Rapid Molecular Diagnosis of Genetically Inherited Neuromuscular Disorders Using Next-Generation Sequencing Technologies

Neuromuscular diseases are genetically highly heterogeneous, and differential diagnosis can be challenging. Over a 3-year period, we prospectively analyzed 268 pediatric and adult patients with a suspected diagnosis of inherited neuromuscular disorder (INMD) using comprehensive gene-panel analysis and next-generation sequencing. The rate of diagnosis increased exponentially with the addition of genes to successive versions of the INMD panel, from 31% for the first iteration (278 genes) to 40% for the last (324 genes). The global mean diagnostic rate was 36% (97/268 patients), with a diagnostic turnaround time of 4–6 weeks. Most diagnoses corresponded to muscular dystrophies/myopathies (68.37%) and peripheral nerve diseases (22.45%). The most common causative genes, TTN, RYR1, and ANO5, accounted for almost 30% of the diagnosed cases. Finally, we evaluated the utility of the differential diagnosis tool Phenomizer, which established a correlation between the phenotype and molecular findings in 21% of the diagnosed patients. In summary, comprehensive gene-panel analysis of all genes implicated in neuromuscular diseases facilitates a rapid diagnosis and provides a high diagnostic yield.

LAMA2 gene mutation update: Toward a more comprehensive picture of the laminin-α2 variome and its related phenotypes

Congenital muscular dystrophy type 1A (MDC1A) is one of the main subtypes of early-onset muscle disease, caused by disease-associated variants in the laminin-α2 (LAMA2) gene. MDC1A usually presents as a severe neonatal hypotonia and failure to thrive. Muscle weakness compromises normal motor development, leading to the inability to sit unsupported or to walk independently. The phenotype associated with LAMA2 defects has been expanded to include milder and atypical cases, being now collectively known as LAMA2-related muscular dystrophies (LAMA2-MD). Through an international multicenter collaborative effort, 61 new LAMA2 disease-associated variants were identified in 86 patients, representing the largest number of patients and new disease-causing variants in a single report. The collaborative variant collection was supported by the LOVD-powered LAMA2 gene variant database (https://www.LOVD.nl/LAMA2), updated as part of this work. As of December 2017, the database contains 486 unique LAMA2 variants (309 disease-associated), obtained from direct submissions and literature reports. Database content was systematically reviewed and further insights concerning LAMA2-MD are presented. We focus on the impact of missense changes, especially the c.2461A > C (p.Thr821Pro) variant and its association with late-onset LAMA2-MD. Finally, we report diagnostically challenging cases, highlighting the relevance of modern genetic analysis in the characterization of clinically heterogeneous muscle diseases.

Type 1 diabetes and GAD65 limbic encephalitis: a case report of a 10-year-old girl

Limbic encephalitis is a rare neurological disorder that may be difficult to recognize. Clinical features include memory impairment, temporal lobe seizures and affective disturbance. We report the case of a 10-year-old girl with type 1 diabetes mellitus that presented with seizures, depressed mood and memory changes. The diagnosis of glutamic acid decarboxylase 65 (GAD65) mediated limbic encephalitis relied on cerebral magnetic resonance imaging lesions and high serological and cerebrospinal fluid GAD65-antibodies titers. High-dose steroidal therapy was started with clinical improvement. Relapse led to a second high-dose steroid treatment followed by rituximab with remission. A correlation between serum GAD65-antibodies levels and symptoms was found, demonstrating GAD65-antibodies titers may be useful for clinical follow-up and immunotherapy guidance. This report raises awareness of this serious neurological condition that may be associated with type 1 diabetes, underlining the importance of an early diagnosis and prompt treatment for a better prognosis.

Reviewing Large LAMA2 Deletions and Duplications in Congenital Muscular Dystrophy Patients

BACKGROUND

Congenital muscular dystrophy (CMD) type 1A (MDC1A) is caused by recessive mutations in laminin-α2 (LAMA2) gene. Laminin-211, a heterotrimeric glycoprotein that contains the α2 chain, is crucial for muscle stability establishing a bond between the sarcolemma and the extracellular matrix. More than 215 mutations are listed in the locus specific database (LSDB) for LAMA2 gene (May 2014).

