Autosomal Recessive Variant Research Articles

Treatment of Hereditary Leukonychia with Intramatricial Triamcinolone: Case Report

Introduction: Hereditary leukonychia is a rare genetic nail disorder characterized by whitening of the nail plate, which is sometimes due to mutations in the phospholipase C delta-1 (PLCδ1) gene. While leukonychia is typically asymptomatic, it carries significant psychosocial burden, and patients often report that others comment that they look like they are wearing nail polish. There are no known treatment options. Case Presentation: A 39-year-old Kuwaiti male with autosomal recessive variant of PLCδ1-related non-syndromic leukonychia affecting nine fingernails presented for treatment because he was socially stigmatized. Treatment with 30% glycolic acid chemical peel was ineffective. Because there is evidence suggesting a link between PLCδ1-related hereditary leukonychia and abnormal keratinization, we hypothesized that intralesional steroids, which inhibit keratinocyte activity and reduce inflammation within the nail matrix, may be an effective treatment. Following treatment with intramatricial triamcinolone, the patient experienced complete resolution of leukonychia in five fingernails and partial improvement in the remaining four. Conclusion: We present a case of successful treatment of hereditary leukonychia due to a phospholipase C δ-1 gene mutation with intramatricial triamcinolone. This case highlights the potential of this treatment approach for leukonychia and warrants further investigation in larger cohort studies.

A Case Report of a New Variant Associated with Vici Syndrome in a Turkish Infant; EPG5 Frameshift Variant

Introduction: Vici syndrome is a congenital multisystem disorder characterized primarily by callosal agenesis, cataracts, cardiomyopathy, combined immunodeficiency, and oculocutaneous hypopigmentation, along with additional newly recognized findings. Autosomal recessive variants in the EPG5 gene, which encodes ectopic P-granules autophagy protein 5 (EPG5), a key regulator of autophagy, are known genetic causes of this syndrome. The aim of this case report is to present a novel disease-causing variant identified through EPG5 gene sequence analysis. Case Presentation: We report on a 2-month-old Turkish girl who presented with developmental delay, bilateral congenital cataracts, microcephaly, hypotonia, hypertrophic cardiomyopathy, hypopigmented skin lesions, and agenesis of the corpus callosum. Genetic analysis revealed a homozygous c.7504delC (p.Gln2502Argfs*4) frameshift variant in the EPG5 gene, which has not been previously documented. Conclusions: Adding a new variant to the literature is crucial, as it highlights the feasibility of reaching an accurate diagnosis through well-conducted physical examination findings in patients with early developmental delay. This case also raises awareness about such rare diseases. Moreover, recognizing new mutations is critical for understanding atypical findings, prognosis, treatment responses, and the genetic risks for other family members.

Characterization of Dnajc12 knockout mice, a model of hypodopaminergia.

Homozygous DNAJC12 c.79-2A>G (p. V27Wfs*14) loss-of-function mutations were first reported as a cause of young-onset Parkinson's disease. However, bi-allelic autosomal recessive pathogenic variants in DNAJC12 may lead to an alternative constellation of neurological features, including infantile dystonia, developmental delay, intellectual disability and neuropsychiatric disorders. DNAJC12 is understood to co-chaperone aromatic amino acid hydroxylases to foster the synthesis of biogenic amines. In vitro, we discover overexpressed DNAJC12 forms a complex with guanine triphosphate cyclohydrolase 1 (GCH1), the rate-limiting enzyme in the synthesis of tetrahydrobiopterin, a cofactor paramount for biogenic amines synthesis. We also confirm DNAJC12's interaction with tyrosine (TH) and tryptophan hydroxylase (TPH), which are rate-limiting enzymes for synthesis of biogenic amines dopamine (DA) and serotonin (5-HT). In-vitro knock-down of DNAJC12 with a siRNA destabilizes the DNAJC12-TH-GCH1 complex, reducing GCH1 levels, whereas reciprocal overexpression of both TH and GCH1 increases endogenous DNAJC12, alluding to the significance of modulating the DNAJC12-TH-GCH1 complex as a therapy for DNAJC12 and other biogenic amine disorders. We extend these investigations to a Cre-conditional knock-out mice (cDKO) in which loxP sites flanking Dnajc12 exon 2 enable its excision by cre-recombinase. With germline Cre expression, we have created a constitutive Dnajc12 knock-out (DKO). DKO mice exhibit reduced locomotion/ exploratory behavior at 3 months in automated open-field testing, accompanied by increased plasma phenylalanine which is a cardinal feature of patients with pathogenic DNAJC12 variants. In striatal tissue, total DA and 5-HT, their metabolites, and electrically-evoked DA release are all reduced. Biochemical alterations in synaptic proteins are also apparent, with enhanced phosphorylation of Th pSer31 and pSer40 reflecting biological compensation. Most immediately, cDKO and DKO mice present models to develop and refine therapeutic approaches for biogenic amines disorders, including dystonia and parkinsonism. They will also enable the pleiotropic functions of biogenic amines (including DA), usually synthesized in the brain or periphery, to be separated.

