Unrelated Kindreds Research Articles

SARS-CoV-2 brainstem encephalitis in human inherited DBR1 deficiency.

Inherited deficiency of the RNA lariat-debranching enzyme 1 (DBR1) is a rare etiology of brainstem viral encephalitis. The cellular basis of disease and the range of viral predisposition are unclear. We report inherited DBR1 deficiency in a 14-year-old boy who suffered from isolated SARS-CoV-2 brainstem encephalitis. The patient is homozygous for a previously reported hypomorphic and pathogenic DBR1 variant (I120T). Consistently, DBR1 I120T/I120T fibroblasts from affected individuals from this and another unrelated kindred have similarly low levels of DBR1 protein and high levels of RNA lariats. DBR1 I120T/I120T human pluripotent stem cell (hPSC)-derived hindbrain neurons are highly susceptible to SARS-CoV-2 infection. Exogenous WT DBR1 expression in DBR1 I120T/I120T fibroblasts and hindbrain neurons rescued the RNA lariat accumulation phenotype. Moreover, expression of exogenous RNA lariats, mimicking DBR1 deficiency, increased the susceptibility of WT hindbrain neurons to SARS-CoV-2 infection. Inborn errors of DBR1 impair hindbrain neuron-intrinsic antiviral immunity, predisposing to viral infections of the brainstem, including that by SARS-CoV-2.

A TNIP1-driven systemic autoimmune disorder with elevated IgG4

Whole-exome sequencing of two unrelated kindreds with systemic autoimmune disease featuring antinuclear antibodies with IgG4 elevation uncovered an identical ultrarare heterozygous TNIP1Q333P variant segregating with disease. Mice with the orthologous Q346P variant developed antinuclear autoantibodies, salivary gland inflammation, elevated IgG2c, spontaneous germinal centers and expansion of age-associated B cells, plasma cells and follicular and extrafollicular helper T cells. B cell phenotypes were cell-autonomous and rescued by ablation of Toll-like receptor 7 (TLR7) or MyD88. The variant increased interferon-β without altering nuclear factor kappa-light-chain-enhancer of activated B cells signaling, and impaired MyD88 and IRAK1 recruitment to autophagosomes. Additionally, the Q333P variant impaired TNIP1 localization to damaged mitochondria and mitophagosome formation. Damaged mitochondria were abundant in the salivary epithelial cells of Tnip1Q346P mice. These findings suggest that TNIP1-mediated autoimmunity may be a consequence of increased TLR7 signaling due to impaired recruitment of downstream signaling molecules and damaged mitochondria to autophagosomes and may thus respond to TLR7-targeted therapeutics.

Clinical, immunological, and genetic description of a Mexican cohort of patients with DOCK8 deficiency.

We aimed to describe the clinical, immunological, and genetic features of patients with DOCK8 deficiency (DOCK8-Def) in a tertiary care center for children. Retrospective chart review of patients' clinical, immunological, and genetic characteristics with DOCK8-Def. Genetic analysis was performed with targeted- or whole-exome sequencing; we also assessed DOCK8 protein expression and a lymphoproliferation assay and analyzed survival by the Kaplan-Meier method. We described 11 patients from 8 unrelated kindreds. The median age at symptoms' onset was 10 months (range 1-54 months). The median follow-up time was 53.4 months (4.8-118.8). All patients presented eczema and recurrent sinopulmonary and cutaneous infections. Besides those symptoms, the most frequent manifestations were bronchiectases (8/11), food allergies (6/11), and severe infections (6/11). Infrequent characteristics were detection of CMV in bronchial lavage, C. parvum-driven sclerosing cholangitis, Takayasu vasculitis, neurological syndromes, pulmonary tuberculosis, and lymphomatoid granulomatosis. DOCK8-Def has a broad spectrum of manifestations, including allergy, autoimmunity, inflammation, infection, and cancer. The hallmark of this inborn error of immunity is IEI-associated eczema with eosinophilia and increased IgE. Here, we report six new mutations causing human DOCK8 deficiency and symptoms previously unrecognized to occur in DOCK8-Def. Therefore, an early diagnosis of DOCK8-Def is essential to facilitate an adequate treatment such as HSCT.

