In this case series we present four different childhood onset lupus patients with five distinct monogenic mutations. None of the above monogenic syndromes were recognized in our patients on clinical grounds before the genetic work up. Notably, all patients had severe forms of SLE, including 2 mortalities, which prompted genetic analysis. This case series highlights several important clinical insights.
Monogenic SLE should be suspected in patients with childhood-onset lupus
Since January 2015 we had 15 patients diagnosed with childhood onset lupus (age range 2–18 years) in our institution. Four patients were eventually diagnosed with monogenic lupus in the subset of six patients we performed genetic testing in. This underscores the need for a high index of suspicion for a genetic SLE, especially in patients with severe childhood-onset presentation and familial consanguinity (Table
2). Our results support the notion that atypical or severe clinical presentations may suggest a genetic etiology for SLE. For instance, patient 3C (
MAN2B1 and
SLC7A7) presented with predominant lung involvement which is an extremely rare manifestation as the first presentation of lupus. Another example is patient 2B (
PTEN) who presented with longstanding lymphadenopathy, which is also an atypical presentation of lupus. Moreover, patients with childhood lupus with clinical features beyond the clinical spectrum of lupus, such as cases 2B and 3C, should alert clinicians to suspect an underlying genetic SLE etiology. Patient 2B had macrocephaly, developmental delay, high birth weight, pigmented macules on the penis and pigmented gums while patient 3C had significantly enlarged kidneys with renal biopsy findings showing tubular damage. Similarly, in case 4D the concomitant severe immune deficiency was another clinical clue. Lastly, two out of four patients presented here did not respond to the conventional SLE treatment, which in our opinion, should also imply consideration of genetic analysis (Table
2).
Table 2Clinical features that should prompt suspicion for monogenic lupus/lupus-like
Early onset – < 10 years of age |
Suspected (e.g. recurrent infections) or proved immunodeficiency |
Clinical features out of the typical clinical classification criteria for SLE |
Severe, life-threatening or organ-threatening presentation |
Aggressive course, rapid deterioration and/or accumulation of organ damage |
Poor response to treatment |
Familial cases |
Consanguinity |
Establishing genetic etiology may influence monitoring and treatment
Revealing the molecular genetic diagnosis in patients with childhood-onset lupus can facilitate a personalized medical approach with targeted monitoring and treatment. The first identified, and most described forms of monogenic lupus are inherited complement deficiencies [
11] as we identified in Case 1A. It is estimated that the prevalence of autoimmunity with lupus-like manifestations in C1q deficiency is as high as 90%. These conditions predispose to lupus due to impaired tolerance and aberrant clearance of apoptotic bodies and immune complexes [
12]. C1q is central in clearing apoptotic debris, but when impaired, autoantigens accumulate and stimulate nucleic acid autoantibodies. Confirming this diagnosis opens a window of opportunity for specific treatments such as fresh frozen plasma or hematopoietic stem cell transplantation [
13], which are not part of the conventional lupus treatment and should be considered early in management.
In case 3C we detected two different metabolic diseases: Lysinuric protein intolerance (LPI) caused by mutations in
SLC7A7 and Alpha-mannosidosis caused by mutations in
MAN2B1. LPI is an autosomal recessive transport disorder of the dibasic amino acids lysine, arginine and ornithine in the renal tubules, intestinal epithelium, hepatocytes and fibroblasts [
14]. Deficiency of arginine and ornithine impairs the function of the urea cycle, causing hyperammonemia. There are few case reports of LPI patients who developed SLE and the pathophysiology is not well understood. However, Lukkarinan et al. showed that the humoral immune responses in some patients with LPI may be defective [
14]. Alpha-mannosidosis is caused by deficiency of lysosomal alpha-mannosidase (LAMAN). Three major clinical subtypes have been suggested [
15] with various severities of skeletal abnormalities and myopathy and neurological manifestations. Associated medical problems may also include corneal opacities, hepatosplenomegaly, aseptic destructive arthritis. The association between alpha mannosidosis and lupus has been reported in the past in several case reports [
16].
