Subtelomeric rearrangement of genes is frequently associated with mental retardation. All of the following techniques can be used to diagnose them, EXCEPT:

MALDI: It is a technique used to assess the molecule, based on their mass only. Most commonly employed methods for dispersing peptides, proteins, and other large biomolecules into the vapor phase for mass spectrometric analysis are electrospray ionization and matrix-assisted laser desorption and ionization, aka MALDI. In electrospray ionization, the molecules to be analyzed are dissolved in a volatile solvent and introduced into the sample chamber in a minute stream through a capillary . As the droplet of liquid emerges into the sample chamber, the solvent rapidly disperses leaving the macromolecule suspended in the gaseous phase. The charged probe serves to ionize the sample. Electrospray ionization is frequently used to analyze peptides and proteins as they elute from an HPLC or other chromatography column already dissolved in a volatile solvent. In MALDI, the sample is mixed with a liquid matrix containing a light-absorbing dye and a source of protons. In the sample chamber, the mixture is excited using a laser, causing the surrounding matrix to disperse into the vapor phase so rapidly as to avoid heating embedded peptides or proteins. Ref: Kennelly P.J., Rodwell V.W. (2011). Chapter 4. Proteins: Determination of Primary Structure. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper's Illustrated Biochemistry, 29e.