Table 1 Demographic and clinical characteristics of the healthy controls (HCs) and patients with major depressive disorder (MDD) with differing levels of treatment resistance

No. of subjects

18

29

33

Age (years)

0.537

 Mean ± SD

68.6 ± 5.5

66.6 ± 6.8

65.0 ± 5.7

 Median (IQR)

68 (64.8–73.0)

65.0 (61.5–71.0)

66.0 (61.5–68.5)

Female gender, n (%)

11 (61.0)

22 (75.9)

25 (75.8)

0.47

Education (years)

0.065

 Mean ± SD

9.8 ± 3.9

7.2 ± 4.2

8.7 ± 4.0

 Median (IQR)

12 (6.0–12.5)

6.0 (6.0–10.5)

6.0 (6.0–12.0)

HAM-D

<0.001***

 Mean ± SD

2.0 ± 1.5

4.9 ± 3.5^a*

10.4 ± 6.5^a***^,b**

 Median (IQR)

1.5(1.0–2.3)

3.0(2.0–7.5)

8.0(6.0–14.5)

MMSE

<0.002**

 Mean ± SD

27.3 ± 1.8

25.2 ± 2.4^a**

24.7 ± 3.1^a**

 Median (IQR)

28 (26.8–28.3)

26.0 (24.0–27.0)

25.5 (22.5–27.0)

ApoE ε4, n (%)

2 (11.1)

5 (17.2)

9 (27.3)

0.347

FSRS

0.998

 Mean ± SD

8.5 ± 1.9

8.7 ± 4.4

8.6 ± 4.1

 Median (IQR)

9.0 (7.0–10.0)

10.0 (4.5–12.5)

9.0 (5.5–12)

Homocysteine (μmol/l)

0.299

 Mean ± SD

8.6 ± 1.8

8.9 ± 2.6

9.8 ± 2.9

 Median (IQR)

8.7 (7.3–9.5)

8.6 (7.0–10.7)

9.4 (7.6–11.1)

Age at onset (years)

–

0.122

 Mean ± SD

–

57.2 ± 12.5

53.8 ± 9.9

 Median (IQR)

–

57.0 (49.5–65.5)

53.0 (49.0–60.0)

Duration of MDD (years)

–

0.183

 Mean ± SD

–

9.3 ± 9.5

11.3 ± 9.0

 Median (IQR)

–

8.0 (1.5–11.5)

10.5 (5.0–13.0)

Number of depressive episodes

–

0.005**

 Mean ± SD

–

1.6 ± 0.6

2.5 ± 1.4^b**

 Median (IQR)

–

1.0 (1.0–2.0)

2.0 (2.0–3.0)

Late-onset MDD, n (%)

–

14 (48.3)

9 (33)

0.088

MSM score

–

<0.001***

 Mean ± SD

–

4.1 ± 1.0

8.4 ± 2.4^b***

 Median (IQR)

–

4.0 (3.0–5.0)

9.0 (7.0–10.0)

CDR 0.5, n (%)

–

12 (41.4)

25 (80.6)^b**

0.002**

CDR-SB

0.001**

 Mean ± SD

0.3 ± 0.5

1.0 ± 0.7b**

 Median (IQR)

–

0 (0.0–0.5)

1 (0.3–1.5)