Mutation of the slow myosin heavy chain rod domain underlies hyaline body myopathy.

OBJECTIVE: To identify the gene and specific mutation underlying hyaline body myopathy in the family studied. METHODS: A microsatellite-based whole genome scan was performed. Linkage analysis assumed autosomal dominant inheritance and equal allele frequencies. A candidate gene approach within the linked interval and direct sequencing were used for mutation detection. RESULTS: Initial analysis indicated a maximum lod score of 3.01 at D14S1280. High-density mapping surrounding the linked locus was performed. Multipoint analysis showed that the linked region with a maximum lod score of 3.01 extended from D14S742 to D14S608 with a peak non-parametric linkage (NPL) score of 3.75 at D14S608. The myosin heavy chain genes MYH6 and MYH7 map to the region between D14S742 and D14S1280. Sequence analysis of the coding regions of MYH7 revealed an A-->T transversion at nucleotide position 25596 (M57965) resulting in a histidine-to-leucine amino acid change at residue 1904 (H1904L). CONCLUSION: Pathogenicity of the MYH7 H1904L mutation most likely results from disruption of myosin heavy chain assembly or stability of the sarcomeric protein. The MYH7 tail domain mutation results in an inclusion body myopathy with an apparent absence of hypertrophic cardiomyopathy usually associated with mutations of this gene.

A novel form of autosomal recessive pure hereditary spastic paraplegia maps to chromosome 13q14.

BACKGROUND: Hereditary spastic paraplegia (HSP) is a clinically and genetically heterogeneous disorder characterized by a progressive weakening and spasticity of the lower limbs. HSP is classified according to the presence or absence of accompanying neurologic problems and by the mode of inheritance. Currently, 17 loci have been linked to the various forms of HSP. OBJECTIVE: To determine the chromosomal location of a gene causing pure autosomal recessive spastic paraplegia. METHODS: Genotyping using fluorescently labeled microsatellite markers was performed on three affected individuals and three unaffected individuals from a family displaying pure autosomal recessive HSP (ARHSP) and sensorineural deafness. All family members were then included in the analysis to narrow the genetic interval. Candidate genes were screened for the presence of mutations by heteroduplex analysis. RESULTS: The paraplegic trait linked to a 1.8-Mb region of chromosome 13q14 flanked by the FLJ11712 gene and the microsatellite marker D13S270. The deafness did not link to this region and did not cosegregate with the paraplegic trait. CONCLUSION: The HSP that this family had represents a novel genetic form of pure ARHSP as no other form of HSP (autosomal dominant or recessive) has been linked to chromosome 13.

Evidence that insulin is imprinted in the human yolk sac.

Allelic variation in the size of the insulin (INS) variable number tandem repeat (VNTR) correlates with the expression of both INS in the pancreas and thymus and IGF2 (the gene downstream of INS) in the placenta. In addition, the shorter, class I alleles are associated with type 1 diabetes, whereas the longer, class III alleles are associated with type 2 diabetes, polycystic ovary syndrome (PCOS), and size at birth. Parent-of-origin effects have been reported for type 2 diabetes and PCOS, thus implicating a role for genomic imprinting in these phenotypes. In mice, Ins2 is imprinted and paternally expressed in the yolk sac. In humans, evidence for the imprinting of INS is circumstantial, with occasional monoallelic expression in the thymus. In the present study, we found evidence for the imprinted paternal expression of INS in the human yolk sac. Two other imprinted genes from the same cluster are also expressed monoallelically in the human yolk sac. IGF2 was expressed solely from the paternal allele, and H19 was expressed solely from the maternal allele. These data suggest not only further functional roles for the human yolk sac in early fetal growth, but also evidence for a potential causal link between the control of insulin expression during development and insulin/growth-related diseases in later life.

Duplication of 7p11.2-p13, including GRB10, in Silver-Russell syndrome.

Silver-Russell syndrome (SRS) is characterized by pre- and postnatal growth failure and other dysmorphic features. The syndrome is genetically heterogeneous, but maternal uniparental disomy of chromosome 7 has been demonstrated in approximately 7% of cases. This suggests that at least one gene on chromosome 7 is imprinted and involved in the pathogenesis of SRS. We have identified a de novo duplication of 7p11.2-p13 in a proband with features characteristic of SRS. FISH confirmed the presence of a tandem duplication encompassing the genes for growth factor receptor-binding protein 10 (GRB10) and insulin-like growth factor-binding proteins 1 and 3 (IGFBP1 and -3) but not that for epidermal growth factor-receptor (EGFR). Microsatellite markers showed that the duplication was of maternal origin. These findings provide the first evidence that SRS may result from overexpression of a maternally expressed imprinted gene, rather than from absent expression of a paternally expressed gene. GRB10 lies within the duplicated region and is a strong candidate, since it is a known growth suppressor. Furthermore, the mouse homologue (Grb10/Meg1) is reported to be maternally expressed and maps to the imprinted region of proximal mouse chromosome 11 that demonstrates prenatal growth failure when it is maternally disomic. We have demonstrated that the GRB10 genomic interval replicates asynchronously in human lymphocytes, suggestive of imprinting. An additional 36 SRS probands were investigated for duplication of GRB10, but none were found. However, it remains possible that GRB10 and/or other genes within 7p11.2-p13 are responsible for some cases of SRS.

