A mutation hot spot for nonspecific X-linked mental retardation in the MECP2 gene causes the PPM-X syndrome

Abstract

We report here the genetic cause of the X-linked syndrome of psychosis, pyramidal signs, and macro-orchidism (PPM-X) in a three-generation family manifesting the disorder as a mutation in the methyl-CpG binding-protein 2 (MECP2) gene in Xq28. The A140V mutation was found in all affected males and all carrier females in the family. To date, descriptions have been published of two patients with independent familial mental retardation (MR) and two patients with sporadic MR who harbor this specific mutation in the MECP2 gene. This strongly suggests that A140V is a hot spot of mutation resulting in moderate to severe MR in males. A simple and reliable PCR approach has been developed for detection of the hot spot A140V mutation to prescreen any other unexplained cases of MR before further extensive mutation analyses.

Figure 1

Segregation of the mutation C419T in the family with PPM-X. A, Pedigree of part of the family. A square with the right half blackened represents an affected male with MR. A blackened square represents an affected male with MR and manic-depressive illness. A circle with a dot represents an obligate carrier female. B, PCR-RFLP assay for mutation detection. AccI-digested PCR products from exon 4, using the primers 4amod (5′-CGCCTACCTTTTCGAAGTAT-3′) and 4a-For.2 (5′-CGCTCTGCCCTATCTCTGA-3′, were separated on a 3% agarose gel; primers are modifications of those described by Buyse et al. [2000]) at an annealing temperature of 65°C. The modified forward primer 4amod, together with the C→T transition in position 419 (nucleotides numbered from the first base of the translation-initiation ATG codon; GenBank accession number X99686), creates an AccI restriction site generating two fragments of 118 bp and 18 bp from the 136-bp PCR product; because of its small size, the 18-bp digestion product is not visible on this agarose gel. M = molecular weight marker V (Roche). C, direct sequencing of the mutation 419C→T found in the family: II-3, carrier female (heterozygote 419C/T); III-7, affected male (hemizygote 419T); III-8, unaffected male (hemizygote 419C).