No abstract

Transgenic fragile X knockout mice have been constructed to provide an animal model to study the physiologic function of the fragile X gene (FMR1) and to gain more insight into the clinical phenotype caused by the absence of the fragile X protein. Initial experiments suggested that the knockout mice show macroorchidism and cognitive and behavioral deficits, abnormalities comparable to those of human fragile X patients. In the present study, we have extended our experiments, and conclude that the Fmr1 knockout mouse is a reliable transgenic model to study the fragile X syndrome. © 1996 Wiley‐Liss, Inc.

The FLNC mutation that we identified is distinct in terms of the associated phenotype, muscle morphology, and underlying molecular mechanism, thus extending the currently recognized clinical and genetic spectrum of filaminopathies. We conclude that filamin C is a dosage-sensitive gene and that FLNC haploinsufficiency can cause a specific type of myopathy in humans.

Subtelomeric rearrangements are believed to be responsible for 5-7% of idiopathic mental retardation cases. Due to the relative complexity and high cost of the screening methods used till now, only preselected patient populations including mostly the more severely affected cases have been screened. Recently, multiplex ligation-dependent probe amplification (MLPA) has been adapted for use in subtelomeric screening, and we have incorporated this technique into routine diagnostics of our laboratory. Since the evaluation of MLPA as a screening method, we tested 275 unselected patients with idiopathic mental retardation and detected 12 possible subtelomeric aberrations: a der(11)t(11;20)(qter;qter), a 19pter duplication, a der(18)t(18;10)(qter; pter), a 15qter deletion, a 8pter deletion, a 6qter deletion, a der(X)t(X;1)(pter;qter), a der(X)t(X;3)(pter;pter), a 5qter duplication, a 3pter deletion, and two 3qter duplications. The patients can be subdivided into two groups: the first containing de novo rearrangements that are likely related to the clinical presentation of the patient and the second including aberrations also present in one of the parents that may or may not be causative of the mental retardation. In our patient cohort, five (1.8%) subtelomeric rearrangements were de novo, three (1.1%) rearrangements were familial and suggestively disease causing, and four (1.5%) were possible polymorphisms. This high frequency of subtelomeric abnormalities detected in an unselected population warrants further investigation about the feasibility of routine screening for subtelomeric aberrations in mentally retarded patients.

Mutations in the gene GJB2, encoding the gap‐junction protein connexin‐26, have been shown to be a major cause of nonsyndromic recessive deafness (NSRD). A single mutation in the GJB2 gene accounts for the majority of NSRD in many different populations. This mutation represents a deletion of a guanine within a stretch of six Gs between nucleotide positions +30 and +35 of the GJB2 cDNA (35delG). Molecular detection of the 35delG mutation is usually performed by direct sequencing analysis of PCR products, or by allele‐specific PCR analysis. To screen for this mutation, we developed an easier and more reliable method, based on the principle of PCR‐mediated site‐directed mutagenesis (PSDM), followed by a BsiYI digestion. We tested 360 unrelated unaffected Belgian individuals for heterozygosity of the 35delG mutation and found a carrier frequency of 1 in 40 (95% CI, 1 in 30 to 1 in 60). As our new screening method is simple and reliable in use, and detects a mutation responsible for a significant part of NSRD, it may find widespread use in DNA diagnostics. Hum Mutat 14:263–266, 1999. © 1999 Wiley‐Liss, Inc.