Optic neuropathy in classical methylmalonic acidemia

Background: Classical MMA, caused by methylmalonyl-CoA mutase deficiency, may result in late-onset dysfunction in several organ systems. To date, 10 cases of optic neuropathy have been reported. The prevalence of optic neuropathy in visually asymptomatic patients has not been determined. This study sought to identify overt and subclinical optic neuropathy in a cohort with classical MMA. Methods and Materials: Neuroophthalmic examinations were performed on 21 patients identified with classical MMA, older than 10years. Diagnosis of optic neuropathy was determined by a combination of visual acuity, optic nerve appearance and electrodiagnostic tests. Tabulated data were analyzed for association of variables using SAS software. Significance was set at p < .05. Results: Two-thirds were Saudi nationals and one third, Syrian. Age range was 11-29years. Eleven (52.4%) patients had optic neuropathy. Nine (81.8%) of these were bilateral, seven (57.9% to 63.6%) reported decreased vision and four (33.1% to 36.4%) were asymptomatic. Two patients had catastrophic vision loss, following acute metabolic crises. Sixteen patients had chronic renal impairment while three had renal hypertension. Seventeen patients had short stature and eight, chronic pancreatitis. Methylmalonic acid levels ranged from 82 to 3,324µmol/L (Normal<1µmol/L). There was a significant association between optic neuropathy and female gender (p = .011) and none with age, nationality, renal impairment, pancreatitis or specific genotype. Conclusion: Optic neuropathy was a frequent finding in classical MMA. It was often bilateral and some cases were sub-clinical, lacking visual symptoms. These findings have important management implications. Full ophthalmic evaluations should be performed early and regularly in patients with MMA, even when patients are asymptomatic.

Exome sequencing identifies novel NTRK1 mutations in patients with HSAN-IV phenotype

Hereditary sensory autonomic neuropathy type IV (HSAN-IV) is a rare autosomal recessive disorder that usually begins in infancy and is characterized by anhidrosis, insensitivity to noxious stimuli leading to self-mutilating behavior, and intellectual disability. HSAN-IV is caused by mutations in the neurotrophic tyrosine kinase receptor type 1 gene, NTRK1, encoding the high-affinity receptor of nerve growth factor (NGF) which maps to chromosome 1q21-q22. Patients with HSAN-IV lack all NGF-dependent neurons, the primary afferents and sympathetic postganglionic neurons leading to lack of pain sensation and the presence of anhidrosis, respectively. Herein, we report nine patients from nine unrelated families with HSAN-IV due to various mutations in NTRK1, five of which are novel. These are three missense and two nonsense mutations distributed in various domains of NTRK1 involved in binding of NGF. The affected patients had variable intellectual deficits, and some had delayed diagnosis of HSAN-IV. In addition to being the first report of HSAN-IV from the Arabian Peninsula, this report expands the mutational spectrum of patients with NTRK1 mutations and provides further insights for molecular and clinical diagnosis.

Defining the Phenotype and Assessing Severity in Phosphoglucomutase-1 Deficiency

OBJECTIVE

To define phenotypic groups and identify predictors of disease severity in patients with phosphoglucomutase-1 deficiency (PGM1-CDG).

STUDY DESIGN

We evaluated 27 patients with PGM1-CDG who were divided into 3 phenotypic groups, and group assignment was validated by a scoring system, the Tulane PGM1-CDG Rating Scale (TPCRS). This scale evaluates measurable clinical features of PGM1-CDG. We examined the relationship between genotype, enzyme activity, and TPCRS score by using regression analysis. Associations between the most common clinical features and disease severity were evaluated by principal component analysis.

RESULTS

We found a statistically significant stratification of the TPCRS scores among the phenotypic groups (P < .001). Regression analysis showed that there is no significant correlation between genotype, enzyme activity, and TPCRS score. Principal component analysis identified 5 variables that contributed to 54% variance in the cohort and are predictive of disease severity: congenital malformation, cardiac involvement, endocrine deficiency, myopathy, and growth.