Familial Variability of Disease Severity in Adult Patients With ADPKD

Autosomal dominant polycystic kidney disease (ADPKD) is the most common monogenic nephropathy and has striking familial variability of disease severity. To better comprehend familial phenotypic variability, we analyzed clinical and pedigree data on 92 unrelated ADPKD kindreds with≥2 affected individuals (N= 292) from an Irish population. All probands underwent genetic sequencing. Age at onset of kidney failure (KF), decline in estimated glomerular filtration rate (eGFR), predicting renal outcome in polycystic kidney disease (PROPKD) score, and imaging criteria were used to assess and grade disease severity as mild, intermediate, or severe. One mild and 1 severe case per family defined marked intrafamilial variability of disease severity. Marked intrafamilial variability was observed in at least 13% of the 92 families, with a higher proportion of families carrying PKD1-nontruncating (PKD1-NT) variants. In families with≥2 members affected by KF, the average intrafamilial age difference was 7 years, and there was no observed difference in intrafamilial variability of age at KF between allelic groups. The prespecified criteria showed marked familial variability in 7.7%, 8.4%, and 24% for age at KF, the PROPKD score, and imaging criteria, respectively. In our multivariate mixed-effects model, the intrafamilial variability in kidney survival was independent of the measured genotypic factors associated with prognosis and survival (P=<0.001). Using objective measures, we quantified marked intrafamilial variability in ADPKD disease phenotype in at least 13% of families. Our findings indicate that intrafamilial phenotypic variability remains incompletely understood and necessitates a more thorough identification of relevant clinical and genotypic factors.

GCM2 p.Tyr394Ser variant in Ashkenazi Israeli patients with suspected familial isolated hyperparathyroidism.

A germline mutation can be identified in up to 10% of patients with primary hyperparathyroidism (PHPT). In 2017, a high frequency of the GCM2 [(NM_ 004752.4) c.1181A> C; p.Tyr394Ser; rs142287570] variant was reported in PHPT Ashkenazi Jews (AJ). To evaluate the presence of the GCM2 p.Tyr394Ser variant in Israeli patients addressed for genetic evaluation to characterize their phenotype and clinical management. Patients with PHPT who underwent addressed for genetic screening for suspected familial hypocalciuric hypercalcemia (FHH), a family history of isolated hyperparathyroidism (FIHP), or failed parathyroidectomy with persistent PHPT were recruited. Those with normal initial selected gene sequencing or hyperparathyroid genetic panel completed the GCM2 p.Tyr394Ser variant sequencing. The prevalence of this variant was evaluated using our local genomic database. A total of 42 single individuals from unrelated kindreds were evaluated. A disease-causing mutation was found in 11 (26.1%) patients: 10 were diagnosed with FHH (eight CASR and two AP2S1 mutations), and one patient had a CKN2B mutation. In 28 of the remaining patients, the GCM2 p.Tyr394Ser variant was positive in three (10.7%), and all were AJ. Within AJ (15/28, 53.5%), the rate of the p.Tyr394Ser variant was 3/15 (20%), and of those, two had a history of familial isolated hyperparathyroidism. Multi-glandular parathyroid adenoma/hyperplasia was also observed in two of these patients. No clinical or laboratory findings could discriminate patients with the GCM2 p.Tyr394Ser variant from those with FHH. Cinacalcet normalized the calcium levels in one patient. The prevalence of the GCM2 p.Tyr394Ser variant in 15,407 tests in our local genomic database was 0.98%. In contrast to previous observations, the GCM2 p.Tyr394Ser variant-associated phenotype may be mild in AJ with FIHP, sometimes mimicking FHH. Because surgery may be curative, surgeons should be aware of the possibility of multiple gland diseases in these patients. The clinical spectrum and clinical utility of screening for this variant warrant further investigation.

