvovec-xioi have changed the natural history of SMA. Methods: We observed seven SMA type I patients, who received both therapies. We compared their motor function trajectories, ventilation hours and cough assist sessions to a control group of patients who received one therapy, in order to investigate whether combination therapy may be more effective than a single intervention alone. Results: Patients who received both therapies, compared to the monotherapy cohort, had the same motor function trajectory. Moreover, it was observed that the evolution of motor function was better in the 6 months following the first therapy than in the first 6 months after adding the second treatment. Conclusions: Our results suggest that early treatment is more important than combined therapy.

WWOX-Related Neurodevelopmental Disorders: Models and Future Perspectives

The WW domain-containing oxidoreductase (WWOX) gene was originally discovered as a putative tumor suppressor spanning the common fragile site FRA16D, but as time has progressed the extent of its pleiotropic function has become apparent. At present, WWOX is a major source of interest in the context of neurological disorders, and more specifically developmental and epileptic encephalopathies (DEEs). This review article aims to introduce the many model systems used through the years to study its function and roles in neuropathies. Similarities and fundamental differences between rodent and human models are discussed. Finally, future perspectives and promising research avenues are suggested.

Autism-associated SHANK3 mutations impair maturation of neuromuscular junctions and striated muscles

Heterozygous mutations of the gene encoding the postsynaptic protein SHANK3 are associated with syndromic forms of autism spectrum disorders (ASDs). One of the earliest clinical symptoms in SHANK3-associated ASD is neonatal skeletal muscle hypotonia. This symptom can be critical for the early diagnosis of affected children; however, the mechanism mediating hypotonia in ASD is not completely understood. Here, we used a combination of patient-derived human induced pluripotent stem cells (hiPSCs), Shank3Δ11(-/-) mice, and Phelan-McDermid syndrome (PMDS) muscle biopsies from patients of different ages to analyze the role of SHANK3 on motor unit development. Our results suggest that the hypotonia in SHANK3 deficiency might be caused by dysfunctions in all elements of the voluntary motor system: motoneurons, neuromuscular junctions (NMJs), and striated muscles. We found that SHANK3 localizes in Z-discs in the skeletal muscle sarcomere and co-immunoprecipitates with α-ACTININ. SHANK3 deficiency lead to shortened Z-discs and severe impairment of acetylcholine receptor clustering in hiPSC-derived myotubes and in muscle from Shank3Δ11(-/-) mice and patients with PMDS, indicating a crucial role for SHANK3 in the maturation of NMJs and striated muscle. Functional motor defects in Shank3Δ11(-/-) mice could be rescued with the troponin activator Tirasemtiv that sensitizes muscle fibers to calcium. Our observations give insight into the function of SHANK3 besides the central nervous system and imply potential treatment strategies for SHANK3-associated ASD.

Neurobehaviour of very preterm infants at term equivalent age is related to early childhood outcomes

AIM

To describe neurodevelopmental outcomes during early childhood among infants born very preterm and define the relationships between neurobehaviour of very preterm infants and neurodevelopmental outcomes at 4 years.

METHODS

Forty-eight infants born ≤32 weeks gestation had neurobehaviour assessed at term equivalent age using the NICU Network Neurobehavioral Scale (NNNS). Outcomes at 4 years were assessed with the Ages and Stages Questionnaire (ASQ-3), the Sensory Profile-Short Form (SF) and the Behavior Rating Inventory of Executive Function-Preschool version (BRIEF-P).

RESULTS

At 4 years, 23 (48%) children had at least one below average score on the ASQ-3, 15 (31%) had a below average total score on the Sensory Profile-SF, and 3 (6%) had an abnormal total score on the BRIEF-P. Children with lower fine motor scores at 4 years had poorer orientation (P = 0.03) and self-regulation (P =0.03), hypertonia (P = 0.01), and more sub-optimal reflexes (P = 0.02) as neonates. Children with lower gross motor scores at 4 years of age had more sub-optimal reflexes (P = 0.03) and lethargy (P = 0.046) as neonates. Children with tactile sensitivity at 4 years of age had poorer orientation (P = 0.01) and tolerance of handling (P = 0.03) as neonates. Children with decreased responsiveness at 4 years of age had low arousal (P = 0.02) as neonates, and those with poor auditory filtering at age 4 years had hypotonia (P = 0.03) as neonates.

