AIMP1 Mutation Long-Term Follow-Up, With Decreased Brain N-Acetylaspartic Acid and Secondary Mitochondrial Abnormalities

Peripheral nerves are involved in hypomyelinating leukodystrophy-3 caused by a homozygous AIMP1 variant

INTRODUCTION

Aminoacyl-tRNA synthetase-interacting multifunctional protein 1 (AIMP1) is a non-catalytic component of the multi-tRNA synthetase complex that catalyzes the ligation of amino acids to their correct tRNAs. Bi-allelic truncating variants in the AIMP1 gene have been associated with hypomyelinating leukodystrophy-3 (HLD3; MIM 260600), which is characterized by hypomyelination, microcephaly, seizures and decreased life expectancy. Although peripheral nerve involvement has been assumed for HLD3, no compelling evidence is available to date.

CASE REPORT

The case was a first-born Filipino male. He showed profound developmental delay, failure to thrive, and spasticity in his limbs. At three months of age he developed refractory epilepsy. Serial magnetic resonance imaging (MRIs) showed profound myelination delay and progressive cerebral atrophy. He showed abnormal nerve conduction studies. Genetic testing revealed a homozygous pathogenic variant in the AIMP1 gene (NM_004757.3: c.115C > T: p.Gln39*). The parents were heterozygous for the same variant.

CONCLUSION

Here, we report a patient with a homozygous nonsense AIMP1 variant showing peripheral neuropathy as well as HLD3. Our case suggests that AIMP1 plays a pivotal role in the peripheral nerve as well as the central nervous system.

Two Siblings With Valproate-Related Hyperammonemia and Novel Mutations in Glutamine Synthetase (GLUL) Treated With Carglumic Acid

This case report describes 2 siblings with myoclonic epilepsy who had novel mutations in the glutamine synthetase (GLUL) gene: c.316C>T, p.(Arg106*) and c.42G>C, p.(Lys14Asn). Valproic acid improved seizure control, but was associated with hyperammonemic encephalopathy. Addition of carglumic acid reduced ammonia levels but drug coverage was declined. We therefore designed a protocol to measure the reduction in plasma ammonia in response to carglumic acid therapy. After the first dose of carglumic acid, Patient 1 showed a reduction in plasma ammonia levels within 3 hours, from 114 umol/L to 68 umol/L (reference 12-47 umol/L), and Patient 2 from 108 umol/L to 80 umol/L, which was sustained over a 2 week period. Overall, there was a strong negative correlation between plasma ammonia levels and carglumic acid levels (r = -0.86, p = 0.0013), and recurrence of hyperammonemic encephalopathy was not observed while the patients were taking carglumic acid.

Rare homozygous nonsense variant in AIMP1 causing Early Onset Epileptic Encephalopathy with Burst Suppression (EOEE-BS)

Pathogenic variants in AIMP1 gene are rare causes of neurologic disorders. Homozygous frameshift and nonsense variants in AIMP1 have been described in severe neurodegenerative disease. This is the third report of a homozygous nonsense variant in AIMP1 [c.115 C > T (p.Gln39*)] in a girl with severe neonatal onset epileptic encephalopathy. Like the two other cases reported, our patient is also of Filipino descent. Clinical features include microcephaly, poor visual motor development, shallow breathing, severe hypertonia in extremities, severe global developmental delay, poor gag and suck reflex, failure to thrive in the neonatal period, and early onset intractable seizures. Brain MRI showed hypoplasia of corpus callosum as well as cerebellar vermis, global volume loss and diminished myelination for her age. Electroencephalogram at four months of age showed background consisting of synchronous and asynchronous intervals of burst suppression with intermittent multifocal spikes predominantly in the bi-temporal region, suggestive of Early Onset Epileptic Encephalopathy with Burst Suppression (EOEE-BS) which has not been previously associated with the c.115 C > T variant in AIMP1. Of note, she presented to us in super refractory status epilepticus which was eventually controlled after administration of ketogenic diet and Epidiolex (cannabidiol). This report expands the genetic landscape of EOEE-BS. This is the first case of this specific variant in which Epidiolex was administered, which along with Ketogenic diet aided in controlling patient's super refractory status epilepticus.