Clinical Features of FOP patients
65 cases of FOP individuals recruited in our study were all Han people from 25 provinces of China. 46.2% (30/65 cases) were male while 53.8% (35/65 cases) were female. According to criterion of classification, 92.3% (60/65 cases) patients were diagnosed as classic FOP patients based on classic defining features of FOP, 3.1% (2/65 cases) of individuals were FOP-plus since they had classic defining features of FOP and other atypical features such as cryptorchidism or childhood glaucoma, and 4.6% (3/65 cases) were determined as FOP variants for their mild malformations of great toes. ACVR1 gene analysis was performed in 50 patients and revealed that 48 cases were canonical c.617G>A mutation. Two of FOP variants did not present canonical c.617G>A mutation: one of FOP variants showed a variant mutation in ACVR1 at c.774G>C (p.R258S), while the rest one had a mutation in ACVR1 at c.1067G>A (p.G356D). (Table 1) In the 65 cases of FOP patients, 84.6% (55 cases) of FOP patients were initially misdiagnosed before their first visit to our clinic, and approximately 36.9% of patients (24 cases) had undergone unnecessary biopsies.
Mortality rate of FOP patients
During the past ten-year period (Dec 2008 to Dec 2018), 9 patients with FOP (3 males and 6 females) were dead while 56 patients (27 males and 29 females) were survival. Hence, the total mortality rate was 13.8% (9/65 cases). The mortality rate in FOP patients aged 18 years and younger at diagnosis was 11.1% (5/45 cases), whereas it was 20% (4/20 cases) in patients aged over 18 years. All non-survivors were confirmed c.617G>A mutation, and were diagnosed as classic FOP for their congenital malformations of great toes and progressive HO (Table 2). The average age at diagnosis (age at first admission to our clinic) of 65 cases was 14.4±8.8 years. Among all non-survivors, 5 cases were 18 years and younger at diagnosis, and the rest 4 cases were over 18 years at diagnosis. The average age at diagnosis of non-survivors over 18 years and non-survivors aged 18 years and younger were 25.5±2.4 years and 11.6±6.3 years. The average age of onset (first flare-up or HO) of all FOP patients was 4.2±3.8 years. There was no significant difference in age at onset between non-survivors over 18 years at diagnosis and non-survivors aged 18 years and younger at diagnosis. The average age at death of all non-survivors was 22.8±8.9 years. The age of death in non-survivors over 18 years at diagnosis was significantly older than that in non-survivors aged 18 years and younger at diagnosis (29.5±2.9 years vs17.4±7.2 years) (Table 3).
Table 1 Clinical Features of FOP patients
|
|
Classic FOP
|
|
FOP-plus
|
|
FOP variants
|
Patient number
|
|
60cases
|
|
46
|
70
|
|
7
|
42
|
54
|
ACVR1 mutation
|
|
|
|
|
|
|
|
|
|
-Coden change
|
|
R206H (45 cases) or not complete (15 cases)
|
|
R206H
|
R206H
|
|
R258S
|
R206H
|
C306D
|
-Nucleotide change (cDNA position)
|
|
c.617G>A (45 cases) or not complete(15 cases)
|
|
c.617G>A
|
c.617G>A
|
|
c.744G>C
|
c.617G>A
|
c.1067G>A
|
Gender
|
|
M&F (26/34)
|
|
M
|
M
|
|
M
|
M
|
F
|
Age of onset (years)
|
|
0-13
|
|
18
|
5
|
|
6
|
2
|
2.5
|
Typical FOP features
|
|
|
|
|
|
|
|
|
|
-Congenital malformations of Great toes
|
|
Y
|
|
Y
|
Y
|
|
N
|
Y
|
Y
|
-progressive HO
|
|
Y
|
|
Y
|
Y
|
|
Y
|
Y
|
Y
|
-onset site
|
|
Scalp(45%);Neck(20%);Back(15%);Shoulder(6.7%); Hip (5%);Others(8.3%)
|
|
Shoulder
|
Back
|
|
Knee
|
Scalp
|
Shoulder
|
Other typical FOP features
|
|
|
|
|
|
|
|
|
|
-Thumb malformations
|
|
1.7%
|
|
Y
|
Y
|
|
Y
|
Y
|
N
|
-Knee osteochondromas
|
|
51.7%
|
|
N
|
N
|
|
Y
|
N
|
N
|
- Scoliosis
|
|
56.7%
|
|
N
|
N
|
|
Y
|
N
|
Y
|
-Conductive hearing impairment
|
|
5%
|
|
N
|
N
|
|
N
|
N
|
N
|
Atypical FOP features features
|
|
N
|
|
Childhood glaucoma
|
Cryptorchidism
|
|
Minimal changes in great toes
|
No changes in great toes
|
Minimal changes in great toes
|
Risk factors for the mortality of FOP patients
The clinical and biochemical data of the survival and non-survival FOP patients were shown in Table 3. In FOP patients aged 18 years and younger at diagnosis, serum OC and ALP levels were significantly lower in non-survival patients compared with survivors. Besides, there was no significant difference in gender ratio, age at diagnosis, serum Ca, P, PTH, ESR, ALT, AST, Cr or BUN at first visit between those two groups. In FOP patients aged over 18 years at diagnosis, there was no significant difference in gender ratio, age at diagnosis, serum OC, Ca, P, ALP, PTH, ESR, ALT, AST, Cr or BUN between survivors and non-survivors (Table 3).