CONCLUSIONS

We established a scoring algorithm to reliably evaluate disease severity in patients with PGM1-CDG on the basis of their clinical history and presentation. We also identified 5 clinical features that are predictors of disease severity; 2 of these features can be evaluated by physical examination, without the need for specific diagnostic testing and thus allow for rapid assessment and initiation of therapy.

Molecular testing of 163 patients with Morquio A (Mucopolysaccharidosis IVA) identifies 39 novel GALNS mutations

Morquio A (Mucopolysaccharidosis IVA; MPS IVA) is an autosomal recessive lysosomal storage disorder caused by partial or total deficiency of the enzyme galactosamine-6-sulfate sulfatase (GALNS; also known as N-acetylgalactosamine-6-sulfate sulfatase) encoded by the GALNS gene. Patients who inherit two mutated GALNS gene alleles have a decreased ability to degrade the glycosaminoglycans (GAGs) keratan sulfate and chondroitin 6-sulfate, thereby causing GAG accumulation within lysosomes and consequently pleiotropic disease. GALNS mutations occur throughout the gene and many mutations are identified only in single patients or families, causing difficulties both in mutation detection and interpretation. In this study, molecular analysis of 163 patients with Morquio A identified 99 unique mutations in the GALNS gene believed to negatively impact GALNS protein function, of which 39 are previously unpublished, together with 26 single-nucleotide polymorphisms. Recommendations for the molecular testing of patients, clear reporting of sequence findings, and interpretation of sequencing data are provided.

Clinical and biochemical features associated with BCS1L mutation

Our study describes a novel phenotype in a series of nine Saudi patients with lactic acidosis, from four consanguineous families three of which are related. Detailed genetic studies including linkage, homozygosity mapping and targeted sequencing identified a causative mutation in the BCS1L gene. All affected members of the families have an identical mutation in this gene, mutations of which are recognized causes of Björnstad syndrome, GRACILE syndrome and a syndrome of neonatal tubulopathy, encephalopathy, and liver failure (MIM 606104) leading to isolated mitochondrial respiratory chain complex III deficiency. Here we report the appearance of a novel behavioral (five patients) and psychiatric (two patients) phenotype associated with a p.Gly129Arg BCS1L mutation, differing from the phenotype in a previously reported singleton patient with this mutation. The psychiatric symptoms emanated after childhood, initially as hypomania later evolving into intermittent psychosis. Neuroradiological findings included subtle white matter abnormalities, whilst muscle histopathology and respiratory chain studies confirmed respiratory chain dysfunction. The variable neuro-psychiatric manifestations and cortical visual dysfunction are most unusual and not reported associated with other BCS1L mutations. This report emphasizes the clinical heterogeneity associated with the mutation in BCS1L gene, even within the same family and we recommend that defects in this gene should be considered in the differential diagnosis of lactic acidosis with variable involvement of different organs.

Phenotypical spectrum of cerebellar ataxia associated with a novel mutation in the CA8 gene, encoding carbonic anhydrase (CA) VIII

We define the neurological characteristics of familial cases from multiple branches of a large consanguineous family with cerebellar ataxia, mental retardation (MR), and dysequilibrium syndrome type 3 caused by a mutation in the recently cloned CA8 gene. The linkage analysis revealed a high logarithm of the odds (LOD) score region on 8q that harbors the CA8 in which a novel homozygous c.484G>A (p.G162R) mutation was identified in all seven affected members. The patients had variable cerebellar ataxia and mild cognitive impairment without quadrupedal gait. The brain MRI showed variable cerebellar volume loss and ill-defined peritrigonal white matter abnormalities. The Fluorodeoxyglucose Positron Emission Tomography (FDG PET) revealed hypometabolic cerebellar hemispheres, temporal lobes, and mesial cortex. This report expands the neurological and radiological phenotype associated with CA8 mutations. CA8 involvement should be considered in the differential diagnosis of other genetically unresolved autosomal recessive cerebellar ataxias.

