Subacute Partially Reversible Leukoencephalopathy Expands the Aicardi-Goutières Syndrome Phenotype.

OBJECTIVE: To report a series of atypical presentations of Aicardi-Goutières syndrome. METHODS: Clinical, neuroimaging, and genetic data. RESULTS: We report a series of six unrelated patients (five males) with a subacute loss of developmental milestones, pyramidal signs, and regression of communication abilities, with onset at ages ranging from 7 to 20 months, reaching a nadir after 4 to 24 weeks. A remarkable improvement of lost abilities occurred in the follow-up, and they remained with residual spasticity and dysarthria but preserved cognitive function. Immunization or febrile illness occurred before disease onset in all patients. CSF was normal in two patients, and in four, borderline or mild lymphocytosis was present. A brain CT scan disclosed a subtle basal ganglia calcification in one of six patients. Brain MRI showed asymmetric signal abnormalities of white matter with centrum semi-ovale involvement in five patients and a diffuse white matter abnormality with contrast enhancement in one. Four patients were diagnosed and treated for acute demyelinating encephalomyelitis (ADEM). Brain imaging was markedly improved with one year or more of follow-up (average of 7 years), but patients remained with residual spasticity and dysarthria without cognitive impairment. Demyelination relapse occurred in a single patient four years after the first event. Whole-exome sequencing (WES) was performed in all patients: four of them disclosed biallelic pathogenic variants in RNASEH2B (three homozygous p.Ala177Thr and one compound heterozygous p.Ala177Thr/p.Gln58*) and in two of them the same homozygous deleterious variants in RNASEH2A (p.Ala249Val). CONCLUSIONS: This report expands the phenotype of AGS to include subacute developmental regression with partial clinical and neuroimaging improvement. Those clinical features might be misdiagnosed as ADEM.

Multiple Independent Gene Disorders Causing Bardet-Biedl Syndrome, Congenital Hypothyroidism, and Hearing Loss in a Single Indian Patient.

We report a 20-year-old, female, adopted Indian patient with over 662 Mb regions of homozy-gosity who presented with intellectual disability, ataxia, schizophrenia, retinal dystrophy, moder-ate-to-severe progressive sensorineural hearing loss (SNHL), congenital hypothyroidism, cleft mi-tral valve with mild mitral valve regurgitation, and dysmorphic features. Exome analysis first on a clinical basis and subsequently on research reanalysis uncovered pathogenic variants in three nu-clear genes following two modes of inheritance that were causal to her complex phenotype. These included (1) compound heterozygous variants in BBS6 potentially causative for Bardet-Biedl syn-drome 6; (2) a homozygous, known pathogenic variant in the stereocilin (STRC) gene associated with nonsyndromic deafness; and (3) a homozygous variant in dual oxidase 2 (DUOX2) gene asso-ciated with congenital hypothyroidism. A variant of uncertain significance was identified in a fourth gene, troponin T2 (TNNT2), associated with cardiomyopathy but not the cleft mitral valve, with mild mitral regurgitation seen in this case. This patient was the product of an apparent first-degree relationship, explaining the multiple independent inherited findings. This case high-lights the need to carefully evaluate multiple independent genetic etiologies for complex pheno-types, particularly in the case of consanguinity, rather than presuming unexplained features are expansions of known gene disorders.

Mechanism of KMT5B haploinsufficiency in neurodevelopment in humans and mice.

Pathogenic variants in KMT5B, a lysine methyltransferase, are associated with global developmental delay, macrocephaly, autism, and congenital anomalies (OMIM# 617788). Given the relatively recent discovery of this disorder, it has not been fully characterized. Deep phenotyping of the largest (n = 43) patient cohort to date identified that hypotonia and congenital heart defects are prominent features that were previously not associated with this syndrome. Both missense variants and putative loss-of-function variants resulted in slow growth in patient-derived cell lines. KMT5B homozygous knockout mice were smaller in size than their wild-type littermates but did not have significantly smaller brains, suggesting relative macrocephaly, also noted as a prominent clinical feature. RNA sequencing of patient lymphoblasts and Kmt5b haploinsufficient mouse brains identified differentially expressed pathways associated with nervous system development and function including axon guidance signaling. Overall, we identified additional pathogenic variants and clinical features in KMT5B-related neurodevelopmental disorder and provide insights into the molecular mechanisms of the disorder using multiple model systems.

Pearls & Oy-sters: Paroxysmal Exercise-Induced Dyskinesias Due to Pyruvate Dehydrogenase Deficiency.

Paroxysmal exercise-induced movement disorders may be caused by energy metabolism disorders, such as Glut 1 deficiency, pyruvate dehydrogenase deficiency, or mitochondrial respiratory chain disorders. A 4-year-old boy with a history of febrile seizures presented with paroxysmal dystonia, triggered by exercise, or occurring at rest. Additional investigations demonstrated pallidal hyperintensities on brain MRI and low CSF glucose. Pyruvate and lactate were elevated. The clinical presentation combined with neuroimaging abnormalities and biochemical profile (the lactate/pyruvate ratio) were clues to pyruvate dehydrogenase deficiency, a treatable metabolic disorder with neurologic presentations.

A 47-Year-Old Man Presenting With Seizures and Prior Stroke.

A 47-year-old man presented to his local hospital in Peru after a generalized tonic-clonic seizure. His family reported a history of prior stroke of unclear etiology. This case report discusses the approach to a first seizure (including in tropical regions like Peru), the relationship between stroke and seizures, the approach to stroke in the young, and how to diagnose rare diseases in resource-limited settings.