Background: Fabry disease is caused by α-galactosidase A deficiency. Substrates of this lysosomal enzyme accumulate, resulting in cellular dysfunction. Patients experience neuropathic pain, kidney failure, heart disease, and strokes. Scope of review:The clinical picture and molecular features of Fabry disease are described, along with updates on disease mechanisms, animal models, and therapies.Major conclusions: How the accumulation of α-galactosidase A substrates, mainly glycosphingolipids, leads to organ damage is incompletely understood. Enzyme replacement and chaperone therapies are clinically available to patients, while substrate reduction, mRNA-based, and gene therapies are on the horizon. Animal models exist to optimize these therapies and elucidate disease mechanisms for novel treatments.General significance: Recent newborn screening studies demonstrate that Fabry disease is the most common lysosomal storage disease. As many countries now include Fabry disease in their screening panels, the number of identified patients is expected to increase significantly. Better knowledge of disease pathogenesis is needed to improve treatment options.

The accumulation of misfolded proteins promotes protein aggregation and neuronal death in many neurodegenerative diseases. To counteract misfolded protein accumulation, neurons have pathways that recognize and refold or degrade aggregation-prone proteins. One U-box-containing E3 ligase, C terminus of Hsc70-interacting protein (CHIP), plays a key role in this process, targeting misfolded proteins for proteasomal degradation. CHIP plays a protective role in mouse models of neurodegenerative disease, and in humans, mutations in CHIP cause spinocerebellar ataxia autosomal recessive type 16 (SCAR16), a fatal neurodegenerative disease characterized by truncal and limb ataxia that results in gait instability. Here, we systematically analyzed CHIP mutations that cause SCAR16 and found that most SCAR16 mutations destabilize CHIP. This destabilization caused mutation-specific defects in CHIP activity, including increased formation of soluble oligomers, decreased interactions with chaperones, diminished substrate ubiquitination, and reduced steady-state levels in cells. Consistent with decreased CHIP stability promoting its dysfunction in SCAR16, most mutant proteins recovered activity when the assays were performed below the mutants' melting temperature. Together, our results have uncovered the molecular basis of genetic defects in CHIP function that cause SCAR16. Our insights suggest that compounds that improve the thermostability of genetic CHIP variants may be beneficial for treating patients with SCAR16.

BACKGROUND Recent reports suggest that maternal immunization against low-frequency, platelet (PLT)-specific glycoprotein (GP) polymorphisms is a more common cause of neonatal alloimmune thrombocytopenia (NATP) than previously thought. STUDY DESIGN AND METHODS Serologic and molecular studies were performed on PLTs and DNA from three families in which an infant was born with apparent NATP not attributable to maternal immunization against known PLT-specific alloantigens. RESULTS Antibodies reactive only with paternal PLTs were identified in each mother. In Cases 2 (Kno) and 3 (Nos), but not Case 1 (Sta), antibody recognized paternal GPIIb/IIIa in solid-phase assays. Unique mutations encoding amino acid substitutions in GPIIb (Case 2) or GPIIIa (Cases 1 and 3) were identified in paternal DNA and in DNA from two of the affected infants. Antibody from all three cases recognized recombinant GPIIIa (Case 1 [Sta] and Case 3 [Nos]) and GPIIb (Case 2, Kno) mutated to contain the polymorphisms identified in the respective fathers. None of 100 unselected normal subjects possessed the paternal mutations. Enzyme-linked immunosorbent assay and flow cytometric studies suggested that failure of maternal serum from Case 1 (Sta) to react with paternal GPIIIa in solid-phase assays resulted from use of a monoclonal antibody AP2, for antigen immobilization that competed with the maternal antibody for binding to the Sta epitope. CONCLUSION NATP in the three cases was caused by maternal immunization against previously unreported, low-frequency GP polymorphisms. Maternal immunization against low-frequency PLT-specific alloantigens should be considered in cases of apparent NATP not resolved by conventional serologic and molecular testing.

The polyglutamine (polyQ) diseases are a group of nine neurodegenerative diseases caused by the expansion of a polyQ tract that results in protein aggregation. Unlike other model organisms, Dictyostelium discoideum is a proteostatic outlier, naturally encoding long polyQ tracts yet resistant to polyQ aggregation. Here we identify serine-rich chaperone protein 1 (SRCP1) as a molecular chaperone that is necessary and sufficient to suppress polyQ aggregation. SRCP1 inhibits aggregation of polyQ-expanded proteins, allowing for their degradation via the proteasome, where SRCP1 is also degraded. SRCP1's C-terminal domain is essential for its activity in cells, and peptides that mimic this domain suppress polyQ aggregation in vitro. Together our results identify a novel type of molecular chaperone and reveal how nature has dealt with the problem of polyQ aggregation.

