Dna Rearrangements Detected By D4f104s1 And D4z4 Repeats

When probe p13E-11 (D4F104S1) is hybridized against genomic DNA digested with the restriction enzyme EcoRI, it identifies a 3.3-kb tandem repeat sequence termed D4Z4 (Fig. 1).[4] The variability in the EcoRI fragment size is because of the deletion of an integral number of D4Z4 repeats. The D4F104S1 EcoRI polymorphism is complex and represents contributions from two separate homologous EcoRI polymorphic loci: one located at 4q35, and the other at 10q26. Both polymorphic elements are composed of a variable number of multiple integral copies of the 3.3-kb Kpnl repeat unit (Fig. 2). There have been no reports of internal deletions within the body of the repeat itself.[5] There is size overlap between the EcoRI D4F104S1 alleles from 4q35 and 10q26. Subsequently, it was established that each of the 10q26-located repeat contains a BlnI restriction site (Fig. 2) that is not present on the 4q35-derived repeats.[6] Therefore a complete distinction between 4q35-derived and 10q26-derived fragments can be obtained by double digestion of the genomic DNA with EcoRI and BlnI; this effectively removes all the 10q-derived repeats. Recently, a XapI restriction site present in only 4q35-derived D4Z4 repeat was identified, and its use complements the EcoRI/ BlnI digests.

In most affected FSHD patients, disease-associated polymorphic alleles range in size from 7 to 38 kb (Fig. 3), which represents the presence of 1-11 D4Z4 repeats compared with the normal allele range of 50-300 kb, representing a D4Z4 copy number greater than 12

Several 4q35-derived and 10q26-derived D4Z4 3.3-kb repeat units from normal individuals have been cloned and sequenced,[7] and it has been found that the sequence of each repeat unit, whether from the 4q35 or the 10q26 tandem array, is virtually identical and is defined by flanking KpnI restriction sites. Each D4Z4 repeat contains a number of known repeat sequence motifs, including LSau and hhspm3, a highly GC-rich low-copy repeat. Analysis of the sequence has revealed the presence of a large open reading frame (ORF), which possesses the potential to encode two homeobox-like sequences that have been the subject of much speculation, although no such transcripts have ever been identified.

GENOTYPE/PHENOTYPE RELATIONSHIP

There is an association between the size of the deleted EcoRI fragment and the age at disease onset. It has been shown that smaller EcoRI fragments are always associated with the most severe form of the disease—a finding not specific to a single ethnic group. Thus the D4F104S1

Fig. 1 (A) Restriction map of the 4q35 region. Relative positions of FRG1, TUB4Q, FRG2, D4F104S1 (p13E11), and D4Z4. (B) EcoRI fragment detected by probe p13E11 predominantly comprises an array of 3.3-kb tandem repeats, which have a copy number of 12-100 in normal controls and usually 11 or less in FSHD patients. (C) Each 3.3-kb repeat comprises two homeodomains (shaded boxes) encompassing an ORF with an in-frame start codon (ATG) and a stop codon. It encodes the DUX4 gene. The position of the GC and TACAA boxes in the promoter-like sequence of DUX4 gene is indicated.

Fig. 1 (A) Restriction map of the 4q35 region. Relative positions of FRG1, TUB4Q, FRG2, D4F104S1 (p13E11), and D4Z4. (B) EcoRI fragment detected by probe p13E11 predominantly comprises an array of 3.3-kb tandem repeats, which have a copy number of 12-100 in normal controls and usually 11 or less in FSHD patients. (C) Each 3.3-kb repeat comprises two homeodomains (shaded boxes) encompassing an ORF with an in-frame start codon (ATG) and a stop codon. It encodes the DUX4 gene. The position of the GC and TACAA boxes in the promoter-like sequence of DUX4 gene is indicated.

EcoRI fragment size range noted in severe childhood cases of FSHD is 10-18 kb; in typical teenage-onset cases, between 18 and 34 kb; and in the oldest late-onset patients, larger than 30 kb.[8] However, it is still impossible to accurately predict the likely severity of disease expression based on repeat number alone. This is because of the high degree of interfamilial and intrafamilial variability of disease expression observed in this disorder, despite the fact that all affected members of a family exhibit the same-sized D4F104S1 allele.

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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