Liver transplantation followed by allogeneic hematopoietic stem cell transplantation for atypical mevalonic aciduria

Increased core body temperature exacerbates defective protein prenylation in mouse models of mevalonate kinase deficiency

Mevalonate kinase deficiency (MKD) is characterized by recurrent fevers and flares of systemic inflammation, caused by biallelic loss-of-function mutations in MVK. The underlying disease mechanisms and triggers of inflammatory flares are poorly understood because of the lack of in vivo models. We describe genetically modified mice bearing the hypomorphic mutation p.Val377Ile (the commonest variant in patients with MKD) and amorphic, frameshift mutations in Mvk. Compound heterozygous mice recapitulated the characteristic biochemical phenotype of MKD, with increased plasma mevalonic acid and clear buildup of unprenylated GTPases in PBMCs, splenocytes, and bone marrow. The inflammatory response to LPS was enhanced in compound heterozygous mice and treatment with the NLRP3 inflammasome inhibitor MCC950 prevented the elevation of circulating IL-1β, thus identifying a potential inflammasome target for future therapeutic approaches. Furthermore, lines of mice with a range of deficiencies in mevalonate kinase and abnormal prenylation mirrored the genotype-phenotype relationship in human MKD. Importantly, these mice allowed the determination of a threshold level of residual enzyme activity, below which protein prenylation is impaired. Elevated temperature dramatically but reversibly exacerbated the deficit in the mevalonate pathway and the defective prenylation in vitro and in vivo, highlighting increased body temperature as a likely trigger of inflammatory flares.

The efficacy and safety of allogeneic stem cell transplantation in Mevalonate Kinase Deficiency

OBJECTIVES

Mevalonate kinase deficiency (MKD) is a rare autoinflammatory syndrome. Several reports have described allogeneic hematopoietic stem cell transplantation in severely affected patients, sometimes with promising results. In view of the scarcity of data, this study aims to analyse the efficacy and safety of allogeneic hematopoietic stem cell transplantation (HSCT) to give a more complete overview of this treatment.

METHODS

This multicentre retrospective study on behalf of the European Society for Blood and Marrow Transplantation aimed to include all MKD patients who had undergone allogeneic HSCT. All centres related to EMBT and centres that have reported cases of allogeneic HSCT in the literature were contacted via the EBMT data office.

RESULTS

We analyzed 9 patients (5 male). Treosulfan based conditioning was the most frequently used conditioning regimen. Engraftment occurred in all but one patient. Source of stem cells was cord blood (n = 2), peripheral blood stem cells (n = 4) and bone marrow (n = 5). Two patients needed a second transplantation due to an incomplete response or primary graft failure. Seven patients went into complete remission after stem cell transplantation. At final follow-up these patients reported no symptoms of MKD. Four patients suffered from grade II-IV acute graft-versus-host disease (GvHD). During follow-up two patients died due to transplantation related complications.

CONCLUSION

In conclusion, allogeneic stem cell transplantation represents an effective treatment for the most severely affected MKD patients. However, treatment-related morbidity and mortality are significant. Transplantation may be justified in patients with a severe disease course on conservative therapy.

Neurological manifestations in mevalonate kinase deficiency: A systematic review

INTRODUCTION

Mevalonate kinase deficiency (MKD) is a monogenic auto-inflammatory disease. Its manifestations range from partial MKD to mevalonic aciduria (MVA). All patients display a periodic fever, and MVA patients additionally exhibit severe neurological involvement. The objective of this work was to describe neurological manifestations of MKD.

METHODS

A systematic literature review was performed from January 1990 to January 2022. Forty-five patients from 18 case reports and five cohort studies were included in the analysis.

RESULTS

In cohort studies, the most-reported manifestations were headaches (41%) and fatigue (31%). Serious involvements including ataxia and developmental delay were described less than 1% of patients but 22-31% of case reports. They consistently appeared in the first years of life. Retinal dystrophy was frequently reported (31%) in case reports. Other manifestations, including uveitis, aseptic meningitis, and stroke remained rare.

