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| Intellectual disability - microarray and sequencing v2.1070 | PMPCA | Rebecca Foulger Classified gene: PMPCA as Amber List (moderate evidence) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Intellectual disability - microarray and sequencing v2.1070 | PMPCA | Rebecca Foulger Added comment: Comment on list classification: Updated rating from Grey to Amber. PMPCA was added and rated Green by Konstantinos Varvagiannis. Although there are sufficient (3) literature cases overall, the phenotype is variable across cases: 3 families with a possible Founder variant in PMID:25808372, no ID reported in PMID:26657514, 1 family in PMID:27148589 and 1 individual in PMID:30617178. Therefore rated Amber awaiting further cases. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Intellectual disability - microarray and sequencing v2.1070 | PMPCA | Rebecca Foulger Gene: pmpca has been classified as Amber List (Moderate Evidence). | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Intellectual disability - microarray and sequencing v2.1069 | PMPCA | Rebecca Foulger commented on gene: PMPCA | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Intellectual disability - microarray and sequencing v2.1046 | PMPCB |
Konstantinos Varvagiannis changed review comment from: Biallelic pathogenic PMPCB variants cause, Multiple mitochondrial dysfunctions syndrome 6 (MIM 617954). 5 relevant individuals from 4 unrelated families (in one case consanguineous) have been reported by Vögtle et al. (2018 - PMID: 29576218). Onset of symptoms (eg. hypotonia) often preceded a period of developmental regression/stagnation which was common in all individuals and occurred within the first 2 years of life, usually following febrile illness. In all cases neurological features were severe (lack of ambulation/speech). Seizures were observed in 4 individuals from 3 families, with onset at the age of 11-24m. MRI images demonstrated T2 signal hyperintensities of the basal ganglia with cerebellar and cerebral atrophy in some. Deterioration with early death was reported on three occasions, though some years after symptom onset. Following exclusion of other diagnoses in some cases (eg. aCGH, epilepsy panel), WES identified biallelic PMPCB missense variants, supported by Sanger confirmation and segregation studies. The following variants were reported (NM_004279.2): - c.523C>T (p.Arg175Cys) in trans with c.601G>C (p.Ala201Pro) [Fam A and B] - c.524G>A (p.Arg175His) in trans with c.530T>G (p.Val177Gly) [Fam C] - c.1265T>C (p.Ile422Thr) in homozygous state [Fam D with 2 affected sibs] The gene encodes the catalytic (beta) subunit of the mitochondrial processing protease (MPP) which is responsible for the cleavage/maturation of nuclear-encoded mitochondrial precursor proteins after their import in mitochondria. The alpha subunit is encoded by PMPCA (green rating proposed for this panel). Extensive studies demonstrated (perhaps a better summary provided by OMIM): - Reduced PMPCB protein levels in mitochondria isolated from patient fibroblasts or patient-derived pluripotent stem cells. - Frataxin maturation was impaired with accumulation of the intermediate form and lower amounts of mature FXN, indicating decrease in MPP activity. - Analysis of the homologous Mas1 S. cerevisiae mutants was carried out, with the exception of Ile422Thr (corresponding to Mas1 - Ile398Thr), the introduction of which did not yield viable yiest strains. Homologous mutations led to a temperature-sensitive phenotype with accumulation of immature/unprocessed precursor proteins and decrease of mature/processed forms both in vivo or in organello (following isolation of mitochondria). Under conditions of heat stress, Mas1 mutations decreased biogenesis of Fe-S clusters. - Respiratory chain complexes I-III contain Fe-S clusters. In muscle biopsy from an affected individual, complex II activity was significantly reduced (although this was not the case in fibroblasts or liver biopsy). Dysfunction of mitochondrial and cytosolic Fe-S cluster-dependent enzymes (eg. aconitase) was also shown in muscle tissue. Regression/stagnation with seizures/non-achievement of milestones may justify testing for an ID / epilepsy gene panel. In addition, metabolic studies or mitochondrial respiratory chain complex studies were sometimes non-informative (lactate elevated in 3/5 subjects) or not carried out at all / in relevant tissues (muscle biopsy in 2 individuals, fibroblasts/liver biopsy did not demonstrate reduced complex activity when tested). PMPCB is included in the ID gene panel of Radboudumc, as well as the SysID database. The gene is included in the DD panel of G2P associated with "Neurodegeneration in Early Childhood" (disease confidence : probable). As a result, PMPCB can be considered for inclusion in both epilepsy and ID panels as green (or amber). Sources: Literature, Radboud University Medical Center, Nijmegen; to: Biallelic pathogenic PMPCB variants cause, Multiple mitochondrial dysfunctions syndrome 6 (MIM 617954). 5 relevant individuals from 4 unrelated families (in one case consanguineous) have been reported by Vögtle et al. (2018 - PMID: 29576218). Onset of symptoms (eg. hypotonia) often preceded a period of developmental regression/stagnation which was common in all individuals and occurred within the first 2 years of life, usually following febrile illness. In all cases neurological features were severe (lack of ambulation/speech). Seizures were observed in 4 individuals from 3 families, with onset at the age of 11-24m. MRI images demonstrated T2 signal hyperintensities of the basal ganglia with cerebellar and cerebral atrophy in some. Deterioration with early death was reported on three occasions, though some years after symptom onset. Following exclusion of other diagnoses in some cases (eg. aCGH, epilepsy panel), WES identified biallelic PMPCB missense variants, supported by Sanger confirmation and segregation studies. The following variants were reported (NM_004279.2): - c.523C>T (p.Arg175Cys) in trans with c.601G>C (p.Ala201Pro) [Fam A and B] - c.524G>A (p.Arg175His) in trans with c.530T>G (p.Val177Gly) [Fam C] - c.1265T>C (p.Ile422Thr) in homozygous state [Fam D with 2 affected sibs] The gene encodes the catalytic (beta) subunit of the mitochondrial processing protease (MPP) which is responsible for the cleavage/maturation of nuclear-encoded mitochondrial precursor proteins after their import in mitochondria. The alpha subunit is encoded by PMPCA (green rating proposed for this panel). Extensive studies demonstrated (perhaps a better summary provided by OMIM): - Reduced PMPCB protein levels in mitochondria isolated from patient fibroblasts or patient-derived pluripotent stem cells. - Frataxin maturation was impaired with accumulation of the intermediate form and lower amounts of mature FXN, indicating decrease in MPP activity. - Analysis of the homologous Mas1 S. cerevisiae mutants was carried out, with the exception of Ile422Thr (corresponding to Mas1 - Ile398Thr), the introduction of which did not yield viable yeast strains. Homologous mutations led to a temperature-sensitive phenotype with accumulation of immature/unprocessed precursor proteins and decrease of mature/processed forms both in vivo or in organello (following isolation of mitochondria). Under conditions of heat stress, Mas1 mutations decreased biogenesis of Fe-S clusters. - Respiratory chain complexes I-III contain Fe-S clusters. In muscle biopsy from an affected individual, complex II activity was significantly reduced (although this was not the case in fibroblasts or liver biopsy). Dysfunction of mitochondrial and cytosolic Fe-S cluster-dependent enzymes (eg. aconitase) was also shown in muscle tissue. Regression/stagnation with seizures/non-achievement of milestones may justify testing for an ID / epilepsy gene panel. In addition, metabolic studies or mitochondrial respiratory chain complex studies were sometimes non-informative (lactate elevated in 3/5 subjects) or not carried out at all / in relevant tissues (muscle biopsy in 2 individuals, fibroblasts/liver biopsy did not demonstrate reduced complex activity when tested). PMPCB is included in the ID gene panel of Radboudumc, as well as the SysID database. The gene is included in the DD panel of G2P associated with "Neurodegeneration in Early Childhood" (disease confidence : probable). As a result, PMPCB can be considered for inclusion in both epilepsy and ID panels as green (or amber). Sources: Literature, Radboud University Medical Center, Nijmegen |
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| Intellectual disability - microarray and sequencing v2.1046 | PMPCB |
