Síndrome de hiperinsulinismo-hiperamoniemia y epilepsia mioclónica grave de la infancia

Characterizing the neurological phenotype of the hyperinsulinism hyperammonemia syndrome

BACKGROUND

Hyperinsulinism hyperammonemia (HI/HA) syndrome is caused by activating mutations in GLUD1, encoding glutamate dehydrogenase (GDH). Atypical absence seizures and neuropsychological disorders occur at high rates in this form of hyperinsulinism. Dysregulated central nervous system (CNS) glutamate balance, due to GDH overactivity in the brain, has been hypothesized to play a role. This study aimed to describe the neurologic phenotype in HI/HA syndrome and investigate CNS glutamate levels using glutamate weighted chemical exchange saturation transfer magnetic resonance imaging (GluCEST MRI). In this cross-sectional study, 12 subjects with HI/HA syndrome had plasma ammonia measurement, self- or parent-completed neurocognitive assessments, electroencephalogram (EEG), and GluCEST MRI at 7 T performed. GluCEST MRI measures were compared to a historic reference population of 10 healthy adults.

RESULTS

Subjects were five males and seven females with median age of 25.5 years. Seventy-five percent of subjects reported a history of neurodevelopmental problems and 42% had neurocognitive assessment scores outside the normal range. Fifty percent had interictal EEG findings of generalized, irregular spike and wave discharges. Higher variability in hippocampal GluCEST asymmetry (p = 0.002), and in peak hippocampal GluCEST values (p = 0.008), was observed in HI/HA subjects (n = 9 with interpretable MRI) compared to the healthy reference population (n = 10).

CONCLUSIONS

The high prevalence of abnormal neurocognitive assessment scores and interictal EEG findings observed highlights the importance of longitudinal neuropsychological assessment for individuals with HI/HA syndrome. Our findings demonstrate the potential application of GluCEST to investigate persistent knowledge gaps in the mechanisms underlying the unique neurophenotype of this disorder.

Hyperinsulinism-hyperammonemia syndrome: a de novo mutation of the GLUD1 gene in twins and a review of the literature

Hyperinsulinism-hyperammonemia (HI/HA) syndrome is a rare autosomal dominant disease characterized by recurrent hypoglycemia and persistent mild elevation of plasma ammonia. HI/HA syndrome is one of the more common forms of congenital hyperinsulinism (CHI), caused by activating mutations within the GLUD1 gene that encodes the mitochondrial enzyme glutamate dehydrogenase (GDH). We report here on monozygotic twin girls presented with fasting- and protein-induced hypoglycemia and mild persistent hyperammonemia. Genetic analysis revealed that both girls were heterozygous for a novel missense mutation within exon 11 [c.1499A>T, p.(R443W)] of the GLUD1 gene. Despite early treatment with diazoxide and a low protein diet, they both developed non-hypoglycemic seizures in early childhood followed by cognitive impairment. In addition to their clinical course, a review of the literature on HI/HA syndrome is provided.

Protein-induced hyperinsulinaemic hypoglycaemia due to a homozygous HADH mutation in three siblings of a Saudi family

Hyperinsulinaemic hypoglycaemia (HH) is caused by mutations in the key genes involved in regulation of insulin secretion from the pancreatic β-cells and mutations in ABCC8 and KCNJ11 are the most common causes of HH. Mutations in HADH (which encodes the enzyme 3-hydroxyacyl-CoA dehydrogenase) are a rare cause of HH. We report three siblings (21, 9, and 7 years old) from a consanguineous Saudi family with HH due to a homozygous mutation in HADH. All three siblings presented with HH in the 1st year of life. HH responded well to medical therapy (diazoxide/octreotide) although the 1st sibling suffered neurological damage. The protein load test revealed protein sensitivity in the 21-year-old proband, the oldest reported patient with HH secondary to a HADH mutation. Genetic analysis revealed a homozygous HADH splicing mutation (c.133-1G>A) in all three siblings. HADH mutations can present in later infancy or childhood with severe HH that is usually diazoxide responsive. Severe neurological complications such as epilepsy and developmental delay can be associated with HADH mutations. This is the 1st report of HH due to HADH mutation in an adult suggesting that HH could persist into adulthood possibly becoming milder over the years.

Metabolic causes of epileptic encephalopathy

Epileptic encephalopathy can be induced by inborn metabolic defects that may be rare individually but in aggregate represent a substantial clinical portion of child neurology. These may present with various epilepsy phenotypes including refractory neonatal seizures, early myoclonic encephalopathy, early infantile epileptic encephalopathy, infantile spasms, and generalized epilepsies which in particular include myoclonic seizures. There are varying degrees of treatability, but the outcome if untreated can often be catastrophic. The importance of early recognition cannot be overemphasized. This paper provides an overview of inborn metabolic errors associated with persistent brain disturbances due to highly active clinical or electrographic ictal activity. Selected diseases are organized by the defective molecule or mechanism and categorized as small molecule disorders (involving amino and organic acids, fatty acids, neurotransmitters, urea cycle, vitamers and cofactors, and mitochondria) and large molecule disorders (including lysosomal storage disorders, peroxisomal disorders, glycosylation disorders, and leukodystrophies). Details including key clinical features, salient electrophysiological and neuroradiological findings, biochemical findings, and treatment options are summarized for prominent disorders in each category.