Familial hypercholesterolemia. The determination of phenotype

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Jansen, A.C.M.

Publication date

2003

Link to publication

Citation for published version (APA):

Jansen, A. C. M. (2003). Familial hypercholesterolemia. The determination of phenotype.

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hypercholesterolemia a

Thee need for genetic testing

AA study in 2400 FH heterozygotes

Emilyy S van Aalst-Cohen

1

, Angelique CM Jansen

1

, Michael WT Tanck

2

,

Antonn FH Stalenhoef

3

and John JP Kastelein

1

Departmentss of Vascular Medicine' and Clinical Epidemiology and Biostatistics2, Academicc Medical Center, University of Amsterdam. Department of Internal Medicine3

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Abstract t

Background d

Wee assembled a large cohort of patients with familial hypercholesterolemia (FH) for both basicc and clinical research. We used a set of established clinical diagnostic criteria to define FH.. Some put forward that a definite diagnosis of FH can only be made when a mutation in thee LDL-receptor gene is identified. We therefore set out to determine in these FH patients whetherr patients with a DNA diagnosis would differ significantly from those diagnosed on thee basis of clinical criteria.

Method d

Wee randomly selected 4000 hypercholesterolemic patients from the Dutch Lipid Clinic networkk database. Phenotypical data were acquired by reviewing medical records.

Result t

Afterr review of all medical records and application of the FH diagnostic criteria, 2400 patients couldd be defined as having FH. An LDL-receptor mutation was identified in 52.3% of these patients.. Patients with and without an LDL-receptor mutation demonstrated different clinical andd laboratory characteristics. LDL-cholesterol was higher in patients with an LDL-receptor mutation,, whereas triglycerides and HDL-cholesterol were higher in patients without an LDL-receptorr mutation. Patients without a known LDL-receptor mutation were older, more oftenn males and had a higher body mass index and blood pressure, in addition to a higher prevalencee of hypertension, smoking, CVD and a positive family history for premature CVD.

Conclusion n

Despitee the use of stringent clinical criteria to define FH patients, two cohorts could be identifiedd within our study population. Our findings suggest that among those without an LDL-receptorr mutation, patients with other causes of dyslipidemia may still be present. Thesee observations confirm the need for genetic testing in FH, both for clinical practice and forr scientific research involving these patients.

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Introduction n

Heterozygouss familial hypercholesterolemia (FH) is a common (1:500) and inherited autosomall dominant disorder of lipoprotein metabolism. Clinically, FH is characterized by elevatedd serum levels of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C),, and the presence of tendon xanthomas, xanthelasmata and/or an arcus cornealis. In mostt patients there is also excessive deposition of cholesterol in the arterial wall, leading to acceleratedd atherosclerosis and premature cardiovascular disease (CVD). Typically, approximatelyy 45% of maie and 20% of female patients suffers from coronary artery disease (CAD)) by the age of 50.1

Thee clinical diagnosis of FH is based on personal and family history, physical examination, andd laboratory findings. The underlying molecular defect of FH consists of mutations in the genee coding for the LDL-receptor protein, detection of which provides the only unequivocal diagnosis.22 Therefore, there is a need for accurate clinical diagnostic criteria as long as a geneticc diagnosis has not been made. We assembled a large cohort of FH patients for both clinicall and basic research. We used a set of established clinical diagnostic criteria'36 to definee FH and subsequently we investigated the clinical and biochemical features of this FH cohortt according to the presence of LDL receptor mutations and to the presence of tendon xanthomas,, which are assumed to be pathognomic for FH.

Methods s

Studyy design and study population

Thee present investigation was a retrospective, multicenter, cohort study. Routinely, Lipid Clinicss in the Netherlands submit DNA samples from clinically suspected FH patients to a centrall laboratory for LDL receptor mutation analysis. This laboratory, located at the Academic Medicall Center of the University of Amsterdam, manages a DNA-bank database, which currentlyy contains over 9300 samples.7 We randomly selected 4000 hypercholesterolemic patientss with the aid of a computer programm (Microsoft Excel) from this database. These patientss had been referred from 27 Lipid Clinics throughout the Netherlands.