Amplicon-based long-read sequencing is useful for confirming zygosity of DSG2 variants associated with Japanese ARVC

Abstract Background Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiomyopathy mainly caused by desmosomal gene variants. Previously, we reported that DSG2 variants were the most common in 153 Japanese ARVC probands (DSG2 multiple, n=62 and single, n=4; PKP2, n=28; others, n=7). Among the multiple DSG2 variant carriers, 22 probands were compound heterozygous carriers, and 25 were homozygous, which were confirmed by genetic testing for family members (Figure A). On the other hand, 88% of their family members with single DSG2 variant carriers were not diagnosed with ARVC, which meant that recessive DSG2 variants were the major cause of ARVC in Japan. However, zygosities in remaining 15 probands with multiple DSG2 variants were unknown due to the lack of genome data from their parents. Purpose This study aimed to clarify the zygosities of multiple DSG2 variants using amplicon-based long-read sequencing. Methods Genomic DNA was extracted from whole blood using standard protocols. The range containing multiple variants was amplified by long-range PCR. Sequencing libraries were prepared using ONT Ligation Sequencing Kit. Each library was loaded onto a flow cell for sequencing on ONT GridION Mk1 running MinKNOW control software. FASTQ files were aligned to hg38 using minimap2. Variants were called using Clair3 and phased using WhatsHap. Integrative Genomics Viewer (IGV) was used for visualization of the phased variants. Results We successfully phased all the multiple DSG2 variants found in the 15 proband. A typical result of amplicon-based LRS was shown in Figure B. It was IGV screen shot of reads at DSG2 containing c.874C>T (p.R292C) and c.1481A>C (p.D494A). The reads colored in red belonged to one haplotype, while the ones in blue belonged to the other. Each of the two variants was on different color reads, indicating they were compound heterozygous variants. Using LRS, we confirmed all the 15 probands had compound heterozygous variants in DSG2. Overall, the 62 probands (40.5%) with DSG2 variants were recessive variant carriers (Figure A). Conclusions Japanese ARVC was mainly caused by autosomal recessive variants in DSG2. Clarifying the zygosity of causative variants is crucial for the diagnosis in recessive diseases including Japanese ARVC. Amplicon-based LRS was helpful for phasing the multiple DSG2 variants directly without genetic testing of the parents.Figure AFigure B

A Novel PTPRQ c.3697del Variant Causes Autosomal Dominant Progressive Hearing Loss in Both Humans and Mice.

PTPRQ plays an important role in the development of inner ear hair cell stereocilia. While many autosomal recessive variants in PTPRQ have been identified as the pathogenic cause for nonsyndromic hearing loss (DFNB84A), so far only one autosomal dominant PTPRQ variant, c.6881G>A (p.Trp2294*), has been reported for late-onset, mild-to-severe hearing loss (DFNA73). By using targeted next-generation sequencing, this study identified a novel PTPRQ truncating pathogenic variant, c.3697del (p.Leu1233Phefs*11), from a Chinese Han family that co-segregated with autosomal dominant, postlingual, progressive hearing loss. A Ptprq-3700del knock-in mouse model was generated by CRISPR-Cas9 and characterized for its hearing function and inner ear morphology. While the homozygous knock-in mice exhibit profound hearing loss at all frequencies at the age of 3 weeks, the heterozygous mutant mice resemble the human patients in mild, progressive hearing loss from age 3 to 12 weeks, primarily affecting high frequencies. At this stage, the homozygous knock-in mice have a normal hair cell count but disorganized stereocilia. Cochlear proteosome analysis of the homozygous mutant mice revealed differentially expressed genes and pathways involved in oxidative phosphorylation, regulation of angiogenesis and synaptic vesicle cycling. Our study provides a valuable animal model for further functional studies of the pathogenic mechanisms underlying DFNA73.

