Cochlear implantation in Bjornstad syndrome: a case series with literature review.

BACKGROUND: To report the presentation, diagnostic process, management and results of cochlear implantation of patients diagnosed with Bjornstad syndrome with profound sensorineural hearing loss (SNHL). CASE PRESENTATION AND MANAGEMENT: A retrospective report of two siblings with Bjornstad syndrome suffering profound SNHL unresponsive to conventional hearing aids treated with bilateral simultaneous cochlear implantation. SETTING: Tertiary-referral center. RESULTS: Cochlear implant surgeries of two siblings (four ears) with profound SNHL and bilateral inner ear anomaly (incomplete partition type 1) were performed without complications. Postoperative audiometric measurements showed a significiant improvement in pure-tone threshold and a word recognition score. In the literature review, no previous case of Bjornstad syndrome treated with cochlear implantation has been reported. CONCLUSIONS: Cochlear implantation is an effective, safe, and ultimate treatment option for Bjornstad syndrome with profound SNHL not responding to hearing aids.

Congenital Hypermetabolism and Uncoupled Oxidative Phosphorylation.

We describe the case of identical twin boys who presented with low body weight despite excessive caloric intake. An evaluation of their fibroblasts showed elevated oxygen consumption and decreased mitochondrial membrane potential. Exome analysis revealed a de novo heterozygous variant in ATP5F1B, which encodes the ß subunit of mitochondrial ATP synthase (also called complex V). In yeast, mutations affecting the same region loosen coupling between the proton motive force and ATP synthesis, resulting in high rates of mitochondrial respiration. Expression of the mutant allele in human cell lines recapitulates this phenotype. These data support an autosomal dominant mitochondrial uncoupling syndrome with hypermetabolism. (Funded by the National Institutes of Health.).

Identification of two novel variants of BCS1L gene in a patient with classical GRACILE syndrome.

BCS1L pathogenic variants cause widely different clinical phenotypes. Disease phenotypes can be as mild as Björnstad syndrome, characterized by pili torti (abnormal flat twisted hair shafts) and sensorineural hearing loss, or as severe as GRACILE syndrome, characterized by growth restriction, aminoaciduria, cholestasis, iron overload, lactic acidosis and early death. BCS1L pathogenic variants are also linked to an undefined complex III deficiency, a heterogeneous condition generally involving renal and hepatic pathologies, hypotonia, and developmental delays. So far, all patients with GRACILE syndrome carry a homozygous p.Ser78Gly variant in BCS1L gene by reviewing articles. A 24-day-old boy presented with typical clinical phenotype of GRACILE syndrome. The Whole Exome Sequencing confirmed that the patient had a missense variant (c.245C > T, p.Ser82Leu) and a small deletion (c.231_232delCA, p. Ser78Cysfs*9) in BCS1L gene inherited from his father and mother separately, he died at 5 months of age. We reported a patient with GRACILE syndrome and identified two novel variants in BCS1L gene. Our study expands the mutational spectrum of BCS1L gene associated with GRACILE syndrome and will be beneficial for genetic diagnosis.

A novel mutation in the ubiquinol-cytochrome c reductase synthesis-like gene associated with complex III deficiency and Björnstad syndrome: A case report.