DISCUSSION

Severe neurological manifestations are rare in MKD but are responsible for major functional disabilities. They are present at onset and never appear at follow-up of patients with mild MKD. Conversely, headaches and fatigue are frequent symptoms that should be investigated. Visual examinations should be performed on the appearance of visual symptoms. The efficacy of anti-IL-1β therapy on neurological manifestations should be further investigated.

Case Report: Mevalonic Aciduria Complicated by Acute Myeloid Leukemia After Hematopoietic Stem Cell Transplantation

Mevalonic aciduria (MA) is the most severe clinical subtype of mevalonate kinase deficiency (MKD) caused by an inherited defect in the mevalonate pathway. The treatment of MKD focuses on the suppression of recurrent hyperinflammatory attacks using anti-inflammatory drugs. Recently, allogeneic hematopoietic stem cell transplantation (HCT) was shown to successfully ameliorate autoinflammatory attacks in patients with MKD. Here, we report a case of an infant who showed severe recurrent systemic inflammation and was diagnosed with MA. Although she responded to steroids, her symptoms relapsed after the dose was tapered, and organ deterioration occurred. Therefore, at the age of 11 months, HCT from a matched, unrelated donor was performed for curative treatment. However, at 50 days after transplantation, acute myeloid leukemia was diagnosed, which was chemo-refractory. A second HCT from her haploidentical father was performed to treat the acute myeloid leukemia, but the patient died of sepsis on day 4 after transplantation. This is the first report of malignancy following HCT for MA. Our findings suggest that normalizing the mevalonate pathway after HCT in patients with MKD impacts patients differently depending on the clinical spectrum and severity of disease.

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.

Compromised Protein Prenylation as Pathogenic Mechanism in Mevalonate Kinase Deficiency

Mevalonate kinase deficiency (MKD) is an autoinflammatory metabolic disorder characterized by life-long recurring episodes of fever and inflammation, often without clear cause. MKD is caused by bi-allelic pathogenic variants in the MVK gene, resulting in a decreased activity of the encoded enzyme mevalonate kinase (MK). MK is an essential enzyme in the isoprenoid biosynthesis pathway, which generates both non-sterol and sterol isoprenoids. The inflammatory symptoms of patients with MKD point to a major role for isoprenoids in the regulation of the innate immune system. In particular a temporary shortage of the non-sterol isoprenoid geranylgeranyl pyrophosphate (GGPP) is increasingly linked with inflammation in MKD. The shortage of GGPP compromises protein prenylation, which is thought to be one of the main causes leading to the inflammatory episodes in MKD. In this review, we discuss current views and the state of knowledge of the pathogenetic mechanisms in MKD, with particular focus on the role of compromised protein prenylation.

Haematopoietic stem cell transplantation in paediatric rheumatic disease

PURPOSE OF REVIEW

A small proportion of children affected by rheumatic diseases suffer from severe, progressive disease, resistant to conventional antirheumatic therapies and to biologic agents interfering with inflammatory cytokines, costimulatory molecules expressed on immune system cells and intracellular signalling pathways. Adding to the poor prognosis is a high risk from significant morbidity and mortality associated with long-term treatment with multiple, often combined anti-inflammatory and immunosuppressive agents. Carefully selected patients from this unfortunate group may benefit from treatment with haematopoietic stem cell transplantation.

RECENT FINDINGS

The majority of patients with severe paediatric rheumatic and autoinflammatory diseases treated with autologous and/or allogeneic haematopoietic stem cell transplantation achieved long-term remission. However, the incidence of disease relapse and transplant related morbidity and mortality is still significant.

SUMMARY

Careful patient and donor selection, timing of the transplant earlier in the course of disease rather than the 'last resort' and choosing the most suitable conditioning regimen for each individual patient are the major factors favouring successful outcome. Close co-operation between the patients, their family, and involved medical teams is essential.

