Autosomal Dominant Hypertension and Brachydactyly in a Turkish Kindred Resembles Essential Hypertension
We examined a Turkish kindred with a unique form of autosomal dominant hypertension that cosegregates 100% with brachydactyly and maps to chromosome 12p. Affected adults were 10 to 15 cm shorter than unaffected people; however, their body mass index (27 kg/m2) was not different. Blood pressure increased steeply with age in the affected people so that by age 40 years, they had a mean blood pressure of 140 mm Hg, compared with 92 mm Hg in unaffected individuals. Complete clinical, roentgenographic, and laboratory evaluation was performed in 6 subjects, including 24-hour blood pressure measurements and humoral determinations before and after volume expansion with 2 L normal saline over 4 hours followed by volume contraction on the following day with a 20-mmol sodium diet and 40 mg furosemide at 8 am, noon, and 4 pm. Two affected men aged 46 and 31 years; 3 affected women aged 40, 31, and 30 years; and 1 unaffected man aged 29 years were studied. Systolic pressures ranged from 170 to 250 mm Hg, and diastolic pressures ranged from 100 to 150 mm Hg in affected people; the unaffected man had a blood pressure of 120/70 mm Hg. Thyroid, adrenal, and renal functions were normal; electrolyte and acid-base statuses were normal. Calcium and phosphate homeostasis was normal. Day-night circadian blood pressure rhythm was preserved. The subjects were not salt sensitive; renin, aldosterone, and catecholamine values reacted appropriately to volume expansion and contraction. Affected people had mild cardiac hypertrophy and increased radial artery wall thickness. Fibroblasts from affected people grew more rapidly in culture than from unaffected people. We conclude that this novel form of inherited hypertension resembles essential hypertension.
Finding genes that cause human hypertension is difficult because the determinants of blood pressure (BP) in primary hypertension are multifactorial.1 One approach is to elucidate the genetic basis for hypertension in rare, monogenic inherited forms of hypertension. If a relevant mutation can be identified, it may provide a rational starting point from which to analyze the pathophysiology of the disease. Bilginturan et al2 in 1973 described a family with autosomal dominant brachydactyly associated with severe hypertension. The brachydactyly invariably cosegregated with the hypertension. Bilginturan et al concluded that both the hypertension and the brachydactyly were caused by a single autosomal dominant gene of pleiotropic action or by two closely located genes. We recently had the opportunity to reexamine this kindred and were able to map the responsible genes to chromosome 12p.3 Since the family lives in a fairly remote area of northeastern Turkey adjacent to the Black Sea, we were not in a position to characterize their hypertension in Turkey. However, subsequently, six family members agreed to come to Berlin for a comprehensive medical examination. We conducted 24-hour BP measurements; determined the humoral responses to volume expansion and contraction; performed roentgenographic, echocardiographic, Doppler, and ultrasound studies; and examined calcium homeostasis.
After approval from Turkish public health authorities, we visited the family first described by Bilginturan et al.2 The family lives on the northeastern Black Sea coast of Turkey. We examined 45 members of the family. Six additional members currently residing in Germany were identified 4 weeks later. Twelve additional family members were included in subsequent visits to Turkey. Height and weight were obtained as well as photographs of each individual's hands and feet. BP and heart rate were measured by an oscillometric automated method (every 2 minutes), 10 minutes standing and 20 minutes supine (Dinamap, Johnson & Johnson). The subjects underwent a physical examination including funduscopic examination. The investigations were approved by the institutional review boards for the protection of human subjects of both Humboldt and Hacettepe universities, and written informed consent in the Turkish language was obtained from all subjects examined or their parents.
Five affected subjects and an unaffected individual were studied in Berlin. All subjects were measured and weighed and underwent complete physical examinations including funduscopy by an ophthalmologist. They were also examined by a pediatric geneticist specifically interested in skeletal dysmorphology. Physical examination disclosed arteriolar narrowing and arteriovenous crossing abnormalities in subject 1, who also had a laterally displaced point of maximal impulse and an atrial gallop rhythm. The affected subjects were otherwise remarkable with respect to their stature, their brachydactyly, and their BP values. All affected subjects had attended school, were literate, and gave no indication of being mentally retarded.