Phenotypicall data were acquired by reviewing these patient's medical records by a trained teamm of data collectors. Only patients that met the inclusion and exclusion criteria (see Tablee 1) were included in the study. The FH diagnostic criteria were based on criteria used inn the US (the MedPed criteria6), the UK (the Simon Broome Register criteria3) and the Netherlandss (the Dutch Lipid Clinic Network criteria-). Contrary to the criteria we applied in

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Tablee 1 Inclusion and exclusion criteria Inclusionn criteria

Mafess and females Agee 18 years and older

FHH diagnostic criteria:

I.. Presence of a documented LDL-receptor mutation Or Or

II.. LDL-cholestero! level above the 95* percentile for sex and age,

Inn combination with at least one of the following:

(a)) the presence of typical tendon xanthomas in the patient or in a first degree relative (b)) an LDL-c ho teste rol level above the 95th_{percentile for age and sex in a first degree relative}

(c)) proven CAD in the patient or in a first degree relative under the age of 60 years

Exclusionn criteria

Secondaryy causes of hypercholesterolemia such as renal, liver or thyroid disease.

Hypercholesterolemiaa due to other genetic defects, such as familial defective apolipoprotein B

ourr study, these sets distinguish 'possible' fromm 'definite' FH patients. Specifically, the Dutch Lipidd Clinic Network uses a numeric score; the higher the score, the more probable the diagnosiss of FH. If a mutation has not been identified, the presence of tendon xanthomas iss required for a definite diagnosis of FH in the MedPed and Simon Broome Register criteria. Inn the Dutch scoring system, the presence of xanthomas is not required but increases the scoree substantially.

Additionall data were collected from the patient's medical records on classical risk factors forr CVD, family history of CVD, medication use, physical examinations, laboratory parameters, andd extensive information on CVD. All patients gave informed consent and the Ethics Institutionall Review Board of each participating hospital approved the protocol.

Definitionn of classical risk factors

Malee gender, age, smoking, body mass index and the presence of hypertension and diabetes mellituss were considered classical risk factors. The lifetime consumption of cigarettes was definedd by start and stop dates. Body mass index was calculated from height and length (kg/m2).. Hypertension was defined when the diagnosis had been made and when anti-hypertensivee medication was prescribed, or if three consecutive measurements of blood pressuree were >140 mmHg systolic or > 90 mmHg diastolic. Diabetes mellitus was defined whenn the diagnosis had been made and medication (insulin or oral anti-diabetics) was prescribed,, or by a fasting plasma glucose of > 6.9 mmol/L

Definitionn of cardiovascular disease

CVDD was diagnosed by the presence of at least one of the following: (I) a myocardial infarction,, proven by at least two of the following: (a) classical symptoms (>15 minutes), (b)) specific ECG abnormalities, (c) elevated cardiac enzymes {> 2x local upper limit of normal);

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(II)) percutaneous coronary intervention or other invasive procedures; (III) coronary artery bypasss grafting ; (IV) angina pectoris, diagnosed as classical symptoms in combination with att least one unequivocal result of one of the following; (a) exercise test, (b) nuclear scintigram, (c)) dobutamine stress ultrasonography, (d) a more than 70% stenosis on a coronary angiogram;; (V) ischemic stroke, focal neurological symptoms lasting for more than 24 hourss and demonstrated by CT- or MRI scan (VI) documented transient ischemic attack; {VII)) peripheral arterial bypass graft; (VIII) peripheral percutaneous transluminal angioplasty orr other percutaneous invasive intervention; (IX) (partial) amputation due to peripheral

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withh at least one unequivocal result of one of the following: (a) ankle/arm index<0.9 or (b) aa stenosis (>50%) on angiogram or duplex scan.

Whenn information on CVD did not strictly fulfill the above mentioned criteria, or when any suspectt history, symptoms or diagnostic evaluations were found in the record, the case wass presented to an independent adjudication committee consisting of a cardiologist, a neurologistt and a vascular surgeon.

Laboratoryy analysis

Alll laboratory parameters were measured in fasting blood samples. Lipid levels, as stated in thee medical record, were determined after at least 6 weeks of withdrawal of any lipid-loweringg medication. Plasma total cholesterol, high-density cholesterol (HDL-cholesterol), andd triglycerides were measured by enzymatic methods. LDL-cholesterol concentrations weree calculated by means of the Friedewald formula. Lipoprotein (a) concentrations were determinedd with immunonephelometric methods.9 Homocysteine concentrations were measuredd using high-performance liquid chromotography.10 Mutations in the LDL-receptor genee were assessed by methods described previously." The most common mutations found inn the Netherlands11 were excluded by PCR analysis.

