Genetic evaluation of the floppy infant

The Approach to a Child with Dysmorphic Features: What the Pediatrician Should Know

The advancement of genetic knowledge and the discovery of an increasing number of genetic disorders has made the role of the geneticist progressively more complex and fundamental. However, most genetic disorders present during childhood; thus, their early recognition is a challenge for the pediatrician, who will be also involved in the follow-up of these children, often establishing a close relationship with them and their families and becoming a referral figure. In this review, we aim to provide the pediatrician with a general knowledge of the approach to treating a child with a genetic syndrome associated with dysmorphic features. We will discuss the red flags, the most common manifestations, the analytic collection of the family and personal medical history, and the signs that should alert the pediatrician during the physical examination. We will offer an overview of the physical malformations most commonly associated with genetic defects and the way to describe dysmorphic facial features. We will provide hints about some tools that can support the pediatrician in clinical practice and that also represent a useful educational resource, either online or through apps downloaded on a smartphone. Eventually, we will offer an overview of genetic testing, the ethical considerations, the consequences of incidental findings, and the main indications and limitations of the principal technologies.

Identifying and Evaluating Young Children with Developmental Central Hypotonia: An Overview of Systematic Reviews and Tools

Children with developmental central hypotonia have reduced muscle tone secondary to non-progressive damage to the brain or brainstem. Children may have transient delays, mild or global functional impairments, and the lack of a clear understanding of this diagnosis makes evaluating appropriate interventions challenging. This overview aimed to systematically describe the best available evidence for tools to identify and evaluate children with developmental central hypotonia aged 2 months to 6 years. A systematic review of systematic reviews or syntheses was conducted with electronic searches in PubMed, Medline, CINAHL, Scopus, Cochrane Database of Systematic Reviews, Google Scholar, and PEDro and supplemented with hand-searching. Methodological quality and risk-of-bias were evaluated, and included reviews and tools were compared and contrasted. Three systematic reviews, an evidence-based clinical assessment algorithm, three measurement protocols, and two additional measurement tools were identified. For children aged 2 months to 2 years, the Hammersmith Infant Neurological Examination has the strongest measurement properties and contains a subset of items that may be useful for quantifying the severity of hypotonia. For children aged 2-6 years, a clinical algorithm and individual tools provide guidance. Further research is required to develop and validate all evaluative tools for children with developmental central hypotonia.

Hypotonia: Is It a Clear Term and an Objective Diagnosis? An Exploratory Systematic Review

BACKGROUND

Hypotonia is considered a determinant factor in multiple developmental disorders and is associated with various characteristics and morbidities. It is necessary to perform a systematic review to know which characteristics are described as associated with hypotonia in children and which methods are used for its diagnosis.

METHODS

Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines were used to develop the systematic review protocol. A search of databases (Pubmed, Cochrane, Web of Knowledge, among others) was performed in May 2021 to identify relevant studies. Those describing characteristics or tests of hypotonia assessment were included, excluding those that exclusively addressed peripheral hypotonia. Two reviewers evaluated the articles and collected the data in a table, noting the authors, date of publication, type of study, and characteristics or tests described in relation to hypotonia. The quality of the studies was also assessed, and data were extracted.

RESULTS

A total of 8778 studies were identified and analyzed, of which 45 met the inclusion criteria. Fifty-three characteristics associated with hypotonia and tests used for its evaluation were located, with pull to sit and vertical suspension being the most frequently referenced.

CONCLUSIONS

The characteristics associated with hypotonia, more highly debated by authors are muscle strength, hypermobility, or the maintenance of antigravity postures. The most used test in the diagnosis of hypotonia is observation, followed by the pull-to-sit test, and adoption of frog posture. A unanimous understanding of the term hypotonia would favor further research.

