Antony E. Shrimpton

Familial dementia caused by polymerization of mutant neuroserpin

Aberrant protein processing with tissue deposition is associated with many common neurodegenerative disorders; however, the complex interplay of genetic and environmental factors has made it difficult to decipher the sequence of events linking protein aggregation with clinical disease. Substantial progress has been made toward understanding the pathophysiology of prototypical conformational diseases and protein polymerization in the superfamily of serine proteinase inhibitors (serpins). Here we describe a new disease, familial encephalopathy with neuroserpin inclusion bodies, characterized clinically as an autosomal dominantly inherited dementia, histologically by unique neuronal inclusion bodies and biochemically by polymers of the neuron-specific serpin, neuroserpin. We report the cosegregation of point mutations in the neuroserpin gene (PI12) with the disease in two families. The significance of one mutation, S49P, is evident from its homology to a previously described serpin mutation, whereas that of the other, S52R, is predicted by modelling of the serpin template. Our findings provide a molecular mechanism for a familial dementia and imply that inhibitors of protein polymerization may be effective therapies for this disorder and perhaps for other more common neurodegenerative diseases.

Dent Disease with mutations in OCRL1.

Dent disease is an X-linked renal proximal tubulopathy associated with mutations in the chloride channel gene CLCN5. Lowe syndrome, a multisystem disease characterized by renal tubulopathy, congenital cataracts, and mental retardation, is associated with mutations in the gene OCRL1, which encodes a phosphatidylinositol 4,5-bisphosphate (PIP(2)) 5-phosphatase. Genetic heterogeneity has been suspected in Dent disease, but no other gene for Dent disease has been reported. We studied male probands in 13 families, all of whom met strict criteria for Dent disease but lacked mutations in CLCN5. Linkage analysis in the one large family localized the gene to a candidate region at Xq25-Xq27.1. Sequencing of candidate genes revealed a mutation in the OCRL1 gene. Of the 13 families studied, OCRL1 mutations were found in 5. PIP(2) 5-phosphatase activity was markedly reduced in skin fibroblasts cultured from the probands of these five families, and protein expression, measured by western blotting, was reduced or absent. Slit-lamp examinations performed in childhood or adulthood for all five probands showed normal results. Unlike patients with typical Lowe syndrome, none of these patients had metabolic acidosis. Three of the five probands had mild mental retardation, whereas two had no developmental delay or behavioral disturbance. These findings demonstrate that mutations in OCRL1 can occur with the isolated renal phenotype of Dent disease in patients lacking the cataracts, renal tubular acidosis, and neurological abnormalities that are characteristic of Lowe syndrome. This observation confirms genetic heterogeneity in Dent disease and demonstrates more-extensive phenotypic heterogeneity in Lowe syndrome than was previously appreciated. It establishes that the diagnostic criteria for disorders resulting from mutations in the Lowe syndrome gene OCRL1 need to be revised.

Association between conformational mutations in neuroserpin and onset and severity of dementia

BACKGROUND The aggregation of specific proteins is a common feature of the familial dementias, but whether the formation of neuronal inclusion bodies is a causative or incidental factor in the disease is not known. To clarify this issue, we investigated five families with typical neuroserpin inclusion bodies but with various neurological manifestations. METHODS Five families with neurodegenerative disease and typical neuronal inclusions had biopsy or autopsy material available for further examination. Immunostaining confirmed that the inclusions were formed of neuroserpin aggregates, and the responsible mutations in neuroserpin were identified by sequencing of the neuroserpin gene (SERPINI1) in DNA from blood samples or from extraction of histology specimens. Molecular modelling techniques were used to predict the effect of the gene mutations on three-dimensional protein structure. Brain sections were stained and the topographic distribution of the neuroserpin inclusions plotted. FINDINGS Each of the families was heterozygous for an amino acid substitution that affected the conformational stability of neuroserpin. The least disruptive of these mutations (S49P), as predicted by molecular modelling, resulted in dementia after age 45 years, and presence of neuroserpin inclusions in only a few neurons. By contrast, the most severely disruptive mutation (G392E) resulted, at age 13 years, in progressive myoclonus epilepsy, with many inclusions present in almost all neurons. INTERPRETATION The findings provide evidence that inclusion-body formation is in itself a sufficient cause of neurodegeneration, and that the onset and severity of the disease is associated with the rate and magnitude of neuronal protein aggregation.