RATIONALE: The ubiquinol-cytochrome c reductase synthesis-like (BCS1L) gene is located on chromosome 2 (2q35) and encodes an ATPase that is associated with various cellular activities and is embedded in the mitochondrial inner membrane; this ATPase is presumed to facilitate the insertion of the Rieske Fe/S protein into precursors of Complex III (CIII) during the assembly of the respiratory chain. We report the first case of a compound heterozygous mutation in the BCS1L gene in China. PATIENT CONCERNS: A 7-month-old girl presented with a 3-month history of psychomotor developmental retardation and a 1-month history of epilepsy combined with parallel psychomotor developmental deterioration. The clinical manifestations in the patient included psychomotor developmental retardation, infantile spasms, pili torti, tubulopathy, hepatic pathologies and lactic acidosis. DIAGNOSIS: Combined with her clinical presentation, the patient was diagnosed with CIII deficiency and Björnstad syndrome caused by a novel mutation in the BCS1L gene after molecular biological examination. Whole exome sequencing revealed a compound heterozygous mutation with a missense mutation (c.548G > A/p. R183H) inherited from her mother and an insertion mutation (c.1061_1062insCTA/p. G354delinsGY) inherited from her father. INTERVENTIONS: Before admission, the patient had received oral topiramate for 1 month. After admission, additional intravenous arginine hydrochloride was administered for five days in the acute metabolic disorder phase, and persistent cocktail therapy was introduced, including coenzyme Q10 (20 mg/d), carnitine (1 g/d) and vitamins (vitamin B1, vitamin B2, vitamin B6, and vitamin C). OUTCOMES: The spasm seizures were decreased by 50% after 2 weeks of treatment. The blood ammonia, myocardial enzyme and urine glucose levels declined to normal levels. At a 1-month follow-up, the patient improved clinically with a decrease in spasm seizures of 75%, stronger sucking and more voluntary activities. However, she still had mild lactic acidosis and mild hepatic damage. LESSONS: We reported the first patient with CIII deficiency and Björnstad syndrome in China and identified 1 novel mutation (C.1061_1062insCTA and P. G354delinsGY) in the BCS1L gene. This finding expands the BCS1L gene mutation profile and will be beneficial for genetic diagnosis.

Mitochondrial DNA Depletion Syndromes.

Mitochondrial disorders present in a myriad of ways, which causes them to be included in the differential diagnosis for many patients with undiagnosed disease. A subset of mitochondrial disorders are caused by intrinsic defects in the mitochondrial replication machinery, leading to loss of cellular mitochondrial content over time. The diagnosis of mitochondrial disease is complex. Several best-practice guides are available that enable a higher likelihood of detecting a mitochondrial disorder. The application of genomic sequencing and advanced physiologic analysis of the electron transport chain can offer more definitive evidence of mitochondrial dysfunction.

Fasting reveals largely intact systemic lipid mobilization mechanisms in respiratory chain complex III deficient mice.

Mice homozygous for the human GRACILE syndrome mutation (Bcs1lc.A232G) display decreased respiratory chain complex III activity, liver dysfunction, hypoglycemia, rapid loss of white adipose tissue and early death. To assess the underlying mechanism of the lipodystrophy in homozygous mice (Bcs1lp.S78G), these and wild-type control mice were subjected to a short 4-hour fast. The homozygotes had low baseline blood glucose values, but a similar decrease in response to fasting as in wild-type mice, resulting in hypoglycemia in the majority. Despite the already depleted glycogen and increased triacylglycerol content in the mutant livers, the mice responded to fasting by further depletion and increase, respectively. Increased plasma free fatty acids (FAs) upon fasting suggested normal capacity for mobilization of lipids from white adipose tissue into circulation. Strikingly, however, serum glycerol concentration was not increased concomitantly with free FAs, suggesting its rapid uptake into the liver and utilization for fuel or gluconeogenesis in the mutants. The mutant hepatocyte mitochondria were capable of responding to fasting by appropriate morphological changes, as analyzed by electron microscopy, and by increasing respiration. Mutants showed increased hepatic gene expression of major metabolic controllers typically associated with fasting response (Ppargc1a, Fgf21, Cd36) already in the fed state, suggesting a chronic starvation-like metabolic condition. Despite this, the mutant mice responded largely normally to fasting by increasing hepatic respiration and switching to FA utilization, indicating that the mechanisms driving these adaptations are not compromised by the CIII dysfunction. SUMMARY STATEMENT: Bcs1l mutant mice with severe CIII deficiency, energy deprivation and post-weaning lipolysis respond to fasting similarly to wild-type mice, suggesting largely normal systemic lipid mobilization and utilization mechanisms.