CONCLUSION

Early neurobehaviour is related to neurodevelopmental outcome in early childhood.

The Weak Link: Hypotonia in Infancy and Autism Early Identification

Background: Presenting symptoms and age specific differential diagnosis of Autism Spectrum Disorder (ASD), determine the age of initial assessment and the age of a definite diagnosis. The AAP recommends screening all children for ASD at 18 and 24 months followed by a comprehensive evaluation for children with developmental concerns. More recently it has been recommended that the evaluation should be performed at a younger age, with a diagnosis being made as early as the beginning of the second year of life resulting in earlier intensive intervention. Objective: To assess early developmental milestones in a cohort of children diagnosed with Autism Spectrum Disorder (ASD) in order to find an objective and reliable early marker. We suggest that low muscle tone- hypotonia, is a sign that meets the above criteria of consistency and reliability and may be related to early diagnosis. Methods: We compared age distributions of ASD diagnosis in the presence of hypotonia in a dataset of 5,205 children diagnosed at Keshet Center. One thousand, one hundred eighty-two children (953 males) were diagnosed with ASD and compared to other developmental diagnoses. Within the ASD cohort we further analyzed for gender and pre-maturity differences. Results: In the presence of hypotonia, the mean age for ASD diagnosis was significantly lower (by 1.5 years for males and females) and this effect increased in children born at term as compared to pre-maturity. Conclusions: Hypotonia is a recognizable marker of ASD and may serve as a "red flag" to prompt earlier recognition and neurodevelopmental evaluation toward an autism diagnosis.

6q13q14.3 Microdeletion Syndrome with Severe Hypotonia and Facial Dysmorphism: Genotype–Phenotype Correlation

Hypotonia is a symptom of diminished tone of skeletal muscle and can be nongenetic or a part of genetic syndrome. Hypotonia, developmental delay, and facial dysmorphism are nonspecific findings observed in many genetic syndromes mostly in chromosomal microdeletion and duplication. Here we report a case with severe hypotonia and facial dysmorphism, diagnosed with deletion at 6q13q14.3 by array comparative genomic hybridization (CGH) at very early age. Recent genetic diagnostic technologies such as array CGH may enable clinicians to diagnose chromosomal abnormalities earlier and provide appropriate medical management

Effects of Microcurrent on Oxygen Saturation by Controlling Rectus Abdominis Activity in Preterm Infant With Desaturation During Feeding: A Pilot Study

Objective: To determine whether a portable microcurrent therapy device (PMTD) of the rectus abdominis muscles is effective for treating desaturation during feeding in preterm infants and to evaluate the association between initial electrical activity of respiratory muscle and long-term development delay. Methods: Twenty preterm infants with desaturation during feeding were recruited. Respiratory muscle activity was quantified by calculating the root mean square (RMS) of the electromyography. All preterm infants received a 30 min PMTD application to the rectus abdominis and diaphragm daily for 2 weeks. RMS of diaphragm and rectus abdominis, feeding volume, frequency of desaturation during feeding at baseline (pre-PMTD) and 1, 2 week post-PMTD were measured. The number of days it took to treat desaturation after PMTD was measured. A Denver developmental screening test was performed and infants were divided into 3 groups: (1) normal; (2) caution; and (3) delayed at 3months after PMTD. Results: The desaturation during feeding of all the preterm infants subsided after PMTD and the mean days took to treat desaturation was 25.4 ± 14.2 days. The RMS of diaphragm, rectus abdominis, and frequency of desaturation during feeding were significantly decreased and the feeding volume was significantly increased after PMTD (p < 0.01). The mean treatment duration for desaturation was negatively correlated with RMS of rectus abdominis at baseline and 1 week post-PMTD, respectively (Pearson's correlation coefficient = -0.461,-0.514, p-value = 0.047, 0.029). RMS of rectus abdominis of Group 3 is lower than that of group 1 and 2 (p < 0.01). Conclusions: This pilot study showed that the microcurrent therapy of rectus abdominis is an efficient therapy for the treatment of preterm infants with desaturation during feeding, especially preterm infants with higher activity of the rectus abdominis. In preterm infants with lower rectus abdominis activity, longer time is required to treat desaturation by microcurrent therapy and developmental delay is observed at months post-treatment.

