Martin B. Delatycki

Iron-overload-related disease in HFE hereditary hemochromatosis.

BACKGROUND Most persons who are homozygous for C282Y, the HFE allele most commonly asssociated with hereditary hemochromatosis, have elevated levels of serum ferritin and transferrin saturation. Diseases related to iron overload develop in some C282Y homozygotes, but the extent of the risk is controversial. METHODS We assessed HFE mutations in 31,192 persons of northern European descent between the ages of 40 and 69 years who participated in the Melbourne Collaborative Cohort Study and were followed for an average of 12 years. In a random sample of 1438 subjects stratified according to HFE genotype, including all 203 C282Y homozygotes (of whom 108 were women and 95 were men), we obtained clinical and biochemical data, including two sets of iron measurements performed 12 years apart. Disease related to iron overload was defined as documented iron overload and one or more of the following conditions: cirrhosis, liver fibrosis, hepatocellular carcinoma, elevated aminotransferase levels, physician-diagnosed symptomatic hemochromatosis, and arthropathy of the second and third metacarpophalangeal joints. RESULTS The proportion of C282Y homozygotes with documented iron-overload-related disease was 28.4% (95% confidence interval [CI], 18.8 to 40.2) for men and 1.2% (95% CI, 0.03 to 6.5) for women. Only one non-C282Y homozygote (a compound heterozygote) had documented iron-overload-related disease. Male C282Y homozygotes with a serum ferritin level of 1000 mug per liter or more were more likely to report fatigue, use of arthritis medicine, and a history of liver disease than were men who had the wild-type gene. CONCLUSIONS In persons who are homozygous for the C282Y mutation, iron-overload-related disease developed in a substantial proportion of men but in a small proportion of women.

Friedreich ataxia: an overview

Friedreich ataxia, an autosomal recessive neurodegenerative disease, is the most common of the inherited ataxias. The recent discovery of the gene that is mutated in this condition,FRDA, has led to rapid advances in the understanding of the pathogenesis of Friedreich ataxia. About 98% of mutant alleles have an expansion of a GAA trinucleotide repeat in intron 1 of the gene. This leads to reduced levels of the protein, frataxin. There is mounting evidence to suggest that Friedreich ataxia is the result of accumulation of iron in mitochondria leading to excess production of free radicals, which then results in cellular damage and death. Currently there is no known treatment that alters the natural course of the disease. The discovery of theFRDA gene and its possible function has raised hope that rational therapeutic strategies will be developed.

C-terminal truncations in human 3'-5' DNA exonuclease TREX1 cause autosomal dominant retinal vasculopathy with cerebral leukodystrophy

Autosomal dominant retinal vasculopathy with cerebral leukodystrophy is a microvascular endotheliopathy with middle-age onset. In nine families, we identified heterozygous C-terminal frameshift mutations in TREX1, which encodes a 3′-5′ exonuclease. These truncated proteins retain exonuclease activity but lose normal perinuclear localization. These data have implications for the maintenance of vascular integrity in the degenerative cerebral microangiopathies leading to stroke and dementias.

GJA1 mutations, variants, and connexin 43 dysfunction as it relates to the oculodentodigital dysplasia phenotype.

The predominantly autosomal dominant disorder, oculodentodigital dysplasia (ODDD) has high penetrance with intra‐ and interfamilial phenotypic variability. Abnormalities observed in ODDD affect the eye, dentition, and digits of the hands and feet. Patients present with a characteristic facial appearance, narrow nose, and hypoplastic alae nasi. Neurological problems, including dysarthria, neurogenic bladder disturbances, spastic paraparesis, ataxia, anterior tibial muscle weakness, and seizures, are known to occur as well as conductive hearing loss, cardiac defects, and anomalies of the skin, hair, and nails. In 2003, our analysis of 17 ODDD families revealed that each had a different mutation within the human gap junction alpha 1 (GJA1) gene which encodes the protein connexin 43 (Cx43). Since then at least 17 publications have identified an additional 26 GJA1 mutations and in this study, we present 28 new cases with 18 novel GJA1 mutations. We include tables summarizing the 62 known GJA1 nucleotide changes leading to Cx43 protein alterations and the phenotypic information available on 177 affected individuals from 54 genotyped families. Mutations resulting in ODDD occur in each of the nine domains of the Cx43 protein, and we review our functional experiments and those in the literature, examining the effects of 13 different Cx43 mutations upon gap junction activity. Hum Mutat 0, 1–10, 2009.