A Rare Case of Paroxysmal Kinesigenic Dyskinesia with Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay

Abstract Paroxysmal kinesigenic dyskinesia (PKD) represents a rare subset of movement disorders characterized by involuntary movements triggered by sudden voluntary actions, without loss of consciousness. Typically manifesting in the first or second decade of life, PKD can present as either familial or sporadic, with the most common mutation identified in familial cases being in the proline-rich transmembrane protein 2 gene. This abstract presents a unique case of PKD accompanied by a progressive spastic ataxic syndrome in a 17-year-old male with a history of consanguinity. The patient exhibited a constellation of symptoms including delayed motor milestones, unsteady gait, slurred speech, and dystonic movements, alongside neurological findings consistent with cerebellar dysfunction and peripheral neuropathy. Genetic testing revealed pathogenic variants in the SACS gene, confirming the diagnosis of autosomal recessive spastic ataxia of Charlevoix-Saguenay. This case underscores the importance of thorough neurological evaluation, including consideration of atypical presentations, in patients with PKD. In addition, it sheds light on the association between SACS gene mutations and an autosomal recessive variant of PKD, emphasizing the need for awareness and recognition of such rare manifestations in clinical practice.

Federated analysis of autosomal recessive coding variants in 29,745 developmental disorder patients from diverse populations.

Autosomal recessive coding variants are well-known causes of rare disorders. We quantified the contribution of these variants to developmental disorders in a large, ancestrally diverse cohort comprising 29,745 trios, of whom 20.4% had genetically inferred non-European ancestries. The estimated fraction of patients attributable to exome-wide autosomal recessive coding variants ranged from ~2-19% across genetically inferred ancestry groups and was significantly correlated with average autozygosity. Established autosomal recessive developmental disorder-associated (ARDD) genes explained 84.0% of the total autosomal recessive coding burden, and 34.4% of the burden in these established genes was explained by variants not already reported as pathogenic in ClinVar. Statistical analyses identified two novel ARDD genes: KBTBD2 and ZDHHC16. This study expands our understanding of the genetic architecture of developmental disorders across diverse genetically inferred ancestry groups and suggests that improving strategies for interpreting missense variants in known ARDD genes may help diagnose more patients than discovering the remaining genes.

Cascade testing in mitochondrial diseases: a cross-sectional retrospective study

BackgroundCascade testing can offer improved surveillance and timely introduction of clinical management for the at-risk biological relatives. Data on cascade testing and costs in mitochondrial diseases are lacking. To address this gap, we performed a cross-sectional retrospective study to provide a framework for cascade testing in mitochondrial diseases, to estimate the eligibility versus real-time uptake of cascade testing and to evaluate the cost of the genetic diagnosis of index cases and the cost of predictive cascade testing.MethodsData was collected through retrospective chart review. The variant inheritance pattern guided the identification of eligible first-degree relatives: (i) Males with mitochondrial DNA (mtDNA) single nucleotide variants (SNVs) – siblings and mothers. (ii) Females with mtDNA SNVs – siblings, mothers and offspring. (iii) Autosomal Dominant (AD) nuclear DNA (nDNA) variants – siblings, offspring and both parents. (iv) Autosomal Recessive (AR) nDNA variants – siblings.ResultsWe recruited 99 participants from the Adult Mitochondrial Disease Clinic in Sydney. The uptake of cascade testing was 55.2% in the mtDNA group, 55.8% in the AD nDNA group and 0% in AR nDNA group. Of the relatives in mtDNA group who underwent cascade testing, 65.4% were symptomatic, 20.5% were oligosymptomatic and 14.1% were asymptomatic. The mean cost of cascade testing for eligible first-degree relatives (mtDNA group: $694.7; AD nDNA group: $899.1) was lower than the corresponding index case (mtDNA group: $4578.4; AD nDNA group: $5715.1) (p < 0.001).ConclusionThe demand for cascade testing in mitochondrial diseases varies according to the genotype and inheritance pattern. The real-time uptake of cascade testing can be influenced by multiple factors. Early diagnosis of at-risk biological relatives of index cases through cascade testing, confirms the diagnosis in those who are symptomatic and facilitates implementation of surveillance strategies and clinical care at an early stage of the disease.