BACKGROUND Recent studies suggest that HPA-1a–specific, low-avidity maternal antibodies not detectable by conventional methods can cause neonatal alloimmune thrombocytopenia (NAIT). We performed studies to further define the incidence and clinical significance of this type of antibody. STUDY DESIGN AND METHODS Surface plasmon resonance analysis was used to detect low-avidity antibodies in HPA-1a–negative, “antibody-negative” mothers of suspected NAIT cases. The ability of antibodies detected to promote immune destruction of human platelets (PLTs) was examined in a newly developed NOD/SCID mouse model. RESULTS Among 3478 suspected cases of NAIT, 677 HPA-1a–negative mothers were identified. HPA-1a–specific antibodies were detected by conventional antibody testing in 616 cases (91%). Low-avidity HPA-1a–specific antibodies were identified in 18 of the remaining 61 cases (9%). Clinical follow-up on 13 cases showed that eight were referred because of suspected NAIT and five because the mother’s sister had previously had an infant with NAIT. Only six infants born to the 13 sensitized mothers had clinically significant thrombocytopenia at birth. Three of four low-avidity antibodies tested in the mouse caused accelerated clearance of HPA-1a/a but not HPA-1b/b PLTs. Only 3 of 12 mothers with low-avidity HPA-1a antibodies were positive for HLA-DRB3*0101. CONCLUSIONS The findings confirm previous reports that low-avidity HPA-1a antibodies can cause NAIT but show that the presence of such an antibody does not predict that an infant will be affected. The low incidence of HLA-DRB3*0101 in this cohort (p < 0.0001) suggests that women negative for DRB3*0101 may be predisposed to produce low-avidity HPA-1a antibodies.

Rare cases of COVID-19 vaccinated individuals develop anti-platelet factor 4 (PF4) antibodies that cause thrombocytopenia and thrombotic complications, a syndrome referred to as vaccine-induced immune thrombotic thrombocytopenia (VITT). Currently, information on the characteristics and persistence of anti-PF4 antibodies that cause VITT after Ad26.COV2.S vaccination is limited, and available diagnostic assays fail to differentiate Ad26.COV2.S and ChAdOx1 nCoV-19-associated VITT from similar clinical disorders, namely heparin-induced thrombocytopenia (HIT) and spontaneous HIT. Here we demonstrate that while Ad26.COV2.S-associated VITT patients are uniformly strongly positive in PF4-polyanion enzyme-linked immunosorbent assays (ELISAs); they are frequently negative in the serotonin release assay (SRA). The PF4-dependent p-selectin expression assay (PEA) that uses platelets treated with PF4 rather than heparin consistently diagnosed Ad26.COV2.S-associated VITT. Most Ad26.COV2.S-associated VITT antibodies persisted for >5 months in PF4-polyanion ELISAs, while the PEA became negative earlier. Two patients had otherwise unexplained mild persistent thrombocytopenia

COVID-19 vaccines have been associated with a rare life-threatening thrombotic and thrombocytopenic adverse reaction, vaccine-induced immune thrombotic thrombocytopenia (VITT) characterized by high levels of platelet-activating anti-platelet factor 4 (PF4) antibodies. In this study, we evaluated the pathogenesis and clonality of VITT antibodies from five patients with VITT secondary to ChAdOx1 nCoV-19 (n=1) and Ad26.COV2.S (n=4) vaccination. For comparative studies with heparin-induced thrombocytopenia (HIT), anti-PF4 antibodies were isolated from patients with spontaneous HIT, "classical" HIT, and patients with non-pathogenic anti-PF4 antibodies. Isolated antibodies were subject to ELISA, functional testing, and mass spectrometric evaluation. All five VITT patients had oligoclonal anti-PF4 antibodies (3 monoclonal, one bi- and one tri-clonal antibodies), while HIT anti-PF4 antibodies were polyclonal. Notably, like VITT, anti-PF4 antibodies from a spontaneous HIT patient were monoclonal. Polyclonal anti-PF4 antibodies were detected by mass spectrometry in one patient with non-pathogenic HIT, while none were detected in two others. The ChAdOx1 nCoV-19-associated VITT patient made an excellent recovery on heparin, and in vitro studies demonstrated inhibition of VITT antibody-induced platelet activation with therapeutic concentrations of heparin in this and all four Ad26.COV2.S-associated VITT patients. Persistent platelet-activating antibodies were detected at 1.5 and 2.5 months after acute presentation in two patients tested. This study demonstrates that mono/oligoclonal anti-PF4 antibodies mediate VITT and are frequently persistent. As VITT antibody-mediated platelet activation is inhibited by heparin, additional studies to evaluate a potential role of heparin treatment in VITT may be warranted.

BACKGROUND Maternal immunization against low-frequency, platelet (PLT)-specific antigens is being recognized with increasing frequency as a cause of neonatal alloimmune thrombocytopenia (NAIT). STUDY DESIGN AND METHODS Serologic and molecular studies were performed on PLTs and DNA from two families in which an infant was born with severe thrombocytopenia not attributable to maternal immunization against known PLT-specific alloantigens. RESULTS Antibodies reactive only with paternal PLTs were identified in each mother using flow cytometry and solid-phase assays. Unique mutations encoding amino acid substitutions K164T in glycoprotein (GP)IIb (Case 1) and R622W in GPIIIa (Case 2) were identified in paternal DNA and in DNA from the affected infants. Each maternal antibody recognized recombinant GPIIb/IIIa mutated to contain the polymorphisms identified in the corresponding father. None of 100 unselected normal subjects possessed these paternal mutations. CONCLUSIONS Severe NAIT observed in the affected infants was caused by maternal immunization against previously unrecognized, low-frequency antigens created by amino acid substitutions in GPIIb/IIIa (αIIb/β3 integrin). A search should be conducted for novel paternal antigens in cases of apparent NAIT not explained on the basis of maternal-fetal incompatibility for known human PLT antigens.