Investigating the Genetic Etiology of Pediatric Patients with Peripheral Hypotonia Using the Next-Generation Sequencing Method

Background  Hypotonia occurs as a result of neurological dysfunction in the brain, brainstem, spinal cord, motor neurons, anterior horn cells, peripheral nerves, and muscles. Although the genotype–phenotype correlation can be established in 15 to 30% of patients, it is difficult to obtain a correlation in most cases.

Aims  This study was aimed to investigate the genetic etiology in cases of peripheral hypotonia that could not be diagnosed using conventional methods.

Methods  A total of 18 pediatric patients with peripheral hypotonia were included. They were referred to our genetic disorders diagnosis center from the Pediatric Neurology Department with a prediagnosis of hypotonia. A custom designed multigene panel, including ACTA1 , CCDC78 , DYNC1H1 , GARS , RYR1 , COL6A1 , COL6A2 , COL6A3 , FKRP , FKTN , IGHMBP2 , LMNA , LAMA2 , LARGE1 , MTM1 , NEM , POMGnT1 , POMT1 , POMT2 , and SEPN1 , was used for genetic analysis using next-generation sequencing (NGS).

Results  In our study, we found 13 variants including pathogenic (two variants in LAMA2) and likely pathogenic variants (three variants in RYR1 and POMGnT1) and variants of uncertain clinical significance (eight variants in RYR1, COL6A3, COL6A2, POMGnT1 and POMT1) in 11 (61%) out of 18 patients. In one of our patients, a homozygous, likely pathogenic c.1649G > A, p.(Ser550Asn) variant was defined in the POMGnT1 gene which was associated with a muscle–eye–brain disease phenotype.

Conclusion  The contribution of an in-house designed gene panel in the etiology of peripheral hypotonia with a clinical diagnosis was 5.5%. An important contribution with the clinical diagnosis can be made using the targeted multigene panels in larger samples.

Multicenter Consensus Approach to Evaluation of Neonatal Hypotonia in the Genomic Era: A Review

Importance

Infants with hypotonia can present with a variety of potentially severe clinical signs and symptoms and often require invasive testing and multiple procedures. The wide range of clinical presentations and potential etiologies leaves diagnosis and prognosis uncertain, underscoring the need for rapid elucidation of the underlying genetic cause of disease.

Observations

The clinical application of exome sequencing or genome sequencing has dramatically improved the timely yield of diagnostic testing for neonatal hypotonia, with diagnostic rates of greater than 50% in academic neonatal intensive care units (NICUs) across Australia, Canada, the UK, and the US, which compose the International Precision Child Health Partnership (IPCHiP). A total of 74% (17 of 23) of patients had a change in clinical care in response to genetic diagnosis, including 2 patients who received targeted therapy. This narrative review discusses the common causes of neonatal hypotonia, the relative benefits and limitations of available testing modalities used in NICUs, and hypotonia management recommendations.

Conclusions and Relevance

This narrative review summarizes the causes of neonatal hypotonia and the benefits of prompt genetic diagnosis, including improved prognostication and identification of targeted treatments which can improve the short-term and long-term outcomes. Institutional resources can vary among different NICUs; as a result, consideration should be given to rule out a small number of relatively unique conditions for which rapid targeted genetic testing is available. Nevertheless, the consensus recommendation is to use rapid genome or exome sequencing as a first-line testing option for NICU patients with unexplained hypotonia. As part of the IPCHiP, this diagnostic experience will be collected in a central database with the goal of advancing knowledge of neonatal hypotonia and improving evidence-based practice.

A floppy infant without lingual frenulum and kyphoscoliosis: Ehlers Danlos syndrome case report

Background

Ehlers-Danlos syndrome (EDS) represents a group of connective tissue disorders characterized by the fragility of the soft connective tissues resulting in widespread skin, ligament, joint, blood vessel and internal organ involvement. The clinical spectrum is highly variable in terms of clinical features, complications, severity, biochemical characteristics and genes mutations.