Human IL-23 is essential for IFN-γ-dependent immunity to mycobacteria

Patients with autosomal recessive (AR) IL-12p40 or IL-12RB1 deficiency display Mendelian susceptibility to mycobacterial disease (MSMD) due to impaired IFN-g production and, less commonly, chronic mucocutaneous candidiasis (CMC) due to impaired IL-17A/F production. We report six patients from four unrelated kindreds with AR IL-23R deficiency. All six patients have a history of MSMD but only two suffered from CMC. The four IL23R variants are associated with IL-23R loss of function, both in an isogenic overexpression assay and in the patients’ derived cells. We observe that IL-23R deficiency impairs baseline IFN-g immunity in at least 19 leukocyte subsets, including lymphoid and myeloid subsets, in vivo, without affecting their development per se. After IL-23 stimulation, we observe IFN-g induction in innate-like adaptive (MAIT, Vd2+ gd T) and innate (NK) lymphocytes in healthy controls but not in IL-23R-deficient patients, suggesting that IL-23 act as an early IFN-g-inducing cytokine in these cells, which, in turn, induce IFN-g-dependent transcriptional programs in both lymphoid and myeloid leukocyte subsets. Upon mycobacterial infection ex vivo, we find impaired IFN-g production by IL-23R-deficient MAIT and Vd2+ gd T cells, and to a lower extend in IL-23R-deficient CD4+ T cells. IL-23 is thus required for both baseline and Mycobacterium-inducible IFN-g immunity in at least MAIT and Vd2+ gd T cells, probably contributing to the complete penetrance of MSMD in IL-23R-deficient patients. MAIT cells from IL-23R-deficient patients display impaired IL-17A induction upon IL-23 stimulation, and PBMCs from IL-23R-deficient patients display impaired IL-17A/F production in response to heat-killed C. albicans, probably accounting for their risk of CMC. We observe normal development of Mycobacterium- and C. albicans-specific CD4+ memory T cells in IL-23R-deficient patients, possibly accounting for the absence of mycobacterial disease recurrence and the incomplete penetrance of CMC in these patients, respectively. Overall, our findings suggest that human IL-12 and IL-23 are functionally more closely related, via their induction of IFN-g, than previously thought based on the classical TH1/TH17 paradigm established in mice. They further suggest that the mechanisms underlying the therapeutic efficacy of IL-23p19 blockers may involve an inhibition, not only of excessive IL-17 immunity, but also of excessive IFN-g immunity.

Strong adaptive immunity in humans with inherited CD4 deficiency

Abstract Since the early 1970s when the T cell receptor was first characterized, the role of human CD4 in adaptative immunity has been extensively studied, especially in the context of HIV infection and inborn error of immunity (e.g. HLA class II deficiency). Nonetheless, it was only recently (2019, 2021) that patients with inactivating germline mutations in CD4has been described. Herein, we present five novel patients from three unrelated kindred with bi-allelic rare variants in CD4. Consistent with previous studies, patients showed a broad spectrum of clinical infectious susceptibility which was rather mild given their lack of detectable CD4 +T cells in peripheral blood mononuclear cells (PBMCs). Despite an almost unremarkable immunophenotype, patient’s PBMCs were characterized by the expansion of an enigmatic CD4 −CD8 −(DN) TCRαβ +T cells population which retained some functional characteristic of typical CD4 +T cells. We observed that the patient’s DN cells transcriptionally (Sc-RNAseq) and functionally (cytokine production/secretion) were comparable to that of healthy donor CD8 −T cells. Interestingly, using cutting-edge long-read sc-RNAseq technology we revealed that patient’s DN cells expressed normal TCR repertoires, and paired TCRαβ sequences comparable to healthy donor CD4 +T cells. Furthermore, via biochemical studies we identified a CD4alternative transcript expressed in patient’s PBMCs (also detected in healthy donor cells) leading to the surface expression of an unreported CD4 shorter isoform which is not detectable with conventional CD4 antibodies. To conclude, our study not only characterizes novel CD4-deficient patients, but also reveals alternative CD4 isoform expression and its compensatory role in immunity. AAI Careers in Immunology Fellowship 2022 (RG222573)

Biallelic deleterious germline SH2B3 variants cause a novel syndrome of myeloproliferation and multi-organ autoimmunity.