Table 2 Clinical Features of FOP non-survivors
Patient number
|
1
|
2
|
8
|
21
|
34
|
39
|
41
|
45
|
98
|
Gender
|
F
|
M
|
F
|
M
|
F
|
M
|
F
|
F
|
F
|
Age of onset
|
4
|
3
|
2
|
0.1
|
6
|
0.7
|
2.5
|
1
|
6
|
Age of diagnose(years)
|
>18
|
>18
|
≤18
|
≤18
|
>18
|
>18
|
≤18
|
≤18
|
≤18
|
Age of death(years)
|
>18
|
>18
|
>18
|
≤18
|
>18
|
>18
|
>18
|
≤18
|
>18
|
Course of disease(years)
|
1
|
6
|
6
|
4
|
6
|
3
|
6
|
6
|
7
|
ACVR1 mutation
|
|
|
|
|
|
|
|
|
|
-Coden change
|
R206H
|
R206H
|
R206H
|
R206H
|
R206H
|
R206H
|
R206H
|
R206H
|
R206H
|
-Nucleotide change (cDNA position)
|
c.617G>A
|
c.617G>A
|
c.617G>A
|
c.617G>A
|
c.617G>A
|
c.617G>A
|
c.617G>A
|
c.617G>A
|
c.1067G>A
|
Typical FOP features
|
|
|
|
|
|
|
|
|
|
-Congenital malformations of Great toes
|
Y
|
Y
|
Y
|
Y
|
Y
|
Y
|
Y
|
Y
|
Y
|
-progressive HO
|
Y
|
Y
|
Y
|
Y
|
Y
|
Y
|
Y
|
Y
|
Y
|
-onset site
|
Scalp
|
Neck
|
Neck
|
Shoulder
|
Back
|
Scalp
|
Scalp
|
Scalp
|
elbow
|
Classification
|
classic FOP
|
classic FOP
|
classic FOP
|
classic FOP
|
classic FOP
|
classic FOP
|
classic FOP
|
classic FOP
|
classic FOP
|
Biochemical tests
|
|
|
|
|
|
|
|
|
|
-OC (u/L)
|
38.1
|
40.7
|
12.7
|
64.7
|
6.58
|
41.5
|
43.9
|
64.8
|
38.0
|
-Ca (mmol/L)
|
2.3
|
2.35
|
2.08
|
2.4
|
2.24
|
2.3
|
2.62
|
2.24
|
2.21
|
-P (mmol/L)
|
1.16
|
1.42
|
1.21
|
1.45
|
0.72
|
1.2
|
1.34
|
1.65
|
1.02
|
-PTH (pg/ml)
|
30.9
|
95.4
|
90.9
|
29
|
53.3
|
86.5
|
37.8
|
50.9
|
78.7
|
Table 3 The baseline characteristics of survivors and non-survivors
FOP patients
|
≤18y
|
|
>18y
|
Total
|
survivors
(group A)
|
non-survivors(group B)
|
|
survivors
(group C)
|
non-survivors(group D)
|
Cases
|
40(88.9%)
|
5(11.1%)
|
|
16(80%)
|
4(20%)
|
65
|
Gender ratio ( M/F)
|
21/19
|
1/4
|
|
6/10
|
2/2
|
30/35
|
Age at diagnose (years)
|
9.6±5.0
|
11.6±6.3
|
|
24.4±7.1 **△△
|
25.5±2.4 **△△
|
14.4±8.8
|
Age of onset
|
3.6±2.9
|
2.3±2.3
|
|
4.6±4.4
|
3.4±2.2
|
4.2±3.9
|
Age at death (years)
|
-
|
17.4±7.2
|
|
-
|
29.5±2.9△△
|
22.8±8.9
|
OC (ng/mL)
|
87.7±32.7
|
48.7±15.5**
|
|
34.7±19.8**
|
26.8±16.1**
|
67.9±37.8
|
Ca (mmol/L)
|
2.32±0.2
|
2.34±0.07
|
|
2.32±0.08
|
2.24±0.05
|
2.32±0.15
|
P (mmol/L)
|
1.58±0.25
|
1.42±0.15
|
|
1.23±0.3**
|
1.02±0.21**△
|
1.45±0.31
|
PTH (pg/mL)
|
63.3±487.4
|
53.2±25.9
|
|
81.5±37.7
|
71.9±14.3
|
67.5±42.8
|
ALP(IU/L)
|
244.0±121.1
|
128.2±85.0*
|
|
121.9±78.6**
|
82.2±24.9*
|
192.3±121.9
|
ESR (mm/hr)
|
7.9±5.2
|
9.4±8.7
|
|
10.2±9.2
|
9.25±5.6
|
8.6±7.8
|
ALT (U/L)
|
14.9±7.2
|
10.6±3.4
|
|
15.0±10.6
|
16.7±13.2
|
14.6±8.0
|
AST (U/L)
|
24.6±9.7
|
23.1±6.0
|
|
25.3±10.9
|
19.57±12.7
|
24.3±13.3
|
Cr (umol/L)
|
38.0±14.3
|
31.0±5.2
|
|
46.8±14.0
|
43.7±11.3
|
39.4±14.0
|
BUN (mmol/L)
|
2.0-5.8
