Molecular and functional characterization of eight novel GAA mutations in Italian infants with Pompe disease.

We characterized 29 unrelated patients presenting with the severe form of Pompe disease (Glycogen Storage Disease Type II, acid maltase deficiency) and identified 26 pathogenic mutations divided over 28 different genotypes. Among the eight new mutations, five were exonic point mutations (c.572A>G, c.1124G>T, c.1202A>G, c.1564C>G and c.1796C>A) leading to codon changes (p.Y191C, p.R375L, p.Q401R, p.P522A and p.S599Y); two were intronic point mutations (c.-32-3C>A and c.1636+5G>C) affecting mRNA processing; one was a single base deletion (c.742delC) generating a truncated protein (p.L248PfsX20). A comprehensive evaluation, based on different methodological approaches, confirmed the detrimental effect of the eight mutations on the protein and its function. Structural alterations potentially induced by the five missense mutations were also predicted through visual inspection of the atomic model of the GAA protein, in terms of both function and spatial orientation of specific residues as well as disturbance generated by amino acid substitutions. Although the remarkable heterogeneity of the mutational spectrum in Pompe disease was already known, our data demonstrate and confirm the power of molecular and functional analysis in predicting the natural course of Pompe disease.

Genotype-phenotype correlation in five Pelizaeus-Merzbacher disease patients with PLP1 gene duplications.

Pelizaeus-Merzbacher disease (PMD) is an X-linked myelination disorder most frequently caused by duplication of a genomic segment of variable length containing the PLP1 gene. We studied five PMD male patients affected by the classic PMD form carrying a PLP1 gene duplication. On the basis of clinical and neuroradiological features, two of the five patients appeared to be the most severely affected. In order to establish a possible genotype-phenotype correlation, the extent of the duplication was determined in each patient and in the respective mother by quantifying the copy number of genomic markers surrounding the PLP1 gene by a real-time PCR-based approach. Duplications, ranging in size from 167-195 to 580-700 kb, were in the same genomic interval of the majority of the reported duplications. The extent of the duplicated genomic segments does not correlate with the clinical severity. Interestingly enough, each duplication had one of the two breakpoints in or near to low copy repeats (LCRs), supporting recent evidence concerning a possible role of LCRs in the generation of the duplications in PMD.