OCRL1 Mutations in Dent 2 Patients Suggest a Mechanism for Phenotypic Variability

Background/Aims: Dent disease is an X-linked renal proximal tubulopathy associated with mutations in CLCN5 (Dent 1) or OCRL1 (Dent 2). OCRL1 mutations also cause the oculocerebrorenal syndrome of Lowe. Methods: Dent patients with normal sequence for CLCN5 were sequenced for mutations in OCRL1. By analyzing these and all other OCRL1 mutations reported, a model relating OCRL1 mutations to the resulting disease (Dent 2 or Lowe’s) was developed. Results: Six boys with Dent disease had novel OCRL1 mutations: two missense (R301H, G304E) and four mutations predicted to produce premature termination codons (L56DfsX1, S149X, P161PfsX3, and M170IfsX1). These include one of the original patients reported by Dent and Friedman. Slit lamp examinations revealed early cataracts in only one boy with normal vision. None of these Dent 2 patients had metabolic acidosis; 3 had mild mental retardation. Analysis of all known OCRL1 mutations show that Dent 2 mutations fall into two classes that do not overlap with Lowe mutations. Bioinformatics analyses identified expressed OCRL1 splice variants that help explain the variability of those clinical features that distinguish Dent disease from Lowe syndrome. Conclusions:OCRL1 mutations can cause the renal phenotype of Dent disease, without acidosis or the dramatic eye abnormalities typical of Lowe syndrome. We propose a model to explain the phenotypic variability between Dent 2 and Lowe’s based on distinctly different classes of mutations in OCRL1 producing splice variants.

Molecular delineation of deletions on 2q37.3 in three cases with an Albright hereditary osteodystrophy‐like phenotype

A minority of the reported cases of terminal 2q37 deletion clinically resemble Albright hereditary osteodystrophy (AHO)/pseudopseudohypoparathyroidism and have only mild‐to‐moderate mental retardation. Our molecular and cytogenetic fluorescence in situ hybridization (FISH) findings on an additional three patients further reduce the size of the minimal critical region deleted in this syndrome to about 3 Mb. This region includes the G‐protein‐coupled receptor 35 (GPR35), glypican 1 (GPC1), and serine/threonine protein kinase 25 (STK25) genes on 2q37.3. We have further defined several polymorphic variants within the coding region and flanking regions of GPR35 gene, which could potentially be useful for rapid detection of GPR35 gene deletion. We postulate that the absence of GPR35 may, at least partly, account for the phenotypic resemblance to the AHO. We also believe that the deletion of GPR35 could be responsible for the entity brachydactyly mental retardation syndrome (OMIM #600430), which was coined based on the above minority of patients with terminal 2q37 deletion. We recommend that every patient with AHO phenotype should undergo 2q subtelomeric FISH screen and subsequently a molecular study on the GPR35 gene. GPC1 and/or STK25 haploinsufficiency may also contribute to the AHO‐like phenotype.

Inheritance of Osteosarcoma and Paget’s Disease of Bone: A Familial Loss of Heterozygosity Study

Pagetoid osteosarcoma is a complication of Pagets disease of bone. Sarcomatous transformation is most often seen in severe, long-standing Pagets disease. Familial clustering of Pagets disease has been described with apparent autosomal dominant inheritance with high penetrance by the sixth decade. Although definitive proof of the specific gene involved remains elusive, some researchers have shown loss of heterozygosity in a region of chromosome 18q in a relatively high percentage of studied patients affected with either Pagets disease alone, in Pagetoid osteosarcoma, and in uncomplicated osteosarcoma. Our patient was diagnosed with Pagetoid osteosarcoma and had a first-degree relative with history of the same. We hypothesized that our patients tumor samples might contain a similar genetic abnormality. Our analysis of several polymorphic markers from the chromosome 18q21-22 region showed loss of maternally inherited alleles throughout the region. This finding is similar to those described previously and provides further evidence of a susceptibility region relating to this disease. This report describes a father and son, their young ages at diagnosis of Pagetoid sarcoma, the identical sites of disease involvement, and a loss of heterozygosity study illustrating the inheritance of the presumed defective gene.

A presenilin 1 mutation (L420R) in a family with early onset Alzheimer disease, seizures and cotton wool plaques, but not spastic paraparesis

Over 100 mutations in the presenilin‐1 gene (PSEN1) have been shown to result in familial early onset Alzheimer disease (EOAD), but only a relatively few give rise to plaques with an appearance like cotton wool (CWP) and/or spastic paraparesis (SP). A family with EOAD, seizures and CWP was investigated by neuropathological study and DNA sequencing of the PSEN1 gene. Aβ was identified in leptomeningeal vessels and in cerebral plaques. A single point mutation, p.L420R (g.1508T > G) that gives rise to a missense mutation in the eighth transmembrane (TM8) domain of PS1 was identified in two affected members of the family. p.L420R (g.1508T > G) is the mutation responsible for EOAD, seizures and CWP without SP in this family.