Statisticall Methods

Student'ss t-test and x2-analysis were used to compare subgroups for continuous and categoricall variables, respectively. Statistical testing of triglycerides, glucose, HbA1c, homocysteinee and lipoprotein (a) was performed after natural logarithmic transformation. Too adjust for the effects of age, gender, smoking, alcohol use, concomitant medication use,, and body mass index (BMI) we used multiple logistic regression and univariate general linearr modeling. Statistical significance was assessed at the 5% level of probability. All statisticall analyses were performed using the statistical package for social sciences (SPSS 11.0;; Chicago, Illinois).

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Results s

Afterr thorough review of the 4000 medical records and application of the FH diagnostic criteria,, 2400 patients were defined as having FH. An LDL-receptor mutation was identified inn 52.3% of these patients (denoted as the LDL-R plus group). In the remaining 47.8% in whichh an LDL-receptor mutation was not yet found (denoted as the LDL-R minus group), thee 14 most prevalent Dutch LDL-receptor gene mutations were excluded", and further sequencingg of the coding regions is currently being performed. Individuals with inherited

Tablee 2 Clinical characteristics of FH patients w i t h an

Demographics s

Malee gender (%) Agee at first visit (years)

Agee at end of observation (years) Totall outpatient clinic foilow-up (years)

Riskk factors

Smoking,, ever (%) Hypertensionn (%) Diabetess mellitus (%)

First-degreee family history of premature CVD (%)

Physicall examination

BMII (kg/m2)

Systolicc blood pressure (mmHg) Diastolicc blood pressure (mmHg) Tendonn xanthomas (%)

Laboratoryy parameters

Totall cholesterol (mmol/L) LDLL cholesterol (mmol/L) HDLL cholesterol (mmol/L) Triglyceridess (mmol/L) Glucosee (mmol/L) H b A KK (%) Lp(a)(mg/L) ) Homocysteinee (micromoJ/L) Cardiovascularr disease

Totall CVD at first visit (%)

Totall CVD at end of observation (%)

Totall coronary artery disease at end of observation (%) Totall cerebrovascular disease at end of observation (%)

dd w i t h o u t a k n o w n LDL-receptor mutation LDL-RR plus n=1255 5 45.8 8 42.11 ( 12.6) 48.00 ( 13.4) 4.33 [2.0-8.5] 68.7 7 7.8 8 5.0 0 56.4 4 24.77 ( 3.4) 1333 ( 19) 811 ( 10) 4 2 % % 10.255 ) 8.188 ) 1.199 ) 1.399 [0.98-2.03] 4.99 [4.5-5.3] 5.55 [5.1-6.0] 1600 [69-410] 11.00 [8.8-13.6] 14.7 7 27.6 6 24.3 3 3.2 2 Totall peripheral ischemic disease at end of observation (% ) 3.7 Valuess are given as mean levels standard deviation,

glucose,, H b A I C , Lp(a), and homocysteine are given

LDL-RR minus n=1145 5 52.8 8 47.66 ( 12.2) 51.77 ( 12.7) 3.11 [1.2-6.1] 79.5 5 11.7 7 6.6 6 65.5 5 25.66 ) 1377 ) 833 ( 10) 4 0 % % 8.800 ( 1.54) 6.611 ( 1.47) 1.233 ) 1.711 [1.24-2.35] 5.00 [4.6-5.5] 5.66 [5.2-6.2] 1700 [60-522] 11.22 [9.2-13.9] 27.9 9 38.1 1 33.8 8 4 3 3 5.6 6 pp value 0.001 1 << 0.001 << 0.001 << 0.001 << 0.001 0.001 1 NS S << 0.001 << 0.001 << 0.001 << 0.001 NS S << 0.001 << 0.001 0.005 5 << 0.001 << 0.001 << 0.001 NS S NS S << 0.001 << 0.001 << 0.001 NS S NS S

exceptt where given as percentages. Triglycerides, ass median w i t h the

brackets.. LDL-R+/- indicates low density lipoprotein receptor k n o w n / u n k n o w r BMI,, body mass index;Lp(a), lipoprotein (a);NS, not s ignificant. .

interquartilee range between ;; CVD, cardiovascular disease;

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hypercholesterolemiaa due to familial defective apolipoprotein B (FDB), caused by mutations inn the apolipoprotein B gene, were excluded from this study.