The kyphoscoliotic type EDS (EDS VIA) is a rare variant of the disease, with an incidence of 1:100.000 live births. EDS VIA presents at birth as severe muscular hypotonia, early onset of progressive kyphoscoliosis, marked hyperelasticity and fragility of the skin with abnormal scarring, severe joint hypermobility, luxations and osteopenia without a tendency to fractures. This condition is due to a mutation in the PLOD1 gene, and less commonly in FKBP14 gene, which results in the erroneous development of collagen molecules with consequent mechanical instability of the affected tissue.

Case presentation

A female newborn, found to be floppy at birth, presented a remarkable physical examination for joint hypermobility, muscle weakness, hyperelastic skin, a slight curve of the spine, the absence of the inferior labial and lingual frenulum. Due to severe hypotonia, neuromuscular disorders such as Spinal Muscular Atrophy (SMA), genetic diseases such as Prader Willi syndrome (PWS), myopathies and connective tissue disorders were considered in the differential diagnosis. Targeted gene sequencing were performed for SMN1, PLOD1, FKBP14, COL6A1, COL6A2, COL6A3. The urinary lysyl and hydroxy-lysyl pyridinoline ratio was diagnostic before discovering the homozygous duplication in the PLOD1 gene, which confirmed kyphoscoliotic EDS diagnosis.

Conclusion

In front of a floppy infant, a large variety of disorders should be considered, including some connective diseases. The presence at the birth of kyphoscoliosis, associated with joint hypermobility and the absence of the lingual and lower lip frenulum, should suggest an EDS.

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.

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.

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.

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.

'Toning' up hypotonia assessment: A proposal and critique

Background

Clinical assessment of hypotonia is challenging due to the subjective nature of the initial clinical evaluation. This poses dilemmas for practitioners in gaining accuracy, given that the presentation of hypotonia can be either a non-threatening or malevolent sign. The research question posed was how clinical assessment can be improved, given the current contentions expressed in the scientific literature.

Objectives

This paper describes the development and critique of a clinical algorithm to aid the assessment of hypotonia.

Methods

An initial exploratory sequential phase, consisting of a systematic review, a survey amongst clinicians and a Delphi process, assisted in the development of the algorithm, which is presented within the framework of the International Classification of Functioning, Disability and Health. The ensuing critique followed a qualitative emergent–systematic focus group design with a purposive sample of 59 clinicians. Data were analysed using semantical content analysis and are presented thematically with analytical considerations.

Results

This study culminated in the development of an evidence-based clinical algorithm for practice. The qualitative critique of the algorithm considered aspects such as inadequacies, misconceptions and omissions; strengths; clinical use; resource implications; and recommendations.

Conclusions

The first prototype and critique of a clinical algorithm to assist the clinical assessment of hypotonia in children has been described. Barriers highlighted include aspects related to knowledge gaps of clinicians, issues around user-friendliness and formatting concerns. Strengths identified by the critique included aspects related to the evidence-based nature of the criteria within the algorithm, the suitability of the algorithm in being merged or extending current practice, the potential of the algorithm in aiding more accurate decision-making, the suitability of the algorithm across age groups and the logical flow. These findings provide a starting point towards ascertaining the clinical utility of the algorithm as an essential step towards evidence-based praxis.

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.

Expanding genotype/phenotype of neuromuscular diseases by comprehensive target capture/NGS

Objective:

To establish and evaluate the effectiveness of a comprehensive next-generation sequencing (NGS) approach to simultaneously analyze all genes known to be responsible for the most clinically and genetically heterogeneous neuromuscular diseases (NMDs) involving spinal motoneurons, neuromuscular junctions, nerves, and muscles.

Methods:

All coding exons and at least 20 bp of flanking intronic sequences of 236 genes causing NMDs were enriched by using SeqCap EZ solution-based capture and enrichment method followed by massively parallel sequencing on Illumina HiSeq2000.