Each of the above mentioned syndromes can present with SLE like symptoms. This made the clinical diagnosis in patient 3C challenging. Hence, this unique situation of patients from consanguineous families harboring two different disease causing mutations should always be considered by clinicians [
17]. Specific treatments for these genetic diseases include enzyme replacement therapy for mannosidosis [
18] and low protein diet with supplementation of citrulline for LPI. Identifying the genetic diagnosis may better define which of the patient’s clinical symptoms can be attributed to autoimmunity as opposed to symptoms arising secondary to the metabolic abnormality, and therefore guide the treatment. Thus, ascribing the severe lung disease in case 2 to lupus-related lung involvement (e.g. pneumonitis) may require maximal immunosuppressive therapy. However, diagnosing the lung disease as part of the LPI presentation which was supported by the patient’s lung histology findings (Fig.
1) mandates a completely different treatment approach and may prevent unnecessary procedures and treatments.
Genetic diagnosis may additionally guide disease specific monitoring. Patients diagnosed with autosomal dominant
PTEN mutations (a known tumor suppression gene) have high risk for benign and malignant tumors of the thyroid, breast, and endometrium, as well as for neurodevelopmental disorders. Additionally, PTEN was found to be important for proper T regulatory cell functioning and autoimmunity prevention [
19]. These observations, as well as the
Pten mice models [
20] support that a lupus-like phenotype can be caused by
PTEN mutations.
Similarly, patients with complement deficiencies or
STAT1 mutations should be monitored for severe bacterial infections [
21]. Heterozygous gain of function mutations in
STAT1 lead to impaired nuclear dephosphorylation of STAT1 and immune aberrations which include lymphopenia, reduced responses to mitogens and antigens, hypogammaglobulinemia, as well as impaired natural killer (NK) cell function. Clinical manifestations in patients with
STAT1 mutation, in addition to immunodeficiency includes inflammatory and autoimmune phenomena such as hypothyroidism (22%), type 1 diabetes (4%), blood cytopenia (4%), and SLE (2%) [
21,
22]. Rarely, patients can have cerebral vasculitis and multiple aneurysms leading to stroke [
23]. Aortic calcifications and aneurism were also reported [
24]. Specific treatments including prophylactic antifungal and antimicrobial agents, IVIG, and recently the utility of JAK inhibitors in these patients has been suggested [
25].
Genes mutated in monogenic forms of lupus converge to signaling pathways that inform disease pathogenesis
Over the last decade the growing use of whole exome sequencing revealed additional culprit genes leading to human monogenic forms of lupus resulting in better understanding of pathogenic pathways. These pathways can be grouped as follows [
5,
12]: [
1] Complement; [
2] Apoptosis and nucleic acid degradation, repair and sensing; [
3] Type I interferon pathway; [
4] B cell and T cell tolerance, and [
5] other (Table
3). Moreover, accounting for additional genes described in monogenic forms of lupus in mouse models, it is likely that many more remain to be identified (Table
4).
