Clinical Description
MIRAGE syndrome is a rare disorder characterized by six core features: myelodysplasia, infection, restriction of growth, adrenal hypoplasia, genital phenotypes, and enteropathy.
To date, no consensus clinical diagnostic criteria for MIRAGE syndrome are available. In this review, a diagnosis of MIRAGE syndrome is defined as:
46,XY individuals with four or more of the core features; or
46,XX individuals with three or more of the core features.
Using these diagnostic criteria, 44 individuals with features of MIRAGE syndrome and a pathogenic variant in SAMD9 have been identified to date [Narumi et al 2016, Buonocore et al 2017, Bluteau et al 2018, Jeffries et al 2018, Kim et al 2018, Sarthy et al 2018, Shima et al 2018a, Shima et al 2018b, Wilson et al 2018, Ahmed et al 2019, Csillag et al 2019, Formankova et al 2019, Mengen et al 2020, Perisa et al 2019, Roucher-Boulez et al 2019, Yoshizaki et al 2019, Zhang et al 2019, Onuma et al 2020, Viaene & Harding 2020]. The following description of the phenotypic features associated with MIRAGE syndrome is based on these reports.
Table 2.
MIRAGE Syndrome: Frequency of Select Features
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Feature | # of Persons w/Feature | Comment |
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Myelodysplasia | 37/44 | Some assoc w/monosomy 7 or del(7q) |
Recurrent infection | 40/44 | |
Restriction of growth | 43/44 | |
Adrenal hypoplasia | 34/44 | |
Atypical external genitalia in 46,XY individuals | 33/34 | Hypospadias, microphallus, bifid shawl scrotum, ambiguous genitalia, or complete female genitalia |
Gastrointestinal complications | 36/44 | |
Myelodysplasia and bone marrow failure. Age of onset of hematologic abnormalities is variable. Two distinct groups with respect to prognosis and severity of cytopenias include individuals diagnosed with severe cytopenias between birth and age two years (~60%) and individuals diagnosed later in childhood (~40%) [Rentas et al 2020]. Prior to the onset of hematopoietic clonal evolution, individuals may present with bone marrow hypoplasia and features consistent with congenital amegakaryocytic thrombocytopenia [Sarthy et al 2018]. Thrombocytopenia is the most common manifestation, followed by anemia and pancytopenia. Severe cytopenias may occur in distinct acute episodes associated with myelosuppressive infections or may be chronic, requiring frequent transfusions. Of note, cytopenias may improve with age in some individuals.
Evolution to myelodysplastic syndrome (MDS) is defined by acquisition of monosomy 7 or del(7q) in the setting of multilineage bone marrow dysplasia. Although myelodysplasia is included as a core feature of MIRAGE syndrome, myelodysplasia in these individuals appears to be due to an acquired deletion of SAMD9, primarily of the SAMD9 allele with a germline gain-of-function pathogenic variant. Notably, individuals with a germline gain-of-function SAMD9 pathogenic variant may acquire somatic alterations (including uniparental disomy 7 or SAMD9 pathogenic variants in
cis with the germline variant) that do not predispose to MDS and may actually improve hematopoietic function (see Penetrance).
Individuals with a germline gain-of-function SAMD9 pathogenic variant may present with myelodysplasia and develop no additional or only limited features of MIRAGE syndrome [Schwartz et al 2017, Hockings et al 2020].
Recurrent infections. Most individuals with MIRAGE syndrome develop recurrent bacterial infections from early infancy including pneumonia, urinary tract infection, gastroenteritis, meningitis, otitis media, dermatitis, subcutaneous abscess, and sepsis. The most common organisms associated with these infections are enteric pathogens such as Klebsiella and Enterococcus. Affected individuals may also be at higher risk for complications from both viral (e.g., cytomegalovirus) and bacterial respiratory pathogens. Affected individuals with severe immune deficiency due either to native immune dysfunction or to stem cell transplant are also at risk for severe fungal infections (e.g., Candida). To date, the etiology of the increased susceptibility to infections is unknown. It may be partly explained by hypogammaglobulinemia or lymphopenia. In four individuals, the thymus was hypoplastic [Narumi et al 2016, Sarthy et al 2018]. Incomplete lasting immunity to vaccinations has been reported in two affected individuals [Jeffries et al 2018].
Growth restriction / growth deficiency. Typically, affected individuals are delivered premature by emergency cæsarean section due to fetal growth failure and suspected fetal distress. Most individuals have persistent growth deficiency (weight, height/length, and head circumference are commonly all below -2.0 SD) despite adequate caloric supply, with the exception of two individuals who showed normal growth after birth [Shima et al 2018b, Roucher-Boulez et al 2019].
Adrenal hypoplasia. Approximately 80% of individuals have primary adrenal insufficiency. They present with prominent diffuse skin hyperpigmentation at birth and may develop severe dehydration and hypotension, which can be life-threatening. The diagnosis of primary adrenal insufficiency is confirmed by low cortisol and markedly elevated ACTH levels. Aplastic or hypoplastic adrenal glands are found on ultrasound examination. Rarely, adrenal insufficiency may emerge in late childhood [Perisa et al 2019].
Genital anomalies. Reported findings in those with 46,XY karyotype included hypospadias, microphallus, bifid shawl scrotum, ambiguous genitalia, or complete female genitalia. The testes were usually hypoplastic or dysgenetic. One individual, age three days, was reported to have undetectable testosterone [Roucher-Boulez et al 2019]. One individual, age 16 years, was reported to have testicular failure [Wilson et al 2018].
No external genital anomalies were reported in individuals with 46,XX karyotype, but four were found to have hypoplastic or dysgenetic ovaries [Narumi et al 2016, Sarthy et al 2018, Viaene & Harding 2020].
Gastrointestinal complications. Chronic diarrhea occurs in about 80% of affected individuals and often results in severe diaper rash. It usually occurs after initiating enteral nutrition. About one third of individuals with MIRAGE syndrome have esophageal problems often accompanied by recurrent aspiration pneumonia. Clinical manifestations include dysphagia, gastroesophageal reflux, vomiting, esophageal hypoperistalsis, esophageal stricture, and achalasia.
Neurologic development. Moderate-to-severe developmental delay is reported in most affected individuals. Reported individuals are often nonambulatory with absent or limited language development. Neuropathologic findings such as microcephaly, hydrocephalus, white matter abnormalities, and perivascular calcifications may be present [Viaene & Harding 2020].
Autonomic dysfunction. Symptoms compatible with autonomic dysfunction such as hypolacrima with corneal ulcer, hypo/anhidrosis with temperature instability, or hyperhidrosis were reported in seven individuals [Jeffries et al 2018, Sarthy et al 2018, Shima et al 2018a, Shima et al 2018b].
Renal dysfunction including proteinuria and renal tubular acidosis were reported in five of 17 individuals who lived beyond age three years. Renal biopsies were performed in four individuals; two were found to have focal segmental glomerular sclerosis [Ahmed et al 2019, Perisa et al 2019], one to have interstitial nephritis [Shima et al 2018b], and one to have C1q nephropathy [Wilson et al 2018].
Prognosis. The median age of death in affected individuals is three years. Nearly 60% of the deaths were due to infectious diseases. The oldest affected individual was reported to be alive at age 20 years [Bluteau et al 2018].