Patterns of atypical muscle tone in the general infant population - Prevalence and associations with perinatal risk and neurodevelopmental status

BACKGROUND

Muscle tone is an indispensable element in motor development. Its assessment forms an integral part of the infant neurological examination. Knowledge on the prevalence of atypical tone in infancy is lacking.

AIM

To assess the prevalence of atypical muscle tone in infancy and of the most common atypical muscle tone patterns, and associations between atypical tone and perinatal risk and neurodevelopmental status.

STUDY DESIGN

Cross-sectional study.

SUBJECTS

1100 infants (585 boys; gestational age 39.4 weeks (27.3-42.4)), 6 weeks-12 months corrected age, representative of the Dutch population.

OUTCOME MEASURES

Muscle tone and neurodevelopmental status were assessed with the Standardized Infant NeuroDevelopmental Assessment (SINDA). Perinatal information was obtained by questionnaire and medical records. Univariable and multivariable statistics were applied.

RESULTS

Ninety-two infants (8%) had atypical muscle tone in 3-4 body parts (impaired pattern), while atypical muscle tone in 1-2 body parts was observed in 50%. Isolated leg hypotonia and isolated arm hypertonia were most common. Isolated arm hypertonia and the impaired pattern were most clearly but only moderately associated with perinatal risk. These patterns were also most clearly associated with lower neurological scores. Only the impaired pattern was associated with lower developmental scores.

CONCLUSION

Atypical muscle tone in one or two body parts is common in infancy and has in general little clinical significance. This finding corresponds to the well-known high prevalence of a typical but non-optimal neurological condition. Eight percent of infants show atypical muscle tone in 3-4 body parts. This clinically relevant pattern is associated with perinatal risk and less favourable neurodevelopmental status.

Effects of a Head Support on Children with Hypotonia in the Cervical Spine

Children with hypotonia of the muscles near the cervical spine have reduced head control and are unable to maintain an upright head posture. These children often use an external head support to hold their heads upright. With their head held in the proper position, they often develop more functional head movements. Previous studies have measured functional changes to subjects using the head support but have not studied the forces exerted on the head support. This study observes subjects with GMFCS Level V and their functional skills alongside the forces exerted on the head support over a 4-month period. A force sensor attached to the base of the head support was used to collect force data to compare with classroom observations of the child's functional performance by occupational and physical therapists. Subjects showed an increase of up to 67% in quadrants where they previously had ¡1% activity at the beginning of the study. Each subject had increased time exerting forces greater than the weight of the head in later weeks of data recording as well as increased peak forces magnitude. Studying the functional impacts of subjects using a head support with measured forces can highlight important aspects of skill development and progress towards milestones for children with hypotonia.Clinical Relevance- While using a head support, children with GMFCS Level V are able to maximize their head movement which helps them develop functional skills.

A newborn screening pilot study using methylation-sensitive high resolution melting on dried blood spots to detect Prader-Willi and Angelman syndromes

Prader-Willi (PWS) and Angelman (AS) syndromes are two clinically distinct imprinted disorders characterized by genetic abnormalities at 15q11-q13. Early diagnosis of both syndromes provides improved treatment and accurate genetic counseling. Whole blood (WB) is the most common DNA source of many methodologies to detect PWS and AS, however, the need of WB makes a massive screening difficult in newborns due to economic and technical limitations. The aim of this study was to adapt a Methylation-sensitive High-Resolution Melting (MS-HRM) approach from dried blood spot (DBS) samples, assessing the different DNA isolation techniques and diagnostic performance. Over a 1-year period, we collected 125 DBS cards, of which 45 had already been diagnosed by MS-HRM (20 PWS, 1 AS, and 24 healthy individuals). We tested three different DBS-DNA extraction techniques assessing the DNA concentration and quality, followed by MS-HRM and statistical comparison. Each DBS-DNA extraction method was capable of accuracy in detecting all PWS and AS individuals. However, the efficiency to detect healthy individuals varied according to methodology. In our experience, DNA extracted from DBS analyzed by the MS-HRM methodology provides an accurate approach for genetic screening of imprinting related disorders in newborns, offering several benefits compared to traditional whole blood methods.

