ORPHA: 85191;
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
Gene/Locus |
Gene/Locus MIM number |
|---|---|---|---|---|---|---|
| 2q24.2 | Singleton-Merten syndrome 1 | 182250 | Autosomal dominant | 3 | IFIH1 | 606951 |
A number sign (#) is used with this entry because of evidence that Singleton-Merten syndrome-1 (SGMRT1) is caused by heterozygous gain-of-function mutation in the IFIH1 gene (606951) on chromosome 2q24.
Singleton-Merten syndrome (SGMRT) is an uncommon autosomal dominant disorder characterized by abnormalities of blood vessels, teeth, and bone. Calcifications of the aorta and aortic and mitral valves occur in childhood or puberty and can lead to early death. Dental findings include delayed primary tooth exfoliation and permanent tooth eruption, truncated tooth root formation, early-onset periodontal disease, and severe root and alveolar bone resorption associated with dysregulated mineralization, leading to tooth loss. Osseous features consist of osteoporosis, either generalized or limited to distal extremities, distal limb osteolysis, widened medullary cavities, and easy tearing of tendons from bone. Less common features are mild facial dysmorphism (high anterior hair line, broad forehead, smooth philtrum, thin upper vermilion border), generalized muscle weakness, psoriasis, early-onset glaucoma, and recurrent infections. The disorder manifests with variable inter- and intrafamilial phenotypes (summary by Rutsch et al., 2015).
Genetic Heterogeneity of Singleton-Merten Syndrome
An atypical form of Singleton-Merten syndrome (SGMRT2; 616298) is caused by mutation in the DDX58 gene (609631) on chromosome 9p21.
Singleton and Merten (1973) and Gay and Kuhn (1976) reported a total of 4 unrelated patients, male and female, with dental dysplasia, progressive calcification of the thoracic aorta, calcific aortic stenosis, osteoporosis, and expansion of the marrow cavities in hand bones like that observed in anemia. In 2 of the 4 patients, there was also generalized muscle weakness and atrophy beginning in the first or second year of life following a febrile illness. Onset was between 4 and 24 months and death between 4 and 18 years. The 2 patients of Gay and Kuhn had a chronic psoriasiform skin eruption. The father of one of their patients was said to have poor teeth and a 'leaky aortic valve,' so the disorder may be dominant.
Feigenbaum et al. (1988) described a family with multiple affected members with variable expression and vertical transmission. Males were affected, and male-to-male transmission occurred. There was early loss of secondary dentition, and dental x-rays showed a type of dentin dysplasia with poor root development that was not like any other reported type.
Feigenbaum et al. (2013) provided follow-up on the family previously reported by Feigenbaum et al. (1988) and reviewed the clinical details of 8 other previously reported cases from 6 families (Singleton and Merten, 1973; Gay and Kuhn, 1976; Rutsch et al., 2005; Valverde et al., 2010). Feigenbaum et al. (2013) noted significant variability in phenotype, even within families. Core manifestations included marked aortic calcification, dental anomalies, osteopenia and acroosteolysis, and, to a lesser extent, glaucoma, psoriasis, muscle weakness, and joint laxity. A particular facies was also observed, consisting of high anterior hairline, broad forehead, smooth philtrum, and thin upper vermilion border.
Bursztejn et al. (2015) reported a French father and 2 sons with cutaneous features resembling those of chilblain lupus (see 610448), with variable neurologic involvement reminiscent of Agouti-Goutieres syndrome (see AGS7, 615846) in the sons as well as features of Singleton-Merton in the father, and mutation in the IFIH1 gene. All 3 patients had ulcerating lesions of the ear helices that were exacerbated by cold and healed with scarring, and biopsy of the helix was consistent with lichenoid lupus. Other cutaneous features included multiple lentigines, primarily on the forearms and legs, and papular lesions on the legs that resolved leaving atrophic scars. Both brothers also exhibited nail fragility with longitudinal striations. The older brother had apparent stiffness of the limbs and only began walking at age 20 months, but stiffness after prolonged sitting persisted and he could not climb stairs unaided at age 3 due to leg pain. However, by the age of 4 years, his motor and intellectual development was considered to be within normal limits. The younger brother had delayed motor development and walked with help at 18 months, but then experienced regression and at age 2.5 years was unable to walk or stand, and also had only a few spoken words. Oral corticosteroid treatment enhanced his mobility, and he was able to walk with the help of a walking frame and began speaking in short sentences. Their 41-year-old father experienced stiffness of the legs after prolonged sitting, and developed deformities of the metacarpophalangeal joints of the hands with tendon retraction and foot deformity, including marked bilateral hallux valgus. After adolescence, his permanent teeth were lost except for molars and premolars, with evident root hypoplasia. He had no history of developmental delay or neurologic dysfunction, but reported lower limb pain with tightening of the Achilles tendon. Echocardiography showed minimal calcification of the aortic valve, and brain CT showed bilateral dense calcification of the globus pallidus. Neurologic examination was normal in the father.