OBJECTIVE

A limited number of large deletions/duplications have been reported in LAMA2. Our main objective was the identification of additional large rearrangements in LAMA2 found in CMD patients and a systematic review of cases in the literature and LSDB.

METHODS

In four of the fifty-two patients studied over the last 10 years, only one heterozygous mutation was identified, after sequencing and screening for a frequent LAMA2 deletion. Initial screening of large mutations was performed by multiplex ligation-dependent probe application (MLPA). Further characterization implied several techniques: long-range PCR, cDNA and Southern-blot analysis.

RESULTS

Three novel large deletions in LAMA2 and the first pathogenic large duplication were successfully identified, allowing a definitive molecular diagnosis, carrier screening and prenatal diagnosis. A total of fifteen deletions and two duplications previously reported were also reviewed. Two possible mutational "hotspots" for deletions may exist, the first encompassing exons 3 and 4 and second in the 3' region (exons 56 to 65) of LAMA2.

CONCLUSIONS

Our findings show that this type of mutation is fairly frequent (18.4% of mutated alleles) and is underestimated in the literature. It is important to include the screening of large deletions/duplications as part of the genetic diagnosis strategy.

Autosomal recessive axonal neuropathy with neuromyotonia: a rare entity

BACKGROUND

Autosomal recessive axonal neuropathy with neuromyotonia is a recently described entity associated to the HINT1 gene, encoding histidine triad nucleotide-binding protein 1.

PATIENT

The authors report a Portuguese 16-year-old girl of Roma ethnicity, descendant of consanguineous parents, with progressive distal muscular atrophy and weakness, beginning at age 6. After several years of extensive investigation with inconclusive results, clinical myotonia was identified. Electrophysiologic studies revealed neuromyotonia associated with a severe chronic predominantly motor axonal neuropathy and homozygous mutation (c.334 C > A, p.H112 N) in HINT1 was detected.

CONCLUSION

This report emphasizes the late onset of clinical myotonia essential to the diagnosis.

Síndromes de Deficiência Cerebral de Creatina

Introdução: As síndromes de deficiência cerebral de creatina (OMIM 300036) são um grupo de patologias recentemente descritas,caracterizadas por defeitos congénitos no metabolismo da creatina. A apresentação clínica compreende um espectro variado deperturbações do neurodesenvolvimento. Os baixos níveis de creatina cerebral verificados nestes doentes devem-se a diferentesmutações nos genes que codificam as enzimas de síntese da creatina [arginina:glicina amidinotransferase (AGAT, EC 2.1.4.1), emetiltransferase do ácido guanidinoacético (GAMT, EC 2.1.1.2)], AGAT e GAMT, respectivamente, ambas de transmissão autossómicarecessiva, ou o seu transportador (CT1), SLC6A8, de transmissão ligada ao cromossoma X.Objectivo: Caracterizar o espectro de apresentação clínica e laboratorial dos doentes com o diagnóstico da síndrome de deficiênciade creatina cerebral seguidos no Hospital Pediátrico Carmona da Mota, bem como a sua orientação diagnóstica e terapêutica. Adivulgação destes erros inatos do metabolismo enquanto doenças neurológicas, nomeadamente do neurodesenvolvimento, entre acomunidade médica é outro dos propósitos almejados.Material e Métodos: Análise retrospectiva dos processos clínicos de doentes com o diagnóstico de deficiência cerebral da creatinaseguidos no Hospital Pediátrico.Resultados: Foram identificados doze doentes com défice cerebral da creatina pertencentes a sete famílias. Cinco apresentam deficiênciade metiltransferase do ácido guanidinoacético e sete do transportador de creatina. Têm actualmente entre dois e 38 anos.Os principais motivos de consulta foram: atraso global de desenvolvimento em sete doentes, dois dos quais também apresentavamepilepsia, e atraso da linguagem em outros dois. Apenas num caso o motivo de consulta foi défice de interacção social e de comunicação.Em todos os casos se registou um quociente de desenvolvimento global na faixa da deficiência intelectual. O estudo imagiológicodemonstrou o padrão patognomónico destas síndromes em oito doentes. No estudo genético foram identificadas mutações nos genesGAMT ou SLC6A8 nos doze casos.Conclusões: A suspeita de deficiência de creatina cerebral deve ser considerada em todos os casos de atraso de desenvolvimentopsicomotor sem outra causa evidente. A terapêutica pré-sintomática tem mostrado resultados promissores em algumas crianças comdéfice cerebral de creatina, sobretudo nos défices de GAMT. A elevada taxa de portadores de mutações do gene GAMT em Portugaltorna esta anomalia elegível para o rastreio neonatal no nosso País.