Clinical Characteristics of Charcot-Marie-Tooth Disease Type 4J.

Charcot-Marie-Tooth disease type 4J (CMT4J) is caused by autosomal recessive variants in the Factor-Induced Gene 4 (FIG4) gene. Recent preclinical work has demonstrated the feasibility of adeno-associated virus serotype 9-FIG4 gene therapy. This study aimed to further characterize the CMT4J phenotype and evaluate feasibility of validated CMT-related outcome measures for future clinical trials. This cross-sectional study enrolled children and adults with genetically confirmed CMT4J, with 2 documented disease-causing variants in the FIG4 gene. Patients were recruited through the Inherited Neuropathy Consortium network. Disease severity was assessed using standardized CMT-specific outcome measures and exploratory biomarkers including muscle MRI fat fraction, electrophysiology, and neurofilament light chain levels. Descriptive statistics and correlation analyses were conducted to explore relationships between variables. We recruited a total of 19 patients, including 14 pediatric patients (mean age 10.9 ± 3.9 years) and 5 adults (mean age 40.0 ± 13.9 years). The most frequent symptoms were gross motor delay and distal more than proximal muscle weakness, which were observed in 14 of 19 patients. The most common non-neuromuscular symptoms were cognitive and respiratory deficits, each seen in 8 of 19 patients. We denoted asymmetric weakness in 2 patients and nonuniform slowing of conduction velocities in 6 patients. Charcot-Marie-Tooth Disease Pediatric Scale (CMTPedS), Pediatric Quality of Life Inventory, and Vineland Adaptive Behavior Scale scores were affected in most patients. We observed a significant positive correlation between neurofilament light chain levels and CMTPedS, but the study was underpowered to observe a correlation between CMTPedS and MRI fat fraction. We obtained baseline clinical and biomarker data in a broad cohort with CMT4J in pediatric and adult patients. Motor delay, muscle weakness, and respiratory and cognitive difficulties were the most common clinical manifestations of CMT4J. Many patients had nerve conduction studies with nonuniform slowing, and 2 had an asymmetric pattern of muscle weakness. We observed that the neurofilament light chain levels correlated with the CMTPedS in the pediatric population. This study showed feasibility of clinical outcomes including CMTPedS in assessment of disease severity in the pediatric patient population and provided baseline characteristics of exploratory biomarkers, neurofilament light chain levels, and muscle MRI fat fraction. The coronavirus disease 2019 pandemic affected some of the visits, resulting in a reduced number of some of the assessments.

Precision Dopaminergic Treatment in a Cohort of Parkinson's Disease Patients Carrying Autosomal Recessive Gene Variants: Clinical Cohort Data and a Mini Review.

Parkinson's disease (PD) patients harboring recessive gene variants exhibit a distinct clinical phenotype with an early disease onset and relatively mild symptoms. Data concerning individualized therapy for autosomal recessive PD forms are still scarce. Demographic and treatment data of a cohort of PD carriers of recessive genes (nine homozygous or compound heterozygous PRKN carriers, four heterozygous PRKN carriers, and three biallelic PINK1 carriers) were evaluated. The average levodopa equivalent daily dose (LEDD) was 806.8 ± 453.5 (range 152-1810) in PRKN carriers and 765 ± 96.6 (range 660-850) in PINK1 carriers. The majority responded to low/moderate doses of levodopa. The response to dopamine agonists (DAs) was often favorable both as initial and longitudinal therapy. In total, 8/13 PRKN and 1/3 PINK1 carriers were treated with amantadine successfully, and this also applied to patients who could not tolerate levodopa or DAs. In the era of personalized treatment, the therapeutic approach in recessive PD gene carriers might differ as compared to idiopathic PD. Lower LEDD doses were efficient even in patients with a very long disease duration, while a few patients were doing well without any levodopa treatment decades after disease initiation. DAs or amantadine could be used as a first and main line treatment regimen if well tolerated. Literature data on therapeutic strategies in carriers of pathogenic mutations in recessive PD genes, including device-aided treatments, will be further discussed.