SH2B3 is a negative regulator of multiple cytokine receptor signalling pathways in haematopoietic tissue. To date, a single kindred has been described with germline biallelic loss-of-function SH2B3 variants characterized by early onset developmental delay, hepatosplenomegaly and autoimmune thyroiditis/hepatitis. Herein, we described two further unrelated kindreds with germline biallelic loss-of-function SH2B3 variants that show striking phenotypic similarity to each other as well as to the previous kindred of myeloproliferation and multi-organ autoimmunity. One proband also suffered severe thrombotic complications. CRISPR-Cas9 gene editing of zebrafish sh2b3 created assorted deleterious variants in F0 crispants, which manifest significantly increased number of macrophages and thrombocytes, partially replicating the human phenotype. Treatment of the sh2b3 crispant fish with ruxolitinib intercepted this myeloproliferative phenotype. Skin-derived fibroblasts from one patient demonstrated increased phosphorylation of JAK2 and STAT5 after stimulation with IL-3, GH, GM-CSF and EPO compared to healthy controls. In conclusion, these additional probands and functional data in combination with the previous kindred provide sufficient evidence for biallelic homozygous deleterious variants in SH2B3 to be considered a valid gene-disease association for a clinical syndrome of bone marrow myeloproliferation and multi-organ autoimmune manifestations.

Liver pathology in retinal vasculopathy with cerebral leukoencephalopathy and systemic manifestations: vasculopathic disease beyond nodular regenerative hyperplasia

Retinal vasculopathy with cerebral leukoencephalopathy and systemic manifestations (RVCL-S) is a rare autosomal dominant disease resulting from a frame-shift mutation in TREX1, an intracellular 3'-5' exonuclease 1. Hepatic findings include an elevated alkaline phosphatase (ALP) and nodular regenerative hyperplasia (NRH). Affected individuals typically succumb to brain lesions before clinically apparent hepatic manifestations; thus, little else is known about the hepatic pathology. Autopsy reports and a liver section from each (n=11) of three unrelated kindreds with the most common mutation in TREX1 (V235Gfs∗6) were studied with standard and immunohistochemical stains. Cases were compared with "normal liver" controls from similar autopsy years. Cases consisted of six men and five women who died at a median age of 50yr(range, 41-60 yr.). Seven had elevated ALP. Two had liver atrophy. Foci of NRH were variably detected in all. Inhomogeneous distribution of other findings included patternless parenchymal fibrous bands, approximation of vascular structures, and commonly, architectural changes of vascular structures. Only bile duct epithelia were unaffected. In addition, small trichrome-positive nodules were found along vein walls or isolated in the parenchyma. Rare foci of non-NRH hepatocytic nodules were noted in 3. Increased CD34 and altered α-SMA IHC expression were variably noted. Periportal ductules and perivenular K7 IHC expression were increased to unpredictable degrees. The extensive but inhomogeneous histopathologic findings in livers of autopsied patients with RVCL-S appear to involve hepatic vascular structures. These findings validate inclusion of vascular liver involvement beyond NRH in this complex hereditary disorder.

Mendelian Susceptibility to Mycobacterial Disease (MSMD): Clinical, Immunological, and Genetic Features of 22 Patients from 15 Moroccan Kindreds.