Results:

The target gene capture/deep sequencing provides an average coverage of ∼1,000× per nucleotide. Thirty-five unrelated NMD families (38 patients) with clinical and/or muscle pathologic diagnoses but without identified causative genetic defects were analyzed. Deleterious mutations were found in 29 families (83%). Definitive causative mutations were identified in 21 families (60%) and likely diagnoses were established in 8 families (23%). Six families were left without diagnosis due to uncertainty in phenotype/genotype correlation and/or unidentified causative genes. Using this comprehensive panel, we not only identified mutations in expected genes but also expanded phenotype/genotype among different subcategories of NMDs.

Conclusions:

Target gene capture/deep sequencing approach can greatly improve the genetic diagnosis of NMDs. This study demonstrated the power of NGS in confirming and expanding clinical phenotypes/genotypes of the extremely heterogeneous NMDs. Confirmed molecular diagnoses of NMDs can assist in genetic counseling and carrier detection as well as guide therapeutic options for treatable disorders.

Development of an evidence-based clinical algorithm for practice in hypotonia assessment: a proposal

Background

Assessing muscle tone in children is essential during the neurological assessment and is often essential in ensuring a more accurate diagnosis for appropriate management. While there have been advances in child neurology, there remains much contention around the subjectivity of the clinical assessment of hypotonia, which is often the first step in the diagnostic process.

Objective

In response to this challenge, the objective of the study is to develop and validate a prototype of a decision making process in the form of a clinical algorithm that will guide clinicians during this assessment process.

Methods

Design research within a pragmatic stance will be employed in this study. Multi-phase stages of assessment, prototyping and evaluation will occur. These will include processes that include a systematic review, processes of reflection and action as well as validation methods. Given the mixed methods nature of this study, use of NVIVO or ATLAS-ti will be used in the analysis of qualitative data and SPSS for quantitative data.

Results

Initial results from the systematic review revealed a paucity of scientific literature that documented the objective assessment of hypotonia in children. The review identified the need for more studies with greater methodological rigor in order to determine best practice with respect to the methods used in the assessment of low muscle tone in the paediatric population.

Conclusions

It is envisaged that this proposal will contribute to a more accurate clinical diagnosis of children with low muscle tone in the absence of a gold standard. We anticipate that the use of this tool will ultimately assist clinicians towards moving to evidenced based practice whilst upholding best practice in the care of children with hypotonia.

Prevalence of Prader-Willi syndrome among infants with hypotonia

OBJECTIVE

To investigate the prevalence of Prader-Willi syndrome (PWS) in infants with hypotonia between the ages of 0 and 2 years.

STUDY DESIGN

Karyotyping studies were performed in all infants with hypotonia. The study group was composed of infants with hypotonia for whom the karyotyping was found to be normal. Fluorescence in situ hybridization and methylation analysis were performed simultaneously in the study group. Molecular studies for uniparental disomy were undertaken in the patients without deletions with an abnormal methylation pattern.

RESULTS

Sixty-five infants with hypotonia with a mean age of 8 months were enrolled. A deletion was detected in 6 patients by fluorescence in situ hybridization analysis. Only 1 patient had no deletion but had an abnormal methylation pattern. A maternal uniparental disomy was observed in this patient. PWS was diagnosed in 10.7 % (7/65) of the infants with hypotonia.

CONCLUSION

The prevalence of PWS syndrome is high among infants with hypotonia. PWS should be considered by pediatricians and neonatologists in the differential diagnosis of all newborns with hypotonia. Early diagnosis of PWS is important for the management of these patients.

Clinical decision making in hypotonia and gross motor delay: a case report of type 1 spinal muscular atrophy in an infant

BACKGROUND AND PURPOSE

Children often are referred for physical therapy with the diagnosis of hypotonia when the definitive cause of hypotonia is unknown. The purpose of this case report is to describe the clinical decision-making process using the Hypothesis-Oriented Algorithm for Clinicians II (HOAC II) for an infant with hypotonia and gross motor delay.

