Israel Medical Association Journal

Background: Traditionally, medication dosage was based on clinical and demographic parameters, but drug metabolism was recently recognized as an important factor for proper dosing and prediction of side effects. Metabolic considerations are crucial when administering drugs with a narrow therapeutic index, such as those of the thioguanides family (azathioprine and 6-MP). These can cause life-threatening myelosuppression due to low activity of a critical metabolic enzyme, thiopurine S-methyl transferase. A number of single nucleotide substitutions encoding variant enzymes account for most enzyme deficiencies.

Objectives: To determine the frequency of individuals from different Israeli ethnic groups who may be at risk for drug toxicity from drugs of the thioguanide family due to enzymatic variants.

Methods: DNA analysis was performed using polymerase chain reaction methods. We tested TPMT[1] allelic variants TPMT*3A (G460A, A719G), TPMT*3B (G460A) and TPMT*3C (A719G) in five subpopulations in Israel: mixed-origin Israeli Jews, Arabs, Druze, Jews of Kurdish extraction, and Ethiopian Jews.

Results: The Druze (P = 0.0002) and Ethiopian Jewish (P = 0.015) subpopulations had a significantly unique distribution of allelic variants compared to the rest of the Israeli population. The Druze subpopulation showed a high number of TPMT variants with decreased activity, and a homozygote for TPMT*3A/ *3A was detected.  Ethiopian Jews were found to carry mainly the TPMT*3C variant, also observed in other studies of African populations.

Conclusions: It is advisable that Druze patients be tested for the TPMT enzyme before starting treatment with 6-MP or azathioprine. Such testing may also be considered for other Israeli ethnic subgroups.

Background: While most allelic pairs of DNA replicate synchronously during the S phase of the cell cycle, some genes normally replicate asynchronously, i.e., genes on the X chromosome and imprinted genes. The replication control mechanism is unknown but was shown to be impaired in malignancies and chromosomal trisomies where replication pattern becomes asynchronous.

Objectives: To determine the level of asynchronization in replication timing of cells from patients with microdeleted genomes.

Methods: We applied monocolor fluorescent in situ hybridization with different probes on leukocytes from microdeleted genomes.

Results: All samples derived from the microdeleted genomes showed significantly higher levels of an asynchronized pattern compared to normal individuals.

Conclusions: Even a “small” genetic imbalance (microdeletion) can interfere with gene replication and cell cycle progression, as previously shown in full trisomies.
 

Background: Genetic factors have been shown to play a major role in the development of peak bone mass, with hereditability accounting for about 50-85% of the variance in bone mass. Numerous candidate genes were proposed to be involved in osteoporosis, but the precise genes and their relative contribution remain unknown.

Objectives: To gain insight into the genetic basis of idiopathic low bone mineral density in Israeli patients by analyzing the impact of two candidate genes: polymorphism of the vitamin D receptor gene and polymorphism A986s in the calcium-sensing receptor gene.

Methods: We analyzed 86 Jewish Israeli patients with LBMD[1]: 38 premenopausal women and 48 men, and compared the allelic pattern distribution with that of the general population (126 men and 112 women). Genotyping of the VDR[2] gene was performed in three polymorphic sites using restriction enzymes, and allelic analysis of A986s polymorphism in the CaSR[3] gene was performed using the denaturing gradient gel electrophoresis technique.  

Reaults: In LBMD women the distributions of VDR alleres in Apal polymorphism were AA=7/28, Aa=16/28 and aa=5/28; in TaqI polymorphism TT=10/31, Tt=16/31 and tt=5/31; and in BsmI polymorphism BB=7/32, Bb=14/32 and 11/32. In LBMD men the distributions were AA=17/39, Aa=21/39 and aa=1/39; in TaqI polymorphism TT=12/42, Tt=23/42 and tt=7/42; and in BsmI polymorphism BB=12/41 Bb=18/41 and bb=11/41. The distributions of all these polymorphisms in the control groups were not significantly different. Adjusting for the independent age and gender parameters confirmed that these three polymorphisms of the VDR gene did not have a significant effect on bone mineral density. Thirty percent (24/79) of LBMD patients of either sex displayed heterozygosity of the CaSR A986s polymorphism, compared with 40 of 203 controls (19.7%) (P=0.059). Adjusting for age and gender in these patients revealed a significant difference in the femoral neck BMD[4] between homozygotes and heterozygotes (P=0.002). The age at menarche of the LBMD women was found to predict 61% of the variance of femoral neck BMD.

Conclusions: In Israeli Jewish men and premenopausal women VDR gene alleles do not seem to be associated with lower lumbar spine or femoral neck BMD. A trend towards heterozygosity for a CaSR polymorphism missense mutation was noted in the LBMD patients. Age at menarche in the LBMD women was found to be an important predictor of BMD. A significant difference was found between LBMD women and healthy control women towards heterozygosity for a CaSR polymorphism, as well between homozygotes and heterozygotes for a CaSR polymorphism in BMD. The significance of these findings and their applicability to a larger population awaits further studies.

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