Utility of metabolic screening in neurological presentations of infancy

Background

The first‐line use of specialized metabolic screening laboratories in the investigation of hypotonia and/or developmental delay remains a standard practice despite lack of supporting evidence. Our study aimed to address the utility of such testing by determining the proportion of patients whose diagnosis was directly supported by metabolic screening.

Methods

We performed a retrospective chart review study of 164 patients under age one who had screening metabolic laboratory testing done within the time period of one calendar year.

Results

Of patients screened, 9/164 (5.5%) had diagnoses supported by metabolic testing (two with nonketotic hyperglycinemia, three with ornithine transcarbamylase deficiency, one with propionic acidemia, one with a congenital disorder of glycosylation, one with D‐bifunctional protein deficiency, and one with GM1 Gangliosidosis). Of patients specifically evaluated for hypotonia and/or developmental delay, 5/79 (6.3%) were diagnosed with the aid of metabolic testing. All patients with positive screens presented with acute decompensation. Outside of this subgroup of high‐risk patients, no patients were diagnosed using metabolic testing. Screening laboratories were also ineffective in an outpatient setting, identifying only one of the seven outpatients who was ultimately diagnosed with an inborn error of metabolism.

Conclusions

These findings demonstrate that the yield of specialized metabolic screening testing is extremely low in infants with hypotonia and/or developmental delay, approaching zero outside of the specific setting of clinical decompensation or multi‐system involvement. Furthermore, many outpatient cases of IEM are not identified by screening studies. This information will help guide the diagnostic evaluation of hypotonia and/or global developmental delay.

Muscle weakness and impaired motor coordination in hyperpolarization-activated cyclic nucleotide-gated potassium channel 1-deficient rats

Hyperpolarization-activated cyclic nucleotide-gated potassium channel 1 (HCN1) contribute to spontaneous rhythmic activity in different tissues, including the heart and brain. Deficiency in HCN1 function is associated with sick sinus syndrome in mice and epilepsy in humans. We recently developed Hcn1-deficient rats and found that they exhibit absence epilepsy. While rearing Hcn1-deficient rats, we noticed loose muscle tension and abnormal gait. We therefore evaluated the muscle strength and motor functions of Hcn1-deficient rats. When subjected to the wire hang test, Hcn1-deficient rats fell down more easily than control F344 rats. Grip strength of Hcn1-deficient rats was significantly smaller than F344 rats. In the inclined plane test, they exhibited a smaller maximum angle. In the rotarod test, the latency to fall was shorter for Hcn1-deficient rats than F344 rats. In the footprint analysis, Hcn1-deficient rats exhibited smaller step length and wider step width than F344 rats. Instead of poor motor coordination ability and muscle weakness, Hcn1-deficient rats exhibited normal electromyograms, muscle histology, and deep tendon reflex. These findings suggest that HCN1 channels contribute to motor coordination and muscle strength, and that the muscle weakness of Hcn1-deficient rats results from the involvement not of the peripheral but of the central nervous system.

Hypotonia and Lethargy in a Two-Day-Old Male Infant

A 2-day old term male infant was found to be hypotonic and minimally reactive during routine nursing care in the newborn nursery. At 40 hours of life, he was hypoglycemic and had intermittent desaturations to 70%. His mother had an unremarkable pregnancy and spontaneous vaginal delivery. The mother's prenatal serology results were negative for infectious risk factors. Apgar scores were 9 at 1 and 5 minutes of life. On day 1 of life, he fed, stooled, and voided well. Our expert panel discusses the differential diagnosis of hypotonia in a neonate, offers diagnostic and management recommendations, and discusses the final diagnosis.