Thee two cohorts demonstrated significantly different clinical and laboratory profiles (Table 2).. LDL-cholesterol was higher in those patients with an LDL-receptor mutation, whereas triglyceridess and HDL-cholesterol were higher in patients without an LDL-receptor mutation. Patientss without a known LDL-receptor mutation were older, more often males and had on averagee higher values of body mass index (BMI), blood pressure, and glycemia, in addition

Tablee 3 Clinical characteristics of FH patients w i t h a

thee presence or absence of tendon xanthomas

Demographics s

Malee gender (%) Agee at first visit (years)

Agee at end of observation (years) Totall outpatient clinic follow-up (years)

Riskk factors

First-degreeFirst-degree family history of premature CVD {%)

BMII (kg/m2)

Systolicc blood pressure (mmHg) Diastolicc blood pressure (mmHg)

Totall cholesterol (mmol/L) LDLL cholesterol (mmol/L) HDLL cholesterol (mmol/L) Triglyceridess (mmol/L) Glucosee (mmol/L) HbA1C(%) ) Lp(a)) (mg/L) Homocysteinee (micromol/L) Cardiovascularr disease

documentedd LDL-receptor m u t a t i o n ; Xanthomas s present t n=464 4 44.8 8 43.77 ( 12.3) 49.88 ( 13.0) 4.6(2.4-8.6] ] 69.3 3 8.7 7 5.8 8 56.5 5 25.00 ) 134{ 19) 811 ) 11.066 ) 8.977 ) 1.188 ) 1.455 [1-02-2.16] 4.99 [4.5-5.3] 5.55 [5.1-6.1] 1811 [69-462] 10.88 [8.8-13.9] 32.5 5 29.5 5 3.7 7 Totall peripheral ischemic disease at end of observation (% ) 4.5

Valuess are given as mean levels + standard deviation, glucose,, HbA1C, Lp(a), and homocysteine are brackets.. LDL-R+/- indicates low density lipoprotei BMI,, body mass index;Lp(a), lipoprotein (a);NS,

given n Xanthomas s absent t n = 6 5 8 8 46.4 4 40.55 ( 12.5) 45.99 ( 13.2) 3.99 [1.5-8.1] 67.3 3 6.4 4 3.8 8 56.0 0 24.44 ( 3.3) 1333 ( 19) 800 { 10) 9.700 ( 1.95) 7.666 ( 1.87) 1.200 ) 1.344 [0.93-1.96] 4.99 [4.5-5.3] 5.44 [5.0-5.9] 1433 [64-685] 11.00 [8.9-13.4] 21.4 4 17.8 8 3.0 0 2.7 7 stratifiedd t o pp value NS S << 0.001 << 0.001 0.001 1 NS S NS S NS S NS S 0.01 1 NS S NS S << 0.001 << 0.001 NS S 0.03 3 NS S 0.001 1 NS S NS S << 0.001 << 0.001 NS S NS S

nn receptor k n o w n / u n k n o w r nott significant.

interquartilee range between i;; CVD, cardiovascular disease;

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too a higher prevalence of hypertension, smoking, CVD and a positive family history for prematuree CVD. The differences in lipid levels, BMI, blood pressure, and glycemia remained afterr adjustment for age and gender. Specifically, the differences in HDL-cholesterol and triglyceridee levels remained significant after adjustment for smoking, alcohol use, concomitant beta-blockerr use, and BMI. No differences were observed in the prevalence of diabetes mellituss and tendon xanthomas.