[Cerebral creatine deficiency syndromes]

INTRODUCTION

Creatine deficiency syndromes are a recently described group of diseases characterized by inborn errors of creatine metabolism. Clinical features include a spectrum of neurodevelopment disorders of diverse severity. They are characterized by low levels of cerebral creatine caused by different pathogenic mutations concerning the genes coding for creatine synthesis enzymes [arginine: glicyne amidinotransferase (AGAT, EC 2.1.4.1) and guanidinoacetate methyltansferase (GAMT, EC 2.1.1.2)], AGAT and GAMT, respectively, or its transporter (CT1 deficiency), SLC6A8. Enzymatic deficiencies are transmitted as autosomal recessive traits, whereas the transporter deficit is X-linked.

OBJECTIVES

To characterize the clinical and laboratorial presentation, diagnosis and treatment of cerebral creatine deficiency patients, followed in Hospital Pediátrico Carmona da Mota. The awareness of these inborn errors of metabolism as neurological disorders, namely of neurodevelopment, among the medical community is a secondary aim of the present work.

METHODS AND MATERIAL

Retrospective analysis of the clinical files of patients followed in our Hospital and diagnosed with cerebral creatine deficiency syndrome.

RESULTS

Twelve patients belonging to seven different families were diagnosed with creatine deficiency syndromes. Five presented GAMT deficiency and seven CT1 deficiency. Present ages are 2 to 38 years old. The most common clinical presentations were: global development delay in seven patients (two with epilepsy), and speech delay in two patients. Only one patient had communication and social interaction dysfunction. In all, global development delay in the range of intellectual delay was identified. The pathognomonic pattern of cerebral creatine deficiency in the brain image was demonstrated in eight patients. Pathogenic mutations in GAMT or SLC6A8 genes were identified in all cases.

CONCLUSIONS

The suspicion of cerebral creatine depletion must be considered in all children presenting unexplained global psychomotor development delay. Pre-symptomatic therapy has shown promising results, especially in GAMT deficiency patients. The high rate of asymptomatic carriers of GAMT mutations in our population makes this disorder eligible to neonatal screening in Portugal.

[Neuropsychological evaluation in children with epilepsy: attention and executive functions in temporal lobe epilepsy]

INTRODUCTION

Attention and executive functions correspond to important areas of cognitive functioning associated with the frontal cortex. The study of attention and executive functions in children with epilepsy has focused on characterizing the group with frontal lobe epilepsy. Still, recent studies have identified deficits in these areas also in children with temporal lobe epilepsy (TLE).

AIM

To investigate attention and executive functions in a group of children with TLE, also considering the influence of clinical variables (age at onset of epilepsy and evolution of seizures).

SUBJECTS AND METHODS

Attention and executive functions were studied in a group of 24 children with TLE, aged 7-15 years and compared with 24 control children of the same age and socio-cultural level. Subjects were assigned the following tasks: Cancellation Task, Trail Making Test, Tower of London and Phonemic Verbal Fluency.

