Expanding the clinical and radiological phenotypes of leukoencephalopathy due to biallelic HMBS mutations.

Pathogenic heterozygous variants in HMBS encoding the enzyme hydroxymethylbilane synthase (HMBS), also known as porphobilinogen deaminase, cause acute intermittent porphyria (AIP). Biallelic variants in HMBS have been reported in a small number of children with severe progressive neurological disease and in three adult siblings with a more slowly, progressive neurological disease and distinct leukoencephalopathy. We report three further adult individuals who share a distinct pattern of white matter abnormality on brain MRI in association with biallelic variants in HMBS, two individuals with homozygous variants, and one with compound-heterozygous variants. We present their clinical and radiological features and compare these with the three adult siblings previously described with leukoencephalopathy and biallelic HMBS variants. All six affected individuals presented with slowly progressive spasticity, ataxia, peripheral neuropathy, with or without mild cognitive impairment, and/or ocular disease with onset in childhood or adolescence. Their brain MRIs show mainly confluent signal abnormalities in the periventricular and deep white matter and bilateral thalami. This recognizable pattern of MRI abnormalities is seen in all six adults described here. Biallelic variants in HMBS cause a phenotype that is distinct from AIP. It is not known whether AIP treatments benefit individuals with HMBS-related leukoencephalopathy. One individual reported here had improved neurological function for 12 months following liver transplantation followed by decline and progression of disease.

Characterisation of retinoblastomas without RB1 mutations: genomic, gene expression, and clinical studies.

BACKGROUND: Retinoblastoma is the childhood retinal cancer that defined tumour-suppressor genes. Previous work shows that mutation of both alleles of the RB1 retinoblastoma suppressor gene initiates disease. We aimed to characterise non-familial retinoblastoma tumours with no detectable RB1 mutations. METHODS: Of 1068 unilateral non-familial retinoblastoma tumours, we compared those with no evidence of RB1 mutations (RB1(+/+)) with tumours carrying a mutation in both alleles (RB1(-/-)). We analysed genomic copy number, RB1 gene expression and protein function, retinal gene expression, histological features, and clinical data. FINDINGS: No RB1 mutations (RB1(+/+)) were reported in 29 (2·7%) of 1068 unilateral retinoblastoma tumours. 15 of the 29 RB1(+/+) tumours had high-level MYCN oncogene amplification (28-121 copies; RB1(+/+)MYCN(A)), whereas none of 93 RB1(-/-) primary tumours tested showed MYCN amplification (p<0·0001). RB1(+/+)MYCN(A) tumours expressed functional RB1 protein, had fewer overall genomic copy-number changes in genes characteristic of retinoblastoma than did RB1(-/-) tumours, and showed distinct aggressive histological features. MYCN amplification was the sole copy-number change in one RB1(+/+)MYCN(A) retinoblastoma. One additional MYCN(A) tumour was discovered after the initial frequencies were determined, and this is included in further analyses. Median age at diagnosis of the 17 children with RB1(+/+)MYCN(A) tumours was 4·5 months (IQR 3·5-10), compared with 24 months (15-37) for 79 children with non-familial unilateral RB1(-/-) retinoblastoma. INTERPRETATION: Amplification of the MYCN oncogene might initiate retinoblastoma in the presence of non-mutated RB1 genes. These unilateral RB1(+/+)MYCN(A) retinoblastomas are characterised by distinct histological features, only a few of the genomic copy-number changes that are characteristic of retinoblastoma, and very early age of diagnosis. FUNDING: National Cancer Institute-National Institutes of Health, Canadian Institutes of Health Research, German Research Foundation, Canadian Retinoblastoma Society, Hyland Foundation, Toronto Netralaya and Doctors Lions Clubs, Ontario Ministry of Health and Long Term Care, UK-Essen, and Foundations Avanti-STR and KiKa.

Trilateral retinoblastoma in a patient with Peutz-Jeghers syndrome.

Germline loss of function mutations in tumor suppressor genes RB1 and LKB1/STK11 are associated with the autosomal dominant cancer predisposing syndromes familial retinoblastoma and Peutz-Jeghers syndrome (PJS), respectively. We present a rare case of a young woman with trilateral retinoblastoma diagnosed as an infant who survived and was then diagnosed with PJS as a teenager. There was no family history of either disorder. Analysis of the LKB1/STK11 gene sequence identified a germline frameshift mutation (c.107del) leading to a nonsense mutation near the N-terminus of the protein, confirming a clinical diagnosis of Peutz-Jeghers syndrome. Extensive RB1 gene analysis failed to detect germline mutations or deletions, and immunohistochemical analysis of her ocular tumors demonstrated nuclear staining of immunoreactive pRB. This result suggests that the RB1 gene is intact. We estimate the chance of trilateral retinoblastoma and PJS occurring in the same individual at approximately 1 in 134 billion live births, and we discuss the possibility that this case could be explained by a putative modifier of pRB action that is associated with the LKB1/STK11 pathway.