Subsequently,, both the LDL-R plus and the LDL-R minus groups were divided into two furtherr groups, namely those characterized by the presence or absence of tendon xanthomas

Tablee 4 Clinical characteristics of FH patients w i t h o u t

thee presence or absence of tendon xanthomas

Demographics s

Malee gender (%} Agee at first visit (years)

Agee at end of observation (years) Totall outpatient clinic follow-up (years)

Riskk factors

First-degreeFirst-degree family history of premature CVD (%)

BMII (kg/m2)

Systolicc blood pressure (mmHg) Diastolicc blood pressure (mmHg)

Totall cholesterol (mmol/L) LDLL cholesterol (mmol/L) HDLL cholesterol (mmol/L) Triglyceridess (mmol/L) Glucosee (mmol/L) HbA1C(%) ) Lp(a)) (mg/L) Homocysteinee (micromol/L) Cardiovascularr disease

aa documented LDL-receptor m u t a t i o n ; Xanthomas s present t n=444 4 4 9 3 3 48.44 ( 13.2) 52.99 ( 13.5) 3.5(1.2-6.7] ] 74.1 1 11.6 6 5.6 6 50.4 4 25.66 ) 1377 ) 833 {+ 11) 9.400 < 1.75) 7.277 ( 1.73) 1.211 ) 1.666 [1.17-2.18] 5.00 [4.5-5.4] 5.77 [5.2-6.5] 1744 [60-450] 11.44 [9.4-14.0] 29.5 5 25.0 0 3.4 4 Totall peripheral ischemic disease at end of observation (% ) 5.6

Valuess are given as mean levels standard deviation, glucose,, HbA1C, Lp(a), and homocysteine are brackets.. LDL-R+/- indicates low density lipoprotei BMI,, body mass index;Lp(a), lipoprotein (a);NS,

given n Xanthomas s absent t n=648 8 53.1 1 46.33 ( 11-8) 50.00 ( 12.4) 2.88 [1.1-5.3] 82.1 1 12.1 1 6.9 9 73.8 8 25.66 ) 1366 ( 20) 833 ( 10) 8.488 ( 1.31) 6.311 ( 1.24) 1.244 ) 1.700 [1.28-2.39 5.00 [4.6-5.5] 55 6 [5.2-6.2] 1700 [60-550] 11.00 [9.0-13.4] 37.8 8 33.6 6 4.5 5 4.9 9 stratifiedd to pp value NS S 0.006 6 << 0.001 0.002 2 0.003 3 NS S NS S << 0.001 NS S NS S NS S << 0.001 << 0.001 NS S NS S NS S NS S NS S NS S 0.005 5 0.002 2 NS S NS S

nn receptor k n o w n / u n k n o w r nott s gnificant. .

interquartilee ran gee between ;; CVD, cardiovascular disease;

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(Tabless 3 and 4). Patients with a documented LDL-R mutation in whom tendon xanthomas aree present are characterized by significantly increased mean total cholesterol and LDL-C whenn compared to LDL-R plus patients without tendon xanthomas (11.06 vs. 9.70 mmol/L andd 8.97 vs. 7.66 mmol/L, respectively, both p<0.001) (Table 3). Moreover, these patients aree characterized by a higher prevalence of coronary artery disease (32.5 vs. 21.4%). Inn the LDL-R minus group, patients with tendon xanthoma were also characterized by significantlyy increased total cholesterol and LDL-C levels (9.40 vs. 8.48 mmol/L and 7.27 vs. 6.311 mmol/L, respectively, both p< 0.001) (Table 4). No differences were detected in any

n t h n rr mr-mmn+or o v r o n t -fnr ^ n o c m n U n n nriH 3 n o c i t i v o familv/ hic:tnr\/ f n r fA/P)

Whenn the LDL-R minus patients with tendon xanthomas were compared with LDL-R plus patients,, total and LDL-cholesterol levels differed significantly (9.40 vs. 10.25 mmol/L and 7.27 vs.. 8.18 mmol/L, respectively, both p<0.001), as wellasHDL-cholesteroland median triglyceride levelss (1.21 vs. 1.19 mmol/L; p O . 0 0 1 , and 1.66 vs. 1.39 mmol/L;p<0.001, respectively).

Discussion n

Wee assembled a cohort of 2400 FH patients for clinical and basic research. We used a set off established clinical diagnostic criteria1-36 to define FH. However, analysis of this cohort revealedd significantly different clinical and laboratory profiles between those patients with andd those without a known LDL-receptor mutation. Our findings suggest that in fact the LDL-RR minus group comprises, partially, patients with other causes of dyslipidemia.