Myotonic Dystrophy and Developmental Regulation of RNA Processing

Myotonic dystrophy (DM) is a multisystemic disorder caused by microsatellite expansion mutations in two unrelated genes leading to similar, yet distinct, diseases. DM disease presentation is highly variable and distinguished by differences in age-of-onset and symptom severity. In the most severe form, DM presents with congenital onset and profound developmental defects. At the molecular level, DM pathogenesis is characterized by a toxic RNA gain-of-function mechanism that involves the transcription of noncoding microsatellite expansions. These mutant RNAs disrupt key cellular pathways, including RNA processing, localization, and translation. In DM, these toxic RNA effects are predominantly mediated through the modulation of the muscleblind-like and CUGBP and ETR-3-like factor families of RNA binding proteins (RBPs). Dysfunction of these RBPs results in widespread RNA processing defects culminating in the expression of developmentally inappropriate protein isoforms in adult tissues. The tissue that is the focus of this review, skeletal muscle, is particularly sensitive to mutant RNA-responsive perturbations, as patients display a variety of developmental, structural, and functional defects in muscle. Here, we provide a comprehensive overview of DM1 and DM2 clinical presentation and pathology as well as the underlying cellular and molecular defects associated with DM disease onset and progression. Additionally, fundamental aspects of skeletal muscle development altered in DM are highlighted together with ongoing and potential therapeutic avenues to treat this muscular dystrophy. © 2018 American Physiological Society. Compr Physiol 8:509-553, 2018.

Interventions to improve sensory and motor outcomes for young children with central hypotonia: A systematic review

OBJECTIVE

To evaluate evidence supporting physical and occupational therapy interventions used to improve sensory and motor outcomes for children 0-6 years with central hypotonia.

METHODS

Four electronic databases were searched from 1996 to March 2017. Level of evidence and study conduct was evaluated using American Academy of Cerebral Palsy and Developmental Medicine criteria. Traffic lighting classification identified interventions that were green (proven effective), yellow (possibly effective) or red (proven ineffective or contraindicated).

RESULTS

Thirty-seven articles were included. Nine studies measured orthotic interventions while four distinct studies published over nine articles measured treadmill interventions. Remaining studies measured impact of compression garments, massage, motor and sensori-motor interventions, positioning and mobility interventions.

CONCLUSIONS

Green light evidence supports treadmill training (to promote ambulation and gait characteristics) and massage (to positively affect muscle tone, motor development and use of vision) for infants with Down syndrome. These interventions are considered Yellow (possibly effective) for other populations. Green light evidence supports impact of orthoses on foot alignment for ambulatory children with hypotonia, while impact on gait characteristics is Yellow light and motor development may be negatively impacted (Red light) in pre-ambulatory children. All other interventions rated Yellow (possibly effective) and therapists should monitor using sensitive outcome measures.

Malignant Hyperthermia Susceptibility and Related Diseases

This review identifies disease states associated with malignant hyperthermia susceptibility based on genotypic and phenotypic findings, and a framework is established for clinicians to identify a potentially malignant hyperthermia–susceptible patient.

Gross Motor Outcomes After Dynamic Weight-Bearing in 2 Children With Trunk Hypotonia: A Case Series

INTRODUCTION

Children with trunk hypotonia may have limited ability to maintain an upright weight-bearing position, resulting in decreased postural control and a delay in achieving gross motor milestones.

PURPOSE

The purpose of this case series is to report the effect of a home-based dynamic standing program on postural control and gross motor activity in 2 children with trunk hypotonia.

DESCRIPTIONS

Child 1 (aged 24 months, Gross Motor Function Classification Scale Level IV) and Child 2 (aged 21 months, Gross Motor Function Classification Scale Level V) participated in a standing program using the Upsee harness at home 3 days per week for 12 weeks.

OUTCOMES

Both children improved their gross motor function, and Child 1 demonstrated improved trunk control in sitting.

WHAT THIS CASE ADDS

The use of the Upsee harness was an effective intervention for these children with trunk hypotonia to achieve weight-bearing and improve gross motor abilities.

