Patient F. complained of a dull abdominal pain, localized in the right upper quadrant, meteorism, nausea and bitter taste after eating. That was the patient’s first episode of biliary colic. Laboratory biochemical study was normal; serum cholesterol level was 190 mg/dL [normal level (N): 150-190 mg/dL] and triglycerides ^{were 98.4 mg/dL (N: 50-150 mg/dL), VLDL 19.7 mg/dL (N: 15-25 mg/dL), LDL 111.3 mg/dL (N: 110-131 mg/dL), HDL 59 mg/dL (N: 27-89 mg/dL); lipoprotein (a) [Lp(a)] 2 mg/dL (N: <7.5 mg/ dL). The subfraction spectrum of LDL showed a predominance of minor dense particles of LDL [retardation factor (Rf) value 0.152; N: <0.144]. Ultrasonography showed an enlarged gallbladder with two echopositive structures, 7.0 x 5.5 and 8.0 x 4.5 mm, with acoustic shadows that were displaced on movement; the biliary content was not homogeneous (Fig. 1). Ultrasonography-based cholecystography revealed reduction in gallbladder motility, with a coefficient reduction of 38% (N: 65-75%). Sphincter of Oddi spasms lasted about 20 min. The clinical diagnosis was gallstone disease, gallbladder hypotonia, sphincter of Oddi hypertonia.}

Patient P. was admitted for polyposis in the gallbladder diagnosed by ultrasonography. She had no complaints and no episodes of biliary colic. However, the patient had experienced dyspepsia upon eating fatty foods. There was mild tenderness in the right upper quadrant on palpation. There was no hyperlipidemia and liver function tests (aspartate aminotransferase or alanine aminotransferase, alkaline phosphatase, and bilirubin levels) were normal. The total cholesterol level was 208 mg/dL; triglycerides 43 mg/dL; VLDL 10 mg/dL; LDL 159 mg/dL; HDL 46 mg/dL; and Lp(a) 2 mg/dL. The subfraction spectrum of LDL was characterized by predominance of minor dense particles (Rf value 0.157). Ultrasonography showed a hypertrophied gallbladder wall, 3.0-5.0 mm thick, with several echopositive structures lacking acoustic shadows (polyps) and measuring 6.0 and 4.0 mm on the front wall and 4.3 and 3.8 mm on the other wall, without displacement on movement, the bile was not homogeneous (Fig. 2). Ultrasonography-based cholecystography revealed normal motility function of the gallbladder, with a coefficient reduction of 67%; sphincter of Oddi spasms lasted about 5 min. The clinical diagnosis was cholesterolosis of gallbladder. Family history revealed that the patients’ father had experienced gallstone disease and surgery for cholesterol cholelithiasis.

For precise determination of twin zygosity, the DNA fingerprinting with various microsatellite and minisatellite probes was used [11] Figure 3 shows typical results of DNA fingerprinting in dizygotic twins (lanes 1 and 2) taken as controls and patients F. and P. (lanes 3 and 4). Two microsatellite core probes, (CAC)_{5 and (GATA)4, used for the analysis, produced different patterns in dizygotic twins and identical fingerprint patterns in patients F. and P. Similar results were also obtained when microsatellite oligonucleotide probes (GACA)4, (TCC)50 and minisatellite core probes M13 and Jeffreys 33.15 were used for such analyses (not shown). The identity of fingerprints obtained for F. and P. proves that these two patients were monozygotic twins.}