Current advances in the understanding and treatment of mevalonate kinase deficiency

The pyrin inflammasome, a leading actor in pediatric autoinflammatory diseases

The activation of the pyrin inflammasome represents a highly intriguing mechanism employed by the innate immune system to effectively counteract pathogenic agents. Despite its key role in innate immunity, pyrin has also garnered significant attention due to its association with a range of autoinflammatory diseases (AIDs) including familial Mediterranean fever caused by disruption of the MEFV gene, or in other genes involved in its complex regulation mechanisms. Pyrin activation is strictly dependent on homeostasis-altering molecular processes, mostly consisting of the disruption of the small Ras Homolog Family Member A (RhoA) GTPases by pathogen toxins. The downstream pathways are regulated by the phosphorylation of specific pyrin residues by the kinases PKN1/2 and the binding of the chaperone 14-3-3. Furthermore, a key role in pyrin activation is played by the cytoskeleton and gasdermin D, which is responsible for membrane pores in the context of pyroptosis. In addition, recent evidence has highlighted the role of steroid hormone catabolites and alarmins S100A8/A9 and S100A12 in pyrin-dependent inflammation. The aim of this article is to offer a comprehensive overview of the most recent evidence on the pyrin inflammasome and its molecular pathways to better understand the pathogenesis behind the significant group of pyrin-related AIDs.

A Potential Partnership between Genetics and the Oral Microbiome in Children Displaying Periodic Fever/Aphthosis/Pharyngitis/Adenitis Syndrome

Periodic fever/aphthosis/pharyngitis/adenitis (PFAPA) syndrome was initially described in a small cohort of American children [...].

The Clinical Chameleon of Autoinflammatory Diseases in Children

The very first line of defense in humans is innate immunity, serving as a critical strongpoint in the regulation of inflammation. Abnormalities of the innate immunity machinery make up a motley group of rare diseases, named ‘autoinflammatory’, which are caused by mutations in genes involved in different immune pathways. Self-limited inflammatory bouts involving skin, serosal membranes, joints, gut and other districts of the human body burst and recur with variable periodicity in most autoinflammatory diseases (ADs), often leading to secondary amyloidosis as a long-term complication. Dysregulated inflammasome activity, overproduction of interleukin (IL)-1 or other IL-1-related cytokines and delayed shutdown of inflammation are pivotal keys in the majority of ADs. The recent progress of cellular biology has clarified many molecular mechanisms behind monogenic ADs, such as familial Mediterranean fever, tumor necrosis factor receptor-associated periodic syndrome (or ‘autosomal dominant familial periodic fever’), cryopyrin-associated periodic syndrome, mevalonate kinase deficiency, hereditary pyogenic diseases, idiopathic granulomatous diseases and defects of the ubiquitin-proteasome pathway. A long-lasting history of recurrent fevers should require the ruling out of chronic infections and malignancies before considering ADs in children. Little is known about the potential origin of polygenic ADs, in which sterile cytokine-mediated inflammation results from the activation of the innate immunity network, without familial recurrency, such as periodic fever/aphthous stomatitis/pharyngitis/cervical adenopathy (PFAPA) syndrome. The puzzle of febrile attacks recurring over time with chameleonic multi-inflammatory symptoms in children demands the inspection of the mixture of clinical data, inflammation parameters in the different disease phases, assessment of therapeutic efficacy of a handful of drugs such as corticosteroids, colchicine or IL-1 antagonists, and genotype analysis to exclude or confirm a monogenic origin.

Clinical impact and disease evolution of SARS-CoV-2 infection in familial Mediterranean fever

The innate immune system is critically involved in the pathogenesis of familial Mediterranean fever (FMF), characterized by dysregulated inflammasome activity and recurrent inflammatory attacks: this is the most common among monogenic autoinflammatory diseases, which shares some biochemical pathways with the severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infection. In this short review we explore the overlap in the pathophysiology of FMF and SARS-CoV-2 infection, discussing how to understand better the interaction between the two diseases and optimize management. A poorer outcome of SARS-CoV-2 infection seems not to be present in infected FMF patients in terms of hospitalization time, need for oxygen support, need for intensive care, rate of complications and exitus. Long-term surveillance will confirm the relatively low risk of a worse prognosis observed so far in SARS-CoV-2-infected people with FMF. In these patients COVID-19 vaccines are recommended and their safety profile is expected to be similar to the general population.