RESULTS

The group with TLE performed significantly lower on selective, sustained and divided attention and on phonemic verbal fluency. In markers concerning commissions and omissions there were no differences between groups in any of the performed tests. A significant slowing of processing speed was reported. In addition, patients with earlier age at onset of epilepsy had more difficulties in sustained attention and planning abilities.

CONCLUSION

These results sustain the need for evaluating and monitoring the area of attention, executive functions and processing speed in children and adolescents with temporal lobe epilepsy, above all those with earlier age at onset of epilepsy.

Value of brain magnetic resonance imaging in mitochondrial respiratory chain disorders

Mitochondrial respiratory chain (MRC) disorders have variable clinical manifestations which are mainly neurologic. Diagnosis in children is more complex than in adults because the classic phenotype, ragged red fibers, and mtDNA mutations are rarely seen in children. Moreover, clinical manifestations of disease in developing brains are less explicit. Although not specific, neuroimaging may be contributory to the diagnosis of these disorders in pediatric patients. Brain magnetic resonance images were reviewed for 133 pediatric patients investigated for a MRC disorder at a single center over a period of 10 years (1997-2006), in an attempt to identify distinctive neuroimaging features of MRC defects. Patients fit into four groups, according to the Bernier criteria: definite (63 cases), probable (53 cases), possible (7 cases) and unlikely diagnosis (10 cases). Brain atrophy (41 cases), supratentorial white matter lesions (14 cases), basal ganglia involvement (9 cases), and delayed myelination (9 cases) were the most frequent anomalies in the definite group, and 8 patients presented Leigh syndrome. Neuroimaging findings of the 63 children in the definite group were compared with the remainder and with those in the possible and unlikely groups. There were no significant differences in brain images between the groups analyzed, and therefore no distinctive brain imaging features were identified specific for MRC disorders.

Novel L2HGDH mutations in 21 patients with L-2-hydroxyglutaric aciduria of Portuguese origin

We studied 21 patients, from 18 families, with L-2-hydroxyglutaric aciduria (L-2-HGA), a rare neurometabolic disorder with a homogeneous presentation: progressive neurodegeneration with extrapyramidal and cerebellar signs, seizures, and subcortical leukoencephalopathy. Increased levels of L-2-hydroxyglutaric acid in body fluids proved the diagnosis of L-2-HGA in all 21 patients. We analyzed the L-2-HGA gene (L2HGDH), recently found to be mutated in consanguineous families with L-2-HGA, and identified seven novel mutations in 15 families. Three mutations appeared to be particularly prevalent in this Portuguese panel: a frameshift mutation (c.529delC) was detected in 12 out of 30 mutant alleles (40%), a nonsense mutation (c.208C>T; p.Arg70X) in 7/30 alleles (23%), and a missense mutation (c.293A>G; p.His98Arg) in four out of 30 mutant alleles (13%), suggesting that common origin may exist. Furthermore, two novel missense (c.169G>A; p.Gly57Arg, c.1301A>C; p.His434Pro) and two splice error (c.257-2A>G, c.907-2A>G) mutations were found. All the mutations presumably lead to loss-of-function with no relationship between clinical signs, progression of the disease, levels of L-2-HGA and site of the mutation. In the three remaining families, no pathogenic mutations in the L-2-HGA were found, which suggests either alterations in regulatory regions of the gene or of its intervening sequences, compound heterozygosity for large genomic deletion and, or further genetic heterogeneity.