None of the subjects was being treated for hypertension at the time of study. They received the usual isocaloric hospital diet containing 150 mmol sodium and chloride and 700 mg calcium daily unless otherwise indicated. The subjects were weighed after voiding each morning. All urine was collected at 24-hour intervals unless otherwise indicated. Creatinine, sodium, potassium, calcium, and phosphate were measured in all urine samples; vanillylmandelic acid was determined once. Fasting blood samples were obtained for complete blood count; electrolytes, including calcium, phosphate, and magnesium concentrations; liver function studies; total cholesterol, high- and low-density lipoprotein cholesterol, triglyceride, and lipoprotein(a) concentrations; thyrotropin, triiodothyronine, and thyroxine values; parathyroid hormone concentrations; and coagulation parameters. Plasma cortisol was measured the morning and afternoon after admission. Dexamethasone (2 mg) was given orally that evening, and cortisol was measured again the following morning.
Roentgenograms were obtained of the chest, hands, and skull. In addition, one subject underwent roentgenograms of the spine, and subjects 1 and 5 agreed to undergo computerized tomography of the brain. All subjects underwent abdominal ultrasound, duplex Doppler, and transthoracic echocardiographic examinations as well as echotracking determinations of their radial arteries for determination of wall thickness and vascular compliance by methods described elsewhere.4 Electrocardiograms were obtained in all subjects.
On the third and fourth hospital days, we performed a volume expansion-contraction protocol to determine salt sensitivity and resistance of BP as well as humoral responses to volume expansion and contraction and differences in posture as described previously.5 6 7 Briefly, on the volume expansion day, the subjects received a 150-mmol/d sodium diet. At 6 am, they had two forearm venous catheters placed, one for blood sampling and the other for saline infusion. After 60 minutes of quiet rest, blood was obtained with subjects in the supine position for plasma renin activity and plasma aldosterone, norepinephrine, and epinephrine concentrations. Thereafter, subjects were encouraged to ambulate for 60 minutes, and blood samples were obtained with subjects in the upright posture for the same determinations. A 24-hour ambulatory oscillometric BP-measuring device (SpaceLabs Inc) was placed on the arm opposite the saline infusion. BP was measured every 10 minutes during saline. The subjects emptied their bladders at 8 am and remained supine for the next 4 hours. Normal saline, 2 L over 4 hours, was infused intravenously between 8 am and noon. Thereafter, blood was obtained with subjects in the supine posture for the above humoral values as well as for sodium, potassium, and creatinine. Urine collection was terminated at noon, although urine was collected for an additional 20 hours until the next morning. On the following morning, the diet was modified to contain less than 20 mmol/d sodium. Blood for humoral determinations was again obtained with subjects in the supine and upright postures. Furosemide (40 mg PO) was given at 8 am, noon, and 4 pm. The 24-hour ambulatory BP measurement was continued on this day as well. On the following morning after furosemide, blood sampling was repeated, and BP was measured every 10 minutes for 1 hour.
Salt sensitivity was defined as the difference between BP values after saline infusion and on the morning after the furosemide day. We discarded the highest and lowest of the six BP values obtained for the respective hour of measurement and took the mean value of the remaining four values to determine BP after saline and after furosemide. According to previous studies, we defined salt sensitivity as a BP difference greater than or equal to 10 mm Hg comparing volume expansion and contraction.5 This method has been shown to be reproducible8 and was also compared with salt sensitivity as determined by a response to a low sodium diet; a significant correlation between the two methods was obtained.9
Fibroblasts were obtained from fresh skin punch biopsies in the five affected Turkish subjects and from five additional normal control subjects. The subjects were matched for age and sex. The cell culture techniques and quantification we routinely use in our laboratory have been described in detail elsewhere.10 Briefly, we used a colorimetric assay with the tetrazolium compound formazan (Promega). Quiescent fibroblasts (96-well plates) were incubated in 10% fetal calf serum for 12 hours. Formazan was added together with fetal calf serum. Absorbance was recorded at 490 nm with an enzyme-linked immunosorbent assay plate reader. Measurements were carried out in triplicate.
