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Familial Predisposition
for Degenerative Disc Disease
A Case-Control Study
Edward D. Simmons, MD, MSc, FRCS(C), Madhuri Guntupalli, Joseph M. Kowalski, MD, Felix Braun, MD, and Thomas Seidel, MD

Study Design. This case-control study was undertaken to determine if relatives of patients who had been admitted for surgery for degenerative disc disease-related problems were at increased risk for lower back pain or sciatica.

Objectives. To determine if familial factors play a role in placing a person at risk for development of degenerative disc disease of the lumbar spine.

Summary of Background Data. It is known that smoking and various occupational factors can place a person at risk for degenerative disc disease problems. It is not known if a familial predisposition may also exist.

Methods. The family members and relatives of 65 patients who had undergone surgery for lumbar degenerative disc disease were interviewed with a standardized questionnaire and compared with a control group of 67 patients who had been admitted to hospital for non-spine-related orthopedic procedures. The same interview and standardized questionnaire was used for both groups by a single observer.

Results. In the study group of 65 patients who had undergone surgery for degenerative disc disease, 44.6% were noted to have a positive family history, whereas 25.4% of the patients in the control group had a positive family history. Eighteen and one-half percent of relatives in the study group had a history of having spinal surgery, compared with only 4.5% of the control group.

Conclusions. The results indicate that a familial predisposition to degenerative disc disease can exist along with other risk factors. [Key words: case-control study, degenerative disc disease, familial predisposition] Spine 1996;21:1527-1529

It is known that degenerative disc disease problems can arise from multifactorial processes, ^2,4 with one possible aspect being genetic factors. There is some literature regarding familial predisposition to adolescent disc herniation, ^5,7 but very little has been done with regard to degenerative disc disease processes in adults. Other risk factors have been identified, including smoking,¹ truck driving, ³ and other occupationally related factors. ^1,2 In a recent paper with regard to familial predisposition to lumbar disc herniations in patients younger than 21 years of age,⁷ it was noted that a familial basis for lumbar disc herniation in adolescents and patients younger than 21 years of age was significant, with the relative risk estimated as being approximately five times greater in patients who had a positive family history. In another paper looking at patients of all age groups, ⁶ it was noted that patients who had undergone a discectomy had an increased incidence of relatives with history of lower back pain compared with a control group.

The object of this study was to determine if a familial predisposition for degenerative disc disease exists in adult patients older than 21 years of age.

Materials and Methods
A chart review and interview of 65 patients who had undergone surgery for lumbar degenerative disc disease was carried out and compared with a chart review of a control group of 67 patients who had been admitted to hospital for orthopedic surgery of a nonspinal diagnosis. All the patients in the study group had undergone lumbar spine fusion with or without discectomy. The patients in the study group presented with clinical findings of mechanical low back pain due to painful degenerative disease with or without associated radiculopathy, and had not responded to prolonged nonoperative management. All patients with spondylolisthesis, scoliosis, fractures, and other diagnoses were not included. Patients in both groups were matched for age and sex.

Typical findings on history included back pain with or without intermittent leg pain aggravated by sitting, driving, bending forward or lifting, and straining. Physical findings included limited range of motion of the lumbar spine, reversal of spinal rhythm, painful/diminished straight leg raising, and various degrees of neurologic involvement involving motor, sensory, and reflex changes. Imaging studies included magnetic resonance imaging scans, often supported by discogram studies.

In the study group of 65 patients, 39 were men and 26 were women, with an average age of 32.7 years. In the control group of 67 patients, 42 were men and 25 women, with an average age of 32.8 years (Table 1).

Group	n	Mean Age (yr.)	No. of Smokers	Positive Family History of  Lumbar Degenerative  Disc Disease	Positive Family History of Spine Surgery
Control group
Male	42	33.2	18	10	2
Female	25	31.1	10	7	1
Total	67	32.8	28	17 (25.4%)	3 (4.5%)
Study group
Male	39	33.0	14	16	4
Female	26	32.1	13	13	8
Total	65	32.7	27	29 (44.6%)	12 (18.5%)

First- and second-degree relatives of patients in the study and control groups were contacted and interviewed by a single observer (MG). Attempts were made to contact as many relatives as possible in each group. A standardized interview and questionnaire were used for each contact. A similar format as previously published by Varlotta et al⁷ for adolescent disc herniation was used, because it was thought that this would provide some standardization in the literature. In each group, relatives were classified as either having no history of lower back problems, or a positive history of lower back problems. A relative was considered to have a positive history only if there had been episodes of lower back pain necessitating visits to a physician or pain problems that had been incapacitating with limitation of daily activities and that had occurred on multiple occasions. Lower back pain as an occasional or mild problem was not considered as being positive. It was also noted if any relatives had undergone surgical treatment for any lower beck disorders. Only first- and second-degree relatives were considered for inclusion in evaluating the incidence of surgery or the incidence of low back pain. Siblings and parents were commonly interviewed and cousins were frequently contacted as well. Grandparents were less often interviewed because many were deceased. Similar numbers of first- and second-degree relatives were contacted for the study and control groups (212 vs. 225).

The average ages of the first- and second-degree relatives in the two groups were also quite similar (37.6 vs. 40.3 years).