Gene Expression Analysis of Mevalonate Kinase Deficiency Affected Children Identifies Molecular Signatures Related to Hematopoiesis

Mevalonate kinase deficiency (MKD) is a rare autoinflammatory genetic disorder characterized by recurrent fever attacks and systemic inflammation with potentially severe complications. Although it is recognized that the lack of protein prenylation consequent to mevalonate pathway blockade drives IL1β hypersecretion, and hence autoinflammation, MKD pathogenesis and the molecular mechanisms underlaying most of its clinical manifestations are still largely unknown. In this study, we performed a comprehensive bioinformatic analysis of a microarray dataset of MKD patients, using gene ontology and Ingenuity Pathway Analysis (IPA) tools, in order to identify the most significant differentially expressed genes and infer their predicted relationships into biological processes, pathways, and networks. We found that hematopoiesis linked biological functions and pathways are predominant in the gene ontology of differentially expressed genes in MKD, in line with the observed clinical feature of anemia. We also provided novel information about the molecular mechanisms at the basis of the hematological abnormalities observed, that are linked to the chronic inflammation and to defective prenylation. Considering the broad and unspecific spectrum of MKD clinical manifestations and the difficulty in its diagnosis, a better understanding of MKD molecular bases could be translated to the clinical level to facilitate diagnosis, and improve management and therapy.

HSCT is effective in patients with PSTPIP1-associated myeloid-related proteinemia inflammatory (PAMI) syndrome

BACKGROUND

Proline-serine-threonine phosphatase-interacting protein 1-associated myeloid-related proteinemia inflammatory (PAMI) syndrome is a novel genetic disorder, causing hypercalprotectinemia and hyperzincemia with inflammatory complications accompanied by cytopenia. Immunosuppressive and/or anticytokine therapy is of limited effect.

OBJECTIVES

Because of cytokine production in nonhematopoietic tissues, the potential therapeutic effect of allogeneic hematopoietic stem cell transplantation (HSCT) in autoinflammatory disorders, including PAMI syndrome, has remained uncertain.

METHODS

Five patients with PAMI syndrome underwent allogeneic HSCT with myeloablative (4) or reduced-intensity (1) conditioning regimens. Lack of PAMI disease control served as indication for the HSCT in 4 patients and myelodysplastic syndrome development in 1.

RESULTS

All 5 patients engrafted; however, 1 patient at day +13 developed hemophagocytic syndrome, followed by graft rejection at day +17. After 5.5 months, a second HSCT was performed from an alternative donor. A further patient at day +116 developed an intense inflammatory syndrome with significant serositis and severe mitral and aortic valve regurgitation, controlled with adalimumab, tacrolimus, and prednisone. No other noninfectious inflammatory episodes, or acute or chronic graft-versus-host disease, occurred in any patient. At the last follow-up (median, 2.2 years), all 5 patients have predominantly or complete donor chimerism and adequate immune recovery and are free of any PAMI symptoms.

CONCLUSIONS

Allogeneic HSCT seems to be an effective option to cure cytopenia and severe autoinflammation in PAMI syndrome and may be a curative option for other proline-serine-threonine phosphatase-interacting protein 1-associated inflammatory disorders with poor therapeutic control.

Mevalonic aciduria: Does stem cell transplant fully cure disease?

MA is a rare, autosomal recessive disorder characterized by episodes of inflammation and periodic fevers. In its most severe form, it can result in facial dysmorphism, growth inhibition, ataxia, liver dysfunction, intellectual disability, and at times can be fatal. A number of case reports exist stating that SCT is curative in these patients. We present the case of a patient diagnosed with MA at birth, who underwent SCT at the age of 14 months with intent to cure. She achieved complete engraftment and urine mevalonate became undetectable. However, 18 months following transplant, she developed frequent episodes of fevers, rashes, arthritis, and a rising urinary mevalonate. She was subsequently diagnosed with relapse. She now requires treatment with steroids and canakinumab to manage her disease. This case is the first report of disease relapse following transplant for MA. It runs contrary to prior reports that SCT is fully curative of MA and suggests that transplant may instead provide a means of decreasing disease severity without entirely eradicating the condition.