Blood chemistries were measured by routine, automated methods. Thyroid hormone values, parathyroid hormone, calcitriol, corticotropin, cortisol, plasma renin activity, and plasma aldosterone were determined by radioimmunoassay. Plasma catecholamines were measured by high-performance liquid chromatography. Data were analyzed with Student's t test for unpaired data or nonparametric tests as appropriate. Data are presented as mean±SD.
Table 1⇓ outlines the characteristics of the affected and unaffected, male and female, adult (>18 years) family members whom we examined on our first visit to Turkey. We did not include subsequently identified family members in this analysis because they do not live in the same rural area and environmental factors may be different. Affected men and women were almost 2 decades younger than unaffected individuals, reflecting their high mortality. Affected people weighed less and were shorter than unaffected people; however, body mass index of the two groups was not significantly different. BP values were much greater in affected than unaffected people. Fig 1⇓ shows the age-corrected values for unaffected and affected people. With this correction, a difference of 30 mm Hg in BP is apparent. We also searched for effects of sex and found none. We obtained detailed social histories from the subjects and were not able to detect any sign of mental retardation. By history, we conclude that the cause of death in family members is generally stroke. We were able to review a computed tomographic scan and magnetic resonance imaging scan from two affected subjects who had had a stroke and identified a cerebral hemorrhage and lacunar infarction. Funduscopic examination disclosed only arteriolar narrowing and increased light reflex. The corneas were unremarkable, and no lenticular abnormalities were visible. The hearts were generally normal, although an occasional subject had a systolic ejection murmur or a fourth heart sound. Abdominal examinations were normal. No subject had edema. We specifically noted no cutaneous abnormalities, and no subcutaneous calcifications were palpated.
Table 2⇓ gives information on the six subjects studied in detail, including body weight, height, body mass index, and admitting BPs and heart rates for each subject as well as echocardiographic data, vascular measurements, and creatinine clearance. The renal function of subject 1 was decreased compared with the expected value. Diagnostic ultrasound revealed that subject 1 had small intrarenal calculi. Subject 1 had a right kidney 2 cm smaller than the left kidney. A renal isotope scan before and after 25 mg captopril showed no evidence of renal vascular hypertension. Furthermore, duplex Doppler studies in the remaining four affected subjects showed renal arteries without evidence of stenosis.
The five affected subjects and the unaffected individual had values in the normal range for the following determinations: complete blood count, blood sugar, 2-hour postprandial blood sugar, liver function tests, and electrolytes. Table 3⇓ shows thyroid and adrenal function, plasma lipids, parathyroid hormone, calcitriol, and electrolyte values. Thyroid function was normal. Dexamethasone (not shown) resulted in the expected cortisol suppression. The subjects had relatively low total cholesterol, low-density lipoprotein cholesterol, and triglyceride values. Subject 1 had a lipoprotein(a) concentration of 38 mg/dL, which was definitely elevated compared with normal values for our laboratory. He was also the only family member with known coronary heart disease and had undergone a coronary bypass operation at Hacettepe University 3 years earlier. Parathyroid hormone and calcitriol values were unremarkable. Urinalysis showed microalbuminuria (Micral Test, Boehringer Mannheim) in two affected subjects.
Fig 2⇓, left, shows representative hand photographs, both extended and clenched, from subject 2. The fourth and fifth metacarpals were shortened in this subject. However, other affected individuals had shortening of the other metacarpals as well. Fig 2⇓, right, shows the same views from subject 6, the unaffected first cousin. Fig 3⇓, top, shows roentgenograms of the left and right hands of subject 2, and Fig 3⇓, bottom, shows the same views for subject 6.
Fig 4⇓, left shows 24-hour ambulatory BPs of the six subjects on the volume expansion day. The marked degree of hypertension in affected subjects is readily apparent. Two affected subjects had no normal nocturnal decrease in BP, and three did. Saline infusion had no consistent effect on BP. Fig 4⇓, right, shows 24-hour ambulatory BPs of the six subjects during the volume contraction day. A pattern of BP responses similar to that on the volume contraction day was evident. Two affected subjects were classified as salt sensitive according to our definition; three affected subjects and the normal subjects were classified as salt resistant.
Table 4⇓ shows plasma renin activity and plasma aldosterone, norepinephrine, and epinephrine concentrations in the supine and upright positions on the morning of the volume expansion and volume contraction days as well as in the supine position after saline infusion. Upright posture resulted in an increase in all these values in all subjects. Volume expansion resulted in a decrease in these values, and volume contraction resulted in an increase. Norepinephrine values were unremarkable. Epinephrine and dopamine values were all somewhat higher than our normal range, including those of the unaffected subject.