CASE DESCRIPTION

The patient was a 5-month-old infant who had been evaluated by a neurologist and then referred for physical therapy by his pediatrician. Physical therapist evaluation results and clinical observations of marked hypotonia, significant gross motor delay, tongue fasciculations, feeding difficulties, and respiratory abnormalities prompted necessary referral to specialists. Recognition of developmental, neurologic, and respiratory abnormalities facilitated clinical decision making for determining the appropriate physical therapy plan of care.

OUTCOMES

During the brief episode of physical therapy care, the patient was referred to a feeding specialist and diagnosed with pharyngeal-phase dysphasia and mild aspiration. Continued global weakness, signs and symptoms of type 1 spinal muscular atrophy (SMA), and concerns about increased work of breathing and respiratory compromise were discussed with the referring physician. After inconclusive laboratory testing for metabolic etiologies of hypotonia, a genetics consult was recommended and confirmed the diagnosis of type 1 SMA at 9 months of age.

DISCUSSION

Physical therapists use clinical decision making to determine whether to treat patients or to refer them to other medical professionals. Accurate and timely referral to appropriate specialists may assist families in obtaining a diagnosis for their child and guide necessary interventions. In the case of type 1 SMA, early diagnosis may affect outcomes and survival rate in this pediatric population.

Objective evaluation of muscle strength in infants with hypotonia and muscle weakness

The clinical evaluation of an infant with motor delay, muscle weakness, and/or hypotonia would improve considerably if muscle strength could be measured objectively and normal reference values were available. The authors developed a method to measure muscle strength in infants and tested 81 typically developing infants, 6-36 months of age, and 17 infants with Prader-Willi Syndrome (PWS) aged 24 months. The inter-rater reliability of the measurement method was good (ICC=.84) and the convergent validity was confirmed by high Pearson's correlations between muscle strength, age, height, and weight (r=.79-.85). A multiple linear regression model was developed to predict muscle strength based on age, height, and weight, explaining 73% of the variance in muscle strength. In infants with PWS, muscle strength was significantly decreased. Pearson's correlations showed that infants with PWS in which muscle strength was more severely affected also had a larger motor developmental delay (r=.75).

A rapid immunohistochemical test to distinguish congenital myotonic dystrophy from X-linked myotubular myopathy

Severe forms of myotubular myopathy (MTM) and congenital myotonic dystrophy type 1 (CDM), both present as floppy infants with hypotonia, respiratory failure and bulbar insufficiency. Muscle biopsy is often performed as part of the diagnostic process, but these two disorders share very similar histopathological features. It is well documented that CDM muscle has nuclear foci that contain muscleblind-like 1 (MBNL1) protein. In muscle biopsies from eight neonates showing central nuclei, MBNL1 immunolocalisation identified discrete, intensely stained foci in three cases that were subsequently confirmed as CDM by DNA analysis. In the five remaining non-CDM patients and two controls, MBNL1 staining was heterogeneous in nuclei, not as foci. MBNL1 staining patterns in CDM were easily distinguishable from MTM. We suggest that in cases of hypotonia with suspected CDM or MTM, when biopsy has been taken, sections should additionally be stained for MBNL1 to provide a rapid indication of a CDM diagnosis.

Neonatal muscular manifestations in mitochondrial disorders

During the last decade rapid development has occurred in defining nuclear gene mutations causing mitochondrial disease. Some of these newly defined gene mutations cause neonatal or early infantile onset of disease, often associated with severe progressive encephalomyopathy combined with other multi-organ involvement such as cardiomyopathy or hepatopathy and with early death. Findings suggesting myopathy in neonates are hypotonia, muscle weakness and wasting, and arthrogryposis. We aim to describe the clinical findings of patients with mitochondrial disease presenting with muscular manifestations in the neonatal period or in early infancy and in whom the genetic defect has been characterized. The majority of patients with neonatal onset of mitochondrial disease have mutations in nuclear genes causing dysfunction of the mitochondrial respiratory chain, leading to defective oxidative phosphorylation.