Two 40-year-old twin sisters (designated F. and P., respectively) were admitted to the Propedeutic Clinic of Internal Disease of the Moscow Sechenov Medical Academy, Moscow, Russia. Ultrasonograthy was done using convectional sensor PVF-375 MT 3,75 MHZ (Toshiba SSH-140A apparatus; Toshiba, Tochigi-Ken, Japan). The concentration of serum triglyceride and very low density lipoprotein (VLDL), LDL, high density lipoprotein (HDL) cholesterol were measured according to Folch et al. [8]. The subfraction spectrum of LDL was analyzed according to Krauss and Berke [9]. DNA was isolated by the standard method using proteinase K (Promega, Madison,WI, USA) and extraction with phenol-chloroform [10]. DNA fingerprinting with various microsatellite and minisatellite probes was carried out according to Limborska et al. [11]. DNA (10 mg) was digested with HinfI (Fermentas, Vilnius, Lithuania) and electrophoresed through 0.8% agarose gels. DNA was denatured, transferred to Hybond-N nylon membrane filters (Amersham Biosciences, Little Chalfont, Buckinghamshire, UK), and probed with ^{32P-labeled oligonucleotides (CAC)_{5 and (GATA)4. Blot hybridization was conducted in a mix of 6 × sodium chloride/sodium citrate (SSC), 0.1% sodium dodecyl sulfate (SDS) and 10 × Denhardt’s solution [0.5% polyvinylpyrrolidone; 0.5% Ficoll 400; 0.5% bovine serum albumin (BSA); Sigma, St Louis, MO, USA]. Filters were washed three times with 6 ´ SSC for 30 min. at room temperature, dried and autoradiographed at –70°C for 1-3 days with an EUI-1 intensifying screen (Renex, Moscow, Russia).}}