Muthusamy, Karthik

ABSTRACT The cohesin complex, composed of SMC1, SMC3, RAD21, and STAG1/STAG2, is essential for chromosome cohesion, DNA repair, and transcriptional regulation. Pathogenic variants in cohesin components cause cohesinopathies. The classical characteristics of cohesinopathies include developmental delay (DD), intellectual disability (ID), feeding difficulties, hypotonia, short stature, hearing loss, and dysmorphic features. Here, we present a 5‐year‐old boy with classical cohesinopathy features, including DD/ID and feeding difficulties, along with non‐classical features such as hypoglycemia, recurrent fever, and immunodeficiency. Trio exome sequencing identified a novel de novo missense variant of uncertain significance (NM_005862.3:c.643G>A(p.Val215Ile)) in the STAG1 gene. The variant localizes to the RAD21 interaction interface, and molecular dynamics (MD) simulations revealed conformational changes comparable to other STAG1 variants reported as likely pathogenic in patients, supporting a deleterious effect which may disrupt the STAG1‐RAD21 interaction interface. This case expands the phenotypic and molecular spectrum of STAG1‐related cohesinopathy and advances our understanding of the disease mechanism.

ABSTRACT MYH11 ‐related hereditary type 2 visceral myopathy is a rare smooth muscle disorder typically presenting in infancy with severe gastrointestinal and genitourinary dysfunction. We describe a 73‐year‐old female with lifelong symptoms of gastrointestinal and urinary dysfunction, including chronic constipation, neurogenic bladder, recurrent urinary tract infections, gastroparesis, and pelvic organ prolapse. A multigenerational family history revealed similar visceral smooth muscle abnormalities among 14 affected individuals over five generations, suggesting autosomal dominant inheritance. Whole‐genome sequencing identified a heterozygous, likely pathogenic variant in MYH11 c.5819del; p.(Pro1940HisfsTer91), consistent with the diagnosis of autosomal dominant type 2 visceral myopathy. This variant causes production of an abnormally elongated myosin‐heavy chain, disrupting muscle contractile function. This individual's survival into her eighth decade reflects long‐term clinical stability, possibly attributable to the variant's milder effect. We describe the clinical course of the disease, along with a comprehensive review of previously described individuals with the same variant. This case broadens the phenotypic spectrum of MYH11 ‐associated visceral myopathy, demonstrating that late‐onset, milder forms can occur and remain compatible with long‐term survival with optimal supportive management. Comprehensive genetic evaluation identifies primary disorders, enabling precise diagnosis, tailored management, and informed genetic counseling for complex phenotypes.

ABSTRACT Polyglucosan body myopathy type 2 (PGBM2; OMIM #616199) is an autosomal recessive myopathy caused by biallelic variants in GYG1 , which encodes glycogenin‐1. It is characterized by progressive muscle weakness and PAS‐positive, diastase‐resistant polyglucosan inclusions on muscle biopsy. We report a 64‐year‐old woman who developed progressive proximal weakness beginning in her early 50s, with polyglucosan bodies identified on muscle histopathology. Genome sequencing (GS) detected a single heterozygous pathogenic splice‐site variant, NM_004130.4( GYG1 ):c.143+3G>C. Given strong histopathologic evidence of PGBM2, GS data were reanalyzed, revealing an additional rare deep intronic variant, NM_004130.4( GYG1 ):c.7+992T>G, predicted to activate a cryptic exon. RNA sequencing (RNA‐seq) confirmed aberrant splicing from both variants, demonstrating exon 2 skipping associated with c.143+3G>C and cryptic exon inclusion caused by c.7+992T>G. Variant phasing posed a diagnostic challenge due to unavailable parental DNA, and long‐range PCR results were inconclusive. Long‐read GS definitively demonstrated that the two variants were in trans , establishing compound heterozygosity and confirming the molecular diagnosis. These findings enabled reclassification of the deep intronic variant as likely pathogenic. This case highlights the diagnostic limitations of conventional phasing approaches in adult‐onset recessive disorders and demonstrates the clinical utility of integrating genome reanalysis, RNA‐seq, and long‐read GS for resolving complex phasing challenges.

ABSTRACT The TLK2 gene encodes a serine/threonine kinase essential for chromatin assembly. Loss‐of‐function heterozygous variants were recently identified as a cause of a rare neurodevelopmental disorder ( TLK2 ‐NDD) characterized by a variable spectrum of developmental delay, autism, behavioral issues, and severe constipation. We describe two unrelated young adult females presenting with neurodevelopmental delay, neurobehavioral abnormalities, and constipation since infancy secondary to truncating TLK2 variants. Case 1 is a 26‐year‐old female who was referred to our clinic for extended assessment of new‐onset psychosis and concern for seizures. She has been diagnosed with autism spectrum disorder and has a history of developmental delay, constipation, and aggressive outbursts since early childhood. At the age of 24 years, she developed an acute onset of persistent daily auditory hallucinations with threatening content that was refractory to medical and electroconvulsive therapy. Video‐ EEG assessment found no correlates for hallucinations. Trio whole genome sequencing revealed a heterozygous de novo pathogenic TLK2 variant, NM_006852.6:c. 367C >T (p. Arg123Ter ). Case 2 is a 19‐year‐old female who was evaluated for developmental delay and intellectual disability. Her phenotype was also notable for constipation since infancy and suggestive hypothalamic features with obesity, metrorrhagia, and hypersomnia. Trio whole genome sequencing revealed a likely pathogenic heterozygous TLK2 variant NM_006852.6:c.587del(p.Ser196ThrfsTer19) inherited from an asymptomatic, mosaic father. We present the adult phenotype of two young females with truncating variants in TLK2 and unusual phenotypic features of refractory hallucinations and possible hypothalamic syndrome. While both features may be independent of TLK2 ‐NDD, evidence from schizophrenia genome‐wide association studies and tissue expression data indicates that these features might be a part of longitudinal phenotype development. Long‐term follow‐up studies are required to unfold the phenotypic spectrum of TLK2 ‐NDD and to better understand the implications of these findings for management and prognosis.