Familiall hypercholesterolemia versus other causes of (familial) dyslipidemia

Inn our study population, patients clinically diagnosed as having FH but yet without a known mutation,, are characterized by lower total cholesterol, lower LDL-cholesterol, higher triglyceridee and HDL-cholesterol levels, a significantly higher prevalence of hypertension, andd higher glucose levels. These patients possess clinical characteristics of other forms of dyslipidemia,, namely familial combined hyperlipidemia, polygenic hypercholesterolemia, familiall dyslipidemic hypertension1213, hyperapobetalipoproteinemia14 and the dyslipidemias associatedd with the metabolic syndrome. FCH, the most common genetic dyslipidemia, is aa complex phenotype which most likely comprises this group of related disorders.17 Accordingly,, FCH is also known as 'multiple-type hyperlipidemia'. An elevated plasma apolipoproteinn B (apoB) level is often implemented to distinguish between these disorders.15

177

Unfortunately, apoB levels were not determined in our study population. Therefore, we considerr the LDL-R minus group to represent a mixture of these lipid disorders, possessing similaritiess with 'the' FCH phenotype.

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tendd to have lower LDL-cholesterol levels, lower HDL-cholesterol levels and higher triglyceride levelss than their FH counterparts.12181S LDL-cholesterol levels found in the LDL-R minus groupp are indeed in the range generally measured in FCH patients. HDL-cholesterol levels foundd in the LDL-R minus group are higher than generally measured in FCH patients. The slightlyy elevated triglyceride levels observed in the LDL-R minus group are somewhat lower thann in most FCH patients in which these values tend to be higher.'b However, a characteristic featuree of FCH is its variability in lipid phenotype expression among patients and even in thee individual patient over time20, suggesting a strong influence of environmental factors. FCHH is often associated with obesity, diabetes mellitus and hypertension.21 Higher BMI valuess and higher values of glycemia were indeed measured in the LDL-R minus group, indicatingg a tendency towards obesity and hyperinsulinemia.

Patientss without a known LDL-receptor mutation were older, more often males, had a higherr prevalence of a positive family history for premature CVD, were more often smokers andd suffered from CVD. This was due to the selection criteria used for the diagnosis of FH. Iff the patient did not have an LDL-receptor mutation, the patient was included on the basis off other criteria, most often proven CAD in the patient or in a first degree relative under the agee of 60 years (data not shown). Patients with CVD were older, more often males and smokerss (data not shown).

Diagnosticc criteria

Thee phenotypic heterogeneity detected in our study cohort challenges the value of the current clinicall criteria for diagnosing familial hypercholesterolemia. Criteria used to identify individuals withh FH include a combination of clinical characteristics, personal and family history of early CVDD and biochemical parameters. In the present study, we used a set of established clinical diagnosticc criteria to identify patients with FH.1'36 The primary diagnostic criterion is the detectionn of an increased plasma LDL-cholesterol. However, due to overlap in plasma lipid levelss between FH heterozygotes and the general population22, the cut off values of LDL-cholesteroll are difficult to define. Arbitrary definition of cut off values for LDL-cholesterol leadss to compromises of sensitivity and specificity of this marker as a diagnostic criterion. Analysiss of the diagnostic value of LDL-cholesterol concentrations has revealed that the best availablee cutoff point to diagnose the disorder is the age- and sex- specific 90th percentile.7 In ourr set of criteria, we used the age- and sex- specific 95th percentile as obtained from the generall Dutch population, to further reduce the inclusion of false positive FH patients. Ann important distinguishing feature of FH is the presence of tendon xanthomas in the patient.12 Inn our study population, the prevalence of tendon xanthomas did not differ between the LDL-RR plus and LDL-R minus group. However, when we further subdivided these groups, we could demonstratee that FH patients, defined by DNA diagnosis and the presence of tendon

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xanthomas,, had more severely elevated total cholesterol and LDL-C levels and were characterizedd by a higher prevalence of coronary artery disease.