|
1.7-7.2
|
|
2.9-6.3
|
2.2-5.3
|
1.7-7.2
|
Compared with group A, * P < 0.05, ** P < 0.01; Compared with group B, △ P < 0.05, △△ P < 0.01;
OC: osteocalcin; Ca: total serum calcium; P: phosphorus; PTH: parathyroid hormone; ALP: alkaline phosphatase ; ESR: erythrocyte sedimentation rate; CRP: C-reactive protein; ALT: alanine aminotransferase; AST: aspartate aminotransferase; Cr: creatinine; BUN: blood urea nitrogen
Spearman correlation analysis showed that serum OC, P, ALP were negatively correlated with the mortality in the total FOP patients (supplementary Table 1), whereas serum OC, ALP were negatively associated with the mortality in FOP patients ≤18 years at diagnosis (supplementary Table 2). No correlation between the mortality and the blood biochemical parameters was found in FOP patients >18 years at diagnosis (supplementary Table 3).
Logistic regression analysis indicated that serum OC level was negatively associated with the mortality in all FOP patients and FOP patients aged 18 years and younger at diagnosis. Further adjustment for age and gender did not change the correlation between serum OC and the mortality in all FOP patients (OR: -1.043; P=0.030) and FOP patients ≤18 years at diagnosis (OR: -1.224; P=0.028). However, in FOP patients aged over 18 years at diagnosis, no association between serum OC level and the mortality was found.
ROC curves were constructed to evaluate the sensitivity and specificity of the blood biochemical parameters as potential factors to discriminate the non-survivors from survivors of FOP patients aged 18 years and younger at diagnosis. The areas under the ROC curves (AUCs) of blood biochemical markers were shown in Fig. 1. Among four blood biochemical markers, serum OC had the largest AUC of 0.855, and serum OC < 65.9 ng/mL displayed a sensitivity of 100% and specificity of 75% in discriminating the non-survival patients from the survivors in FOP patients ≤18 years at diagnosis. Furthermore, the AUC of serum ALP, P and PTH was 0.837, 0.728 and 0.535 separately. The cut-off points of those four blood biochemical markers as predictors for the mortality in FOP patients aged 18 years and younger at diagnosis were presented in Table 4.
Table 4 Area under the Curve and related parameters
|
AUC
|
Cut-off point
|
Sensitivity
|
Specificity
|
P-value
|
95%CI
|
OC
|
0.855
|
<65.9ng/mL
|
100%
|
75%
|
0.010*
|
0.739-0.971
|
P
|
0.728
|
<1.47mmol/L
|
80%
|
70%
|
0.100
|
0.547-0.908
|
ALP
|
0.837
|
< 122.9IU/L
|
80%
|
90%
|
0.017*
|
0.605-1.068
|
PTH
|
0.535
|
<55.7 pg/mL
|
80%
|
52.5%
|
0.800
|
0.320-0.750
|
* P <0.05
OC: osteocalcin; P: phosphorus; ALP: alkaline phosphatase; PTH: parathyroid hormone