A novel arginine vasopressin-neurophysin II mutation causes autosomal dominant neurohypophyseal diabetes insipidus and morphologic pituitary changes.

To determine the genetic basis of autosomal dominant neurohypophyseal diabetes insipidus (ADNDI) in a Cypriot family, we ascertained and studied a large, four-generation kindred in which all participating family members had arginine vasopressin-neurophysin II (AVP-NP-II) gene analyses done. A G to A transition was found by DNA sequence analysis at position 1773 (G1773A) of the AVP-NPII gene which is predicted to encode a substitution of tyrosine for cysteine in codon 59 (CYS59TYR). The mutation was confirmed by restriction endonuclease analysis of PCR amplification products that contain the corresponding segment of the AVP-NPII gene. To clarify the morphologic status of the pituitaries of family members, 12 affected and 3 nonaffected members had magnetic resonance imaging (MRI) studies. The bright spot of the posterior pituitary lobe was completely absent in 75% and faintly identified in 25% of the affected members who were examined with MRI. We conclude that (1) a novel G1773A transition in exon 2 of the AVP-NPII gene causes ADNDI in the large Cypriot kindred studied, (2) this mutation is predicted to encode a CYS59TYR substitution in NPII, and (3) MRI studies of the posterior pituitary lobes of affected family members show either a decreased intensity or a complete absence of the bright spot in all cases studied.

Molecular screening of fragile X (FRAXA) and FRAXE mental retardation syndromes in the Hellenic population of Greece and Cyprus: incidence, genetic variation, and stability.

This study presents the first large, population-based molecular investigation of the fragile X (FRAXA) and FRAXE mental retardation syndromes in the Hellenic populations of Greece and Cyprus. The aims of this population screening were to determine the prevalence of FRAXA and FRAXE syndromes among idiopathic mentally retarded (IMR) individuals, to estimate the incidence in the general population, and to investigate the molecular mechanism of instability and expansion of the FMR1-repeat. Ten FRAXA patients were identified to have either the full mutation (eight) or premutation (two) from a Hellenic population of 866 unrelated IMR individuals (611 males and 255 females, age range 3-25 years). No FRAXE patients were identified among the 611 IMR males. The incidence of FRAXA in the Hellenic population of Cyprus is estimated at 1 in 4,246 males. The repeat sites from the FMR1 and FMR2 alleles were accurately determined and showed similar distribution and frequencies with other population studies. The analysis of AGG interspersion within the FMR1-repeat in normal males revealed long, pure CGG repeats within the "gray zone" as well as variation within the 3' end showing polarity of instability. This finding supports the hypothesis that the AGG interspersion and the length of the pure repeat are major factors in determining allele stability. Analysis of FRAXAC1, DXS548, and FRAXAC2 identified particular alleles and haplotypes to have a significant association with either gray zone alleles or alleles >15 pure CGG repeats. We hypothesize that this subgroup of alleles and haplotypes are associated with long pure CGGs (>15 CGG) or 35 repeats and, having shared an evolutionary past, would have the tendency to expand.

Genetic variation and intergenerational FMR1 CGG-repeat stability in 100 unrelated three-generation families from the normal population.

In order to identify genetic factors governing expansion of the CGG repeat in the FMR1 gene and to determine what predisposes or causes a normal stable allele to change to an unstable premutation allele, it is essential to study and understand the basis of normal variation. The aim of this study was to investigate genetic variation and intergenerational stability of the FMR1 CGG-repeat region in 100 unrelated three-generation families from the general population (651 meioses). The number of CGG-repeats in the FMR1 gene was determined in all 750 individuals from the 100 families (a total of 1,132 X-chromosomes), and the allele frequencies and variability were analyzed. Thirty-six different alleles (12-60 repeats) were seen with 30 (45.8%) as the most common allele; overall female heterozygosity was 73%. Most (>96%) of the normal array lengths were less than 40 repeats. Fifteen families with at least one allele equal to or greater than 40 repeats (40-60) were identified; in one of these families there was an increase of one triplet repeat during transmission from a mother to son. These findings, together with future molecular analyses, may provide data to test proposed models that attempt to explain the mutational process and the population dynamics of the triplet repeat region of the FMR1 gene, including the transition from normal to unstable alleles, or to test other putative cis-acting sequences that may be involved with instability in the FMR1 gene.