Congenital muscular dystrophy: from muscle to brain

Congenital muscular dystrophies (CMDs) are a wide group of muscular disorders that manifest with very early onset of muscular weakness, sometime associated to severe brain involvement.The histologic pattern of muscle anomalies is typical of dystrophic lesions but quite variable depending on the different stages and on the severity of the disorder.Recent classification of CMDs have been reported most of which based on the combination of clinical, biochemical, molecular and genetic findings, but genotype/phenotype correlation are in constant progression due to more diffuse utilization of the molecular analysis.In this article, the Authors report on CMDs belonging to the group of dystroglycanopathies and in particular on the most severe forms represented by the Fukuyama CMD, Muscle-Eye-Brain disease and Walker Walburg syndrome.Clinical diagnosis of infantile hypotonia is particularly difficult considering the different etiologic factors causing the lesions, the difficulty in localizing the involved CNS area (central vs. peripheral) and the limited role of the diagnostic procedures at this early age.The diagnostic evaluation is not easy mainly in differentiating the various types of CMDs, and represents a challenge for the neonatologists and pediatricians. Suggestions are reported on the way to reach a correct diagnosis with the appropriate use of the diagnostic means.

Next-generation sequencing-based molecular diagnosis of neonatal hypotonia in Chinese Population

Neonatal hypotonia is extremely challenging to diagnose because numerous disorders present similar clinical manifestations. Two panels for diagnosing neonatal hypotonia were developed, which enriches 35 genes corresponding to 61 neonatal hypotonia-related disorders. A cohort of 214 neonates with hypotonia was recruited from 2012 to 2014 in China for this study. Of these subjects, twenty-eight neonates with hypotonia were eliminated according to exclusion criteria and 97 were confirmed using traditional detection methods. The clinical diagnoses of the remaining 89 neonates with hypotonia were approached by targeted next-generation sequencing (NGS). Among the 89 tested neonates, 25 potentially pathogenic variants in nine genes (RYR1, MECP2, MUT, CDKL5, MPZ, PMM2, MTM1, LAMA2 and DMPK) were identified in 22 patients. Six of these pathogenic variants were novel. Of the 186 neonates with hypotonia, we identified the genetic causes for 117 neonates by the traditional detection methods and targeted NGS, achieving a high solving rate of 62.9%. In addition, we found seven neonates with RETT syndrome carrying five mutations, thus expanding the mutation profiles in Chinese neonates with hypotonia. Our study highlights the utility of comprehensive molecular genetic testing, which provides the advantage of speed and diagnostic specificity without invasive procedures.

Relationship Between Central Hypotonia and Motor Development in Infants Attending a High-Risk Neonatal Neurology Clinic

PURPOSE

To study the relationship between central hypotonia and motor development, and to determine the relative contribution of nuchal, truncal, and appendicular hypotonia domains to motor development.

METHODS

Appendicular, nuchal, and truncal tones of high-risk infants were assessed, as was their psychomotor developmental index (PDI). Infants with peripheral hypotonia were excluded.

RESULTS

We included 164 infants (mean age 9.6 ± 4 months), 36 with normal tone in all 3 domains and 128 with central hypotonia. Twenty-six of the latter had hypotonia in 1 domain and 102 had multiple combinations of 3 domains. Hypotonia domains were distributed as follows: truncal (n = 115), appendicular (n = 93), and nuchal (n = 70). Each domain was significantly associated with PDI scores (P < .001) but not with a later diagnosis of cerebral palsy. On linear regression, nuchal hypotonia had the strongest contribution to PDI scores (β = -0.6 [nuchal], -0.45 [appendicular], and -0.4 [truncal], P < .001).

CONCLUSIONS

Central hypotonia, especially nuchal tone, is associated with lowered motor development scores.

ADCY5-related dyskinesia: Broader spectrum and genotype-phenotype correlations

OBJECTIVE

To investigate the clinical spectrum and distinguishing features of adenylate cyclase 5 (ADCY5)-related dyskinesia and genotype-phenotype relationship.

METHODS

We analyzed ADCY5 in patients with choreiform or dystonic movements by exome or targeted sequencing. Suspected mosaicism was confirmed by allele-specific amplification. We evaluated clinical features in our 50 new and previously reported cases.