Itt is of course possible that the current study has misclassified patients who have yet to be geneticallyy diagnosed with FH. Nevertheless, we would expect the misclassification of true FH casess to have reduced the differences observed between the two groups. The presence of tendonn xanthomas as recorded in the medical record is therefore subject to speculation. Accordingg to the Simon Broome Register criteria and the MedPed criteria, in which the presence off tendon xanthomas is the key feature of 'definite' FH, we included 'possible' FH patients in ourr study, which may have contributed to the heterogeneity of the study population. One couldd conclude that we therefore should have restricted inclusion of patients to those with tendonn xanthomas if a mutation had not been identified. However, when the LDL-R minus groupp was subdivided into those patients with and without xanthomas, the phenotypic differencess between the LDL-R plus and LDL-R minus groups remained. A possible explanation forr this is the false-positive palpation of tendon xanthomas. Objective palpation (i.e. without knowingg a patient's LDL-cholesterol concentrations) is not likely in an outpatient clinic setting. AA definite diagnosis of FH is made after identification of an LDL-receptor mutation known too cause FH. A molecular diagnosis of FH can be made in 50-80% of clinically identified cases.11 U3'Z4 This broad detection range is due to clinical misdiagnosis, technical insensitivity, orr causes of familial hypercholesterolemia not related to the LDL-receptor gene.6'8'2"6 A higherr mutation detection rate has been reported in 'definite' FH patients (those with tendonn xanthomas) as opposed to those with 'possible' FH (without tendon xanthomas).24 Unfortunately,, the presence of an arcus cornealis and a positive family history for premature CADD are insensitive diagnostic markers. The presence of an arcus cornealis by the age of 50 yearss occurs in 50% of patients, but not until a decade later in non-FH patients.27 However, ann arcus cornealis can also be observed in subjects with normal lipid levels.1 A strong family historyy for premature CAD contributes to a patients risk of coronary heart disease, however onlyy 5-10% of early familial CAD can be attributed to FH.19i2S

Thee sensitivity and specificity of similar existing sets of diagnostic criteria have yet to be compared,, possibly leading to the creation of more decisive clinical diagnostic criteria. In thee meantime, advances in the application of DNA diagnostic techniques will hopefully favorr the ultimate decisive criterion, namely, the genetic test.

Thee need for genetic testing in clinical practice

FHH is a disorder that begins early in life. Effective treatment to reduce cardiovascular morbidity andd mortality has been available since the introduction of statins. In children with FH, increasedd LDL-cholesterol deteriorates endothelial function at a very young age, in addition too rapid increases in the intima-media thickness of peripheral arteries.29 Such findings support

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thee notion of taking preventive measures when children are young instead of waiting until theyy reach adulthood. It has also been suggested that lifestyle changes in these children cann lower LDL-cholesterol levels and improve endothelial function.'0 Furthermore, genetic testingg is possible at a young age, whereas clinical manifestations such as a high LDL-cholesteroll and tendon xanthomas often appear at a later age. Thus, there is a need for accuratee criteria for the early diagnosis of FH.

Distinguishingg FH from other causes of hypercholesterolemia has additional advantages in clinicall practice. Definition of the underlying diagnosis is essential for cardiovascular risk assessment.. For example, the average age of myocardial infarction in untreated FH patients iss earlier than that of FCH patients.''9 Differences in phenotypic characteristics between FH andd FDB patients have also been described.31 The suggestion that atherosclerosis could be moree severe in genetically determined FH patients than in hypercholesterolemic non-FH patients32333 also supports the role of accurate diagnosis in cardiovascular risk evaluation.

Thee need for genetic testing in research

Properr definition of study subjects is essential in any type of research. Moreover, international collaborationn in research is facilitated when study subjects are defined according to highly sensitivee and specific criteria. In the various forms of hyperlipidemia, hypercholesterolemia iss due to different underlying defects in lipid metabolism. Careful interpretation of the outcomess of clinical drug trials including FH patients that have not been genetically diagnosed34366 is therefore justified.

Inn summary, the present study emphasizes the need for genetic testing in FH for accurate cardiovascularr risk assessment and treatment of FH patients and for proper definition of studyy subjects in research with FH patients.

Acknowledgments s

Thiss study was supported by a grant of the Netherlands Heart Foundation (98/165). J.J.P. Kasteleinn is an established investigator of the Netherlands Heart Foundation (grant D039/ 66510).. We thank the members of the independent adjudication committee for their expert advice:: Dr. R.J.G. Peters, cardiologist, Prof. Dr. J. Stam, neurologist and Prof. Dr. D. Legemate, vascularr surgeon. We thank all patients who participated in the study anó the specialists of thee participating Lipid Clinics throughout the Netherlands.

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hypercholesterolemiaa using new practical criteriaa validated by molecular genetics. Am JJ Cardiol. 1993;72:171-176.

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