Identification of mutations causing hereditary tyrosinemia type I in patients of Middle Eastern origin

Hereditary Tyrosinemia Type 1 (HT1) is an autosomal recessive disorder resulting from a deficiency of fumarylacetoacetase caused by mutations in the fumarylacetoacetate hydrolase (FAH) gene. We detected 11 novel and 6 previously described pathogenic mutations in a cohort of 43 patients originating from the Middle East with the acute form HT1. All of the mutations were homozygous and we did not find the presence of a "founder mutation".

GM2 gangliosidosis in Saudi Arabia: multiple mutations and considerations for future carrier screening

The GM2 gangliosidose, Tay-Sachs and Sandhoff diseases, are a class of lysosomal storage diseases in which relentless neurodegeneration results in devastating neurological disability and premature death. Primary prevention is the most effective intervention since no effective therapy is currently available. An extremely successful model for the prevention of GM2 gangliosidosis in the Ashkenazi Jewish community is largely attributable to the very limited number of founder mutations in that population. Consistent with our previous observation of allelic heterogeneity in consanguineous populations, we show here that these diseases are largely caused by private mutations which present a major obstacle in replicating the Ashkenazi success story. Alternative solutions are proposed which can also be implemented for other autosomal recessive diseases in our population.

Novel mutation in GLRB in a large family with hereditary hyperekplexia

Hereditary hyperekplexia (HH) is a disorder of the inhibitory glycinergic neurotransmitter system. Mutations in five genes have been reported to cause the disease. However, only single mutation in GLRB, the gene encoding beta-subunit of the glycine receptor, in a singleton patient with HH has been found to date. In this study, 13 patients with HH were identified through neurology and genetic clinics. Formal clinical examinations, linkage analysis, homozygosity mapping, in-mutation screening of GLRB and in silico functional analyses were carried out. A novel mutation in GLRB among nine patients was identified. This c.596 T>G perturbation results in the change of the highly conserved methionine at position 177 to arginine. Besides the classical HH phenotype, seven patients had esotropia and few of them had behavioral problems. This study presents a large family with HH as a result of homozygous mutation in GLRB and expands the clinical spectrum of HH to include eye misalignment disorder. Moreover, the report of these familial cases supports the previous evidence in a single patient of an autosomal recessive inheritance of HH because of defects in GLRB.

Clinical, biochemical and molecular characterization of peroxisomal diseases in Arabs

Peroxisomes are single membrane-bound cellular organelles that carry out critical metabolic reactions perturbation of which leads to an array of clinical phenotypes known as peroxisomal disorders (PD). In this study, the largest of its kind in the Middle East, we sought to comprehensively characterize these rare disorders at the clinical, biochemical and molecular levels. Over a 2-year period, we have enrolled 17 patients representing 16 Arab families. Zellweger-spectrum phenotype was observed in 12 patients and the remaining 5 had the rhizomelic chondrodysplasia punctata phenotype. We show that homozygosity mapping is a cost-effective strategy that enabled the identification of the underlying genetic defect in 100% of the cases. The pathogenic nature of the mutations identified was confirmed by immunofluorescence and complementation assays. We confirm the genetic heterogeneity of PD in our population, expand the pool of pathogenic alleles and draw some phenotype/genotype correlations.

Medium-chain acyl-CoA dehydrogenase deficiency in Saudi Arabia: incidence, genotype, and preventive implications