The first molecular evidence of a monogenic predisposition to mycobacteria came from the study of Mendelian susceptibility to mycobacterial disease (MSMD). We aimed to study this Mendelian susceptibility to mycobacterial diseases in Moroccan kindreds through clinical, immunological, and genetic analysis. Patients presented with clinical features of MSMD were recruited into this study. We used whole blood samples from patients and age-matched healthy controls. To measure IL-12 and IFN-γ production, samples were activated by BCG plus recombinant human IFN-γ or recombinant human IL-12. Immunological assessments and genetic analysis were also done for patients and their relatives. Our study involved 22 cases from 15 unrelated Moroccan kindreds. The average age at diagnosis is 4years. Fourteen patients (64%) were born to consanguineous parents. All patients were vaccinated with the BCG vaccine, and twelve of them (55%) developed locoregional or disseminated BCG infections. The other symptomatic patients had severe tuberculosis and/or recurrent salmonellosis. Genetic mutations were identified on the following genes: IL12RB1 in 8 patients, STAT1 in 7 patients; SPPL2A, IFNGR1, and TYK2 in two patients each; and TBX21 in one patient, with different modes of inheritance. All identified mutations/variants altered production or response to IFN-γ or both. Severe forms of tuberculosis and complications of BCG vaccination may imply a genetic predisposition present in the Moroccan population. In the presence of these infections, systematic genetic studies became necessary. BCG vaccination is contraindicated in MSMD patients and should be delayed in newborn siblings until the exclusion of a genetic predisposition to mycobacteria.

Analysis of a large case series of fatal familial insomnia to determine tests with the highest diagnostic value.

Fatal familial insomnia (FFI) is a rare prionopathy with unusually high incidence in the Basque Country. We report detailed data on clinical, diagnostic, histopathological, and biochemical characteristics of a recent FFI case series. The Basque Brain Bank database was screened for patients diagnosed from 2010 to 2021 with standard genetic and/or neuropathological criteria. This series includes 16 patients, 25% without family history, with 12 cases from 9 unrelated (but geographically-linked, Basque country) kindreds, onset ranging from 36 to 70 years, and disease course from 7 to 11.5 months. Insomnia was the initial symptom in most cases, with consistent polysomnography in 92% of the cases. In contrast, 14-3-3 and RT-QuIC from cerebrospinal fluid were negative. Most patients were homozygous for methionine. Gliosis and neuronal loss in basal ganglia and thalamus were the main histopathological findings; Western blotting identified preferentially the protease-resistant prion protein (PrPres) type 2, although detection of the scrapie isoform of the prion protein (PrPSc) identified using brain tissue RT-QuIC was more successful. This is one of the largest current studies on FFI patients performed to provide improvements in diagnostic reliability. Among the analyzed tests, polysomnography and the genetic study show the highest diagnostic value in FFI.

Biallelic Deleterious Germline SH2B3 Variants Cause a Novel Clinical Syndrome of Myeloproliferation and Multi-Organ Autoimmunity

SH2B3 is a negative regulator of cytokine receptor signalling pathways in hematopoietic tissue. Acquired deleterious SH2B3 variants resulting in increased JAK/STAT signalling are observed in myeloproliferative neoplasms (MPN) however the clinical implications and phenotype of deleterious germline variants in SH2B3 are less clear. A single consanguineous kindred has been previously described with homozygous deleterious germline SH2B3 variants presenting with hepatosplenomegaly, autoimmune hepatitis, developmental delay, autoimmune thyroiditis and acute lymphoblastic leukemia (Perez-Garcia, A., et al, Blood, 2013), however a clinically valid gene-disease pair according to formal criteria has not been met to date for SH2B3. We identified two probands from unrelated kindred with germline homozygous deleterious SH2B3 variants. The first patient presented with splenomegaly, thrombocytosis, neutrophilia and a leukoerythroblastic blood film at 3 months old. He developed alopecia areata at 2 years and autoimmune hypothyroidism at 6 years. He was otherwise developmentally normal without any detected liver abnormalities or thrombotic episodes. Whilst his splenomegaly and neutrophil count gradually improved throughout life, his platelet count remained markedly elevated (~1000x109/L at 18 years of age). Targeted NGS identified a homozygous frameshift variant in SH2B3 (NM_005475.3:c.441_468del; p.(Arg148Profs*40)). Both parents were heterozygous carriers of this variant. The second patient was a male born to consanguineous parents and noted shortly after birth to have isolated splenomegaly. He was diagnosed with autoimmune hypothyroidism and Raynaud syndrome at 12 years and was noted to have a persistent thrombocytosis ranging from 550 - 780 x109/L. He developed autoimmune hepatitis and insulin dependent diabetes at 17 years and around the same time he also suffered a right-sided middle cerebral artery territory infarct with a right carotid artery thrombus. Whole genome sequencing detected a homozygous missense variant in SH2B3 (NM_005475.3:c.1204G>A; p.(Val402Met)) in the patient with both parents being heterozygous carriers. In order to understand these variants further we modelled the human p.(Arg148Profs*40) variant from patient 1 in zebrafish. CRISPR-Cas9 gene editing was targeted to the analogous region of zebrafish sh2b3 to create assorted carboxyl-truncating mutations in F0 crispants. On-target gene-editing was verified by Sanger sequencing and NGS. F0 crispants had a significantly increased number of macrophages and CD41-expressing cells (HSCs and thrombocytes), replicating the patient phenotype. Treatment of the sh2b3 crispant fish with the JAK inhibitor ruxolitinib intercepted the myeloproliferative phenotype. The myeloproliferative phenotype was not observed in stable deletion mutants, likely reflecting genetic compensation not present in crispants. Skin-derived fibroblasts from patient 2 who carried the Val402Met homozygous variant, showed increased phosphorylation of JAK2, STAT5 and STAT3 by immunoblotting after stimulation with IL3, GH, GM-CSF and EPO compared to healthy controls. In conclusion, these newly described kindreds showing striking phenotypic similarity to each other as well as the previously described kindred and in conjunction with our functional data provide sufficient evidence for biallelic homozygous deleterious variants in SH2B3 to be considered a valid gene-disease association with a clinical syndrome of bone marrow myeloproliferation and multi-organ autoimmune manifestations. Notably, neither of our patients had evidence of acute lymphoblastic leukemia or overt hematological malignancy and further affected individuals will need to be described in order to fully understand the breadth of the phenotype. Moreover, our data supports ruxolitinib as being a potential therapeutic option for patients with this rare novel immune dysregulatory syndrome.