Mevalonate kinase deficiency masked by cytomegalovirus infection and obscure liver disease

BACKGROUND

Chronic liver disease with conjugated hyperbilirubinaemia and failure to thrive can have multifactorial aetiologies. Investigations can be complex and difficult especially when obscured by a viral infection affecting liver function.

METHODS

A 5 month old male infant was referred for investigation of chronic liver disease and a history of jaundice with multiple febrile episodes. Liver function tests were performed followed by a liver biopsy and microbiological workup for infectious disease. In addition, urine analysis of organic acids was also performed.

RESULTS

There was marked conjugated hyperbilirubinaemia with markedly elevated hepatocellular enzymes and normal ductal enzymes. Proteinuria and near normal renal function suggested early renal impairment. There was also leukocytosis and bicytopenia. An extensive bacteriological investigation including TB workup was negative. CMV infection was confirmed by viral load and antibody reactivity. There was prolonged PT and PTT and high INR. The liver biopsy showed giant cell transformation of hepatocytes with mild cholestasis, portal and peri-cellular fibrosis with alpha-1-antitrypsin positive granules in the hepatocyte cytoplasm suggesting alpha-1-antitrypsin deficiency. Urine organic acids revealed significantly elevated mevalonolactone.

CONCLUSIONS

We confirmed the genetic diagnosis of mevalonic aciduria caused by MVK deficiency which had been masked by liver disease and the possible misdiagnosis of alpha-1-antitrypsin deficiency.

A case report of mevalonate kinase deficiency in a 14-month-old female with fevers and lower extremity weakness

Background

This case follows a 14-month-old female, who despite multiple presentations to several physicians, continued to have recurrent febrile episodes with gross motor delay. Her case revealed an often missed diagnosis of Mevalonate Kinase Deficiency, that now has an FDA approved treatment that both reduces recurrence and produces remission.

Case presentation

A 14-month-old female with a history of gross motor delay, frequent Upper Respiratory Tract infections, and otitis media presented to an urgent care for inconsolability and refusal to bear weight on her right leg. She had recently been treated with amoxicillin for acute otitis media and had developed a diffuse maculopapular rash, without any associated respiratory or gastrointestinal distress that persisted beyond cessation of the antibiotics. The patient presented multiple times to an urgent care over the subsequent week for fussiness, fever, anorexia, lymphadenopathy, with labs concerning for worsening anemia and elevated inflammatory markers. Subsequently, the patient was admitted to the hospital for suspected osteomyelitis versus oncologic process. X-Ray imaging of the patient’s lower extremities showed osseous abnormalities inconsistent with infection. A metabolic work-up showed elevated urine mevalonic acid, and follow-up genetic testing was positive for mutations in both copies of her mevalonate kinase gene. This led to the diagnosis of MKD.

Conclusions

Often, episodic presentations require multiple perspectives to reveal the underlying cause. This case illustrates how apparent simple febrile episodes has the potential for more complexity upon further evaluation.

Autoinflammatory Diseases with Periodic Fevers

PURPOSE OF REVIEW

One purpose of this review was to raise awareness for the new autoinflammatory syndromes. These diseases are increasingly recognized and are in the differential diagnosis of many disease states. We also aimed to review the latest recommendations for the diagnosis, management, and treatment of these patients.

RECENT FINDINGS

Familial Mediterranean fever (FMF), cryopyrin-associated periodic syndrome (CAPS), tumor necrosis factor receptor-associated periodic fever syndrome (TRAPS), and hyperimmunoglobulinemia D and periodic fever syndrome/mevalonate kinase deficiency (HIDS/MVKD) are the more common autoinflammatory diseases that are characterized by periodic fevers and attacks of inflammation. Recently much collaborative work has been done to understand the characteristics of these patients and to develop recommendations to guide the physicians in the care of these patients. These recent recommendations will be summarized for all four diseases. FMF is the most common periodic fever disease. We need to further understand the pathogenesis and the role of single mutations in the disease. Recently, the management and treatment of the disease have been nicely reviewed. CAPS is another interesting disease associated with severe complications. Anti-interleukin-1 (anti-IL-1) treatment provides cure for these patients. TRAPS is characterized by the longest delay in diagnosis; thus, both pediatricians and internists should be aware of the characteristic features and the follow-up of these patients. HIDS/MVKD is another autoinflammatory diseases characterized with fever attacks. The spectrum of disease manifestation is rather large in this disease, and we need further research on biomarkers for the optimal management of these patients.