Role of genetic testing in retinoblastoma management at a tertiary referral centre.

BACKGROUND: Retinoblastoma (MIM +180 200) is a malignant neoplasm affecting embryonal retina, associated with mutations in the RB1 gene. This paper investigates the results of RB1 testing in retinoblastoma management in a tertiary referral centre. METHODS: A retrospective audit of genetic testing for retinoblastoma from 2003 to 2008, to determine epidemiology, rate of mutation detection and spectrum was undertaken. Eligible probands were identified from the department database and hospital records examined. DNA extracted from tumour tissue and/or peripheral blood was analysed. All patients and families underwent genetic counselling. RESULTS: Twenty patients, including one family, were identified. Eight had bilateral tumours, of whom seven presented before 2 years of age, whereas 10 of 12 unilateral cases presented after 2 years of age. Ten patients (50%) were European, four Maori (20%), three Pacific (15%), two Asian (10%), and one of mixed ancestry (5%). Genetic analysis achieved mutation detection on all affected alleles of all the patients, with tumour tissue available for testing in 19 cases. Ten (40%) had germline mutations (eight bilateral and two unilateral), including one mosaic. 75% of affected Maori had germline mutations compared with 40% Europeans. A wide range of mutations was detected with one novel mutation identified in a familial case. CONCLUSION: Advances in gene testing have enabled a high rate of mutation detection, particularly when tumour tissue is genotyped. Genetic analysis is integral to the management of retinoblastoma patients allowing enhanced follow-up care, avoidance of unnecessary examinations, family screening, counselling and reproductive planning, with early tumour detection in predisposed individuals.

A case of hereditary coproporphyria with posterior reversible encephalopathy and novel coproporphyrinogen oxidase gene mutation c.863T>G (p.Leu288Trp).

A 21-year-old female had recurrent presentations to the emergency department with myalgia, vomiting, abdominal pain and subsequently developed generalized seizures. She was volume depleted with a plasma sodium of 125 mmol/L (reference interval: 135-145) and she had fluctuating hypertension. Acute porphyria was suspected and confirmed with raised urine porphobilinogen/creatinine ratio of 12:4 µmol/mmoL (reference interval < 1:5) and she was treated with intravenous haem arginate. Urinary porphyrin/creatinine ratio was 673 nmol/mmoL (reference interval <35) and faecal porphyrins 2430 µmol/kg dry weight (reference interval: <200) were markedly elevated, with raised faecal CIII:CI ratio, consistent with acute coproporphyria. Diagnosis was confirmed by the demonstration of a novel missense variant in the coproporphyrinogen oxidase gene c.863T > G (p.Leu288Trp) predicted to be deleterious and which segregated with three other affected family members. Although CT head was normal, magnetic resonance imaging scan revealed symmetrical signal abnormalities and swelling in the parietal and occipital lobes consistent with posterior reversible encephalopathy. Over several days, her seizures ceased and sodium and blood pressure normalized. The aetiology of the acute porphyric attack was likely multifactorial with contributions from a recent viral illness and caloric deprivation. No drug precipitant was identified. We postulate that untreated hypertension played a key role in the development of posterior reversible encephalopathy. Early clinical suspicion and urine porphobilinogen testing are the key components in preventing morbidity and mortality in acute porphyrias.

Improved clinical management of retinoblastoma through gene testing.

AIMS: To investigate the relative benefits of retinoblastoma gene testing over conventional ophthalmological screening methods in a New Zealand setting, and to determine the importance of tumour material in resolving germline status. METHODS: Three cases of gene testing are described to illustrate the clinical advantages over conventional ophthalmological screening. To determine the role of tumour material in resolving germline status, 24 New Zealand families were tested, of which tumour material was available for eight. RESULTS: In the three cases reported, we found genetic testing of the RB1 gene resulted in clinically significant benefits and cost savings. When fresh tumour was available for high molecular weight DNA extraction, germline status was resolved in 8/8 (100%) cases. In these cases tumour mutations were not present in the corresponding peripheral blood DNA, indicating that the tumours were sporadic. In the absence of tumour DNA, mutations were identified in only 8/13 (62%) heritable cases. Germline status remains unresolved in all of the three cases of unilateral tumour without a family history or tumour DNA. CONCLUSIONS: Our experience indicates that retinoblastoma gene testing has significant benefits to the affected individuals and their families in New Zealand. Moreover, DNA extracted from fresh tumour allows retinoblastoma germline status in most cases to be defined. Without rumour material, the germline status of potentially sporadic cases will remain undetermined since the absence of detectable RB1 coding region mutations does not exclude all possible mutations in the RB1 gene, which is too large for DNA analysis. A lack of conclusive results will mean that infants will be subjected to the unnecessary inconvenience of surveillance under general anaesthesia.