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD), caused by mutated ACADM gene, is a potentially fatal fatty acid oxidation defect. Detection of MCADD is now part of tandem mass spectrometry (MS-MS)-based newborn screening programs worldwide. To date, more than 67 mutations have been reported to cause MCADD with a single allele, c.985A>G, being the most common in patients of northwestern European descent. In Saudi Arabia, the Newborn Screening Program, officially launched in 2005, screens for 16 disorders including MCADD. Over a period of 3 years, 237,812 newborns were screened; 13 were identified to have MCADD giving an incidence of 1:18,293. Since the introduction of MS-MS to our institution, however, a total of 30 patients were detected to have MCADD. These cases were either newborns, at high-risk family members, or clinically suspected. The C8-carnitine levels (median 3.31, range 0.81-16.33 µM) were clearly diagnostic in all analyzed samples. Sequencing ACADM in 20 DBS revealed two novel mutations: c.362C>T (p.T121I) and c.347G>A (p.C116Y) substitutions, neither of which were detected in 300 chromosomes from controls. Eighteen (90%) patients were homozygous for the T121I mutation and two (10%) were compound heterozygous (T121I/C116Y). Our molecular data lend further support to MS-MS biochemical screening for MCADD and provide evidence for the relatively high incidence of MCADD in the Arab population. The identification of a founder mutation for MCADD has important implications for the preventive screening programs not only in Saudi Arabia but potentially also in other countries in the region.

Novel mutations underlying argininosuccinic aciduria in Saudi Arabia

Background

Argininosuccinic aciduria (ASAuria) is an autosomal recessive disorder of the urea cycle relatively common in Saudi Arabia as a consequence of extensive consanguinity. It is the most common urea cycle disorder identified in the Saudi population, which therefore prioritizes the need to delineate the underlying molecular defects leading to disease.

Findings

We utilized Whole Genome Amplification (WGA), PCR and direct sequencing to identify mutations underlying ASAuria cases diagnosed by our institution. A missense mutation that accounts for 50% of Saudi ASAuria patients was recently reported by our laboratory. In this study we report a further six novel mutations (and one previously reported) found in Saudi patients with ASAuria. The novel four missense, one nonsense and one splice-site mutation were confirmed by their absence in >300 chromosomes from the normal population. Pathogenicity of the novel splice-site mutation was also confirmed using reverse transcriptase-PCR analysis. Cross species amino acid conservation at the substituted residues described were observed in some but not all instances.

Conclusions

Together, the eight mutations described by our laboratory, encompass >90% of ASAuria patients in Saudi Arabia and add to about 45 other ASAuria mutations reported worldwide.

Novel FBP1 gene mutations in Arab patients with fructose-1,6-bisphosphatase deficiency

Deficiency of fructose-1,6-bisphosphatase (FBP) results in impaired gluconeogenesis, which is characterized by episodes of hyperventilation, apnea, hypoglycemia, and metabolic and lactic acidosis. This autosomal recessive disorder is caused by mutations in the FBP1 gene, which encodes for fructose-1,6-bisphosphatase 1 (FBP1). Although FBP1 gene mutations have been described in FBP-deficient individuals of various ethnicities, there has been limited investigation into the genetics of this disorder in Arab patients. This study employed five consanguineous Arab families, in which 17 patients were clinically diagnosed with FBP deficiency. Seven patients and six carrier parents were analyzed for mutations in the FBP1 gene. DNA sequencing of the FBP1 gene identified two novel mutations in these families. A novel six nucleotide repetitive insertion, c114_119dupCTGCAC, was identified in patients from three families. This mutation encodes for a duplication of two amino acids (p.Cys39_Thr40dup) in the N-terminal domain of FBP1. A novel nonsense c.841G>T mutation encoding for a p.Glu281X truncation in the active site of FBP1 was discovered in patients from two families. The newly identified mutations in the FBP1 gene are predicted to produce FBP1 deficiency. These mutations are the only known genetic causes of FBP deficiency in Arab patients. The p.Cys39_Thr40dup is the first reported amino acid duplication in FBP deficiency patients.

CONCLUSION

This study provides a strong rationale for genetic testing of FBP deficient patients of Arab ethnicity for recurrent or novel mutations in the FBP1 gene.

