Table 3

The stepwise univariable linear regression analysis of each of the five radiographic features scorings for all three spine segments, as well as their sum, as dependent variables. Age, body height, body weight, body mass index, sHGA, uHGA₂₄, eye and ear ochronosis of patients with alkaptonuria were entered into the regression as independent variables

Variable	Model	R²	Significance F change	B (SE)	Beta	Significance	Tolerance
Narrowing of the intervertebral space	Age	0.60	<0.0001	Constant: −4.14 (0.56)		<0.0001
	Age	0.60	<0.0001	Age: 0.16 (0.01)	0.78	<0.0001	1.00
	Age Ear ochronosis	0.63	<0.0001	Constant: −3.96 (0.56)		<0.0001
				Age: 0.15 (0.01)	0.70	<0.0001	0.84
				Ear ochronosis: 0.15 (0.04)	0.20	<0.0001	0.84
	Age Ear ochronosis sHGA	0.65	<0.0001	Constant: −4.45 (0.58)		<0.0001
				Age: 0.14 (0.01)	0.66	<0.0001	0.80
				Ear ochronosis: 0.15 (0.04)	0.20	0.001	0.84
				sHGA: 0.03 (0.01)	0.13	0.015	0.95
Calcifications	Age	0.55	<0.0001	Constant: −3.4 (0.50)		<0.0001
	Age	0.55	<0.0001	Age: 0.13 (0.01)	0.74	<0.0001	1.00
	Age Ear ochronosis	0.60	<0.0001	Constant: −3.05 (0.50)
				Age: 0.11 (0.01)	0.64	<0.0001	0.84
				Ear ochronosis: 0.16 (0.04)	0.25	<0.0001	0.84
Vacuum phenomena	Age	0.21	<0.0001	Constant: −1.50 (0.61)		0.019
	Age	0.21	<0.0001	Age: 0.07 (0.01)	0.46	<0.0001	1.00
	Age sHGA	0.23	0.020	Constant: −2.01 (0.65)		0.002
				Age: 0.07 (0.01)	0.42	<0.0001	0.95
				sHGA: 0.03 (0.01)	0.18	0.020	0.95
Osteophytes or hyperostosis	Age	0.53	<0.0001	Constant: −3.99 (0.57)		0.02
	Age	0.53	<0.0001	Age: 0.13 (0.01)	0.66	<0.0001	1.00
	Age Ear ochronosis	0.55	<0.0001	Constant: −3.76 (0.57)		<0.0001
				Age: 0.13 (0.01)	0.65	<0.0001	0.84
				Ear ochronosis: 0.13 (0.05)	0.17	0.005	0.84
Fusions	Age	0.21	<0.0001	Constant: −1.65 (0.38)		<0.0001
	Age	0.21	<0.0001	Age: 0.04 (0.01)	0.46	<0.0001	1.00
	Age Height	0.26	0.003	Constant: 3.50 (1.73)		0.044
				Age: 0.04 (0.01)	0.36	<0.0001	0.84
				Height: −0.03 (0.01)	−0.25	0.003	0.84
	Age Height sHGA	0.29	0.015	Constant: 3.06 (1.70)		0.077
				Age: 0.03 (0.01)	0.32	<0.0001	0.81
				Height: −0.03 (0.01)	−0.24	0.003	0.84
				sHGA: 0.02 (0.01)	0.18	0.015	0.95
Sum of all X-ray features	Age	0.61	<0.0001	Constant: −14.62 (1.85)		<0.0001
	Age	0.61	<0.0001	Age: 0.55 (0.04)	0.78	<0.0001	1.00
	Age Ear ochronosis	0.64	<0.0001	Constant: −13.99 (1.79)		<0.0001
				Age: 0.50 (0.04)	0.71	<0.0001	084
				Ear ochronosis: 0.51 (0.15)	0.20	0.001	0.84
	Age Ear ochronosis sHGA	0.66	<0.0001	Constant:−15.90 (1.90)
				Age: 0.48 (0.04)	0.68	<0.0001	0.80
				Ear ochronosis: 0.50 (0.14)	0.19	0.001	0.84
				sHGA: 0.10 (0.04)	0.13	0.013	0.95

Serum homogentisic acid (sHGA), 24-h urinary homogentisic acid excretion (uHGA₂₄).
uHGA24, Serum homogentisic acid (sHGA), 24-h urinary homogentisic acid excretion.