Table 3Single gene causes of lupus or lupus-like syndrome in Humans
Complement | C1QA | C1Q | AR | SLE in 88% Recurrent infections | | 120550 |
C1QB | AR | | 120570 |
C1QC | AR | | 120575 |
C1R | C1R | AR | SLE in 65% Sjogren syndrome Recurrent infections | | 613785 |
C1S | C1S | AR | | 120580 |
C2 | C2 | AR | SLE in 10% Recurrent infections | | 613927 |
C3 | C3 | AR | SLE in a minority of affected | | 120700 |
C4 | C4 | AR | SLE in 75% Recurrent infections | | 142974 |
Type 1 interferon | TMEM173 | STING | AD | STING associated vasculopathy with onset in infancy | | 612374 |
SAMHD1 | SAMHD1 | AR | Mild Aicardi–Goutie` res syndrome Mouth ulcers Deforming arthropathy Cerebral vasculopathy | | 606754 |
ADAR1 | ADAR1 | AR/AD | Aicardi–Goutie’res syndrome Bilateral striatal necrosis | | 146920 |
IFIH1 | IFIH1 | AD | Classical or mild Aicardi–Goutie’res syndrome Singleton–Merton syndrome SLE | | 606951 |
RNASEH2B | RNASEH2B | AR | Aicardi–Goutie’res syndrome | | 610326 |
APC5 | APC5 | AR | SLE Sjogren syndrome Autoimmune cytopenias Raynaud phenomenon Recurrent infections Spondyloenchondrodysplasia | | 606948 |
TREX1 | TREX1 | AR | Aicardi–Goutie’res syndrome | | 606609 |
Nucleic acids degradation | DNASE1 | DNASE1 | AD | SLE Sjogren syndrome | | 125505 |
DNASE1L3 | DNASE1L3 | AR | SLE Hypocomplementemic urticarial vasculitis syndrome | | 602244 |
TREX1 | TREX1 | AD | Aicardi–Goutie’res syndrome | | 606609 |
RNASEH2A | RNASEH2A | AR | Aicardi–Goutie’res syndrome | | 606034 |
RAS/MAPK | SHOC2 | SHOC2 | AD | Noonan syndrome with loose anagen hair SLE | | 602775 |
KRAS | KRAS | AD | Noonan syndrome SLE | | 190070 |
PTPN11 | PTPN11 | AD | Noonan syndrome SLE (polyarthritis, photosensitivity, leukopenia and lymphopenia) Hashimoto thyroiditis | | 176876 |
Proteasome | PSMA3 | PSMA3 | AD | CANDLE (chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature) | | 176843 |
PSMB4 | PSMB4 | AD | | 602177 |
PSMB8 | PSMB8 | AD | | 177046 |
Apoptosis | TNFRSF6 | FAS | AD | ALPS | | 134637 |
FASLG | FASL | AD | ALPS SLE with lymphoadenopathies | | 134638 |
Tolerance | PRKCD | PRKCD | AR | SLE (Malar rash & nephritis 100%) | | 176977 |
RAG2 | RAG2 | AR/AD | SCID Omenn syndrome SLE | | 179616 |
Phagocytes oxidase system | CYBB | NADPH oxidase 2 | X-linked | Chronic granulomatous disease Cutaneous lupus erythematosus SLE | | 300481 |
DNA repair | NEIL3 | NEIL3 | AR | Autoimmune cytopenias Chronic diarrhea Recurrent Infections | | 608934 |
AKT/PKB | PTEN | PTEN | AD | SLE Malignancy Bannayan–Riley–Ruvalcaba syndrome Cowden syndrome | | 601728 |
Collagen degradation | PEPD | PEPD | AR | Prolidase deficiency Leg ulcers SLE | | 613230 |
Amino acid transporter | SLC7A7 | SLC7A7 | | Lysinuric protein intolerance SLE | | 603593 |
Carbohydrate catabolism | MAN2B1 | Lysosomal α mannosidase | AR | Alpha-mannosidosis SLE | | 609458 |
Table 4Mouse models of lupus
1 | C1qa | |
2 | C4b | |
3 | Cd40lg | |
4 | Cdkn1a | |
5 | Def6 | |
6 | Dnase1 | |
7 | Ep300 | |
8 | Fas | |
9 | Fcgr2b | |
10 | Gadd45a | |
11 | Ifih1 | |
12 | Ikzf3 | |
13 | Jak1 | |
14 | Junb | |
15 | Lbr | |
16 | Lyn | |
17 | Man2a1 | |
18 | Mta2 | |
19 | Pdcd1 | |
20 | Polb | |
21 | Pparg | |
22 | Prdm1 | |
23 | Ptprc | |
24 | Rasgrp1 | |
25 | Rassf5 | |
26 | Rc3h1 | |
27 | Rxra | |
28 | Trl7 | |
29 | Tnfrst13b | |
30 | Traf3ip2 | |
31 | Trove2 | |