National survey of Japanese patients with mevalonate kinase deficiency reveals distinctive genetic and clinical characteristics

OBJECTIVES

Mevalonate kinase deficiency (MKD), a rare autosomal recessive autoinflammatory syndrome, is caused by disease-causing variants of the mevalonate kinase (MVK) gene. A national survey was undertaken to investigate clinical and genetic features of MKD patients in Japan.

METHODS

The survey identified ten patients with MKD. Clinical information and laboratory data were collected from medical records and by direct interviews with patients, their families, and their attending physicians. Genetic analysis and measurement of MVK activity and urinary excretion of mevalonic acid were performed.

RESULTS

None of the 10 patients harbored MVK disease-causing variants that are common in European patients. However, overall symptoms were in line with previous European reports. Continuous fever was observed in half of the patients. Elevated transaminase was observed in four of the 10 patients, two of whom fulfilled the diagnostic criteria for hemophagocytic lymphohistiocytosis. About half of the patients responded to temporary administration of glucocorticoids and NSAIDs; the others required biologics such as anti-IL-1 drugs.

CONCLUSION

This is the first national survey of MKD patients in a non-European country. Although clinical symptoms were similar to those reported in Europe, the incidence of continuous fever and elevated transaminase was higher, probably due to differences in disease-causing variants.

Monogenic Periodic Fever Syndromes: Treatment Options for the Pediatric Patient

Autoinflammatory diseases are disorders of the innate immune system characterized by uncontrolled inflammation. The most commonly encountered autoinflammatory diseases are the hereditary periodic fever syndromes, which present with fever and other features of the skin, serosal membranes, and musculoskeletal system. The main inherited (monogenic) periodic fever syndromes are familial Mediterranean fever (FMF), cryopyrin-associated periodic syndrome (CAPS), tumor necrosis factor receptor-associated periodic syndrome (TRAPS), and hyperimmunoglobulin D syndrome (HIDS)/mevalonate kinase deficiency (MKD). Recent advances in our understanding of the molecular and pathophysiological basis of autoinflammatory diseases have provided new treatment strategies. Patients with periodic fever syndromes have clearly benefited from anti-interleukin (IL)-1 treatment. Colchicine is still the mainstay of FMF therapy, but IL-1 blockade is also effective if colchicine fails. Early diagnosis and effective treatment can prevent irreversible organ damage. The scope of pathogenic mutations and more targeted therapy for better management of these rare diseases remains to be defined.

Mevalonate kinase deficiency: current perspectives

Mevalonate kinase deficiency (MKD) is a recessively inherited autoinflammatory disorder with a spectrum of manifestations, including the well-defined clinical phenotypes of hyperimmunoglobulinemia D and periodic fever syndrome and mevalonic aciduria. Patients with MKD have recurrent attacks of hyperinflammation associated with fever, abdominal pain, arthralgias, and mucocutaneous lesions, and more severely affected patients also have dysmorphisms and central nervous system anomalies. MKD is caused by mutations in the gene encoding mevalonate kinase, with the degree of residual enzyme activity largely determining disease severity. Mevalonate kinase is essential for the biosynthesis of nonsterol isoprenoids, which mediate protein prenylation. Although the precise pathogenesis of MKD remains unclear, increasing evidence suggests that deficiency in protein prenylation leads to innate immune activation and systemic hyperinflammation. Given the emerging understanding of MKD as an autoinflammatory disorder, recent treatment approaches have largely focused on cytokine-directed biologic therapy. Herein, we review the current genetic and pathologic understanding of MKD, its various clinical phenotypes, and the evolving treatment approach for this multifaceted disorder.

