Rapid molecular prenatal diagnosis of ataxia-telangiectasia by direct mutational analysis.

Mutations of the ataxia-telangiectasia-mutated (ATM) gene are responsible for the autosomal recessive disorder ataxia-telangiectasia (A-T). This study reports the first A-T prenatal diagnosis performed in Spain by direct molecular analysis. The pregnant woman had a previous child suffering from A-T due to a deletion in the ATM gene. The ATM coding region was sequenced in the A-T patient and her parents. Then, a specific polymerase chain reaction (PCR) to detect the deletion was performed for prenatal diagnosis. Additionally, polymorphic HLA loci were examined in order to exclude the possible contamination by maternal DNA. In this family of Gypsy origin, we carried out a rapid molecular diagnosis of A-T. Then, a prenatal diagnosis was carried out, identifying the deletion in the fetal DNA. Additionally, we performed a population study in unrelated Spanish Gypsies and in unrelated controls, showing that the deletion described could be a hotspot in the Spanish Gypsy population. The size of the coding region and the genomic structure, together with the absence of hotspots, make the mutation screening of the ATM gene difficult. The ability to identify ATM mutations provides a tool that can be applied in confirmatory diagnosis, genetic counselling, carrier prediction and prenatal diagnosis.

A novel RMRP mutation in a Spanish patient with cartilage-hair hypoplasia.

Cartilage-hair hypoplasia (CHH), or McKusick type metaphyseal chondrodysplasia, was first recognized as a distinct entity in the Old Order Amish in the USA, but was later identified in other groups, and found to be unusually frequent among Finns. CHH is highly pleiotropic with manifestations that include short stature, defective cellular immunity and predisposition to several cancers. CHH is caused by mutations in the RNA component of RNase MRP (RMRP, ribonuclease mitochondrial RNA processing) and is transmitted as an autosomal recessive trait. In the present work, a Spanish CHH patient was extensively characterized at the immunological and molecular DNA level. Several parameters of cellular and humoral immunity were analyzed in this patient: lymphocyte subpopulation, proliferative responsiveness in mitogen stimulation and quantification of serum immunoglobulins. Sequencing of the RMRP gene allowed identification of two mutations in the patient: a +4 C>T substitution previously described on one allele, and a duplication of 15 nucleotides at position -11 on the other allele. This mutation has not previously been described.

Rapid molecular diagnosis of ataxia-telangiectasia by optimised RT-PCR and direct sequencing analysis.

Ataxia-telangiectasia (A-T) is a severe autosomal recessive disorder involving cerebellar degeneration, immunodeficiency, chromosomal instability, radiosensitivity, and cancer predisposition. A-T results from mutations in a single gene (ataxia-telangiectasia mutated, ATM) on chromosome 11 that encodes a 3056 amino acid protein (ATM). The purpose of this study is the design of an easy and rapid method for the molecular diagnosis of A-T which could be applied to clinical diagnosis, genetic counselling, carrier prediction, and prenatal diagnosis. Sixteen primer pairs were designed for RT-PCR. The PCR conditions were optimised to obtain a unique profile for the amplification of the 16 PCR products. These fragments were purified, directly sequenced and interpreted. The mutations found in three Spanish A-T families were reconfirmed with the optimised PCR and direct sequencing analysis. Up to now more than 400 A-T associated mutations have been reported in the ATM gene that do not support the existence of one or several hotspots. The immense size (transcript with 9168 nucleotides) and the structure of this gene (66 exons) greatly complicate the process of screening for all sequence variations. Our simple method allows identification of mutations in the coding region of the ATM gene from cDNA and represents a very useful tool for early diagnosis and genetic counselling in families with A-T.