A novel pericentric inversion of chromosome 3 cosegregates with a developmental-behavioural phenotype

Current advances in genetic knowledge and analysis have facilitated the shift in emphasis from single gene disorders to complex traits such as cancer and atopic disorders where changes in more than one gene usually contribute to the disease phenotype. A challenging area of complex trait research is the determination of the genetic basis of behavioural phenotypes. Early studies in this area focused on classical linkage analysis in pedigrees which segregated the trait of interest and led to the identification of genes for intellectual disability, such as fraX(A).1,2 In this disorder, mutations in a single gene are sufficient to generate the disease phenotype. In contrast, with other neurodevelopmental disorders, results to date have been much more complex. With ADHD, for example, a large number of genes affecting neurotransmitter function, particularly dopamine, have been implicated. However, results from linkage or association studies have not been reliably replicated. Even the most promising gene candidates are implicated in only a small percentage of ADHD cases.3,4 Identification of the genes involved is a challenging task. Firstly, accurate phenotype definition is crucial to successful outcomes in these pooled studies. Secondly, neurodevelopmental disorders such as ADHD are multifactorial, with a number of different genes, likely to be of varying effect and interacting with environmental influences, presumably contributing to the development of the observed phenotypes. We have identified an extended family where the proband, a child with moderate intellectual disability as well as severe conduct disturbance, was found to have a pericentric inversion of chromosome 3. The inversion was found to cosegregate with developmental-behavioural problems in other members of the family. In order to describe the phenotype, a developmental-behavioural paediatrician undertook a standardised clinical evaluation of eight of the juvenile members of the extended family. The findings are presented in this paper. ### Participants The parents/guardians …

Direct evidence that mitochondrial iron accumulation occurs in Friedreich ataxia

Friedreich ataxia (FRDA) is due to mutations in the FRDA gene (FRDA). When the gene homologous to FRDA is knocked out in yeast, there is accumulation of iron in mitochondria and reduced respiratory function. So far, there is only indirect evidence to support the hypothesis that FRDA is due to accumulation of mitochondrial iron leading to increased production of free radicals. We show here that mitochondrial iron is significantly higher in fibroblasts from patients with FRDA than in control fibroblasts. This is the first direct evidence that the findings in yeast are reproducible in cells from patients with FRDA. Ann Neurol 1999;45:673–675

Mutations in PHF6 are associated with Borjeson-Forssman-Lehmann syndrome

Börjeson–Forssman–Lehmann syndrome (BFLS; OMIM 301900) is characterized by moderate to severe mental retardation, epilepsy, hypogonadism, hypometabolism, obesity with marked gynecomastia, swelling of subcutaneous tissue of the face, narrow palpebral fissure and large but not deformed ears. Previously, the gene associated with BFLS was localized to 17 Mb in Xq26–q27 (refs 2–4). We have reduced this interval to roughly 9 Mb containing more than 62 genes. Among these, a novel, widely expressed zinc-finger (plant homeodomain (PHD)-like finger) gene (PHF6) had eight different missense and truncation mutations in seven familial and two sporadic cases of BFLS. Transient transfection studies with PHF6 tagged with green fluorescent protein (GFP) showed diffuse nuclear staining with prominent nucleolar accumulation. Such localization, and the presence of two PHD-like zinc fingers, is suggestive of a role for PHF6 in transcription.

