A mutation in the rett syndrome gene, MECP2, causes X-linked mental retardation and progressive spasticity in males

Abstract

Heterozygous mutations in the X-linked MECP2 gene cause Rett syndrome, a severe neurodevelopmental disorder of young females. Only one male presenting an MECP2 mutation has been reported; he survived only to age 1 year, suggesting that mutations in MECP2 are male lethal. Here we report a three-generation family in which two affected males showed severe mental retardation and progressive spasticity, previously mapped in Xq27.2-qter. Two obligate carrier females showed either normal or borderline intelligence, simulating an X-linked recessive trait. The two males and the two obligate carrier females presented a mutation in the MECP2 gene, demonstrating that, in males, MECP2 can be responsible for severe mental retardation associated with neurological disorders.

Figure 1

Segregation of the mutation in the family; 3% agarose gel of AvrII-digested PCR products of segment D of exon 3 (396 bp) obtained as reported elsewhere (De Bona et al. 2000). The C→T transition in position 1216 creates the “ccTagg” AvrII restriction site from the normal “cccagg” sequence, generating two fragments of 213 and 183 bp. Line 1, molecular weight marker VI (Roche), following lines as reported in pedigree above; ND = nondigested control.

Figure 2

Quantitative RT-PCR of total RNA from lymphoblastoid cells of patient (OE) and male (XY) and female (XX) controls. Primers were MECP-2 RT-S: 5′-CGC TCC ATC ATC CGT GAC-3′; MECP-2 RS-A: 5′-TCT GCC AGT TCC TGG AGC-3′; GAPDH-F: 5′-AAC ACA GTC CAT GCC ATC AC-3′; GAPDH-R: 5′-TCC ACC ACC CTG TTG CTG TA-3′. The RT was done with (+) and without (−) retrotranscriptase, as described elsewhere (Bione et al. 1996), using 1 μg of total RNA. We amplified 2.5 μl of the RT reaction in a 50-μl PCR reaction. C = PCR control without template DNA. PCR conditions were the following: GAPDH: 5 min at 94°C; 30 s at 94°C, 30 s at 60°C, and 30 s at 72°C for 25 cycles; MECP-2: 5 min at 94°C; 30 s at 94°C, 30 s at 60°C, and 30 s at 72°C for 35 cycles.

Figure 3

Results of X-inactivation assay: 6% polyacrylamide silver-stained gel of PCR product of CAG repeat of the androgen-receptor gene (Allen et al. 1992) from HpaII digested (D) and nondigested (ND) DNA of the carrier females. Primers used for PCR amplification were RS-6: 5′-GTC CAA GAC CTA CCG AGG AG-3′ and RS-7: 5′-CCA GGA CCA GGT AGC CTG TG-3′. Band intensities were measured by Diversity Database program (Biorad), and the values were corrected for preferential allele amplification (Pegoraro et al. 1994). Results showed a balanced X-inactivation: ∼56% of X-bearing allele b active (b) and 44% of X-bearing allele a active (a) in the mother (right panel); ∼60% of normal paternal X active (c) and 40% of mutated X active (a) in the daughter (left panel).