Antenatal diagnosis

A small supernumerary marker chromosome present in a Turner syndrome patient not derived from X- or Y-chromosome: a case report

Background

Small supernumerary marker chromosomes (sSMC) can be present in numerically abnormal karyotypes like in a 'Turner-syndrome karyotype' mos 45,X/46,X,+mar.

Results

Here we report the first case of an sSMC found in Turner syndrome karyotypes (sSMC^T) derived from chromosome 14 in a Turner syndrome patient. According to cytogenetic and molecular cytogenetic characterization the karyotype was 46,X,+del(14)(q11.1). The present case is the third Turner syndrome case with an sSMC^T not derived from the X- or the Y-chromosome.

Conclusion

More comprehensive characterization of such sSMC^T might identify them to be more frequent than only ~0.6% in Turner syndrome cases according to available data.

Beta-thalassemia mutations in western India

OBJECTIVE

To study occurrence of common mutations in the population of Gujarat and the most prevalent mutation in certain high-risk communities.

METHODS

The mutation screening was carried out using ARMS-PCR in children with beta thalassemia.

RESULTS

Population screening has identified certain communities like Sindhis, Lohana, Rajputs, and SC/ST/OBC to be at higher risk as compared to others. The most common mutation was IVS 1-5 (G-->C) followed by 619 bp deletions of the total cases coming to Gujarat.

CONCLUSION

Molecular evaluation for Thalassemia should be considered for families whose ethnicity indicates origin from high-risk community.

Distribution of beta-thalassemia mutations in the Indian population referred to a diagnostic center

Hemoglobinopathies are the most commonly inherited genetic disorders in India. Population screening has identified certain communities in India with high risk of beta-thalassemia, the prevalence of carrier status in some being as high as 17%. Over a period of 6 years we have conducted DNA analysis on 1,233 carriers of 23 beta-thalassemia mutations and Hb E, using the amplification refractory mutation system. The studies included analyses of five common mutations for Asian Indians, namely IVS-I-5 (G-->C), 619 bp deletion, IVS-I-1 (G-->T), and the frameshifts at codons 8/9 (+G) and 41/42 (-TTCT). The occurrence of these was seen in 1,066 (86.45%) of the carriers referred to us, the percentage of mutations varying between 5.03-42.58%. We found codon 15 (TGG-->TAG) in 47 (3.81%) samples which was also considered a common mutation in the Indian population. Rare beta-thalassemia mutations were found in 87 (7.06%) individuals. We have designed five new primers and modified four primers for nine rare mutations. These were seen in nine (0.73%) samples. The beta-thalassemia anomaly in 33 (2.68%) carriers remained uncharacterized. State-wide and community-wide distribution patterns of mutations indicated that IVS-I-5 (G-->C) is the most common beta-thalassemia allele in the Indian population. Sindhis settled in Gujrat, and Maharashtra and Lohanas from Gujrat showed a prevalence of the 619 bp deletion mutation in 49.2 and 45.5% carriers, respectively. High frequency of the IVS-I-1 (G-->T) mutation was also found in Sindhis (25.5%), Punjabi Hindus (34.7%), and Lohanas (31.2%). These studies of mutation patterns in different communities have helped us in the quick identification of beta-thalassemia mutations for prenatal diagnosis.

Diverse genetic mechanisms operate to generate atypical betaS haplotypes in the population of Guadeloupe

In a survey of the chromosomal background associated with the sickle cell gene in Guadeloupe, a French Caribbean island, we identified 37 unrelated patients with sickle cell disease (27 SS, nine SC, and one S-beta-thalassemia) of 477 unrelated sickle cell patients where the beta3 gene was linked to 20 different atypical haplotypes. These atypical chromosomes account for about 5% of the overall betaS chromosomes in this population. To investigate the origin of these atypical betaS haplotypes, we performed extensive typing of betaS and betaA chromosomes. Twenty-two different 5' subhaplotypes were identified among the betaS chromosomes. Fifteen of 20 different atypical haplotypes are likely to be the product of recombination by a single crossover around the <<hot-spot>> 5' to the beta-globin gene, or between a major betaS haplotype and one of the betaS haplotypes present in the population. The remaining cases require genetic mechanisms (gene conversions, additional substitutions in a given haplotype) other than crossovers to generate these atypical haplotypes.