De Carvalho et al. (2017) reported 5 patients from 2 unrelated families (1938 and 1972) with Singleton-Merten syndrome and mutation in the IFIH1 gene. All 5 patients exhibited progressive joint disease of the hands and feet that began in infancy or early adulthood, and was severely deforming in the 4 oldest patients. Calcifications, subluxations, tendon rupture, and tendon insertion calcification were major features, becoming more prominent over time. All 5 patients also experienced significant dental problems, with delayed eruption of primary and/or secondary dentition, and premature tooth loss of the permanent dentition due to resorption of dental roots. All exhibited the characteristic high hairline and broad forehead of the disorder. The proband, her mother, and a maternal aunt from family 1938 all showed calcification of the basal ganglia, in the absence of any neurologic symptoms; no brain imaging was performed in the affected father and daughter in family 1972. In addition, 3 patients were diagnosed with psoriasis, 2 with cardiac valve calcification, 1 with glaucoma, and 1 with tendon rupture. Laboratory evaluation revealed marked upregulation of interferon-induced gene transcripts in all 5 patients. In family 1938, a maternal uncle and 2 children of the affected maternal aunt were described as having severe arthropathy, but were not available for evaluation. In family 1972, the proband's paternal grandmother was reported to have experienced delayed tooth eruption and early loss of secondary dentition, as well as hallux valgus and thickening of the Achilles tendons. Other family members were said to have had glaucoma as well as bone and dental abnormalities, but no further details were available. The authors suggested that IFIH1-associated deforming arthropathy and tendon rupture could be considered to be a mendelian mimic of Jaccoud arthropathy.
Riou et al. (2022) reported a 10-year-old boy with Singleton-Merten syndrome and mutation in the IFIH1 gene. After 1 year of age he developed difficulty walking due to muscle weakness and was wheelchair-bound by age 10. He had severe dental caries of almost all teeth with abscesses, and malpositioned teeth. Examination revealed thin roots in the primary teeth and undeveloped shortened roots in the permanent teeth. Teeth were mobile and there was moderate to severe gingival inflammation. Panoramic x-ray revealed a reduction in alveolar bone height. Other features in the proband included dry skin, glaucoma, scoliosis, and clubfeet.
Reviews
Riou et al. (2022) tabulated the dental findings reported in 20 patients with IFIH1 mutations, noting that short roots, delayed eruption, and premature loss of permanent teeth were the most frequent features, present in 100% of screened patients. In addition, impacted permanent teeth were seen in 89%, decreased height of alveolar bone in 86%, and carious lesions in 67%. Analysis of published x-rays did not show any radiographic signs of resorption; however, the authors observed closed root apices, and suggested that the root defects in SGMRT1 patients are due to impairment of root elongation rather than a resorptive phenomenon. Riou et al. (2022) concluded that the lack of root development was the cause of premature loss of permanent teeth.
The transmission pattern of Singleton-Merten syndrome in the family described by Feigenbaum et al. (1988) was consistent with autosomal dominant inheritance.
In affected individuals from 3 unrelated families with Singleton-Merten syndrome, previously reported by Feigenbaum et al. (1988), Rutsch et al. (2005), and Valverde et al. (2010), respectively, Rutsch et al. (2015) performed whole-exome sequencing and identified heterozygosity for a missense mutation in the IFIH1 gene (R822Q; 606951.0009). The variant was not found in any unaffected family members; analysis of 17 additional family members from the largest family (Feigenbaum et al., 1988) showed that all but 1 individual with dental anomalies carried the mutation, and 1 individual with only psoriasis carried the mutation, whereas 3 others with only psoriasis did not. Functional analysis demonstrated that R822Q is a gain-of-function substitution that triggers production of type 1 interferon (see 147660), resulting in a heightened inflammatory state.
In a French father and 2 sons with ulcerating lesions of the ears, neurologic features in the sons, and loss of dentition and joint deformation in the father, who were negative for mutation in chilblain lupus-associated genes, Bursztejn et al. (2015) performed whole-exome sequencing and identified heterozygosity for a missense mutation in the IFIH1 gene (A489T; 606951.0015). RNA expression of 6 interferon-stimulated genes demonstrated significant upregulation in all 3 patients compared to controls.
In 5 affected individuals from 2 unrelated families with Singleton-Merten syndrome, de Carvalho et al. (2017) sequenced the IFIH1 gene and identified heterozygosity for 2 different missense mutations at the same residue: a T331I substitution (606951.0016) in family 1938, and a T331R substitution (606951.0017) in family 1972. Familial segregation was not reported. The variant was not found in the ExAC database. Both variants resulted in markedly increased levels of IFN signaling.