Three families with Perry syndrome from distinct parts of the world.

OBJECTIVES: Perry syndrome consists of autosomal dominant Parkinsonism, depression, weight loss, and central hypoventilation. Eight mutations in 16 families have been reported: p.F52L, p.G67D, p.G71R, p.G71E, p.G71A, p.T72P, p.Q74P, and p.Y78C located in exon 2 of the dynactin 1 (DCTN1) gene on chromosome 2p13.1. METHODS: Genealogical, clinical, genetic, and functional studies were performed in three kindreds from New Zealand, the United States, and Colombia. A diaphragmatic pacemaker was implanted in the proband from the Colombian family to treat her respiratory insufficiency. Dopaminergic therapy was initiated in probands from two families. RESULTS: Besides the probands, 17 symptomatic relatives from all families were identified. The cardinal signs of Perry syndrome were present in all three probands with symptomatic disease onset in their fifth or sixth decade of life. Parkinsonism was moderate with a partial response to dopaminergic treatment. All affected persons but two died of respiratory insufficiency. The proband from the Colombian family is alive most likely due to early diagnosis and implantation of a diaphragmatic pacemaker. Two-and-a-half-year follow-up examination has revealed that the diaphragmatic pacemaker is optimally functioning without any major complications. In the Colombian and US families, the DCTN1 p.G71R and in the New Zealand family the DCTN1 p.Y78C mutations were identified. In functional assays, both mutations altered microtubule binding consistent with a pathogenic role. CONCLUSIONS: Perry syndrome is a rare condition, but new cases are expected to be diagnosed worldwide. Early diagnosis prevents life-threatening acute respiratory failure. Diaphragmatic pacemakers should be considered as an effective symptomatic treatment option.

Four cases of autosomal dominant hypocalcaemia with hypercalciuria including two with novel mutations in the calcium-sensing receptor gene.

We present four cases with clinical and biochemical hypocalcaemia and evidence supportive of hypoparathyroidism. One case had been previously ascribed a diagnosis of idiopathic hypoparathyroidism. Following the detection of relative hypercalciuria, all cases were found to have autosomal dominant hypocalcaemia with hypercalciuria and mutations of the calcium-sensing receptor gene, of which two were novel. Increased awareness of this condition and access to genotyping enables prompt accurate diagnosis and cascade screening of first-degree relatives.

Spectrum of MECP2 mutations in New Zealand Rett syndrome patients.

BACKGROUND: Classical Rett syndrome is a severe neurodevelopmental X-linked dominant disorder affecting 1/15,000 girls worldwide. MECP2 has been identified as the predominant gene associated with Rett syndrome. Approximately 65-85% of patients with classical Rett syndrome have identifiable MECP2 mutations. In comparison, up to 57% of patients with atypical Rett have mutations in the MECP2 gene. OBJECTIVES: To investigate the spectrum and frequency of MECP2 mutations in New Zealand Rett syndrome patients and evaluate whether available clinical criteria were sufficient to direct molecular testing for Rett syndrome. PATIENTS: and Methods MECP2 coding regions were analysed by direct automated DNA sequencing and multiplex ligation dependent probe assay (MLPA) in samples from 74 patients referred for investigation of possible Rett syndrome. Necessary clinical criteria were examined in detail in 18 patients, with 7/18 having identifiable MECP2 mutations. RESULTS: Fifteen patients (20%) carried MECP2 mutations, four of which were novel (one insertion mutation, one complex rearrangement and two deletions). Eleven previously described disease-causing sequence changes and several known polymorphisms were also detected. Ninety per cent of the observed point mutations were cytosine to thymidine (C to T) transitions at a CpG dinucleotide. Only three patients with MECP2 mutations displayed all major clinical criteria associated with Rett syndrome, four were atypical cases. Of the patients not having an identified MECP2 mutation, 8 out of 11 had clinical criteria consistent with variant Rett syndrome and one of these had a balanced translocation involving chromosomes 2p25 and 6p11-12. CONCLUSIONS: This is the first genetic study of Rett syndrome in New Zealand patients describing the MECP2 mutational spectrum. The relatively low observed frequency of MECP2 mutations reflects a wide spectrum of mental disability disorders. In some cases there were insufficient clinical criteria to justify referral for Rett gene testing.