A loss-of-function IFNAR1 allele in Polynesia underlies severe viral diseases in homozygotes.

Globally, autosomal recessive IFNAR1 deficiency is a rare inborn error of immunity underlying susceptibility to live attenuated vaccine and wild-type viruses. We report seven children from five unrelated kindreds of western Polynesian ancestry who suffered from severe viral diseases. All the patients are homozygous for the same nonsense IFNAR1 variant (p.Glu386*). This allele encodes a truncated protein that is absent from the cell surface and is loss-of-function. The fibroblasts of the patients do not respond to type I IFNs (IFN-α2, IFN-ω, or IFN-β). Remarkably, this IFNAR1 variant has a minor allele frequency >1% in Samoa and is also observed in the Cook, Society, Marquesas, and Austral islands, as well as Fiji, whereas it is extremely rare or absent in the other populations tested, including those of the Pacific region. Inherited IFNAR1 deficiency should be considered in individuals of Polynesian ancestry with severe viral illnesses.

RET Proto-Oncogene Mutational Analysis in 45 Iranian Patients Affected with Medullary Thyroid Carcinoma: Report of a New Variant.

Background The aim of this study was to identify germline mutation of the RET (rearranged during transfection) gene in patients with medullary thyroid carcinoma (MTC) and their first-degree relatives to find presymptomatic carriers for possible prophylactic thyroidectomy. Methods/Patients. We examined all six hot spot exons (exons 10, 11, 13, and 14–16) of the RET gene by PCR and bidirectional Sanger sequencing in 45 Iranian patients with MTC (either sporadic or familial form) from 7 unrelated kindred and 38 apparently sporadic cases. First-degree relatives of RET positive cases were also genotyped for index mutation. Moreover, presymptomatic carriers were referred to the endocrinologist for further clinical management and prophylactic thyroidectomy if needed. Results Overall, the genetic status of all of the participants was determined by RET mutation screening, including 61 affected individuals, 22 presymptomatic carriers, and 29 genetically healthy subjects. In 37.5% (17 of 45) of the MTC referral index patients, 8 distinct RET germline mutations were found, including p.C634R (35.3%), p.M918T (17.6%), p.C634Y (11.8%), p.C634F (5.9%), p.C611Y (5.9%), p.C618R (5.9%), p.C630R (5.9%), p.L790F (5.9%), and one uncertain variant p.V648I (5.9%). Also, we found a novel variant p.H648R in one of our apparently sporadic patients. Conclusion RET mutation detection is a promising/golden screening test and provides an accurate presymptomatic diagnostic test for at-risk carriers (the siblings and offspring of the patients) to consider prophylactic thyroidectomy. Thus, according to the ATA recommendations, the screening of the RET proto-oncogene is indicated for patients with MTC.

