A BclI RFLP for DXS296 (VK21) near the fragile X

Mutations of the iduronate-2-sulfatase (IDS) gene in patients with Hunter syndrome (mucopolysaccharidosis II)

Genomic DNA and cDNA from fibroblasts from nine unrelated German patients with X-linked iduronate-2-sulfatase (IDS) deficiency showing variable clinical manifestation were screened for point mutations and small structural aberrations. Direct sequencing revealed a splice mutation skipping exon A, one nonsense mutation, and five missense mutations concerning the exons B, F and I of the IDS gene. Several novel missense mutations were found: A68E, S426X, I485R, Q293H, and D478G. One of the point mutations eliminating a recognition site for the restriction enzyme MspI was used as a direct marker for a prenatal diagnosis. A relationship between type of mutation and clinical picture could not be recognized.

Carrier detection of Hunter syndrome (MPS II) by biochemical and DNA techniques in families at risk

DNA based and biochemical diagnosis of MPS II was performed on 13 unrelated families using Southern blotting. The 35S-sulphate accumulation in cultured fibroblasts was investigated and the iduronate-2-sulphatase (IDS) activity in the serum determined. Sixteen patients and 36 females at risk were screened for structural aberrations and by RFLP analysis using the intragenic probe pc2S15 and probes VK23B, VK21A, and II-10 for the flanking loci DXS297, DXS296, and DXS466. Structural alterations were found in the DNA of two patients. One of them showed a major deletion including the whole coding sequence of the IDS gene. An aberrant Southern fragment occurred in the HindIII/pc2S15 blot of the other patient suggesting a new HindIII restriction site by point mutation in an IDS gene intron. Twenty-nine females were confirmed as carriers, and for five women the heterozygous state could be excluded. Prenatal diagnosis can be offered to 27 women if requested.

46,XY/47,XYY male with the fragile X syndrome: cytogenetic and molecular studies

We report the first case of a 46,XY/47,XYY mosaic male with fragile X [Fra(X)] expression in both cell lines. Cytogenetic analysis, DNA linkage analysis, and direct detection of the pre- and full mutation for the affected individual and his at-risk female relatives were performed. Southern analysis of PstI-digested DNA with probe pX6 clearly distinguished the normal genotype, the premutation, and the full mutation in various individuals in the patient's family. Fra(X) carriers who had normal cytogenetic results were clearly identified by direct mutation analysis.

Genetic mapping of new DNA probes at Xq27 defines a strategy for DNA studies in the fragile X syndrome

The fragile X syndrome is the most common cause of familial mental retardation and is characterized by a fragile site at the end of the long arm of the X chromosome. The unusual genetics and cytogenetics of this X-linked condition make genetic counseling difficult. DNA studies were of limited value in genetic counseling, because the nearest polymorphic DNA loci had recombination fractions of 12% or more with the fragile X mutation, FRAXA. Five polymorphic loci have recently been described in this region of the X chromosome. The positions of these loci in relation to FRAXA were defined in a genetic linkage study of 112 affected families. The five loci--DXS369, DXS297, DXS296, IDS, and DXS304--had recombination fractions of 4% or less with FRAXA. The closest locus, DXS296, was distal to FRAXA and had a recombination fraction of 2%. The polymorphisms at these loci can be detected in DNA enzymatically digested with a limited number of restriction endonucleases. A strategy for DNA studies which is based on three restriction endonucleases and on five probes will detect one or more of these polymorphisms in 94% of women. This strategy greatly increases the utility of DNA studies in providing genetic advice to families with the fragile X syndrome.