Recognizing clinical features of primary ciliary dyskinesia in the perinatal period.

Primary ciliary dyskinesia (PCD) is a rare, motile ciliopathy inherited through mostly autosomal recessive variants that results in chronic ear, sinus, and respiratory disease. Despite neonatal respiratory distress being a common presenting symptom in term infants with PCD, the diagnosis is often delayed due to non-familiarity of neonatal caregivers with phenotypic and diagnostic features of this disease. Organ laterality defects, prenatal cerebral ventriculomegaly, and a family history of suppurative respiratory disease may occur in PCD and should prompt neonatal testing for this condition. In this review of neonatal PCD diagnoses in a large PCD clinic, prevalence and details of neonatal PCD issues are presented, highlighting the typically delayed onset of neonatal respiratory distress and lobar atelectasis on chest radiography, specific presentations in premature neonates, and responses to perinatal therapies.

Efficacy of T-cell assays for the diagnosis of primary defects in cytotoxic lymphocyte exocytosis

AbstractPrimary hemophagocytic lymphohistiocytosis (HLH) is a life-threatening disorder associated with autosomal recessive variants in genes required for perforin-mediated lymphocyte cytotoxicity. A rapid diagnosis is crucial for successful treatment. Although defective cytotoxic T lymphocyte (CTL) function causes pathogenesis, quantification of natural killer (NK)–cell exocytosis triggered by K562 target cells currently represents a standard diagnostic procedure for primary HLH. We have prospectively evaluated different lymphocyte exocytosis assays in 213 patients referred for evaluation for suspected HLH and related hyperinflammatory syndromes. A total of 138 patients received a molecular diagnosis consistent with primary HLH. Assessment of Fc receptor–triggered NK-cell and T-cell receptor (TCR)–triggered CTL exocytosis displayed higher sensitivity and improved specificity for the diagnosis of primary HLH than routine K562 cell–based assays, with these assays combined providing a sensitivity of 100% and specificity of 98.3%. By comparison, NK-cell exocytosis after K562 target cell stimulation displayed a higher interindividual variability, in part explained by differences in NK-cell differentiation or large functional reductions after shipment. We thus recommend combined analysis of TCR-triggered CTL and Fc receptor–triggered NK-cell exocytosis for the diagnosis of patients with suspected familial HLH or atypical manifestations of congenital defects in lymphocyte exocytosis.

The Uptake of Partner Participation in Sequential Preconception Carrier Screening