Haploidentical α/β T-cell and B-cell depleted stem cell transplantation in severe mevalonate kinase deficiency

OBJECTIVE

Mevalonic aciduria represents the most severe form of mevalonate kinase deficiency (MKD). Patients with mevalonic aciduria have an incomplete response even to high doses of anti-cytokine drugs such as anakinra or canakinumab and stem cell transplantation (SCT) represents a possible therapy for this severe disease.

METHODS

We report the first two children affected by severe MKD who received haploidentical α/β T-cell and B-cell depleted SCT. Both patients received a treosulfan-based conditioning regimen and one received a second haploidentical-SCT for secondary rejection of the first.

RESULTS

Both patients obtained a stable full donor engraftment with a complete regression of clinical and biochemical inflammatory signs, without acute organ toxicity or acute and chronic GvHD. In both, the urinary excretion of mevalonic acid remained high post-transplant in the absence of any inflammatory signs.

CONCLUSION

Haploidentical α/β T-cell and B-cell depleted SCT represents a potential curative strategy in patients affected by MKD. The persistence of urinary excretion of mevalonic acid after SCT, probably related to the ubiquitous expression of MVK enzyme, suggests that these patients should be carefully monitored after SCT to exclude MKD clinical recurrence. Prophylaxis with anakinra in the acute phase after transplant could represent a safe and effective approach. Further biological studies are required to clarify the pathophysiology of inflammatory attacks in MKD in order to better define the therapeutic role of SCT.

The everchanging framework of autoinflammation

The innate immunity works as a defence bullwark that safeguards healthy tissues with the power of detecting infectious agents in the human body: errors in the context of innate immunity identify autoinflammatory disorders (AIDs), which arise as bouts of aberrant inflammation with little or no involvement of T and B cells and neither recognized infections, nor associated autoimmune phenomena. Hereditary AIDs tend to have a pediatric-onset heralded by stereotyped inflammatory symptoms and fever, while AIDs without an ascertained cause, such as systemic juvenile idiopathic arthritis, derive from the interaction of genetic factors with environmental noxae and are unevenly defined. A dysregulated inflammasome activation promotes the best-known family of AIDs, as well as several degenerative and metabolic disorders, but also nuclear factor κB- and interferon-mediated conditions have been framed as AIDs: the zenith of inflammatory flares marks different phenotypes, but diagnosis may go unnoticed until adulthood due to downplayed symptoms and complex kaleidoscopic presentations. This review summarizes the main AIDs encountered in childhood with special emphasis on the clinical stigmata that may help establish a correct framework and blueprints to empower young scientists in the recognition of AIDs. The description focuses inflammasomopathies as paradigms of interleukinopathies, nuclear factor-κB -related disorders and interferonopathies. The challenges in the management of AIDs during childhood have been recently boosted by numerous therapeutic options derived from genomically-based approaches, which have led to identify targeted biologic agents as rationalized treatments and achieve more tangible perspectives of disease control.

Overview of the rarest causes of fever in newborns: handy hints for the neonatologist

Neonatal causes of fever are a major source of concern for clinicians. If fever is combined with organ-specific sterile inflammatory manifestations the suspicion of autoinflammatory disorders should be considered, and the list of such conditions starting in the neonatal period includes chronic infantile neurological cutaneous articular syndrome, mevalonate kinase deficiency, deficiency of the interleukin-1 receptor antagonist, otulipenia, STING-associated vasculopathy with onset in infancy and Blau syndrome. Other causes of noninfectious fever that can rarely occur in newborns are Kawasaki disease, Behçet's disease, and hemophagocytic lymphohistiocytosis. Diagnosis of these exceptionally rare disorders is challenging for neonatologists. An early recognition of these complex diseases might lead to use more specific or rational drugs preventing permanent consequences. This review focuses on the rarest causes of fever occurring in the neonatal age with the aim of portraying many protean clinical pictures associated with fever and reviewing the potential available treatments.

