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Absence of learning difficulties in a hyperactive boy with a terminal Xp deletion encompassing the MRX49locus
  1. E S Tobiasa,
  2. G Bryceb,
  3. G Farmerc,
  4. J Bartonb,
  5. J Colgana,
  6. N Morrisona,
  7. A Cookea,
  8. J L Tolmiea
  1. aDuncan Guthrie Institute of Medical Genetics, Yorkhill, Glasgow G3 8SJ, UK, bDepartment of Child and Family Psychiatry, Yorkhill NHS Trust, Glasgow G3 8SJ, UK, cDepartment of Paediatrics, Raigmore Hospital, Old Perth Road, Inverness IV2 3UJ, UK
  1. Dr Tobias, gbcv55{at}

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Editor—The genetic counselling of a pregnant woman who carries an Xp chromosomal deletion is far from straightforward. While the precise locations of the CDPX1(arylsulphatase E), steroid sulphatase (STS), and Kallman (KAL1) genes are known and FISH probes are available for these well characterised genes, the positions of putative mental retardation genes in this region have not yet been determined. Clinical and molecular studies undertaken over the past 10 years on patients with distal Xp deletions imply, however, that the putative X linked mental retardation (XLMR) gene,MRX49, lies distal toGS1 and STS but proximal to DXS31 and CDPX1 (fig1).1-4

Figure 1

(a) Case 6, (b) case 8, (c) case 9, (d) case 4, (e) case 12, and (f) case 13 of Ballabio et al,1 (g)-(j) cases BA16, BA20, BA139, and BA75 of Schaefer et al,3 (k) boy with IQ of 46, short stature, generalised ichthyosis, hypogonadotrophic hypogonadism, nystagmus, and photophobia,2 (l) boy with aggressive and hyperactive behaviour, myoclonic epilepsy, developmental delay, and no speech aged 4 years 8 months,4 (m) monozygous male twins with X linked ichthyosis, learning difficulties (LD), and epilepsy,10 (n) our patient, with short stature, Binder syndrome, and ichthyosis (consistent with the loss of the SHOX, CDPX1, and STS genes, respectively) but no significant learning difficulties. The presence (+) or absence (-) of LD is indicated for each case. A broken line indicates the chromosomal region within …

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