小坂 仁

Creatine transporter deficiency (CTD) caused by mutations in SLC6A8 encoding the creatine transporter (CRT), leads to cerebral creatine deficiency syndromes; however, the cellular impact of CRT loss remains unclear. In this study, we investigated the consequences of the G561R mutation by examining fibroblasts using proteomics and functional assays. We observed severe intracellular creatine deficiency (> 90% reduction), leading to impaired energy metabolism (low ATP and high ADP/ATP). Proteomic analysis revealed significant alterations in the mitochondrial and extracellular vesicle pathways. Our investigation revealed impaired mitochondrial oxidative phosphorylation, reduced spare respiratory capacity, elevated oxidative stress, and significant alterations in amino acid transporter activity. Protein misfolding associated with G561R exacerbated these deficits compared to the deletion model. These findings elucidate the key pathological mechanisms induced by the CRT-G561R mutation-including energy metabolic reprogramming, mitochondrial dysfunction, and cellular stress-which significantly contribute to our understanding of the pathogenesis of creatine transporter deficiency and suggest potential therapeutic targets.

Pathogenic SNF2 related chromatin remodeling ATPase 1 (SMARCA1) variants have been reported in patients with X-linked intellectual disability (XLID) characterized by macrocephaly and variable neurological symptoms. Here, we report two unrelated male patients with XLID due to novel SMARCA1 variants detected by exome sequencing. Patient 1 showed macrocephaly, behavioral difficulty, and learning disability with a hemizygous SMARCA1 variant (NM_003069.5:c.1795 C > T p.[Gln599*]) leading to nonsense-mediated decay. Patient 2 had ataxia and speech delay with a hemizygous missense variant (NM_003069.5:c.1343 G > T p.[Arg448Leu]). Structural modeling suggested that the missense variant, p.(Arg448Leu) might destabilize interactions between SMARCA1 and nucleosomal DNA, thereby contributing to the abberant effect of mutant SMARCA1 protein. Both variants were inherited from their unaffected healthy mothers. This study suggests that hemizygous variants impairing SMARCA1 function can cause XLID with other variable features, such as macrocephaly and ataxia, in men.

The 4-hydroxyphenylpyruvate dioxygenase-like protein (HPDL) is a mitochondria-localized protein involved in the biosynthesis of coenzyme Q10 in the electron transfer system, and its variants have been reported to cause progressive neurodegenerative diseases such as neonatal leukoencephalopathy and hereditary spastic paraplegia. In this case report, we present a case of a nine-year-old girl with exotropia with a novel HPDL variant who underwent strabismus surgery. She was referred to the ophthalmology department with exotropia and a history of progressive spastic paraplegia with gait disturbance. Brain MRI showed no remarkable findings. Whole-exome sequencing revealed a homozygous variant c.1040delC (p.Thr347Metfs*66) in the HPDL gene. Ophthalmic examination revealed a best-corrected visual acuity of 20/12 in both eyes. Fundoscopy showed retinal discoloration at the level of the retinal pigment epithelium in the right eye. As the patient had intermittent exotropia with good convergence, she was followed up conservatively. One year after the initial examination, the patient could not keep her eyes in a central position by convergence. The alternate prism cover test revealed exotropia of 80 prism diopters. We diagnosed that intermittent exotropia had deteriorated into constant exotropia. The patient's family requested a strabismus surgery, which was conducted under general anesthesia. Standard left lateral rectus recession, left medial rectus resection, and right lateral rectus recession were also performed. Postoperatively, her exotropia was reduced, and she achieved good convergence. The patient and her family were satisfied with the surgical outcome, and no recurrence was noted one year postoperatively. Our results provide important information for the associations of variant in HPDL with progressive spastic paraplegia, strabismus and retinal changes and broaden the genetic spectrum of HPDL-related disease. This is the first report to present a novel HPDL variant and document the performance of strabismus surgery for constant exotropia.

Seizures in patients with developmental and epileptic encephalopathies (DEEs) are often highly resistant to various antiseizure medications. Perampanel (PER) is a novel antiseizure medication that non-competitively inhibits the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor and is expected to reduce seizure frequency not only for focal seizures and generalized tonic-clonic seizures (GTCS) but also for other seizure types. This study aimed to clarify the long-term therapeutic efficacy and tolerability of PER in patients with DEEs. We analyzed data regarding patients' background characteristics, medication retention, trends in seizure frequency, and adverse events obtained from 24 patients with DEEs who had been on PER treatment for 60 months. The retention rates were 62.5% and 46.9% at 12 and 60 months, respectively. At 60 months after PER initiation, the rate of patients with > 50% seizure reduction was 33.3%, 33.3%, 38.5%, 54.5%, 54.5%, and 36.4% among patients with atypical absence seizures, tonic seizures, focal seizures, GTCS, myoclonic seizures, and atonic seizures, respectively. The frequency of adverse events was 70.8%. PER showed long-term efficacy in various seizure types. PER is a promising treatment option for patients with DEEs.

We report a case of severe Aicardi-Goutières syndrome caused by a novel homozygous RNASEH2B intronic variant, NC_000013.10(NM_024570.4):c.65-13G > A p.Glu22Valfs*5. The patient was born with pseudo-TORCH symptoms, including intracranial calcification, cataracts, and hepatosplenomegaly. Furthermore, the patient exhibited profound intellectual impairment and died at 14 months due to aspiration pneumonia accompanied by interstitial lung abnormalities. The severity of the patient's symptoms underscores the critical role of the C-terminal region of RNase H2B.