Primary Immunodeficiency and Thrombocytopenia

Primary immunodeficiency (PID) or Inborn errors of immunity (IEI) refers to a heterogeneous group of disorders characterized by immune system impairment. Although patients with IEI manifest highly variable symptoms, the most common clinical manifestations are recurrent infections, autoimmunity and malignancies. Some patients present hematological abnormality including thrombocytopenia due to different pathogenic mechanisms. This review focuses on primary and secondary thrombocytopenia as a complication, which can occur in IEI. Based on the International Union of Immunological Societies phenotypic classification for IEI, the several innate and adaptive immunodeficiency disorders can lead to thrombocytopenia. This review, for the first time, describes manifestation, mechanism and therapeutic modalities for thrombocytopenia in different classes of IEI.

Phenotype variability of autoinflammatory disorders in the pediatric patient: A pictorial overview

Disruption of innate immunity leading to systemic inflammation and multi-organ dysfunction is the basilar footprint of autoinflammatory disorders (AIDs), ranging from rare hereditary monogenic diseases to a large number of common chronic inflammatory conditions in which there is a simultaneous participation of multiple genetic components and environmental factors, sometimes combined with autoimmune phenomena and immunodeficiency. Whatever their molecular mechanism, hereditary AIDs are caused by mutations in regulatory molecules or sensors proteins leading to dysregulated production of proinflammatory cytokines or cytokine-inducing transcription factors, fever, elevation of acute phase reactants, and a portfolio of manifold inflammatory signs which might occur in a stereotyped manner, mostly with overactivity or misactivation of different inflammasomes. Symptoms might overlap in the pediatric patient, obscuring the final diagnosis of AIDs and delaying the most appropriate treatment. Actually, the fast-paced evolution of scientific knowledge has led to recognize or reclassify an overgrowing number of multifactorial diseases, which share the basic pathogenetic mechanisms with AIDs. The wide framework of classic hereditary periodic fevers, AIDs with prominent skin involvement, disorders of the ubiquitin-proteasome system, defects of actin cytoskeleton dynamics, and also idiopathic nonhereditary febrile syndromes occurring in children is herein presented. Interleukin-1 dependence of these diseases or involvement of other predominating molecules is also discussed.

Hints for Genetic and Clinical Differentiation of Adult-Onset Monogenic Autoinflammatory Diseases

Monogenic autoinflammatory diseases (mAIDs) are inherited errors of innate immunity characterized by systemic inflammation recurring with variable frequency and involving the skin, serosal membranes, synovial membranes, joints, the gastrointestinal tube, and/or the central nervous system, with reactive amyloidosis as a potential severe long-term consequence. Although individually uncommon, all mAIDs set up an emerging chapter of internal medicine: recent findings have modified our knowledge regarding mAID pathophysiology and clarified that protean inflammatory symptoms can be variably associated with periodic fevers, depicting multiple specific conditions which usually start in childhood, such as familial Mediterranean fever, tumor necrosis factor receptor-associated periodic syndrome, cryopyrin-associated periodic syndrome, and mevalonate kinase deficiency. There are no evidence-based studies to establish which potential genotype analysis is the most appropriate in adult patients with clinical phenotypes suggestive of mAIDs. This review discusses genetic and clinical hints for an ideal diagnostic approach to mAIDs in adult patients, as their early identification is essential to prompt effective treatment and improve quality of life, and also highlights the most recent developments in the diagnostic work-up for the most frequent hereditary periodic febrile syndromes worldwide.

Familial Mediterranean Fever: Assessing the Overall Clinical Impact and Formulating Treatment Plans

Recurrent self-limited attacks of fever and short-lived inflammation in the serosal membranes, joints, and skin are the leading features of familial Mediterranean fever (FMF), the most common autoinflammatory disorder in the world, transmitted as autosomal recessive trait caused by MEFV gene mutations. Their consequence is an abnormal function of pyrin, a natural repressor of inflammation, apoptosis, and release of cytokines. FMF-related mutant pyrins are hypophosphorylated following RhoA GTPases’ impaired activity and show a propensity to relapsing uncontrolled systemic inflammation with inappropriate response to inflammatory stimuli and leukocyte spread to serosal membranes, joints or skin. Typical FMF phenotype 1 consists of brief episodes of inflammation and serositis, synovitis, and/or erysipelas-like eruption, whereas phenotype 2 is defined by reactive amyloid-associated (AA) amyloidosis, which is the most ominous complication of FMF, in otherwise asymptomatic individuals.