Introduction: Carrier screening that is performed in the preconception period allows for couples at risk for having children affected with certain single gene (Mendelian) conditions to be identified. This is the most optimal timeframe to perform such screening. Most obstetric providers utilize a sequential process in which the patient first undergoes screening and their partner is only offered testing if the initial results reveal that the first is a carrier for one or more autosomal recessive (AR) deleterious variants. If the partner fails to undergo screening, the couple cannot obtain meaningful and actionable risk information for future or current pregnancies. In this study, we sought to assess the frequency of completed carrier screening risk assessment among individuals and couples who were undergoing preconception screening at two prenatal screening programs staffed by genetic counselors and geneticists. Materials and Methods: We reviewed the screening outcomes for individuals and couples who presented for preconception carrier screening from January 1, 2020 through December 30, 2021 at Insight Medical Genetics and the clinical genetics program at Northwestern Medicine. All individuals received pretest genetic counseling prior to screening and posttest counseling after results were available. We evaluated individuals who were found to be a carrier of at least one deleterious variant and whether the partner of that person underwent carrier screening, and, if so, which type of screening. Results: 548 patients who identified as women underwent preconception carrier screening during the study period, along with 3 men presenting for initial screening. These screens consisted of a panel containing primarily autosomal recessive conditions with a few X-linked conditions. 247 individuals (45.1%) were positive for at least one pathogenic variant; of these, 244 (98.8%) were variants in genes associated with autosomal recessive conditions. A total of 219 partners (88.7%) underwent carrier screening, including the 3 female partners of the men who initiated carrier screening. Of note, 4 of the patients who underwent carrier screening reported not having a partner at the time of screening; accordingly, the partners who underwent screening represent 89.8% of individuals eligible for partner screening following an initial positive result. Of the 219 partners who underwent carrier screening, 201 (91.8%) chose a carrier screening panel of 150+ conditions, while 18 chose a more limited panel that included the gene(s) of relevance based on their partner’s results, with or without additional genes relevant to their learned/self-identified ethnicity or race. Conclusions: Approximately 10% of couples presenting for preconception genetic counseling and carrier screening found to be at potential risk for a child with an autosomal recessive condition did not obtain the requisite information to fully assess their risk of having an affected child. It is possible that the frequency of couples who do not obtain complete and actionable screening information is even higher when carrier screening is provided without the assistance of certified genetic counselors or geneticists. Recently, cell free DNA-based maternal screening has been introduced that assesses the risk for a limited number of genetic conditions in the fetus that may not require assessment of the partner. Nonetheless, providers must communicate to their patients that meaningful risk information can only be obtained when the partner undergoes screening in cases where the initial member of the couple is found to be a carrier of at least one autosomal recessive condition. Laboratories and professional societies need to develop effective educational outreach to patients and providers alike to improve the screening process for couples who want to determine if they are at risk to have a child with an inherited condition.

Generation of hiPSC lines from four glutaric aciduria type I (GA1) patients carrying pathogenic biallelic variants in GCDH

GCDH encodes for the enzyme catalyzing the sixth step of the lysine degradation pathway. Autosomal recessive variants in GCDH are associated with glutaric aciduria type I (GA1), of which a wide genotypic spectrum of pathogenic variants have been described. In this study, hiPSC lines derived from four GA1 patients with different genotypes were generated and fully characterized. Two patients carry compound heterozygous variants in GCDH, while the other two patients carry a variant in homozygosis. These hiPSC lines can significantly contribute to better understand the molecular mechanism underlying GA1 and provide excellent models for the development of new therapeutic strategies.

A novel homozygous missense variant identified in the myosin VIIA motor domain of a Moroccan patient with usher syndrome.

Usher syndrome 1 (USH1) is the most severe subtype of Usher syndrome characterized by severe sensorineural hearing impairment, retinitis pigmentosa, and vestibular areflexia. USH1 is usually induced by variants in MYO7A, a gene that encodes the myosin-VIIa protein. Myosin-VIIA is effectively involved in intracellular molecular traffic essential for the proper function of the cochlea, the retinal photoreceptors, and the retinal pigmented epithelial cells. In this study, we report a new homozygous missense variant (NM_000260.4: c.1657C > T p.(His553Tyr)) in MYO7A of a 28-year-old female with symptoms consistent with USH1. This variant, c.1657C > T p.(His553Tyr) is positioned in the highly conserved myosin-VIIA motor domain. Previous studies showed that variants in this domain might disrupt the ability of the protein to bind to actin and thus cause the disorder. Our findings contribute to our understanding of the phenotypic and mutational spectrum of USH1 associated with autosomal recessive MYO7A variants and emphasize the important role of molecular testing in accurately diagnosing this syndrome. More advanced research is required to understand the functional effect of the identified variant and the genotype-phonotype correlations of MYO7A-related Usher syndrome 1.

Deoxyguanosine kinase deficiency: natural history and liver transplant outcome.