Fibroblasts from the subjects were cultured from skin punch biopsy specimens. The results are shown in Fig 5⇓. The values are compared with normal values obtained from biopsy specimens from normotensive, sex-matched volunteers similar in age. A significantly faster cell growth rate in affected than in control subjects was apparent.
The important findings in this study are that affected individuals were not salt sensitive; had renin, aldosterone, and catecholamine values that responded appropriately to provocative maneuvers; and had fibroblasts that grew slightly faster in artificial medium than those of normal control subjects. Affected subjects had some cardiac hypertrophy and increased radial wall thickness. Thus, our subjects resemble individuals with severe, normal-renin essential hypertension.
One affected person had renal calculi; however, we were not able to document abnormal urinary calcium excretion11 in this small sample. That individual had a difference in renal size; however, his captopril renogram did not suggest renovascular hypertension. The other four affected people we examined had kidneys similar in size bilaterally and had duplex Doppler flow studies that suggested symmetrical flow bilaterally. We elected not to perform angiography on subject 1; however, we admit that we have not absolutely excluded a vascular basis for the hypertension in our subjects. In addition to possible renovascular hypertension, anomalies in the posterior inferior cerebellar artery, which can be detected only by magnetic resonance imaging angiography, have been associated with hypertension.12 Our subjects did not have such examinations. We did not perform invasive hemodynamic studies in our subjects; however, by echocardiography, their stroke volumes were normal in the face of markedly elevated BP, supporting the notion that the primary hemodynamic mechanism for hypertension in these individuals is a marked increase in peripheral vascular resistance. Stroke seemed to be the primary cause of death in affected individuals. Low-density lipoprotein cholesterol and triglyceride values were generally not elevated. We found only a single subject with coronary disease, and he had increased lipoprotein(a) values. The putative mechanism by which lipoprotein(a) increases cardiovascular risk has been outlined elsewhere.13
An interesting feature in our subjects was an increase in the rate of fibroblast growth. This observation is interesting in light of the fact that spontaneously hypertensive rats also exhibit an increased rate of fibroblast and smooth muscle cell growth compared with Wistar-Kyoto control rats. Furthermore, immortalized B lymphoblasts from individuals with essential hypertension proliferate more quickly than those from control subjects, which is perhaps related to genetically determined increased G protein activation.14
The 100% cosegregation of hypertension with brachydactyly is particularly interesting. We believe that the two phenotypes are caused by either a single pleiotropic gene or two closely situated genes. We have mapped to the chromosomal region 12p11.2-12.2.3 We eliminated the presence of a microdeletion by appropriate cytogenetic studies (850 bands resolution). The short, fourth metacarpal in the subjects resembles the anomaly associated with type I pseudohypoparathyroidism or Albright's hereditary osteodystrophy. This condition is also associated with hypertension; however, the hypertension appears to be related to the excessive body weight.15 Our subjects were not obese or mentally retarded, as is commonly the case in individuals with pseudohypoparathyroidism.16 Our subjects had normal parathyroid hormone values and normal plasma calcium and phosphate values. Moreover, they did not show evidence of intracerebral calcifications, including by computerized tomography in one subject, and they did not have subcutaneous calcifications. Finally, all metacarpals were frequently shortened in our subjects, whereas in pseudohypoparathyroidism, only the fourth metacarpal is particularly shortened.16 Nevertheless, pseudohypoparathyroidism would have been an interesting possibility. In the type I variant of that disease, the genetic defect has been attributed to a malfunction of the G protein family.17 We ruled out the GNAS1 gene locus on chromosome 20 as responsible for the hypertension in our subjects by using intragenic and flanking microsatellite markers. Interestingly, an Albright's osteodystrophy variant with brachydactyly has recently been mapped to chromosome 2q37; however, these individuals were retarded and not hypertensive.18
The monogenic forms of hypertension described thus far are decidedly different from the condition we describe. Glucocorticoid remediable aldosteronism and Liddle's syndrome, which both display renin suppression, volume expansion, and salt sensitivity, are examples of autosomal-dominant hypertension. The former features a chimeric gene that incorporates the regulatory region of the 11β-hydroxylase gene and the structural portion of the aldosterone synthase gene.19 The latter is characterized by a mutation in the gene encoding for either the β- or γ-subunit of the epithelial amiloride-sensitive sodium channel.20 Furthermore, an autosomal recessive form of hypertension, termed apparent mineralocorticoid excess, has recently been characterized. In this disease, mutations were found in the gene encoding the enzyme 11β-hydroxysteroid dehydrogenase.21 Failure of cortisol-to-cortisone degradation in the distal tubule results in inappropriate activation of the mineralocorticoid receptor, volume expansion, salt sensitivity, and renin suppression.