Furthermore, FMF phenotype 3 is referred to the presence of two MEFV mutations with neither clinical signs of FMF nor AA amyloidosis. The influence of epigenetic and/or environmental factors can contribute to the variable penetrance and phenotypic heterogeneity of FMF. Colchicine, a tricyclic alkaloid with anti-microtubule and anti-inflammatory properties, is the bedrock of FMF management: daily administration of colchicine prevents the recurrence of FMF attacks and the development of secondary AA amyloidosis. Many recent studies have also shown that anti-interleukin-1 treatment is the best therapeutic option for FMF patients nonresponsive or intolerant to colchicine. This review aims to catch readers’ attention to the clinical diversity of phenotypes, differential diagnosis, and management of patients with FMF.

The Broad-Ranging Panorama of Systemic Autoinflammatory Disorders with Specific Focus on Acute Painful Symptoms and Hematologic Manifestations in Children

Systemic autoinflammatory disorders (SAIDs) are inherited defects of innate immunity characterized by recurrent sterile inflammatory attacks involving skin, joints, serosal membranes, gastrointestinal tube, and other tissues, which recur with variable rhythmicity and display reactive amyloidosis as a potential long-term complication. Dysregulated inflammasome activity leading to overproduction of many proinflammatory cytokines, such as interleukin-1 (IL-1), and delayed shutdown of inflammation are considered crucial pathogenic keys in the vast majority of SAIDs. Progress of cellular biology has partially clarified the mechanisms behind monogenic SAIDs, such as familial Mediterranean fever, tumor necrosis factor receptor-associated periodic syndrome, cryopyrin-associated periodic syndrome, mevalonate kinase deficiency, hereditary pyogenic diseases, idiopathic granulomatous diseases and defects of the ubiquitin-proteasome pathway. Whereas, little is clarified for the polygenic SAIDs, such as periodic fever, aphthous stomatitis, pharyngitis, and cervical adenopathy (PFAPA) syndrome. The puzzle of symptomatic febrile attacks recurring over time in children requires evaluating the mixture of clinical data, inflammatory parameters in different disease phases, the therapeutic efficacy of specific drugs such as colchicine, corticosteroids or IL-1 antagonists, and genotype analysis in selected cases. The long-term history of periodic fevers should also need to rule out chronic infections and malignancies. This review is conceived as a practical template for proper classification of children with recurring fevers and includes tips useful for the diagnostic approach to SAIDs, focusing on the specific acute painful symptoms and hematologic manifestations encountered in childhood.

New mosaic tiles in childhood hereditary autoinflammatory disorders

The protean clinical phenotypes of hereditary autoinflammatory disorders (HAID) are caused by abnormal activation of innate immunity and consist of seemingly unprovoked inflammatory flares localized to multiple organs, such as the skin, joints, serosal membranes, gut, and central nervous system. Different mutations in genes implied in activation of the interleukin-1 (IL-1)-structured inflammasome, cytoskeletal signaling and apoptosis contribute to the pathogenesis of different HAID, which mostly start in childhood with self-limited flares unrelated to infectious agents, autoantibody production or autoreactive cells. Though IL-1 remains pivotal in many inflammasome-mediated diseases, other cytokinopathies involving IL-18, nuclear factorκ-B, interferons, and tumor necrosis factor have provided new horizons in the definition of HAID of children: the list of HAID has expanded as a consequence of a better understanding of their pathogenetic molecular mechanisms and also application of new genetic technologies. However, diagnosis of most HAID is clinical and focused on several evidence-based criteria sets: their discrimination remains challenging for unexperienced pediatricians as there are no universally accepted algorithms, and a still relevant number of patients may linger without any clarifying genetic analysis, whose interpretation combined with processing of treatment options should be discussed on a multidisciplinary basis.