Autosomal recessive pathogenetic variants in the DGUOK gene cause deficiency of deoxyguanosine kinase activity and mitochondrial deoxynucleotides pool imbalance, consequently, leading to quantitative and/or qualitative impairment of mitochondrial DNA synthesis. Typically, patients present early-onset liver failure with or without neurological involvement and a clinical course rapidly progressing to death. This is an international multicentre study aiming to provide a retrospective natural history of deoxyguanosine kinase deficient patients. A systematic literature review from January 2001 to June 2023 was conducted. Physicians of research centres or clinicians all around the world caring for previously reported patients were contacted to provide followup information or additional clinical, biochemical, histological/histochemical, and molecular genetics data for unreported cases with a confirmed molecular diagnosis of deoxyguanosine kinase deficiency. A cohort of 202 genetically confirmed patients, 36 unreported, and 166 from a systematic literature review, were analyzed. Patients had a neonatal onset (≤ 1 month) in 55.7% of cases, infantile (>1 month and ≤ 1 year) in 32.3%, pediatric (>1 year and ≤18 years) in 2.5% and adult (>18 years) in 9.5%. Kaplan-Meier analysis showed statistically different survival rates (P < 0.0001) among the four age groups with the highest mortality for neonatal onset. Based on the clinical phenotype, we defined four different clinical subtypes: hepatocerebral (58.8%), isolated hepatopathy (21.9%), hepatomyoencephalopathy (9.6%), and isolated myopathy (9.6%). Muscle involvement was predominant in adult-onset cases whereas liver dysfunction causes morbidity and mortality in early-onset patients with a median survival of less than 1 year. No genotype-phenotype correlation was identified. Liver transplant significantly modified the survival rate in 26 treated patients when compared with untreated. Only six patients had additional mild neurological signs after liver transplant. In conclusion, deoxyguanosine kinase deficiency is a disease spectrum with a prevalent liver and brain tissue specificity in neonatal and infantile-onset patients and muscle tissue specificity in adult-onset cases. Our study provides clinical, molecular genetics and biochemical data for early diagnosis, clinical trial planning and immediate intervention with liver transplant and/or nucleoside supplementation.

An autosomal recessive variant in PYGM causes myophosphorylase deficiency in Red Angus composite cattle

BackgroundBetween 2020 and 2022, eight calves in a Nebraska herd (composite Simmental, Red Angus, Gelbvieh) displayed exercise intolerance during forced activity. In some cases, the calves collapsed and did not recover. Available sire pedigrees contained a paternal ancestor within 2–4 generations in all affected calves. Pedigrees of the calves’ dams were unavailable, however, the cows were ranch-raised and retained from prior breeding seasons, where bulls used for breeding occasionally had a common ancestor. Therefore, it was hypothesized that a de novo autosomal recessive variant was causative of exercise intolerance in these calves.ResultsA genome-wide association analysis utilizing SNP data from 6 affected calves and 715 herd mates, followed by whole-genome sequencing of 2 affected calves led to the identification of a variant in the gene PYGM (BTA29:g.42989581G > A). The variant, confirmed to be present in the skeletal muscle transcriptome, was predicted to produce a premature stop codon (p.Arg650*). The protein product of PYGM, myophosphorylase, breaks down glycogen in skeletal muscle. Glycogen concentrations were fluorometrically assayed as glucose residues demonstrating significantly elevated glycogen concentrations in affected calves compared to cattle carrying the variant and to wild-type controls. The absence of the PYGM protein product in skeletal muscle was confirmed by immunohistochemistry and label-free quantitative proteomics analysis; muscle degeneration was confirmed in biopsy and necropsy samples. Elevated skeletal muscle glycogen persisted after harvest, resulting in a high pH and dark-cutting beef, which is negatively perceived by consumers and results in an economic loss to the industry. Carriers of the variant did not exhibit differences in meat quality or any measures of animal well-being.ConclusionsMyophosphorylase deficiency poses welfare concerns for affected animals and negatively impacts the final product. The association of the recessive genotype with dark-cutting beef further demonstrates the importance of genetics to not only animal health but to the quality of their product. Although cattle heterozygous for the variant may not immediately affect the beef industry, identifying carriers will enable selection and breeding strategies to prevent the production of affected calves.

A novel ITGA2B double cytosine frameshift variant (c.1986_1987insCC) leads to Glanzmann's thrombasthenia in a cat.