Atrofia muscular espinhal – Apoio ventilatório não invasivo em pediatria

The deterioration of the respiratory function in children suffering from degenerative neuromuscular disease is the main cause of the high mortality rate associated with these diseases. Noninvasive ventilation (NIV) has reduced the morbidity and mortality due to respiratory insufficiency in these children. However, the use of support ventilation in some cases of spinal muscular atrophy (SMA) is still controversial. A retrospective study of 22 patients suffering from SMA who were followed up in the Paediatric Hospital of Coimbra is presented: 7 of type I, 11 of type II, and 4 of type III. In 17 of these cases, non-invasive ventilation by mask was begun, and in 3 of them NIV was applied for prophylactic purposes. The 7 children with SMA type I began NIV when they were 13 months of age on average (3 months-3 years); 5 of them died, between 1 and 15 months after the beginning of the ventilation. Of the 11 children with SMA type II, 8 were submitted to NIV and one died 22 months later. Three of the children in this group began NIV in a prophylactic way, and in all of them a decrease in the thoracic deformity was observed. Of the 4 patients of type III, 2 of them were submitted to non-invasive ventilation. In all of the symptomatic cases, a decrease in the frequency and severity of respiratory infections was observed, after ventilation was started. The respiratory support with NIV may improve the quality of life of children suffering from SMA as well as prolong their life expectancies. In SMA type I, whose clinical manifestations are precocious and whose prognostic is very serious, the application of this support has been debated.

Recessive ataxia with ocular apraxia: review of 22 Portuguese patients

BACKGROUND

The recessive ataxias are a heterogeneous group of neurodegenerative disorders characterized by cerebellar ataxia associated with a number of different neurologic, ophthalmologic, or general signs. They are often difficult to classify in clinical terms, except for Friedreich ataxia, ataxia-telangiectasia, and a relatively small group of rare conditions for which the molecular basis has already been defined.

OBJECTIVES

To study the clinical presentation and to define diagnostic criteria in a group of Portuguese patients with ataxia and ocular apraxia, an autosomal recessive form without the essential clinical and laboratory features of ataxia-telangiectasia.

PATIENTS AND METHODS

We reviewed 22 patients in 11 kindreds, identified through a systematic survey of hereditary ataxias being conducted in Portugal.

RESULTS

Age at onset ranged from 1 to 15 years, with a mean of 4.7 years. The duration of symptoms at the time of last examination varied from 5 to 58 years. All patients presented with progressive cerebellar ataxia, the characteristic ocular apraxia, and a peripheral neuropathy. Associated neurologic signs included dystonia, scoliosis, and pes cavus. Magnetic resonance imaging was performed in 16 patients, all of whom showed cerebellar atrophy.

CONCLUSIONS

Ataxia with ocular apraxia may be more frequent than postulated before, and may be identified clinically using the following criteria: (1) autosomal recessive transmission; (2) early onset (for most patients in early childhood); (3) combination of cerebellar ataxia, ocular apraxia, and early areflexia, with later appearance of the full picture of peripheral neuropathy; (4) absence of mental retardation, telangiectasia, and immunodeficiency; and (5) the possibility of a long survival, although with severe motor handicap.

L-2-Hydroxyglutaric aciduria: clinical, biochemical and magnetic resonance imaging in six Portuguese pediatric patients

We present clinical, biochemical and cranial magnetic resonance imaging data of six pediatric patients with L-2-hydroxyglutaric aciduria. All the children have the same ethic origin and lived in the northern area of Portugal. Our findings reinforce the described phenotype of this rare metabolic disease with mental deficiency, severe cerebellar dysfunction, mild extrapyramidal and pyramidal symptoms, progressive macrocephaly and seizures. Magnetic resonance imaging revealed subcortical leukoencephalopathy, cerebellar atrophy and signal changes in the putamina and dentate nuclei. These were similar to those of the previous reports in all patients. The urinary excretion of L-2-hydroxyglutaric acid was variably increased in all patients. The other persistent biochemical abnormality was hyperlysinemia. We have found a strong correlation between the severity of the clinical manifestations and the extension of the lesions in the neuroimaging studies. There was no correlation between the clinical findings and the amount of urinary excretion of L-2-hydroxyglutaric acid. We report the second case in the literature of a cerebral thalamic tumor in L-2-hydroxyglutaric aciduria; neuropathological examination of the surgical biopsy demonstrated a diffuse fibrillary astrocytoma.