Autoinflammatory Reaction in Dogs Treated for Cancer via G6PD Inhibition

Glucose-6-phosphate dehydrogenase (G6PD) is an oncoprotein that is overexpressed in cancer cells to provide the NADPH required for their increased anabolism. NADPH, sourced from G6PD fuels nucleotide biosynthesis, maintains redox potential of thioredoxin and glutathione and drives the mevalonate pathway that powers many of the basic mechanisms by which cancer cells escape host control. G6PD is thus a target for cancer treatment being addressed by many groups around the world. We have discovered that systemic inhibition of G6PD by high dose dehydroepiandrosterone (DHEA) causes a severe autoinflammatory response in dogs, which does not occur in mice or rats. Since dogs more closely model the human adrenal androgen system than do common laboratory animals, this finding is relevant to the design of G6PD-inhibiting drugs for humans. The autoinflammatory reaction observed closely resembles mevalonate kinase deficiency (MKD), a rare autosomal recessive disease in humans characterized by recurrent febrile attacks, arthralgia, skin rash, and aphthous ulcers of mucocutaneous tissues. In a manner comparable to animal models of MKD, the reconstitution of protein geranylgeranylation blocked the autoinflammatory reaction caused by systemic G6PD inhibition. This autoinflammatory response to systemic G6PD inhibition represents an unexpected result that must be taken into consideration when targeting this oncoprotein.

An Up-to-date Approach to a Patient with a Suspected Autoinflammatory Disease

Autoinflammatory diseases (AID) are characterized by seemingly unprovoked self-limited attacks of fever and systemic inflammation potentially leading to amyloidosis. Familial Mediterranean fever (FMF) is the most common AID and therefore the most studied. Besides FMF, the other main hereditary AID are tumor necrosis factor-associated periodic fever syndrome (TRAPS), mevalonate kinase deficiency (MKD), and cryopyrin-associated periodic fever syndrome (CAPS). These hereditary diseases result from a mutant gene that is involved in the regulation of inflammation, resulting in a characteristic clinical phenotype. The differential diagnosis of AID can be challenging due to a wide overlap in clinical manifestations. Moreover, a considerable proportion of patients present with autoinflammatory symptoms but without a pathogenetic variant on genetic analysis. Furthermore, non-hereditary AID, such as the periodic fever, aphthous stomatitis, pharyngitis, adenitis (PFAPA) syndrome, which is the most common AID in children worldwide, must be excluded in certain circumstances. Herein we shall review the main AID and describe a practical approach to diagnosis in a patient with a clinical suspicion of AID.

Mevalonate kinase deficiency associated with ataxia and retinitis pigmentosa in two brothers with MVK gene mutations

PURPOSE

To report the clinical and molecular genetic findings in two brothers with retinitis pigmentosa (RP) and mevalonate kinase deficiency (MKD).

METHODS

The brothers were examined clinically and with fundus autofluorescence, near-infrared autofluorescence, and spectral domain optical coherence tomography. Targeted resequencing was done with a custom designed gene panel containing 78 genes associated with RP. Mutations were confirmed by direct Sanger sequencing.

RESULTS

Both brothers, aged 46 and 47 years, were found to carry compound heterozygous mutations in the MVK gene (c.59A>C, c.1000G>A) encoding mevalonate kinase. They presented with severe ataxia, pseudophakia due to early onset cataract, and progressed retinitis pigmentosa. In one brother with cystoid macular edema, treatment with dorzolamide was beneficial. Serum IgD levels were markedly increased in both brothers and mevalonic acid blood and urine levels were markedly increased in the one brother who could be examined. The disease severity differed between the brothers-one had more severe ataxia and less severe visual deficiency compared to the other.

CONCLUSION

MKD can be associated with RP and early onset cataract. Most MKD patients developing RP carry the (p.Ala334Thr) mutation. Macular edema can be treated using local dorzolamide.

Anti-inflammatory and cytoprotective effects of a squalene synthase inhibitor, TAK-475 active metabolite-I, in immune cells simulating mevalonate kinase deficiency (MKD)-like condition