Molecular genetic investigations identify new clinical phenotypes associated with BCS1L-related mitochondrial disease.

BCS1L encodes a homolog of the Saccharomyces cerevisiae bcs1 protein, which has a known role in the assembly of Complex III of the mitochondrial respiratory chain. Phenotypes reported in association with pathogenic BCS1L variants include growth retardation, aminoaciduria, cholestasis, iron overload, lactic acidosis and early death (GRACILE syndrome), and Björnstad syndrome, characterized by abnormal flattening and twisting of hair shafts (pili torti) and hearing problems. Here we describe two patients harbouring biallelic variants in BCS1L; the first with a heterozygous variant c.166C>T, p.(Arg56*) together with a novel heterozygous variant c.205C>T, p.(Arg69Cys) and a second patient with a novel homozygous c.325C>T, p.(Arg109Trp) variant. The two patients presented with different phenotypes; the first patient presented as an adult with aminoaciduria, seizures, bilateral sensorineural deafness and learning difficulties. The second patient was an infant who presented with a classical GRACILE syndrome leading to death at 4 months of age. A decrease in BCS1L protein levels was seen in both patients, and biochemical analysis of Complex III revealed normal respiratory chain enzyme activities in the muscle of both patients. A decrease in Complex III assembly was detected in the adult patient's muscle, whilst the paediatric patient displayed a combined mitochondrial respiratory chain defect in cultured fibroblasts. Yeast complementation studies indicate that the two missense variants, c.205C>T, p.(Arg69Cys) and c.325C>T, p.(Arg109Trp), impair the respiratory capacity of the cell. Together, these data support the pathogenicity of the novel BCS1L variants identified in our patients.

Respiratory chain complex III deficiency due to mutated BCS1L: a novel phenotype with encephalomyopathy, partially phenocopied in a Bcs1l mutant mouse model.

BACKGROUND: Mitochondrial diseases due to defective respiratory chain complex III (CIII) are relatively uncommon. The assembly of the eleven-subunit CIII is completed by the insertion of the Rieske iron-sulfur protein, a process for which BCS1L protein is indispensable. Mutations in the BCS1L gene constitute the most common diagnosed cause of CIII deficiency, and the phenotypic spectrum arising from mutations in this gene is wide. RESULTS: A case of CIII deficiency was investigated in depth to assess respiratory chain function and assembly, and brain, skeletal muscle and liver histology. Exome sequencing was performed to search for the causative mutation(s). The patient's platelets and muscle mitochondria showed respiration defects and defective assembly of CIII was detected in fibroblast mitochondria. The patient was compound heterozygous for two novel mutations in BCS1L, c.306A > T and c.399delA. In the cerebral cortex a specific pattern of astrogliosis and widespread loss of microglia was observed. Further analysis showed loss of Kupffer cells in the liver. These changes were not found in infants suffering from GRACILE syndrome, the most severe BCS1L-related disorder causing early postnatal mortality, but were partially corroborated in a knock-in mouse model of BCS1L deficiency. CONCLUSIONS: We describe two novel compound heterozygous mutations in BCS1L causing CIII deficiency. The pathogenicity of one of the mutations was unexpected and points to the importance of combining next generation sequencing with a biochemical approach when investigating these patients. We further show novel manifestations in brain, skeletal muscle and liver, including abnormality in specialized resident macrophages (microglia and Kupffer cells). These novel phenotypes forward our understanding of CIII deficiencies caused by BCS1L mutations.

Novel compound heterozygous mutations in BCS1L gene causing Bjornstad syndrome in two siblings.

Bjornstad syndrome is a rare condition characterized by pili torti and sensorineural hearing loss associated with pathological variations in BCS1L. Mutations in this gene are also associated with the more severe complex III deficiency and GRACILE syndrome. We report the first Italian patients with Bjornstad syndrome, two siblings with pili torti and sensorineural hearing loss, in whom we detected two novel compound heterozygous mutations in BCS1L. A thorough clinical evaluation did not reveal any features consistent with complex III deficiency or GRACILE syndrome.