Zellweger syndrome caused by PEX13 deficiency: report of two novel mutations

Peroxisomal biogenesis disorders represent a group of genetically heterogeneous conditions that have in common failure of proper peroxisomal assembly. Clinically, they are characterized by a spectrum of dysmorphia, neurological, liver, and other organ involvement. To date, mutations in 13 PEX genes encoding peroxins have been identified in patients with peroxisomal biogenesis disorders. Mutations in PEX13, which encodes peroxisomal membrane protein PEX13, are among the least common causes of peroxisomal biogenesis disorders with only three mutations reported so far. Here, we report on two infants whose clinical and biochemical profile was consistent with classical Zellweger syndrome and whose complementation analysis assigned them both to group H of peroxisomal biogenesis disorders. We show that they harbor two novel mutations in PEX13. One patient had a genomic rearrangement resulting in a 147 kb deletion that spans the whole of PEX13, while the other had an out-of-frame deletion of 14 bp. This represents the first report of a PEX13 deletion and suggests that further work is needed to examine the frequency of PEX13 mutations among Arab patients with peroxisomal biogenesis disorders.

Preimplantation genetic diagnosis for Zellweger syndrome

OBJECTIVE

To report on the first live birth of a normal child after performance of preimplantation genetic diagnosis (PGD) for Zellweger syndrome (ZS).

DESIGN

Case report.

SETTING

Tertiary-care hospital.

PATIENT(S)

A family with four children diagnosed with ZS, who were all born at term and who expired around 4 months of age.

INTERVENTION(S)

In vitro fertilization and preimplantation genetic diagnosis.

MAIN OUTCOME MEASURE(S)

Preimplantation genetic diagnosis of ZS in embryos, and live birth from the transferred normal embryos.

RESULT(S)

After PGD, two genotypically normal embryos were transferred back to the mother. Pregnancy ensued, and a healthy baby girl was delivered in week 40 of pregnancy. The baby was confirmed as genotypically wild-type, and free of any sign of ZS.

CONCLUSION(S)

To the best of our knowledge, this is the first successful PGD for ZS caused by mutation in PEX26 gene, with the subsequent delivery of a homozygous normal baby.

Identification of a common novel mutation in Saudi patients with argininosuccinic aciduria

We have identified a common novel mutation (Q354X) in the argininosuccinate lyase (ASL) gene in Saudi patients with argininosuccinic aciduria (ASAuria; McKusick 207900). The two index patients were siblings, had a neonatal onset of the disease and were diagnosed based on the clinical presentation and confirmed by analysis of their dried blood spots (DBS) by tandem mass spectrometry (MS/MS). The ASL gene was then analysed by direct sequencing. A further 28 patients with a confirmed diagnosis of ASAuria based on MS/MS of their DBS were tested by sequencing for the presence of the Q354X mutation. This mutation was found in 14 out of the 28 patients (50%) tested. Our work indicates that the Q354X allele is common, may account for 50% of the abnormal ASL genes in the Saudi population, and is likely to be associated with the neonatal form of the disease. We recommend that all patients diagnosed with ASAuria in Saudi Arabia or of Arab origin be tested for this mutation and for Q116X, which has been described previously. In addition, further analysis is needed to identify other underlying disease mutations for ASAuria in the Saudi population.

The optimum time for tumour imaging with thallium-201

Following the intravenous injection of 75 MBq 201Tl-chloride we have assessed the uptake kinetics in the myocardium and in the primary tumour in 56 patients with lung cancer, 26 with breast cancer and 13 with mediastinal lymphoma. The time of maximal tumour uptake ranged from 8-20 min post-injection and did not differ significantly between lung cancer (mean +/- SD = 11.9 +/- 3.34 min), breast cancer (11.21 +/- 1.88 min) and lymphoma (11.76 +/- 3.25 min). The time of maximum cardiac uptake of 201Tl was 11.61 +/- 3.25 min. There was no significant washout of 201Tl from the tumours in the first hour after injection in the various malignant lesions studied. The time of maximal tumour to background activity was 18.3 +/- 0.59 min for lung cancer, 13.0 +/- 1.16 min for breast cancer and 16.7 +/- 1.04 min for lymphoma. The time course of 201Tl uptake in the tumours suggests that the mechanism of uptake is similar to that in the myocardium. The optimal time of 201Tl tumour imaging is from 20-60 min following injection and did not differ in various tumours studied.