Newborn screening (NBS) for spinal muscular atrophy (SMA) and severe combined immunodeficiency (SCID) faces challenges. Accurate and precise SMN1 and SMN2 copy number determination, confirmed by two orthogonal methods, are vital for SMA prognostication and treatment. Single SMN1 copy detection also enables the further feasibility to screen for compound heterozygotes. In SCID, low-level T-cell receptor excision circle (TREC) quantification by quantitative PCR is imprecise, necessitating replicates for reliable results. An assay with enhanced accuracy, precision, and high throughput is warranted for NBS SMA and SCID. False positive of SMN1 deletions due to allele dropout are also a potential pitfall in PCR-based methods. We evaluated a first-tier fully automated quadruplex droplet digital PCR (ddPCR) assay detecting SMN1, SMN2, TREC, and RPP30 using dried blood spots together with a second-tier Sanger sequencing to exclude SMN1 allele dropout. Five proficiency test samples and six patient samples with known SMN1 and SMN2 copy numbers confirmed by multiplex ligation-dependent probe amplification were used for accuracy evaluation with full concordance. The ddPCR assay showed high precision for SMN1 and SMN2 (<7% coefficient of variation (CV) for ≥0 copy) and TREC (14.6% CV at 37 copies/µL blood). Second-tier Sanger sequencing identified all SMA cases with homozygous deletions. Accuracy for TREC classification was concordant with 10 proficiency samples. The reference interval of TREC concentration was established for newborns ≥ 34 weeks (n = 1812) and the 2.5th percentile was 57 copies/µL blood. A two-tiered approach with fully automated quadruplex ddPCR and Sanger sequencing delivers accurate and precise quantitation for NBS SMA and SCID, enabling early treatment and counseling.

Familial hypercholesterolemia (FH) is a prevalent but often underdiagnosed monogenic disorder affecting lipoprotein metabolism, and genetic testing for FH has not been widely conducted in Asia in the past. In this cross-sectional study of 31 probands (19 adults and 12 children) and an addition of 15 individuals (12 adults and 3 children), who underwent genetic testing and cascade screening for FH, respectively, during the period between February 2015 and July 2023, we identified a total of 25 distinct LDLR variants in 71.0% unrelated probands. Among the adult proband cohort, a higher proportion of genetically confirmed cases exhibited a positive family history of premature cardiovascular disease. Treatment intensity required to achieve an approximate 50% reduction in pretreatment low-density lipoprotein cholesterol (LDL-C) exhibited potentially better diagnostic performance compared to pretreatment LDL-C levels, Dutch Lipid Clinic Network Diagnostic Criteria (DLCNC) score, and modified DLCNC score. Adult individuals identified through cascade screening demonstrated less severe phenotypes, and fewer of them met previously proposed local criteria for FH genetic testing compared to the probands, indicating that cascade screening played a crucial role in the early detection of new cases that might otherwise have gone undiagnosed. These findings underscore the significance of genetic testing and cascade screening in the accurate identification and management of FH cases.

Amyotrophic lateral sclerosis (ALS), which is characterized by progressive deterioration of upper and lower motor neurons resulting in severe muscle atrophy, respiratory failure, and death, is a rare and fatal neurodegenerative disease. TARDBP p.G298S was recently identified as a founder mutation in southern Chinese. This article first presented case summaries of three ALS patients: two families with TARDBP p.G298S presenting with heterogeneous clinical phenotypes, including a case with an unusual extraocular muscle onset. A review of TARDBP p.G298S cases reported worldwide was conducted, surveying the age and site of onset, disease duration, and motor neuron involvement. Finally, an overview of genetic mutations reported locally for ALS was presented, showing that TARDBP p.G298S is a common mutation detected in this locality. This article highlighted the distinct clinical manifestations and genetic background in ALS patients and will be useful for developing genetic screening and counseling strategies in Hong Kong and southern China.

Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) is a rare mitochondrial neurodegenerative disorder characterized by stroke-like episodes, seizure, and lactic acidosis. The diagnosis of MELAS is often challenging due to its variable phenotypic manifestations and rarity of this disease. In this article, we report the case of a 38-year-old woman who presented with repeated seizures and clinical stroke-like symptoms. She had no positive family history, and lactic acidosis was only present in her initial episode. Magnetic resonance imaging (MRI) of the brain was also normal in her first presentation. However, subsequent scans due to new clinical events showed migratory stroke-like lesions that were hyperintense on T2/fluid attenuated inversion recovery (FLAIR) sequence and had restricted diffusion. They did not conform to vascular territories but had a predilection for posterior temporal, occipital and parietal regions. The radiological findings prompted the suspicion of MELAS, which diagnosis was confirmed with genetic testing. Here, we also reviewed the MRI features of MELAS from literature, in particular the diffusion-weighted sequence findings, as debate still exists on whether the apparent diffusion coefficient (ADC) signal should be high or low in these lesions. Our case highlights the importance of recognizing key imaging features of this rare and highly heterogenous disease. In addition to helping with earlier diagnosis, these imaging findings also provide more insight into the underlying pathophysiology of MELAS.

Background and Clinical Significance: Paroxysmal extreme pain disorder (PEPD) is an extremely rare autosomal dominant sodium channelopathy caused by SCN9A gain-of-function variants. It is characterized by infantile-onset excruciating paroxysmal pain, typically in rectal, ocular, or mandibular regions, triggered by innocuous stimuli and accompanied by autonomic flares. Carbamazepine is dramatically effective in most reported cases. To date, only two genetically confirmed cases have been documented in Chinese patients, and fewer than 20 disease-causing variants are reported worldwide. We report the third Chinese case harboring a novel likely pathogenic SCN9A variant (p.Leu1623Gln), notable for its unusually severe, progressive, and carbamazepine-refractory phenotype, as well as life-threatening psychiatric sequelae, highlighting phenotypic heterogeneity and the devastating impact when standard therapy fails. Case Presentation: A Chinese male proband with positive family history presented with lifelong trigger-induced catastrophic burning and tearing pain in the perineum and lower limbs, associated with erythema, swelling, and occasional non-epileptic seizures. Attacks worsened with age despite escalating polypharmacy, including high-dose opioids, benzodiazepines, topical lidocaine and carbamazepine. Both the proband and his father developed profound psychosocial sequelae including severe depression and suicidal attempts. Next-generation sequencing in the proband revealed a novel heterozygous likely pathogenic variant NM_001365536.1 (SCN9A): c.4868T>A p.(Leu1623Gln). Conclusions: This third reported ethnic Chinese PEPD case expands the genotypic and phenotypic spectrum of SCN9A-related channelopathies, demonstrating that some variants can produce carbamazepine-refractory, progressive, and profoundly disabling disease with high suicidality risk. Early genetic diagnosis is critical in family planning and cascade testing, and has the potential in guiding targeted therapy that is under active research.