Table 1.

JDM disease features

Epidemiology	Median age of onset (IQR):	6.3 (3.8–9.6) years [1]
	Incidence:	7.98 cases/million/year [2]
	Prevalence:	14/100,000 [2]
	Sex distribution (F:M):	2.1:1 [3]
Clinical features	Muscle weakness	Most patients
	Cutaneous manifestations	30–70% [3]
	Calcinosis	12–47% [4, 5]
	Lipodystrophy	8–14% [6]
	Interstitial lung disease	8–19% [7]
	Myocardial involvement	Common, non-specific [8]
	Vasculopathy	Most patients, central to pathogensis [9]
Autoantibodies	MSA 49% + ve for MSA	- Transcriptional intermediary factor 1 (TIF-1γ) 22–29%
		- Nuclear matrix protein 2 (NXP2) 23–25%
		-Aminoacyl tRNA synthetase (ASA) 2–4%
		-Signal recognition particle (SRP) < 2%
		−3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) < 1%
		-Nucleosome-remodelling deacetylase complex (Mi-2) 4–10%
		-Small ubiquitin-like modifier activating enzyme (SAE) < 1%
		-Melanoma differentiation associated gene 5 (MDA5) 7–38% [10]
Pathogenesis	Type I IFN signature	Muscle, blood [11, 12]
	Mononuclear cells	Muscle [15]
	FOXP3+ regulatory T cells	Increased in muscle [16]
	pDCs	Increased in muscle/skin [17]
	Myogenic pre-cursor cells	Increased source of IFN in muscle [18, 19]
	Mast cells	Increased in skin [20]
	Natural killer cells	Decreased in blood [21]
	Cytokines
	Blood:	Increased IRF-4, IL-6, IL-17F, Il-23A, IL-21, GATA3, IL-1β
	Muscle:	Increased GATA3, IL-13, STAT5B [22]