Further molecular and clinical delineation of co-locating 17p13.3 microdeletions and microduplications that show distinctive phenotypes

Background Chromosome 17p13.3 contains extensive repetitive sequences and is a recognised region of genomic instability. Haploinsufficiency of PAFAH1B1 (encoding LIS1) causes either isolated lissencephaly sequence or Miller–Dieker syndrome, depending on the size of the deletion. More recently, both microdeletions and microduplications mapping to the Miller–Dieker syndrome telomeric critical region have been identified and associated with distinct but overlapping phenotypes. Methods Genome-wide microarray screening was performed on 7678 patients referred with unexplained learning difficulties and/or autism, with or without other congenital abnormalities. Eight and five unrelated individuals, respectively, were identified with microdeletions and microduplications in 17p13.3. Results Comparisons with six previously reported microdeletion cases identified a 258 kb critical region, encompassing six genes including CRK (encoding Crk) and YWHAE (encoding 14-3-3ε). Clinical features included growth retardation, facial dysmorphism and developmental delay. Notably, one individual with only subtle facial features and an interstitial deletion involving CRK but not YWHAE suggested that a genomic region spanning 109 kb, encompassing two genes (TUSC5 and YWHAE), is responsible for the main facial dysmorphism phenotype. Only the microduplication phenotype included autism. The microduplication minimal region of overlap for the new and previously reported cases spans 72 kb encompassing a single gene, YWHAE. These genomic rearrangements were not associated with low-copy repeats and are probably due to diverse molecular mechanisms. Conclusions The authors further characterise the 17p13.3 microdeletion and microduplication phenotypic spectrum and describe a smaller critical genomic region allowing identification of candidate genes for the distinctive facial dysmorphism (microdeletions) and autism (microduplications) manifestations.

Clinical and genetic study of Friedreich ataxia in an Australian population

Friedreich ataxia is an autosomal recessive disorder caused by mutations in the FRDA gene that encodes a 210-amino acid protein called frataxin. An expansion of a GAA trinucleotide repeat in intron 1 of the gene is present in more than 95% of mutant alleles. Of the 83 people we studied who have mutations in FRDA, 78 are homozygous for an expanded GAA repeat; the other five patients have an expansion in one allele and a point mutation in the other. Here we present a detailed clinical and genetic study of a subset of 51 patients homozygous for an expansion of the GAA repeat. We found a correlation between the size of the smaller of the two expanded alleles and age at onset, age into wheelchair, scoliosis, impaired vibration sense, and the presence of foot deformity. There was no significant correlation between the size of the smaller allele and cardiomyopathy, diabetes mellitus, loss of proprioception, or bladder symptoms. The larger allele size correlated with bladder symptoms and the presence of foot deformity. The duration of disease is correlated with wheelchair use and the presence of diabetes, scoliosis, bladder symptoms and impaired proprioception, and vibration sense but no other complications studied.

Effects of MECP2 mutation type, location and X-inactivation in modulating Rett syndrome phenotype.

Rett syndrome (RTT) is a clinically defined disorder that describes a subset of patients with mutations in the X‐linked MECP2 gene. However, there is a high degree of variability in the clinical phenotypes produced by mutations in MECP2, even amongst classical RTT patients. In a large‐scale screening project, this variability has been examined by looking at the effects of mutation type, functional domain affected and X‐inactivation. Mutations have been identified in 60% of RTT patients in this study (25% of whom were atypical), including 23 novel mutations and polymorphisms. More mutations were found in classical patients (63%) compared to atypical patients (44%). All of the pathogenic mutations were de novo in patients for whom parent DNA was available for screening. A composite phenotype score was developed, based on the recommendations for reporting clinical features in RTT of an international collaborative group. This score proved useful for summarising phenotypic severity, but did not correlate with mutation type, domain affected or X‐inactivation, probably due to complex interactions between all three. Other correlations suggested that truncating mutations and mutations affecting the methyl‐CpG‐binding domain tend to lead to a more severe phenotype. Skewed X‐inactivation was found in a large proportion (43%) of our patients, particularly in those with truncating mutations and mutations affecting the MBD. It is therefore likely that X‐inactivation does modulate the phenotype in RTT.