Congenital myotonic dystrophy: ventriculomegaly and shunt considerations for the pediatric neurosurgeon

Cognitive function, behaviour and quality of life in children with myotonic dystrophy type 1 in South - Eastern Norway

BACKGROUND

Cognitive and behavioural problems may be predominant in the clinical picture of myotonic dystrophy (DM1) in childhood. This can lead to a diagnostic delay and thus prevent optimal therapeutic measures.

OBJECTIVE

To obtain an overview of children with DM1 in our health region and study their cognitive and behavioural function, quality of life and neurological status.

METHODS

Patients diagnosed with DM1 were recruited to this cross-sectional study through local habilitation teams of our health region. Neuropsychological testing and physical examination were performed for the majority. For some patients information was retrieved from medical records and through telephone interviews. A questionnaire was administered regarding quality of life.

RESULTS

27 subjects <18 years diagnosed with DM1 were identified, giving a frequency of DM1 of 4.3/100 000 in this age group. Twenty consented to participate. Five had congenital DM1. Most of the participants had only mild neurological deficits. Two with congenital type had hydrocephalus requiring a shunt. Ten, whereof none with congenital DM1, had a cognitive function within normal range. Three were diagnosed with an autism spectrum disorder, and additional three were reported with autistic traits. Many parents reported social and school problems for their child.

CONCLUSIONS

Intellectual disability and varying degrees of autistic behaviour were quite common. Motor deficits were most often mild. A strong focus regarding support at school and in social communication is needed for children growing up with DM1.

Antisense oligonucleotides as a potential treatment for brain deficits observed in myotonic dystrophy type 1

Myotonic dystrophy, or dystrophia myotonica type 1 (DM1), is a multi-systemic disorder and is the most common adult form of muscular dystrophy. It affects not only muscles but also many organs, including the brain. Cerebral impairments include cognitive deficits, daytime sleepiness, and loss of visuospatial and memory functions. The expression of mutated transcripts with CUG repeats results in a gain of toxic mRNA function. The antisense oligonucleotide (ASO) strategy to treat DM1 brain deficits is limited by the fact that ASOs do not cross the blood-brain barrier after systemic administration, indicating that other methods of delivery should be considered. ASO technology has emerged as a powerful tool for developing potential new therapies for a wide variety of human diseases, and its potential has been proven in a recent clinical trial. Targeting DMPK mRNA in neural cells derived from human induced pluripotent stem cells obtained from a DM1 patient with the IONIS 486178 ASO abolished CUG-expanded foci, enabled nuclear redistribution of MBNL1/2, and corrected aberrant splicing. Intracerebroventricular injection of the IONIS 486178 ASO in DMSXL mice decreased the levels of mutant DMPK mRNAs by up to 70% throughout different brain regions. It also reversed behavioral abnormalities following neonatal administration. The present study indicated that the IONIS 486178 ASO targets mutant DMPK mRNAs in the brain and strongly supports the feasibility of a therapy for DM1 patients based on the intrathecal injection of an ASO.

Deciphering the mechanisms underlying brain alterations and cognitive impairment in congenital myotonic dystrophy

Myotonic dystrophy type 1 (DM1) is a multisystemic and heterogeneous disorder caused by the expansion of CTG repeats in the 3' UTR of the myotonic dystrophy protein kinase (DMPK) gene. There is a congenital form (CDM1) of the disease characterized by severe hypotonia, respiratory insufficiency as well as developmental delays and intellectual disabilities. CDM1 infants manifest important brain structure abnormalities present from birth while, in contrast, older patients with adult-onset DM1 often present neurodegenerative features and milder progressive cognitive deficits. Promising therapies targeting central molecular mechanisms contributing to the symptoms of adult-onset DM1 are currently in development, but their relevance for treating cognitive impairment in CDM1, which seems to be a partially distinct neurodevelopmental disorder, remain to be elucidated. Here, we provide an update on the clinical presentation of CDM1 and review recent in vitro and in vivo models that have provided meaningful insights on its consequences in development, with a particular focus on the brain. We discuss how enhanced toxic gain-of-function of the mutated DMPK transcripts with larger CUG repeats and the resulting dysregulation of RNA-binding proteins may affect the developing cortex in utero. Because the methylation of CpG islets flanking the trinucleotide repeats has emerged as a strong biomarker of CDM1, we highlight the need to investigate the tissue-specific impacts of these chromatin modifications in the brain. Finally, we outline promising potential therapeutic treatments for CDM1 and propose future in vitro and in vivo models with great potential to shed light on this disease.

Fetal Macrocephaly: A Novel Sonographic Finding in Congenital Myotonic Dystrophy

Objective  Sonographic clues to the diagnosis of congenital myotonic dystrophy (CDM) are limited, particularly in the absence of family history of myotonic dystrophy (DM). We reviewed cases of CDM for unique prenatal findings. Study Design  A single-center case series of fetuses with CMD with characteristic prenatal findings confirmed postnatally. Results  Four fetuses with pre- or postnatally diagnosed CDM presented with macrocephaly in utero. While head measurements were appropriate for gestational age until midgestation, third-trimester head circumference and biparietal diameter were both >2 standard deviation (SD) above the mean in all. Abdominal and femur measurements were otherwise appropriate for gestation. Postnatally, the occipitofrontal circumference was >2 SD above the mean in all, confirming the diagnosis of macrocephaly. Conclusion  CDM should be included in the differential diagnosis of third-trimester macrocephaly, especially in the presence of additional sonographic clues and when maternal medical history and physical examination are suggestive of DM.

Neonatal hypotonia and neuromuscular conditions

The differential diagnosis of neonatal hypotonia is a complex task, as in newborns hypotonia can be the presenting sign of different underlying causes, including peripheral and central nervous system involvement and genetic and metabolic diseases. This chapter describes how a combined approach, based on the combination of clinical signs and new genetic techniques, can help not only to establish when the hypotonia is related to peripheral involvement but also to achieve an accurate and early diagnosis of the specific neuromuscular diseases with neonatal onset. The early identification of such disorders is important, as this allows early intervention with disease-specific standards of care and, more importantly, because of the possibility to treat some of them, such as spinal muscular atrophy, with therapeutic approaches that have recently become available.

Myotonic Dystrophies: State of the Art of New Therapeutic Developments for the CNS

Myotonic dystrophies are multisystemic diseases characterized not only by muscle and heart dysfunction but also by CNS alteration. They are now recognized as brain diseases affecting newborns and children for myotonic dystrophy type 1 and adults for both myotonic dystrophy type 1 and type 2. In the past two decades, much progress has been made in understanding the mechanisms underlying the DM symptoms allowing development of new molecular therapeutic tools with the ultimate aim of curing the disease. This review describes the state of the art for the characterization of CNS related symptoms, the development of molecular strategies to target the CNS as well as the available tools for screening and testing new possible treatments.