Morphological analyses in fragility of pili torti with Björnstad syndrome.

Pili torti is an extremely rare hair phenotype characterized by short length of hairs with hair shafts being easily broken. However, the mechanism of fragility in pili torti is unclear. In this study, we examined the underlying morphological features responsible for pili torti formation using transmission electron microscopy (TEM). We used pili torti samples from a patient with Björnstad syndrome and normal hairs from a healthy subject as a comparison. The macroscopic morphological features of the samples agreed with the results of a previous study showing that pili torti is twisted, flattened, thin and with partial trichorrhexis. Young's modulus of the samples was lower than that of normal hairs. Because the cross-sectional area of the pili torti samples was also smaller than that of normal hairs, it was clarified that the tensile strength of pili torti is 2.1-times lower than that of normal hair. Assessment of morphological features by TEM showed that the cuticle layers of the samples had wavy shapes with different thicknesses. Additionally, the cortex in the samples showed loose keratin intermediate filaments (IF). Our results suggested that these abnormalities in pili torti had already occurred below the infundibulum. Thus, the weakness of pili torti in tensile strength is thought to result from loose IF because of dysformation of disulfide bonds.

Could we offer mitochondrial donation or similar assisted reproductive technology to South African patients with mitochondrial DNA disease?

The decision of the UK House of Commons in 2015 to endorse the use of pioneering in vitro fertilisation techniques to protect future generations from the risk of mitochondrial DNA (mtDNA) disease has sparked worldwide controversy and debate. The availability of such technologies could benefit women at risk of transmitting deleterious mutations. MtDNA disease certainly occurs in South Africa (SA) in all population groups. However, diagnostic strategies and practices for identifying individuals who would benefit from technologies such as IVF have in the past been suboptimal in this country. New developments in the molecular diagnostic services available to SA patients, as well as better education of referring clinicians and the implementation of more structured, population-appropriate diagnostic strategies, may open the floor to this debate in SA.

A NEONATE PRESENTING WITH GRACILE SYNDROME AND BJORNSTAD PHENOTYPE ASSOCIATED WITH BCS1L MUTATION.

GRACILE Syndrome, is an autosomal recessive disease presenting with growth retardation, severe lactic acidosis, Fanconi type tubulopathy, cholestasis, iron overload and early death without any dysmorphological or neurological features. The BCSIL gene mutation is responsible for GRACILE syndrome, Bjornstad syndrome and complex III deficiency. Bjomstad syndrome is characterized by sensorineural hearing loss and abnormal flat twisted hair shafts. The case is GRACILE syndrome with Bjomstad phenotype in neonatal period due to BCSL1 gene mutation.

A novel mutation in BCS1L associated with deafness, tubulopathy, growth retardation and microcephaly.

UNLABELLED: We report a novel homozygous missense mutation in the ubiquinol-cytochrome c reductase synthesis-like (BCS1L) gene in two consanguineous Turkish families associated with deafness, Fanconi syndrome (tubulopathy), microcephaly, mental and growth retardation. All three patients presented with transitory metabolic acidosis in the neonatal period and development of persistent renal de Toni-Debré-Fanconi-type tubulopathy, with subsequent rachitis, short stature, microcephaly, sensorineural hearing impairment, mild mental retardation and liver dysfunction. The novel missense mutation c.142A>G (p.M48V) in BCS1L is located at a highly conserved region associated with sorting to the mitochondria. Biochemical analysis revealed an isolated complex III deficiency in skeletal muscle not detected in fibroblasts. Native polyacrylamide gel electrophoresis (PAGE) revealed normal super complex formation, but a shift in mobility of complex III most likely caused by the absence of the BCS1L-mediated insertion of Rieske Fe/S protein into complex III. These findings expand the phenotypic spectrum of BCS1L mutations, highlight the importance of biochemical analysis of different primary affected tissue and underline that neonatal lactic acidosis with multi-organ involvement may resolve after the newborn period with a relatively spared neurological outcome and survival into adulthood. CONCLUSION: Mutation screening for BCS1L should be considered in the differential diagnosis of severe (proximal) tubulopathy in the newborn period. WHAT IS KNOWN: • Mutations in BCS1L cause mitochondrial complex III deficiencies. • Phenotypic presentations of defective BCS1L range from Bjornstad to neonatal GRACILE syndrome. What is New: • Description of a novel homozygous mutation in BCS1L with transient neonatal acidosis and persistent de Toni-Debré-Fanconi-type tubulopathy. • The long survival of patients with phenotypic presentation of severe complex III deficiency is uncommon.

