Diagnostic capabilities of nanopore long-read sequencing in muscular dystrophy.

Many individuals with muscular dystrophies remain genetically undiagnosed despite clinical diagnostic testing, including exome sequencing. Some may harbor previously undetected structural variants (SVs) or cryptic splice sites. We enrolled 10 unrelated families: nine had muscular dystrophy but lacked complete genetic diagnoses and one had an asymptomatic DMD duplication. Nanopore genomic long-read sequencing identified previously undetected pathogenic variants in four individuals: an SV in DMD, an SV in LAMA2, and two single nucleotide variants in DMD that alter splicing. The DMD duplication in the asymptomatic individual was in tandem. Nanopore sequencing may help streamline genetic diagnostic approaches for muscular dystrophy.

Nusinersen for Patients With Spinal Muscular Atrophy: 1415 Doses via an Interdisciplinary Institutional Approach.

BACKGROUND: Spinal deformity and prior spinal fusion pose technical challenges to lumbar puncture (LP) for nusinersen administration for patients with spinal muscular atrophy (SMA). In this retrospective study over two study phases, we evaluated (1) factors associated with difficult LP or unscheduled requirement for image guidance and (2) effectiveness of a triage pathway for selective use of image guidance and nonstandard techniques, particularly for patients with spinal instrumentation/fusion to the sacrum. METHODS: With institutional review board approval, electronic health records, imaging, and administrative databases were analyzed for patients receiving nusinersen from January 2012 through September 2021. Descriptive statistics and univariate analyses were used. RESULTS: From January 2012 to March 2018 (phase 1), among 82 patients with SMA, 461 of 464 (99.4%) LP attempts were successful. Univariate analyses associated difficulty with prior spinal instrumentation, higher body mass index, and severity of the spinal deformity. Based on this experience, starting in April 2018 (phase 2), 125 patients were triaged selectively for ultrasound, fluoroscopy, or Dyna computed tomography. Patients with spinal instrumentation/fusion to the sacrum were treated primarily via intrathecal ports (137 doses) or transforaminal LP (55 doses). From April 2018 through September 2021, 704 of 709 (99.3%) LPs were successful. In total from January 2012 to September 2021, 1415 doses were administered. Over 50% of LPs were performed by neurology nurse practitioners without image guidance. Safety outcomes were excellent. CONCLUSIONS: A stratified approach resulted in successful intrathecal nusinersen delivery and efficient resource allocation for patients with SMA, with or without complex spinal anatomy.

5,10-methenyltetrahydrofolate synthetase deficiency causes a neurometabolic disorder associated with microcephaly, epilepsy, and cerebral hypomyelination.

Folate metabolism in the brain is critically important and serves a number of vital roles in nucleotide synthesis, single carbon metabolism/methylation, amino acid metabolism, and mitochondrial translation. Genetic defects in almost every enzyme of folate metabolism have been reported to date, and most have neurological sequelae. We report 2 patients presenting with a neurometabolic disorder associated with biallelic variants in the MTHFS gene, encoding 5,10-methenyltetrahydrofolate synthetase. Both patients presented with microcephaly, short stature, severe global developmental delay, progressive spasticity, epilepsy, and cerebral hypomyelination. Baseline CSF 5-methyltetrahydrolate (5-MTHF) levels were in the low-normal range. The first patient was treated with folinic acid, which resulted in worsening cerebral folate deficiency. Treatment in this patient with a combination of oral L-5-methyltetrahydrofolate and intramuscular methylcobalamin was able to increase CSF 5-MTHF levels, was well tolerated over a 4 month period, and resulted in subjective mild improvements in functioning. Measurement of MTHFS enzyme activity in fibroblasts confirmed reduced activity. The direct substrate of the MTHFS reaction, 5-formyl-THF, was elevated 30-fold in patient fibroblasts compared to control, supporting the hypothesis that the pathophysiology of this disorder is a manifestation of toxicity from this metabolite.

GM2 Activator Deficiency Caused by a Homozygous Exon 2 Deletion in GM2A.

GM2 activator (GM2A) deficiency (OMIM 613109) is a rare lysosomal storage disorder, with onset typically in infancy or early childhood. Clinically, it is almost indistinguishable from Tay-Sachs disease (OMIM 272800) or Sandhoff disease (OMIM 268800); however, traditionally available biochemical screening tests will most likely reveal normal results. We report a 2-year-old male with initially normal development until the age of 9 months, when he presented with developmental delay and regression. Workup at that time was unrevealing; at 15 months, he had abnormal brain MRI findings and a cherry red spot on ophthalmological examination. Family history and all laboratory studies were uninformative. The combination of a cherry red spot and developmental regression was strongly suggestive of a lysosomal storage disorder. Sequence analysis of GM2A did not reveal any pathogenic variants; however, exon 2 of GM2A could not be amplified by PCR, raising suspicion for a large, homozygous deletion. Subsequent copy number analysis confirmed a homozygous deletion of exon 2 in GM2A. This is the first reported case of GM2A deficiency being caused by a whole exon deletion. We describe previously unreported electron microscopy findings in this disease, thus expanding the clinical and variant spectrum for GM2 activator deficiency. These findings demonstrate the increased degree of suspicion required for diagnosis of this rare disorder. Brief Summary: This case of GM2 activator deficiency was caused by a homozygous deletion in GM2A, demonstrating the need to include exon level copy number analysis in any workup to fully exclude this disorder.