Comparative analysis of allele variation using allele frequencies according to sample size in Korean population.

BACKGROUND: Allele frequency using short tandem repeats (STRs) is used to calculate likelihood ratio for database match, to interpret DNA mixture and to estimate ethnic groups in forensic genetics. In Korea, three population studies for 23 STR loci have been conducted with different sample size for forensic purposes. OBJECTIVE: We performed comparative analysis to determine how the difference of sample size affects the allele frequency and allele variation within same ethnic population (i.e. Korean). Furthermore, this study was conducted to check how the sampling group and multiplex kit also affect allele variation such as rare alleles and population specific alleles. METHODS: To compare allele variation, we used allele frequencies of three population data published from three Korean forensic research groups. Allele frequencies were calculated using different sample sizes and multiplex kits: 526, 1000, and 2000 individuals, respectively. RESULTS: The results showed the different distribution of allele frequencies in some loci. There was also a difference in the number of rare alleles observed by the sample size and sampling bias. In particular, an allele of 9.1 in the D2S441 locus was not observed in population study with 526 individuals due to multiplex kits. CONCLUSION: Because the allele frequencies play an important role in forensic genetics, even if the samples are derived from the same population, it is important to consider the effects of sample size, sampling bias, and selection of multiplex kits in population studies.

[Distribution of genetic polymorphisms of serum amyloid protein A1 in healthy Chinese Han and Uighur populations in Xinjiang].

OBJECTIVE: To investigate the genetic polymorphisms of rs2229338 and rs12218 loci of serum amyloid protein A1 (SAA1) gene in healthy Chinese Han and Uighur populations of Xinjiang. METHODS: The genotypes of the SAA1 gene were detected in 316 Uighur and 362 Han healthy individuals by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP). RESULTS: The genotype distributions of both populations were in the Hardy-Weinberg equilibrium (both P>0.05). The frequencies of AA, AG and GG genotypes of the rs2229338 locus were 76.6%, 23.4%, and 0 in the Uighurs, and 91.7%, 7.7% and 0.6% in the Hans. There was significant difference in distribution of genotypes between the two populations (P<0.01). The frequencies of CC, CT and TT genotypes of the rs12218 locus were 10.1%, 47.5%, and 42.4% in Uighurs, and 3.3%, 34.3% and 62.4% in Hans. There was also significant difference in distribution of genotypes between the two populations (P<0.01). The A-C and G-T haplotypes were more frequent in the Uighur but the A-T haplotype was more common in the Han population, respectively (both P<0.01). CONCLUSION: The mutational frequencies of the tagging SNPs in rs2229338 and rs12218 loci of theSAA1 gene in the Uighurs may be higher than those in Hans.

Connexin 26 preverbal hearing impairment: mutation prevalence and heterozygosity in a selected population.

The objective of this investigation was to determine the prevalence of Cx26 mutations in familial and sporadic cases of non-syndromic preverbal hearing impairment (HI). Molecular analysis of the Connexin 26 (Cx26/GJB2) gene was performed in 271 non-consanguineous individuals from the north of Italy, enrolled in the study because of the presence of non-syndromic preverbal sensorineural HI. One hundred and forty-six subjects (group 1) were referred from different ENT, paediatric and clinical genetic services, while 125 individuals (group 2) underwent Cx26 analysis based on precise anamnestic and clinical criteria for non-syndromic HI and low risk of acquired deficit. All of the cases were also classified as familial or sporadic due to the presence or absence of other documented childhood HI in the family. Of the total 271 individuals, 36.9% were positive for Cx26 mutations: 37 belonged to group 1 and 63 to group 2, which delineates a statistically significant difference between the two groups. The difference is mainly attributable to sporadically occurring cases. No significant differences between group 1 and group 2 were found regarding the prevalence of the common 35delG variant and the number of unidentified putative Cx26 alleles, although these latter were shown to be higher in sporadically occurring cases of the unselected group 1. The difference observed in Cx26 prevalence can be explained by the clinical selection of group 2, which ensures minimum risk of including cases of acquired HI. In particular, in cases of sporadically occurring HI, the use of a defined protocol increases the chances of a positive molecular result, improving genetic counselling and the possibility of establishing better genotype-phenotype correlation. Our data raise questions about the possible interpretation of Cx26 heterozygosity in a selected population of hearing-impaired individuals.

Apolipoprotein E genotype and cognitive impairment in community-dwelling black older adults.

OBJECTIVE: The relationship between the epsilon 4 allele of the apolipoprotein E gene (APOE-epsilon4) located on chromosome 19 and Alzheimer's disease is well documented among Caucasian populations. However, the findings of research addressing the link between APOE polymorphism and neurocognitive functioning in populations of African origin from around the world have been equivocal. Therefore, the current study explored the relation of APOE-epsilon4 with cognitive impairment in a sample of community-dwelling English-speaking elderly blacks. METHODS: All participants (N = 57) were recruited consecutively from a community memory-screening program at a University affiliated Memory Disorders Clinic and evaluated using standardized assessment procedures. Cognitive impairment was classified according to an age and education adjusted Mini-Mental State Exam score of less than 24 as well as poorer functioning on a measure of delayed verbal memory. RESULTS: Increased risk for global cognitive dysfunction (OR = 9.5, 95 percent CI = 2.3-55.3, p = .004) and poorer verbal recall performance (beta = -.36, p = .006) were linked with the APOE epsilon4 allele after controlling for the potentially confounding effects of age, education, and gender. CONCLUSIONS: This investigation supports the role of APOE polymorphism in determining neurocognitive impairment among black elders residing in the community.