An analysis of common isodisomic regions in five mUPD 16 probands.

Intrauterine growth retardation (IUGR) with or without additional abnormalities is recognised as a common feature of maternal uniparental disomy for chromosome 16 (mUPD 16) and is usually associated with confined placental mosaicism (CPM). Although it is likely that the CPM largely contributes to the IUGR, postnatal growth retardation and other common abnormalities may also be attributed to the mUPD. Five cases with mUPD 16 and CPM were analysed for common regions of isodisomy using polymorphic markers distributed along the length of the chromosome. In each case the aberration was consistent with a maternal meiosis I error. Complete isodisomy was not detected in any of the patients although two patients were found to be mixed with both iso- and heterodisomy. Interestingly, the patient with the greater region of isodisomy was the most severely affected. The fact that there were no common regions of isodisomy in any of the patients supports the hypothesis that imprinted genes, rather than recessive mutations, may play a role in the shared phenotypes.

An analysis of the distribution of hetero- and isodisomic regions of chromosome 7 in five mUPD7 Silver-Russell syndrome probands.

Silver-Russell syndrome (SRS) shares common features of intrauterine growth retardation (IUGR) and a number of dysmorphic features including lateral asymmetry in about 50% of subjects. Its genetic aetiology is complex and most probably heterogeneous. Approximately 7% of patients with SRS have been found to have maternal uniparental disomy of chromosome 7 (mUPD7). Genomic DNA samples from five SRS patients with mUPD7 have been analysed for common regions of isodisomy using 40 polymorphic markers distributed along the length of chromosome 7. No regions of common isodisomy were found among the five patients. It is most likely that imprinted gene(s) rather than recessive mutations cause the common phenotype. Heterodisomy of markers around the centromere indicated that the underlying cause of the mUPD7 is a maternal meiosis I non-disjunction error in these five subjects.

Human EGFR, a candidate gene for the Silver-Russell syndrome, is biallelically expressed in a wide range of fetal tissues.

Maternal uniparental disomy of chromosome 7 (mUPD7) has been reported in around 10% of cases of Silver-Russell syndrome (SRS). This suggests that at least one gene on chromosome 7 is imprinted and involved in the pathogenesis of this condition. One candidate is epidermal growth factor receptor (EGFR) which maps to chromosome 7p12, a region homologous to an imprinted region on mouse chromosome 11. Using a restriction fragment length polymorphism, biallelic expression of EGFR was found in a range of normal human fetal tissues. Expression was also demonstrated in fibroblasts and lymphoblasts from SRS patients with mUPD7. Thus no evidence that EGFR is imprinted was found, making its involvement in SRS unlikely. However, EGFR was shown to be widely expressed in the human fetus, evidence that this gene plays an important role in early development.

Expression of the insulin-like growth factors and their receptors in term placentas: a comparison between normal and IUGR births.

Intrauterine growth retardation (IUGR) is defined as growth retarded to be below the tenth centile. The insulin-like growth factors and their receptors are implicated in pre- and postnatal growth and development, and it is believed that alteration in their activity may contribute to IUGR. In this study nine normal and nine intrauterine growth retarded births were followed and term placentas examined for expression of the insulin-like growth factors and their receptors. It was found that the expression of insulin-like growth factor 1 (IGF1), insulin-like growth factor 2 (IGF2), and the insulin, IGF1 and IGF2 receptor transcripts (IGF1R and IGF2R, respectively) was present in all term placentas examined. Expression of insulin was not detected. Quantitative polymerase chain reaction (PCR) was used to compare transcription levels in term placentas from normal with IUGR births. There was no significant difference in the levels of transcripts for IGF1, insulin receptor, or IGF2R between normal and IUGR term placentas. However, the IUGR term placentas had significantly higher levels of IGF2 and IGF1R expression compared with the normal term placentas. The increase in the transcription of IGF2 and IGF1R in IUGR term placentas may represent a counter regulatory mechanism in response to the growth retardation.

Nucleotide-sequence analysis indicates that a DNA plasmid in a diseased isolate of Ophiostoma novo-ulmi is derived by recombination between two long repeat sequences in the mitochondrial large subunit ribosomal RNA gene.

The nucleotide sequence of a mitochondrial plasmid (2234 bp) in a diseased isolate of Ophiostoma novo-ulmi, and sequences of the mitochondrial DNA that overlap and flank the plasmid end-points, have been determined. The plasmid was shown to be derived from the O. novo-ulmi mitochondrial large subunit ribosomal RNA gene and contained most of intron 1, the whole of exon 2, and probably the first part of intron 2. Within intron 1 there is an open reading frame with the potential to encode a 323 amino-acid polypeptide which contained dodecapeptide sequences typical of RNA maturases and DNA endonucleases. The endpoints of the plasmid in the mtDNA were located within two 90-bp direct imperfect repeat sequences, one of which comprised the last 7 bp of exon 1 and the first 83 bp of intron 1 whilst the other comprised the last 7 bp of exon 2 and the first 83 bp of intron 2. It is proposed that the Ld plasmid was generated by intramolecular recombination between these two repeats with the crossover point probably within the last 15 bp.