All results were compared using a Microsoft Excel version 5.0, spreadsheet software program, and tested for statistical significance using Student's t test, chi-squared test, and odds ratio.

Results
In the study group of 65 patients who had undergone surgery for degenerative disc disease, 44.6% were noted to have a positive family history using the criteria noted previously, whereas only 25.4% of patients in the control group had a positive family history (P < 0.05). By odds ratio analysis, these data show that patients in the study group were 2.37 times more likely to have a family history of degenerative disc disease than the control group (Table 2). It was also noted that 18.5% of relatives in the study group had a history of spinal surgery, compared with only 4.5% of the control group (P < 0.05). This reveals that patients in the study group were 4.83 times more likely to have a family history of spinal surgery than the control group (Table 2). The incidence of smoking was the same in both groups, being 37% in the study group and 42% in the control group (Table 1). No ethnic, cultural, or socioeconomic differences were detectable between the two groups. Of interest, there was a slightly stronger familial predisposition in women than men (Table 1). Labor versus nonlabor or sedentary work was evenly distributed throughout the two groups. In the study group, 46% were considered labor workers, and in the control group 52% were considered laborers.

Discussion
In this study, the incidence of a positive family history for lower back pain disorder or degenerative disc disease was noted to be different between a group of patients who had undergone surgery for degenerative disc disease compared to a control group. Patients with degenerative disc disease were more than twice as likely to have a positive family history compared with the control group of patients. In the design of the study, we used a format of interview and questionnaire that had been previously used ⁷ because it appeared to accommodate for the potential of any lower back disorder or degenerative disc disease-related problems. Other potential factors include those related to smoking, ethnicity, and occupation. There was no difference in the incidence of smoking between the two groups. Occupational and ethnic factors were not significantly different between the relatives of the control and study groups. The high incidence of family history for spinal surgery in the study group could have affected decision making for other relatives considering surgery, but this may have played a positive or negative role depending on the perceived success and results of the surgery (Figure 1). Interestingly, women were noted to have a somewhat stronger tendency for familial predisposition than men. Although the significance of this cannot be precisely determined in this study, the question of a sex-linked means of genetic transfer must be raised.

Table 2.
Odds Ratios for Association Between Degenerative Disc Disease and Family History

Family History (Ist or 2nd degree relative)	Odds Ratio	95% Confidence Limits
Spine surgery	4.83	1.29-18.02
Low back pain	2.37	1.13-4.95
No low back pain*	1.00

* Reference group.
Results show that patients in the study group were 2.37 times more likely to have a family history of low back pain and 4.83 times more likely to have a family history of spine surgery than those in the control group. The 95% confidence intervals do not include 1.0 and therefore one can reject the null hypotheses of equal nsk among those patients with and without a family history of low back pain or spine surgery. These results do not indicate a causal relationship, but rather, demonstrate that a family history of low back pain or spine surgery puts one at risk for developing back pain and requiring spine surgery.

Figure 1. A 45-year-old woman presenting with problems related to degenerative disc disease in the lumbar spine. She was noted to have a strong family history of degenerative disc-related problems and was a nonsmoking, sedentary office worker. A, Anteroposterior radiograph of lumbar spine. B, Lateral radiograph of lumbar spine. C, Magnetic resonance (MR) Tl-weighted image of lumbar spine. D, MR T2-weighted image of lumbar spine.

The precise basis for the increased familial risk of degenerative disc disease-related problems cannot be determined from this study. Familial predisposition may be on the basis of biochemical differences within the discs, hereditary factors such as body habitus or other physical characteristics that are inherited, proprioceptive differences, social sources of familial similarity, and other unknown factors. Further research in these directions for the etiology of this apparent familial predisposition are needed. Familial predisposition to lower back pain and degenerative disc disease should be regarded as a potential risk factor for any given patient with a positive family history for these types of problems, and in combination with other risk factors such as smoking, the tendency for degenerative disc disease-related problems could be heightened.

References
1. Bigos SJ, Barrie MC, Spengler DM, et al. A longitudinal, prospective study of industrial back injury reporting. Clin Orthop 1992;279:21-34.
2. Bigos SJ, Spengler DM, Martin NA, Zeh J, Fisher L, Nachemson A. Back injuries in industry: A retrospective study. 111. Employee-related factors. Spine 1986;11:252-6.
3. Kelsey JL, Githens PB, O'Connor T, et al. Acute prolapsed lumbar intervertebral disc: An epidemiologic study with special reference to driving automobiles and cigarette smoking. Spine 1984;9:608-13.
4. Kelsey JL, Ostfeld AM. Demographic characteristics of persons with acute herniated lumbar intervertebral disc. J Chronic Dis 1975;28:37-50.
5. Matsui H, Terahata N, Tsuji H, Hirano N, Naruse Y. Familial predisposition and clustering for juvenile lumbar disc herniation. Spine 1992;17:1323-7.
6. Porter RW, Thorpe L. Familial aspects of disc protrusion. Orthop Trans 1986;10:524.
7. Varlotta GP, Brown MD, Kelsey JL, Golden AL. Familial predisposition for herniation of a lumbar disc in patients who are less than twenty-one years old. J Bone joint Surg [Am] 1991;73:124-8.

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