Glanzmann's thrombasthenia (GT) is a congenital platelet disorder affecting approximately 1:1 000 000 people globally and characterized by impaired platelet aggregation and clot retraction. Autosomal recessive, loss-of-function, variants in ITGA2B or ITGB3 of the αIIbβ3 receptor cause the disease in humans. A cat affected by Glanzmann's and macrothrombocytopenia was presented to the UC Davis VMTH. Severe thrombopathia in this cat has an underlying genetic etiology. A single affected patient, 2 age-matched clinically healthy controls, and a geriatric population (n = 20) of normal cats. Physical examination and clinical pathology tests were performed on the patient. Flow cytometry and platelet aggregometry analyses for patient phenotyping were performed. Patient and validation cohort gDNA samples were extracted for Sanger sequencing of a previously identified ITGA2B (c.1986delC) variant. Reverse transcriptase PCR was performed on patient and healthy control PRP samples to verify ITGA2B variant consequence. A novel c.1986_1987insCC autosomal recessive variant in ITGA2B was identified. This variant was absent in a population of 194 unrelated cats spanning 44 different breeds. Complete loss of ITGA2B transcript and protein expression was verified by RT-PCR and flow cytometry, explaining the underlying etiology of GT, and likely macrothrombocytopenia, in this cat. This study emphasizes the role of precision medicine in cardiovascular disease of cats and identified yet another variant that may be of utility for screening in the feline population. This study provides a small-volume, standardized, successful protocol for adequate platelet RNA isolation and subsequent molecular assessment of gene expression in cats.

Congenital Myasthenic Syndromes

Congenital myasthenic syndromes (CMS) are characterized by congenital defects in the neuromuscular signal transmission and are caused by pathogenic variants in 36 genes. Recently identified forms of CMS include TOR1AIP1-CMS, CHD8-CMS, PURA-CMS, and TEFM-CMS. Most forms of CMS are caused by autosomal recessive variants, whereas four forms of CMS are caused by autosomal dominant variants, in which adult-onset cases are not rare. As myasthenic features are not always observed and muscle hypotrophy is sometimes observed, CMS should be considered in differential diagnosis of congenital myopathies and other neuromuscular diseases. Low- and high-frequency repetitive nerve stimulation is essential to diagnose CMS for patients who develop muscle weakness at less than 2 years of age. Tubular aggregates are observed in muscle biopsy in four forms of CMS, and serum CK levels are elevated in some forms of CMS. As rational therapies are available for most forms of CMS, identification of causative gene variants by genetic analysis is required.

Prenatal detection of novel compound heterozygous variants of the PLD1 gene in a fetus with congenital heart disease.

Congenital heart disease (CHD) is the most common birth defect and heart valve defects are the most common cardiac defect, accounting for over 25% of all congenital heart diseases. To date, more than 400 genes have been linked to CHD, the genetic analysis of CHD cases is crucial for both clinical management and etiological determination. Patients with autosomal-recessive variants of PLD1 are predisposed to Cardiac Valvular Dysplasia-1 (CVDP1), which predominantly affects the right-sided heart valves, including the pulmonic, tricuspid, and mitral valves. Databases were utilized to predict the impact of the c.1062-59A>G variant on splicing. Whole-exome sequencing (WES), reverse transcription polymerase chain reaction (RT-PCR), Sanger sequencing, and TA clone sequencing were conducted on both the parents and the fetus. A compound heterozygous variation in the PLD1(NM_002662.5):c.1937G>C (p. G646A) from the father and PLD1(NM_002662.5):c.1062-59A>G from the mother, was identified and confirmed in the fetus. The c.1937G>C (p. G646A) and the c.1062-59A>G variants were all classified as variant of uncertain significance (VUS) per ACMG guidelines. RT-PCR and TA clone sequencing revealed a 76-bp intronic insertion and exon 11 skipping in the proband and her mother's transcripts, causing a frameshift and premature stop codon in PLD1. Consequently, after being informed about the risks of their variant of unknown significance (VUS), the couple chose pre-implantation genetic testing for monogenic disorders (PGT-M) and had a healthy child. Our study identified novel variants to expand the mutation spectrum of CHD and provided reliable evidence for the recurrent risk and reproductive care options.