AbstractNeurofibromatosis type 1 (NF1) is a common neurocutaneous disorder characterized by development of pigmentary skin changes, neurogenic tumors, and other manifestations involving multiple organ systems. Penetrance is complete, though expressivity is quite variable even among the family members. Given that NF1 is a common hereditary condition, existence of a second genetic disorder in NF1 patients is not unexpected. During comprehensive evaluations of individuals with NF1, we encountered 11 patients with dual diagnosis who contributed to phenotypic complexity and challenges for long‐term management. Examples include Prader–Willi Syndrome, Autosomal Dominant Polycystic Kidney Disease, Down syndrome, infantile myofibromatosis, Craniosynostosis, cleft lip and palate, 47,XYY, 22q11.2 duplication, 15q13.3 deletion syndrome, and BRCA2‐ and ATM‐ related cancer predisposition syndromes. Presence of dysmorphism, developmental delay, atypical tumors, and family history of other genetic disorders including cancers appears as determinants to consider a second genetic etiology and helps to differentiate from an extreme phenotypic spectrum of NF1. Clinicians should have high index of suspicion to exclude coexisting disorders, as apart from providing comprehensive medical care. This also has potential implications in genetic counseling. Long‐term effects of the synergistic mechanisms leading to phenotypic complexity and patient outcomes are yet to be characterized, with follow‐up needed.

ObjectiveEpalrestat, an aldose reductase inhibitor increases phosphomannomutase (PMM) enzyme activity in a PMM2‐congenital disorders of glycosylation (CDG) worm model. Epalrestat also decreases sorbitol level in diabetic neuropathy. We evaluated the genetic, biochemical, and clinical characteristics, including the Nijmegen Progression CDG Rating Scale (NPCRS), urine polyol levels and fibroblast glycoproteomics in patients with PMM2‐CDG.MethodsWe performed PMM enzyme measurements, multiplexed proteomics, and glycoproteomics in PMM2‐deficient fibroblasts before and after epalrestat treatment. Safety and efficacy of 0.8 mg/kg/day oral epalrestat were studied in a child with PMM2‐CDG for 12 months.ResultsPMM enzyme activity increased post‐epalrestat treatment. Compared with controls, 24% of glycopeptides had reduced abundance in PMM2‐deficient fibroblasts, 46% of which improved upon treatment. Total protein N‐glycosylation improved upon epalrestat treatment bringing overall glycosylation toward the control fibroblasts’ glycosylation profile. Sorbitol levels were increased in the urine of 74% of patients with PMM2‐CDG and correlated with the presence of peripheral neuropathy, and CDG severity rating scale. In the child with PMM2‐CDG on epalrestat treatment, ataxia scores improved together with significant growth improvement. Urinary sorbitol levels nearly normalized in 3 months and blood transferrin glycosylation normalized in 6 months.InterpretationEpalrestat improved PMM enzyme activity, N‐glycosylation, and glycosylation biomarkers in vitro. Leveraging cellular glycoproteome assessment, we provided a systems‐level view of treatment efficacy and discovered potential novel biosignatures of therapy response. Epalrestat was well‐tolerated and led to significant clinical improvements in the first pediatric patient with PMM2‐CDG treated with epalrestat. We also propose urinary sorbitol as a novel biomarker for disease severity and treatment response in future clinical trials in PMM2‐CDG. ANN NEUROL 20219999:n/a–n/a

AbstractBackgroundBiallelic pathogenic variants in HTRA1 cause CARASIL. More recently, monoallelic variants have been associated with the autosomal dominant disorder CADASIL2 but not all carriers develop disease manifestations. We describe the clinicoradiologic and mutation spectrum of four new CADASIL2 individuals.MethodsMedical records at Mayo Clinic between 2013 and 2020 were retrospectively reviewed to identify patients with cerebral small vessel disease related to monoallelic HTRA1 variants.ResultsFour patients met the study inclusion criteria for cerebral small vessel disease related to HTRA1 monoallelic variants. The mean age at onset of first clinical stroke was 51.25 years (range 41–64 years). The mean disease duration was 6.5 years (range 4–12). All individuals had recurrent strokes within the duration of follow‐up with a mean number of strokes per patient being 5.5 (range 2–12). Three individuals had leukoencephalopathy with brain stem involvement. Microhemorrhages were seen on brain MRI in three patients. HTRA1 monoallelic variants identified in our cohort were missense variants in three patients and a novel frameshift variation in one patient. Interestingly, two of these missense variants were previously reported in an autosomal recessive pattern of inheritance and here are associated with a dominant effect.ConclusionsClinicoradiologic characteristics of heterozygous HTRA1‐related CSVD may overlap with sporadic CSVD. Heterozygous HTRA1 variants can contribute to dominant or recessive disease mechanisms.