Natural history of mevalonate kinase deficiency: a literature review

Mevalonate kinase deficiency (MKD), a very rare autosomal recessive autoinflammatory disease with multiple organ involvement, presents clinically as hyperimmunoglobulinemia D syndrome (HIDS), a less severe phenotype and more common form, and mevalonic aciduria (MVA), a more severe phenotype and rare form. MKD is characterized by recurrent febrile attacks that are frequently accompanied by lymphadenopathy, gastrointestinal symptoms, arthralgia, myalgia, skin rash, and aphthous ulcers. Patients with MVA also have intrauterine growth retardation, congenital defects (cataracts, shortened limbs, and dysmorphic craniofacial features), neurological disease, and failure to thrive. Mean age at onset of symptoms is within the first year of life. There is a delay by several years between symptom onset and diagnosis, which is in part attributable to the initial misdiagnosis due to the rarity and nonspecific clinical manifestations of disease. The frequency of recurrent febrile attacks is highest in childhood and gradually decreases after adolescence. MKD is associated with rare long-term complications such as type AA amyloidosis, joint contractures, abdominal adhesions, renal angiomyolipoma, and severe pneumococcal infections. Frequent febrile attacks significantly impair several aspects of patients' and caregivers' quality of life, with an adverse impact on patients' daily activities, education, and employment. Lifespan is generally normal for HIDS whereas MVA can be fatal in early childhood.

To Extinguish the Fire from Outside the Cell or to Shutdown the Gas Valve Inside? Novel Trends in Anti-Inflammatory Therapies

Cytokines are the most important soluble mediators of inflammation. Rare pediatric diseases provided exemplar conditions to study the anti-inflammatory efficacy of new generation therapies (biologics/biopharmaceuticals) selectively targeting single cytokines. Monoclonal antibodies and recombinant proteins have revolutionized anti-inflammatory therapies in the last two decades, allowing the specific targeting of single cytokines. They are very effective in extinguishing inflammation from outside the cell, even with the risk of an excessive and prolonged immunosuppression. Small molecules can enter the cell and shutdown the valve of inflammation by directly targeting signal proteins involved in cytokine release or in response to cytokines. They are orally-administrable drugs whose dosage can be easily adjusted to obtain the desired anti-inflammatory effect. This could make these drugs more suitable for a wide range of diseases as stroke, gout, or neurological impairment, where inflammatory activation plays a pivotal role as trigger. Autoinflammatory diseases, which have previously put anti-cytokine proteins in the limelight, can again provide a valuable model to measure the real potential of small inhibitors as anti-inflammatory agents.

Hyper-IgD syndrome/mevalonate kinase deficiency: what is new?

Mevalonate kinase deficiency or hyper-IgD syndrome is a hereditary autoinflammatory syndrome caused by mutations in the mevalonate kinase gene. In this review, we will discuss new findings in this disorder that have been published in the last 2 years. This includes new insights into pathophysiology, treatment, and the clinical phenotype linked to the genetic defect.

Long-term outcome of a successful cord blood stem cell transplant in mevalonate kinase deficiency

Mevalonate kinase deficiency (MKD) is a rare autosomal recessive inborn error of metabolism with an autoinflammatory phenotype that may be expressed as a spectrum of disease phenotypes, from those with prevailing autoinflammatory syndrome and variable response to anti-inflammatory therapies, to mevalonic aciduria, which is associated with dysmorphic features, severe neurologic involvement, and the worst prognosis. We describe a boy, aged 2 years, 10 months, with severe phenotype of mevalonate kinase deficiency who underwent allogeneic hematopoietic stem cell transplantation (HSCT) from HLA-identical unrelated cord blood because his condition had failed to improve with antiinflammatory treatment as first-line therapy and an anticytokine drug as second-line therapy. The child had a sustained remission of febrile attacks and inflammation after transplant, and during a 5-year follow-up period, psychomotor and neurologic development were normal, without signs of underlying disease or late transplant-related effects. This case confirms that allogeneic HSCT is a safe and effective cure for patients affected by MKD in whom anticytokine drugs alone are insufficient for the management of autoinflammatory syndrome and for the unfavorable outcome of the disease.