Potential long-term risks associated with maternal aging (the role of the mitochondria).

The mean age at which women create families in Western society is increasing. This is in spite of the fact that reproduction in later life is subject to various difficulties, such as the lower probability of conception in relation to maternal age, the increase in spontaneous pregnancy loss, and higher obstetric risk. In this review of recent data, we suggest that a fourth effect, the decrease in lifespan of children in relation to the age of conception of the mother, can be added to the list. We discuss this effect in relation to the transmission of the mitochondria exclusively through the female germ line and the effect of age on this organelle. Data from our own studies and the animal literature as a whole suggest that this effect could be due to the transmission of damaged mitochondrial DNA, and further indicate that the effect is more widespread than previously considered.

Exome sequencing reveals novel BCS1L mutations in siblings with hearing loss and hypotrichosis.

As a powerful tool to identify the molecular pathogenesis of Mendelian disorders, exome sequencing was used to identify the genetic basis of two siblings with hearing loss and hypotrichosis and clarify the diagnosis. No pathogenic mutations in GJB2, GJB3 and GJB6 genes were found in the siblings. By analysis of exome of the proband, we identified a novel missense (p.R306C) mutation and a nonsense (p.R186*) mutation in the BCS1L gene. Mutations were confirmed by Sanger sequencing. The siblings were compound heterozygotes, and the inheritance mode of autosomal recessive was postulated. BCS1L is the causative gene of Björnstad syndrome, which is characterized by sensorineural hearing loss and pili torti. The longitudinal gutters along the hair shaft were found by scanning electron microscopy in our patient. Therefore the diagnosis of Björnstad syndrome was eventually made for the patients. Our study extends the phenotypic spectrum of Björnstad syndrome and highlights the clinical applicability of exome sequencing as a diagnostic tool for atypical Mendelian disorders.

BCS1L gene mutation causing GRACILE syndrome: case report.

GRACILE syndrome is a rare autosomal recessive disease characterized by fetal growth retardation, Fanconi type aminoaciduria, cholestasis, iron overload, profound lactic acidosis, and early death. It is caused by homozygosity for a missense mutation in the BCS1L gene. The BCS1L gene encodes a chaperone responsible for assembly of respiratory chain complex III. Here we report that a homozygous mutation c.296C > T (p.P99L), in the first exon of BCS1L gene found in an affected 2-month-old boy of asymptomatic consanguineous parents results in GRACILE syndrome. This genotype is associated with a severe clinical presentation. So far no available treatments have changed the fatal course of the disease, and the metabolic disturbance responsible is still not clearly identified. Therefore, providing prenatal diagnosis in families with previous affected infants is of major importance. Mitochondrial disorders are an extremely heterogeneous group of diseases sharing, in common, the fact that they all ultimately impair the function of the mitochondrial respiratory chain. A clinical picture with fetal growth restriction, postnatal lactacidosis, aminoaciduria, hypoglycemia, coagulopathy, elevated liver enzymes, and cholestasis should direct investigations on mitochondrial disorder.