TAK-475 (lapaquistat acetate) and its active metabolite-I (TAK-475 M-I) inhibit squalene synthase, which catalyzes the conversion of farnesyl diphosphate (FPP) to squalene. FPP is a substrate for synthesis of other mevalonate-derived isoprenoids (MDIs) such as farnesol (FOH), geranlygeranyl diphosphate (GGPP), and geranylgeraniol. In patients with MKD, a rare autosomal recessive disorder, defective activity of mevalonate kinase leads to a shortage of MDIs. MDIs especially GGPP are required for prenylation of proteins, which is a posttranslation modification necessary for proper functioning of proteins like small guanosine triphosphatases. Malfunction of prenylation of proteins results in upregulation of the inflammatory cascade, leading to increased production of proinflammatory cytokines like interleukin-1β (IL-1β), eventually leading to episodic febrile attacks. In vitro, TAK-475 M-I incubation in a concentration dependent manner increased levels of FPP, GGPP, and FOH in human monocytic THP-1 cells. In subsequent experiments, THP-1 cells or human peripheral blood mononuclear cells (PBMCs) were incubated with simvastatin, which inhibits hydroxymethylglutaryl-coenzyme A reductase and thereby decreases levels of the precursors of MDIs, leading to the depletion of MDIs as expected in MKD patients. Increased levels of GGPP and FPP attenuated lipopolysaccharide (LPS)-induced IL-1β production in THP-1 cells and human PBMCs in statin-treated conditions. The MDIs also significantly reduced the damaged cell ratio in this active MKD-like condition. Moreover, TAK-475 M-I directly inhibited LPS-induced IL-1β production from statin-treated THP-1 cells. These results show anti-inflammatory and cytoprotective effects of MDIs via TAK-475 M-I treatment in statin-treated immune cells, suggesting that possible therapeutic effects of TAK-475 treatment in MKD patients.

How Low Cholesterol Is Good for Anti-viral Immunity

York et al. identify a role for decreased cholesterol biosynthesis in virally infected cells as a critical event in the induction of the anti-viral response. The mechanism involves enhanced signaling by STING in the ER membrane in response to the second messenger cGAMP, promoting increased transcription of type I interferons. The authors suggest that a "lipid code" is being sensed by STING to allow it to signal.

Limiting Cholesterol Biosynthetic Flux Spontaneously Engages Type I IFN Signaling

Cellular lipid requirements are achieved through a combination of biosynthesis and import programs. Using isotope tracer analysis, we show that type I interferon (IFN) signaling shifts the balance of these programs by decreasing synthesis and increasing import of cholesterol and long chain fatty acids. Genetically enforcing this metabolic shift in macrophages is sufficient to render mice resistant to viral challenge, demonstrating the importance of reprogramming the balance of these two metabolic pathways in vivo. Unexpectedly, mechanistic studies reveal that limiting flux through the cholesterol biosynthetic pathway spontaneously engages a type I IFN response in a STING-dependent manner. The upregulation of type I IFNs was traced to a decrease in the pool size of synthesized cholesterol and could be inhibited by replenishing cells with free cholesterol. Taken together, these studies delineate a metabolic-inflammatory circuit that links perturbations in cholesterol biosynthesis with activation of innate immunity.

Lights and shadows in autoinflammatory syndromes from the childhood and adulthood perspective

In a high percentage of cases, the monogenic autoinflammatory syndromes (AIS), caused by subversion in the inflammasome homeostasis leading to cytokine oversecretion and characterized by multiple inflammatory pictures, start in childhood. However, the description of tardive manifestations, veiled phenotypes, and atypical clinical signs beginning in adulthood has been more and more reported in recent times, requiring that many specialists become confident with concepts, details, and management strategies of AIS. Differences between child- and adult-onset syndromes raise the question of whether pathogenic mechanisms might differ when the timetable of AIS onset diverges, but show that carefulness is needed to establish a straightforward diagnosis.

Autoinflammatory syndromes as causes of fever of unknown origin

The systemic autoinflammatory syndromes often present with recurrent fevers. They have proved exceptionally informative about the innate immune system. Although extremely rare, they are important to recognise, as many can now be completely controlled by long-term drug therapies. Diagnosis relies on clinical suspicion followed by genetic testing.

The protean ocular involvement in monogenic autoinflammatory diseases: state of the art

Ocular involvement is frequent in the monogenic autoinflammatory disorders and generally occurs as spontaneously recurring inflammatory events at different ocular sites caused by the aberrant release of proinflammatory cytokines, mainly IL-1β. Over the past decade, we witnessed a significant growth of eye abnormalities associated with idiopathic granulomatous disorders, familial Mediterranean fever, tumor necrosis factor receptor-associated periodic syndrome, mevalonate kinase deficiency, and cryopyrin-associated periodic syndrome. The pathogenetic mechanisms of these disorders have shown the evidence of disrupted cytokine signaling, but the explanation for the heterogeneous ocular involvement remains to be elucidated. We herein review the monogenic autoinflammatory disorders affecting the eye, describing their main clinical features with specific regard to the ocular involvement, which can lead to decreased visual acuity and even blindness, if the primary disorder is undetected or left untreated.