In summary, our data indicate that a single genetic defect on chromosome 12p is responsible for an age-corrected BP difference of 30 mm Hg between affected and unaffected people by age 50 years in this family with autosomal dominant hypertension and brachydactyly. Thus, the genetic mechanism at work in these subjects is phenomenally powerful. Our clinical studies suggest that the renin-angiotensin-aldosterone and sympathetic nervous systems may not be responsible for the hypertension. We suggest that elucidation of the gene mutation and pathogenesis of the hypertension may be of relevance to individuals with non–salt-sensitive, normal-renin essential hypertension. It is possible that a not yet appreciated mechanism of BP elevation is involved.
This study was supported by a grant-in-aid (F6170895W0069) from the United States Air Force. We are grateful to the physicians, nurses, and technicians of the Franz Volhard Clinic, who helped make these studies possible. Astra GmbH (Wedel, FRG) supplied the medications for the subjects. Friedrich C. Luft is supported by a grant from the Bundesministerium für Forschung und Technologie. These data satisfy in part the requirements for the MD degree of Hakan R. Toka.
- Received April 4, 1996.
- Revision received May 20, 1996.
- Revision received July 3, 1996.
Bilginturan N, Zileli S, Karacadag S, Pirnar T. Hereditary brachydactyly associated with hypertension. J Med Genet. 1973;10:253-259.
Meister JJ, Tardy Y, Stergiopulos N, Hayoz D, Brunner HR, Etienne JD. Non-invasive method for the assessment of non-linear elastic properties and stress of forearm arteries in vivo. J Hypertens. 1992;10(suppl 6):S23-S26.
Weinberger MH, Miller JZ, Luft FC, Grim CE, Fineberg NS. Definitions and characteristics of sodium sensitivity and blood pressure resistance. Hypertension. 1986;8:127-134.
Grim CE, Miller JZ, Luft FC, Christian JC, Weinberger MH. Genetic influence on renin, aldosterone, and the renal excretion of sodium and potassium following volume expansion and contraction in normal man. Hypertension. 1979;1:583-590.
Grim CE, Luft FC, Fineberg NS, Weinberger MH. Responses to volume expansion and contraction in categorized hypertensive and normotensive man. Hypertension. 1979;1:476-485.
Weinberger MH, Fineberg NS. Sodium and volume sensitivity of blood pressure: age and pressure change over time. Hypertension. 1991;18:67-71.
Haller H, Lindschau C, Quass P, Distler A, Luft FC. Differentiation of vascular smooth muscle cells and the regulation of protein kinase C-α. Circ Res. 1995;76:21-29.
Siffert W, Rosskopf D, Moritz A, Wieland T, Kaldenberg-Stasch S, Kettler N, Hartung K, Beckmann S, Jakobs KH. Enhanced G protein activation in immortalized lymphoblasts from patients with essential hypertension. J Clin Invest. 1995;96:759-766.
Spiegel AM. Pseudohypoparathyroidism. In: Scriver CR, Beaudet AL, Sly WS, Valle D, eds. The Metabolic Basis of Inherited Disease. New York, NY: McGraw-Hill Publishing Co; 1989:2013-2027.
Shimkets RA, Warnock DG, Bositis CM, Nelson-Williams C, Hansson JH, Schambelan M, Gill JR, Ulick S, Milora RV, Findling JW, Canessa CM, Rossier BC, Lifton RP. Liddle's syndrome: heritable human hypertension caused by mutations in the β subunit of the epithelial sodium channel. Cell. 1994;79:407-414.