Epistatic interaction of PDE4DIP and DES mutations in familial atrial fibrillation with slow conduction

The genetic causes of atrial fibrillation (AF) with slow conduction are unknown. Eight kindreds with familial AF and slow conduction, including a family affected by early-onset AF, heart block, and incompletely penetrant nonischemic dilated cardiomyopathy (DCM) underwent whole exome sequencing. A known pathogenic mutation in the desmin (DES) gene resulting in p.S13F substitution (NM_001927.3:c.38C>T) at a PKC phosphorylation site was identified in all four members of the kindred with early-onset AF and heart block, while only two developed DCM. Higher penetrance for AF and heart block prompted a genetic screening for DES modifier(s). A deleterious mutation in the phosphodiesterase-4D-interacting-protein (PDE4DIP) gene resulting in p.A123T substitution (NM_001002811:c.367G>A) was identified that segregated with early-onset AF, heart block, and the DES mutation. Three additional novel deleterious PDE4DIP mutations were identified in four other unrelated kindreds. Characterization of PDE4DIPA123T in vitro suggested impaired compartmentalization of PKA and PDE4D characterized by reduced colocalization with PDE4D, increased cAMP activation leading to higher PKA phosphorylation of the β2-adrenergic-receptor, and decreased PKA phosphorylation of desmin after isoproterenol stimulation. Our findings identify PDE4DIP as a novel gene for slow AF and unravel its epistatic interaction with DES mutations in development of conduction disease and arrhythmia.

B-AB13-03 NOVEL ROLE OF PDE4DIP IN FAMILIAL ATRIAL FIBRILLATION WITH SLOW VENTRICULAR RESPONSE

The genetic causes of atrial fibrillation (AF) with slow conduction are unknown. To investigate the genetic causes of familial atrial fibrillation with slow conduction. Eight kindreds with familial AF and slow conduction, including a family affected by early onset AF, heart block and incompletely penetrant non-ischemic cardiomyopathy (NICM) underwent whole exome sequencing. A known pathogenic mutation in the desmin (DES) gene resulting in S13F substitution at a PKC phosphorylation site was identified in all four members of the kindred with early-onset AF and heart block, while only two developed NICM. Higher penetrance of the mutation for AF and heart block prompted the screening for DES modifier(s). A second deleterious mutation in the phosphodiesterase 4D interacting-protein (PDE4DIP) gene resulting in A123T substitution segregated with early onset AF, heart block and the DES mutation. Three additional novel deleterious PDE4DIP mutations were identified in four other unrelated kindreds. Characterization of PDE4DIPA123T in vitro suggested impaired compartmentalization of PKA and PDE4D characterized by reduced colocalization with PDE4D, increased cAMP activation leading to higher PKA phosphorylation of the β2-adrenergic-receptor, and decreased PKA phosphorylation of Desmin in response to isoproterenol stimulation compared to wildtype PDE4DIP. Our findings identify an epistatic interaction between DES and PDE4DIP variants, increasing the penetrance for conduction disease and arrhythmia.