Complete maternal uniparental isodisomy of chromosome 4 in a subject with major depressive disorder detected by high density SNP genotyping arrays

Uniparental isodisomy (iUPD) is a rare genetic condition caused by non‐disjunction during meiosis that ultimately leads to a duplication of either the maternal or paternal chromosome in the affected individual. Two types of disorders can result, those due to imprinted genes and those due to homozygosity of recessive disease‐causing mutations. Here, we describe the third known case of complete chromosome 4 iUPD of maternal origin. This condition became apparent during whole genome linkage studies of psychiatric disorders in the Portuguese population. The proband is an adult female with normal fertility and no major medical complaints, but a history of major depressive disorder and multiple suicide attempts. The probands siblings and parents had normal chromosome 4 genotypes and no history of mood disturbance. A brief review of other studies lends support for the possibility that genes on chromosome 4 might confer risk for mood disorders. We conclude that chromosome 4 maternal uniparental disomy (UPD) is a rare disorder that may present with a major depressive phenotype. The lack of a common disease phenotype between this and two other cases of chromosome 4 iUPD [Lindenbaum et al. [1991] Am J Med Genet 49(Suppl 285):1582; Spena et al. [2004] Eur J Hum Genet 12:891–898) would suggest that there is no vital maternal gene imprinting on chromosome 4. However, since there is no reported case of paternal chromosome 4 UPD, paternal gene imprinting on chromosome 4 cannot be excluded.

Karyotype–phenotype analysis and molecular delineation of a 3p26 deletion/8q24.3 duplication case with a virtually normal phenotype and mild cognitive deficit

The terminal ends of most human chromosomes are G-band negative and are usually gene-rich, containing a higher than average density of genes [Niimura and Gojobori, 2002]. Microscopically discernible deletions of the terminal band of a chromosome are usually associated with significant clinical abnormality. For example, chromosome 4p deletion (Wolf-Hirschhorn syndrome) and chromosome 5p deletion (cri du chat syndrome) have critical regions in the most distal 4p16 and 5p15 band, respectively [de Grouchy and Turleau, 1984]. Since the terminal band of 3p26 is an exception as it is G-band positive, one can predict that a deletion of 3p26 might be accompaniedbymilder clinical symptoms than those resulting from deletion of the terminal bands of other chromosomes. We report here clinical findings in a boy with concurrent 3p26 deletion and 8q24.3 duplication,whoseonly clinical symptom is deficient cognitive skills. We suggest that his reduced cognitive skills are more likely the result of duplication of genes on terminal 8q, rather than deletion of genes on terminal 3p. Our patient was born at term after an uneventful pregnancy with a birth weight of 3,450 g and a length of 50 cm. His developmental milestones were normal. He sat at 6 months, crawled at 9 months, and walked independently at 14 months. Psychological testing (Stanford Binet Intelligence Scale) at 3 years of age revealed a composite IQ score of 97 (range 91–103). Subsequent developmental assessments, in conjunction with his enrollment in kindergarten, showed a definitive delay in cognitive skills, speech and language skills, and fine motor skills. He was categorized as multiply disabled. His Peabody Picture Vocabulary Test III scores were at the 39th centile at 41⁄2 years and the 35th centile at 51⁄2 years. He scored solidly in the 36–41 months range but had some scattered scores in the 42– 47 months range of the test. He was first seen at the genetics clinic at 51⁄2 years of age. He was quiet, but answered simple questions himself. He had occasional staring spells and absent-mindedness. A seizure disorder was ruled out. He wore glasses for hypermetropia. He was not able to write his own name. His weight and height were between 25th and 50th centile, and head circumference was at the 75th centile. No dysmorphic feature was noted. A year later, the staring spells subsided. He needed extra help in kindergarten and was placed in a special education class in the first grade. A chromosome study was subsequently requested to rule out the possibility of a sex chromosome aberration. He was last seen at 91⁄2 years of age; he remained a friendly and enthusiastic boy, but had become more talkative over the years and stuttering had become apparent. He continued to receive physical, occupational, and speech/language therapies.

Primary Nodal Marginal Zone B-Cell Lymphoma Arising From More Than One Clonal Neoplastic Population

Primary nodal marginal zone B-cell lymphoma is an uncommon monoclonal B-cell lymphoproliferative disorder. We report a case of a 79-year-old woman who presented with generalized lymphadenopathy. Histologic and immunohistochemical examinations of biopsy sections from an axillary lymph node were consistent with nodal marginal zone B-cell lymphoma. Flow cytometry analysis showed 2 distinct clonal B-cell populations expressing lambda or kappa light chain restriction. Subsequently, genomic deoxyribonucleic acid (DNA) isolated from a paraffin-embedded lymph node section was analyzed for the presence of gene rearrangements. Polymerase chain reaction (PCR) analysis of immunoglobulin heavy chain genes revealed 3 rearranged DNA bands, confirming the presence of more than one clonal B-cell population. These immunophenotypic and genotypic findings have not been previously described in association with this type of lymphoma. To our knowledge, this represents the first reported case of biclonal nodal marginal zone B-cell lymphoma.