By whole-genome sequencing in a 10-year-old boy with Singleton-Merten syndrome, Riou et al. (2022) identified heterozygosity for the recurrent R822Q mutation in the IFIH1 gene.
Bursztejn, A.-C., Briggs, T. A., del Toro Duany, Y., Anderson, B. H., O'Sullivan, J., Williams, S. G., Bodemer, C., Fraitag, S., Gebhard, F., Leheup, B., Lemelle, I., Oojageer, A., Raffo, E., Schmitt, E., Rice, G. I., Hur, S., Crow, Y. J. Unusual cutaneous features associated with a heterozygous gain-of-function mutation in IFIH1: overlap between Aicardi-Goutieres and Singleton-Merten syndromes. Brit. J. Derm. 173: 1505-1513, 2015. [PubMed: 26284909] [Full Text: https://doi.org/10.1111/bjd.14073]
de Carvalho, L. M., Ngoumou, G., Park, J. W., Ehmke, N., Deigendesch, N., Kitabayashi, N., Melki, I., Souza, F. F. L., Tzschach, A., Nogueira-Barbosa, M. H., Ferriani, V., Louzada-Junior, P., Marques, W., Lourenco, C. M., Horn, D., Kallinich, T., Stenzel, W., Hur, S., Rice, G. I., Crow, Y. J. Musculoskeletal disease in MDA5-related type I interferonopathy: a mendelian mimic of Jaccoud's arthropathy. Arthritis Rheumatol. 69: 2081-2091, 2017. [PubMed: 28605144] [Full Text: https://doi.org/10.1002/art.40179]
Feigenbaum, A., Kumar, A., Weksberg, R. Singleton-Merten (S-M) syndrome: autosomal dominant transmission with variable expression. (Abstract) Am. J. Hum. Genet. 43: A48 only, 1988.
Feigenbaum, A., Muller, C., Yale, C., Kleinheinz, J., Jezewski, P., Kehl, H. G., MacDougall, M., Rutsch, F., Hennekam, R. C. M. Singleton-Merten syndrome: an autosomal dominant disorder with variable expression. Am. J. Med. Genet. 161A: 360-370, 2013. [PubMed: 23322711] [Full Text: https://doi.org/10.1002/ajmg.a.35732]
Gay, B., Jr., Kuhn, J. P. A syndrome of widened medullary cavities of bone, aortic calcification, abnormal dentition, and muscular weakness (the Singleton-Merten syndrome). Radiology 118: 389-395, 1976. [PubMed: 175395] [Full Text: https://doi.org/10.1148/118.2.389]
Riou, M. C., de La Dure-Molla, M., Kerner, S., Rondeau, S., Legendre, A., Cormier-Daire, V., Fournier, B. P. J. Oral phenotype of Singleton-Merten syndrome: a systematic review illustrated with a case report. Front. Genet. 13: 875490, 2022. [PubMed: 35754802] [Full Text: https://doi.org/10.3389/fgene.2022.875490]
Rutsch, F., Kehl, H. G., Ruf, N., Vogt, J., Kleinheinz, J., Rauch, F., Hofbauer, L. C., Rehder, H., Arslan-Kirchner, M., Nurnberg, P. Singleton-Merten syndrome: evidence of autosomal dominant inheritance in the first European family. (Abstract) Europ. J. Hum. Genet. 13: 112-113 (P0154), 2005.
Rutsch, F., MacDougall, M., Lu, C., Buers, I., Mamaeva, O., Nitschke, Y., Rice, G. I., Erlandsen, H., Kehl, H. G., Thiele, H., Nurnberg, P., Hohne, W., Crow, Y. J., Feigenbaum, A., Hennekam, R. C. A specific IFIH1 gain-of-function mutation causes Singleton-Merten syndrome. Am. J. Hum. Genet. 96: 275-282, 2015. [PubMed: 25620204] [Full Text: https://doi.org/10.1016/j.ajhg.2014.12.014]
Singleton, E. B., Merten, D. F. An unusual syndrome of widened medullary cavities of the metacarpals and phalanges, aortic calcification and abnormal dentition. Pediat. Radiol. 1: 2-7, 1973. [PubMed: 4272099] [Full Text: https://doi.org/10.1007/BF00972817]
Valverde, I., Rosenthal, E., Tzifa, A., Desai, P., Bell, A., Pushparajah, K., Qureshi, S., Beerbaum, P., Simpson, J. Singleton-Merten syndrome and impaired cardiac function. J. Am. Coll. Cardiol. 56: 1760 only, 2010. [PubMed: 21070929] [Full Text: https://doi.org/10.1016/j.jacc.2010.02.078]