RESULTS

We identified 3 new families and 12 new sporadic cases with ADCY5 mutations. These mutations cause a mixed hyperkinetic disorder that includes dystonia, chorea, and myoclonus, often with facial involvement. The movements are sometimes painful and show episodic worsening on a fluctuating background. Many patients have axial hypotonia. In 2 unrelated families, a p.A726T mutation in the first cytoplasmic domain (C1) causes a relatively mild disorder of prominent facial and hand dystonia and chorea. Mutations p.R418W or p.R418Q in C1, de novo in 13 individuals and inherited in 1, produce a moderate to severe disorder with axial hypotonia, limb hypertonia, paroxysmal nocturnal or diurnal dyskinesia, chorea, myoclonus, and intermittent facial dyskinesia. Somatic mosaicism is usually associated with a less severe phenotype. In one family, a p.M1029K mutation in the C2 domain causes severe dystonia, hypotonia, and chorea. The progenitor, whose childhood-onset episodic movement disorder almost disappeared in adulthood, was mosaic for the mutation.

CONCLUSIONS

ADCY5-related dyskinesia is a childhood-onset disorder with a wide range of hyperkinetic abnormal movements. Genotype-specific correlations and mosaicism play important roles in the phenotypic variability. Recurrent mutations suggest particular functional importance of residues 418 and 726 in disease pathogenesis.

A pilot study for evaluation of hypotonia in children with neurofibromatosis type 1

There are currently no objective criteria to evaluate pediatric hypotonia. The purpose of this pilot study was to identify diagnostic criteria for assessing hypotonia in children with neurofibromatosis type 1. Fifty-five subjects between the ages of 1 and 7 years with a diagnosis of neurofibromatosis type 1 were evaluated. A physical therapist recorded a subjective tone assessment and objective tone metrics, including ankle dorsiflexion, knee extension, hip abduction, triceps fat percentage, grip strength, and head lag during a pull-to-sit test. Multivariate logistic regression analysis showed the presence of head lag paired with increased hip range of motion was a significant predictor of hypotonia. The presence of head lag on a pull-to-sit test paired with increased hip range of motion is an accurate predictor of hypotonia in children with neurofibromatosis type 1. These objective measures should be prospectively evaluated in other pediatric populations for their ability to predict hypotonia.

Factors associated with feeding difficulties in the very preterm infant

AIM

To investigate early medical and family factors associated with later feeding risk in preterm infants.

METHODS

For this longitudinal study, 136 infants born ≤30 weeks gestation were enrolled. Medical and social background factors were assessed at term equivalent age. Infants underwent magnetic resonance imaging, neurobehavioral evaluation and feeding assessment. Parent involvement in the neonatal intensive care unit was tracked, and maternal mental health was assessed at neonatal intensive care unit discharge. At age 2 years, feeding outcome was assessed using the Eating Subscale of the Infant-Toddler Social Emotional Assessment (n = 80). Associations between feeding problems at age 2 years and (i) early medical factors, (ii) neurobehavioral functioning and feeding at term equivalent age, (iii) cerebral structure and (iv) maternal mental health were investigated using regression.

RESULTS

Eighteen (23%) children had feeding problems at age 2 years. Feeding problems were associated with early hypotonia (p = 0.03; β = 0.29) and lower socio-economic status (p = 0.046; β = -0.22). No associations were observed between early medical factors, early feeding performance, cerebral structure alterations or maternal well-being and feeding outcome.

CONCLUSION

Early hypotonia may disrupt the development of oral-motor skills. Hypotonia and poor feeding also may share a common aetiology. Associations with lower socio-economic status highlight the potential influence of family background factors in feeding problems in the preterm infant.

Genetic evaluation of the floppy infant

Hypotonia in infants in the first year of life is a common diagnostic and management challenge for pediatricians and neonatologists. Several published clinical studies have shown that a substantial proportion of cases are accounted for by genetic disorders. Rapid advances in biotechnology, bioinformatics, and molecular genetic testing have made it possible to offer specific genetic diagnoses in a timely manner. The value of clinical examination in the localization of hypotonia within the nervous system as the first step towards a diagnosis cannot be overemphasized. Due importance should be given to specific features on examination and in the selection of appropriate laboratory tests to minimize laboratory costs. Inborn errors of metabolism, although infrequently encountered, are of importance. Based on clinical evidence from published studies, an algorithm is suggested that would incorporate the clinical features and testing modalities in providing a high diagnostic yield for the clinician.