Inborn errors of metabolism underlying primary immunodeficiencies

A number of inborn errors of metabolism (IEM) have been shown to result in predominantly immunologic phenotypes, manifesting in part as inborn errors of immunity. These phenotypes are mostly caused by defects that affect the (i) quality or quantity of essential structural building blocks (e.g., nucleic acids, and amino acids), (ii) cellular energy economy (e.g., glucose metabolism), (iii) post-translational protein modification (e.g., glycosylation) or (iv) mitochondrial function. Presenting as multisystemic defects, they also affect innate or adaptive immunity, or both, and display various types of immune dysregulation. Specific and potentially curative therapies are available for some of these diseases, whereas targeted treatments capable of inducing clinical remission are available for others. We will herein review the pathogenesis, diagnosis, and treatment of primary immunodeficiencies (PIDs) due to underlying metabolic disorders.

Sterol metabolism disorders and neurodevelopment-an update

Cholesterol has numerous quintessential functions in normal cell physiology, as well as in embryonic and postnatal development. It is a major component of cell membranes and myelin, and is a precursor of steroid hormones and bile acids. The development of the blood brain barrier likely around 12-18 weeks of human gestation makes the developing embryonic/fetal brain dependent on endogenous cholesterol synthesis. Known enzyme defects along the cholesterol biosynthetic pathway result in a host of neurodevelopmental and behavioral findings along with CNS structural anomalies. In this article, we review sterol synthesis disorders in the pre- and post-squalene pathway highlighting neurodevelopmental aspects that underlie the clinical presentations and course of Smith-Lemli-Opitz Syndrome (SLOS), mevalonic aciduria (MVA) or the milder version hyper-immunoglobulinemia D and periodic fever syndrome (HIDS), Antley-Bixler syndrome with genital anomalies and disordered steroidogenesis (ABS1), congenital hemidysplasia with icthyosiform nevus and limb defects (CHILD) syndrome, CK syndrome, sterol C4 methyl oxidase (SC4MOL) deficiency, X-linked dominant chondrodysplasia punctata 2(CDPX2)/ Conradi Hunermann syndrome, lathosterolosis and desmosterolosis, We also discuss current controversies and share thoughts on future directions in the field.

Treatment of Smith-Lemli-Opitz syndrome and other sterol disorders

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive genetic condition with a broad phenotype that results from deficiency of the final enzyme of the cholesterol synthesis pathway. This defect causes low or low-normal plasma cholesterol levels and increased 7- and 8-dehydrocholesterol (DHC) levels. Many therapies for SLOS and other disorders of sterol metabolism have been proposed, and a few of them have been undertaken in selected patients, but robust prospective clinical trials with validated outcome measures are lacking. We review the current literature and expert opinion on treatments for SLOS and other selected sterol disorders, including dietary cholesterol therapy, statin treatment, bile acid supplementation, medical therapies, and surgical interventions, as well as directions for future therapies and treatment research.

Mevalonate kinase deficiency, a metabolic autoinflammatory disease

Mevalonate kinase deficiency is a rare autosomal recessive inborn error of metabolism with an autoinflammatory phenotype. In this review we discuss its pathogenesis, clinical presentation and treatment. Mutations in both copies of the MVK-gene lead to a block in the mevalonate pathway. Interleukin-1beta mediates the inflammatory phenotype. Shortage of a non-sterol isoprenoid product of the mevalonate pathway, Geranylgeranylpyrophosphate leads to aberrant activation of the small GTPase Rac1, and inflammasome activation. The clinical phenotype ranges widely, depending on the severity of the enzyme defect. All patients show recurrent fevers, lymphadenopathy and high acute phase proteins. Severely affected patients have antenatal disease onset, dysmorphic features, growth retardation, cognitive impairment and progressive ataxia. Diagnosis relies on mutation analysis of the MVK-gene. There is no evidence based therapy. IL-1 blockade is usually effective. Severe cases require allogeneic stem cell transplantation. Targeted therapies are needed.