Inherited deficiency of stress granule ZNFX1 in patients with monocytosis and mycobacterial disease

Human inborn errors of IFN-γ underlie mycobacterial disease, due to insufficient IFN-γ production by lymphoid cells, impaired myeloid cell responses to this cytokine, or both. We report four patients from two unrelated kindreds with intermittent monocytosis and mycobacterial disease, including bacillus Calmette-Guérin-osis and disseminated tuberculosis, and without any known inborn error of IFN-γ. The patients are homozygous for ZNFX1 variants (p.S959* and p.E1606Rfs*10) predicted to be loss of function (pLOF). There are no subjects homozygous for pLOF variants in public databases. ZNFX1 is a conserved and broadly expressed helicase, but its biology remains largely unknown. It is thought to act as a viral double-stranded RNA sensor in mice, but these patients do not suffer from severe viral illnesses. We analyze its subcellular localization upon overexpression in A549 and HeLa cell lines and upon stimulation of THP1 and fibroblastic cell lines. We find that this cytoplasmic protein can be recruited to or even induce stress granules. The endogenous ZNFX1 protein in cell lines of the patient homozygous for the p.E1606Rfs*10 variant is truncated, whereas ZNFX1 expression is abolished in cell lines from the patients with the p.S959* variant. Lymphocyte subsets are present at normal frequencies in these patients and produce IFN-γ normally. The hematopoietic and nonhematopoietic cells of the patients tested respond normally to IFN-γ. Our results indicate that human ZNFX1 is associated with stress granules and essential for both monocyte homeostasis and protective immunity to mycobacteria.

Neurodevelopmental disorder in an Egyptian family with a biallelic ALKBH8 variant

Alkylated DNA repair protein AlkB homolog 8 (ALKBH8) is a member of the AlkB family of dioxygenases. ALKBH8 is a methyltransferase of the highly variable wobble nucleoside position in the anticodon loop of tRNA and thus plays a critical role in tRNA modification by preserving codon recognition and preventing errors in amino acid incorporation during translation. Moreover, its activity catalyzes uridine modifications that are proposed to be critical for accurate protein translation. Previously, two distinct homozygous truncating variants in the final exon of ALKBH8 were described in two unrelated large Saudi Arabian kindreds with intellectual developmental disorder and autosomal recessive 71 (MRT71) syndrome (MIM# 618504). Here, we report a third family-of Egyptian descent-harboring a novel homozygous frame-shift variant in the last exon of ALKBH8. Two affected siblings in this family exhibit global developmental delay and intellectual disability as shared characteristic features of MRT71 syndrome, and we further characterize their observed dysmorphic features and brain MRI findings. This description of a third family with a truncating ALKBH8 variant from a distinct population broadens the phenotypic and genotypic spectrum of MRT71 syndrome, affirms that perturbations in tRNA biogenesis can contribute to neurogenetic disease traits, and firmly establishes ALKBH8 as a novel neurodevelopmental disease gene.

Neuro-Ophthalmological Findings in Early Fatal Familial Insomnia.

Fatal familial insomnia (FFI) is a rare inherited prion disease characterized by sleep, autonomic, and motor disturbances. Neuro-ophthalmological abnormalities have been reported at the onset of disease, although not further characterized. We analyzed video recordings of eye movements of 6 patients with FFI from 3 unrelated kindreds, seen within 6 months from the onset of illness. Excessive saccadic intrusions were the most prominent findings. In patients with severe insomnia, striking saccadic intrusions are an early diagnostic clue for FFI. The fact that the thalamus is the first structure affected in FFI also suggests its role in the control of steady fixation. ANN NEUROL 2021;89:823-827.

Mutations in ASPRV1 Cause Dominantly Inherited Ichthyosis

The discovery of genetic causes of inherited skin disorders has been pivotal to the understanding of epidermal differentiation, function, and renewal. Here we show via exome sequencing that mutations in ASPRV1 (aspartic peptidase retroviral-like 1) cause a dominant Mendelian disorder featuring palmoplantar keratoderma and lamellar ichthyosis, a phenotype that has otherwise been exclusively recessive. ASPRV1 encodes a mammalian-specific and stratified epithelia-specific protease important in processing of filaggrin, a critical component of the uppermost epidermal layer. Three different heterozygous ASPRV1 missense mutations in four unrelated ichthyosis kindreds segregate with disease and disrupt protein residues within close proximity to each other and autocatalytic cleavage sites. Expression of mutant ASPRV1 proteins demonstrates that all three mutations alter ASPRV1 auto-cleavage and filaggrin processing, a function vital to epidermal barrier integrity.