Konstantinos Varvagiannis gene: PMPCB was added gene: PMPCB was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen Mode of inheritance for gene: PMPCB was set to BIALLELIC, autosomal or pseudoautosomal Phenotypes for gene: PMPCB were set to Multiple mitochondrial dysfunctions syndrome 6, 617954 Penetrance for gene: PMPCB were set to Complete Review for gene: PMPCB was set to GREEN gene: PMPCB was marked as current diagnostic Added comment: Biallelic pathogenic PMPCB variants cause, Multiple mitochondrial dysfunctions syndrome 6 (MIM 617954). 5 relevant individuals from 4 unrelated families (in one case consanguineous) have been reported by Vögtle et al. (2018 - PMID: 29576218). Onset of symptoms (eg. hypotonia) often preceded a period of developmental regression/stagnation which was common in all individuals and occurred within the first 2 years of life, usually following febrile illness. In all cases neurological features were severe (lack of ambulation/speech). Seizures were observed in 4 individuals from 3 families, with onset at the age of 11-24m. MRI images demonstrated T2 signal hyperintensities of the basal ganglia with cerebellar and cerebral atrophy in some. Deterioration with early death was reported on three occasions, though some years after symptom onset. Following exclusion of other diagnoses in some cases (eg. aCGH, epilepsy panel), WES identified biallelic PMPCB missense variants, supported by Sanger confirmation and segregation studies. The following variants were reported (NM_004279.2): - c.523C>T (p.Arg175Cys) in trans with c.601G>C (p.Ala201Pro) [Fam A and B] - c.524G>A (p.Arg175His) in trans with c.530T>G (p.Val177Gly) [Fam C] - c.1265T>C (p.Ile422Thr) in homozygous state [Fam D with 2 affected sibs] The gene encodes the catalytic (beta) subunit of the mitochondrial processing protease (MPP) which is responsible for the cleavage/maturation of nuclear-encoded mitochondrial precursor proteins after their import in mitochondria. The alpha subunit is encoded by PMPCA (green rating proposed for this panel). Extensive studies demonstrated (perhaps a better summary provided by OMIM): - Reduced PMPCB protein levels in mitochondria isolated from patient fibroblasts or patient-derived pluripotent stem cells. - Frataxin maturation was impaired with accumulation of the intermediate form and lower amounts of mature FXN, indicating decrease in MPP activity. - Analysis of the homologous Mas1 S. cerevisiae mutants was carried out, with the exception of Ile422Thr (corresponding to Mas1 - Ile398Thr), the introduction of which did not yield viable yiest strains. Homologous mutations led to a temperature-sensitive phenotype with accumulation of immature/unprocessed precursor proteins and decrease of mature/processed forms both in vivo or in organello (following isolation of mitochondria). Under conditions of heat stress, Mas1 mutations decreased biogenesis of Fe-S clusters. - Respiratory chain complexes I-III contain Fe-S clusters. In muscle biopsy from an affected individual, complex II activity was significantly reduced (although this was not the case in fibroblasts or liver biopsy). Dysfunction of mitochondrial and cytosolic Fe-S cluster-dependent enzymes (eg. aconitase) was also shown in muscle tissue. Regression/stagnation with seizures/non-achievement of milestones may justify testing for an ID / epilepsy gene panel. In addition, metabolic studies or mitochondrial respiratory chain complex studies were sometimes non-informative (lactate elevated in 3/5 subjects) or not carried out at all / in relevant tissues (muscle biopsy in 2 individuals, fibroblasts/liver biopsy did not demonstrate reduced complex activity when tested). PMPCB is included in the ID gene panel of Radboudumc, as well as the SysID database. The gene is included in the DD panel of G2P associated with "Neurodegeneration in Early Childhood" (disease confidence : probable). As a result, PMPCB can be considered for inclusion in both epilepsy and ID panels as green (or amber). Sources: Literature, Radboud University Medical Center, Nijmegen |
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| Intellectual disability - microarray and sequencing v2.1046 | PMPCA |
Konstantinos Varvagiannis gene: PMPCA was added gene: PMPCA was added to Intellectual disability. Sources: Literature,Radboud University Medical Center, Nijmegen Mode of inheritance for gene: PMPCA was set to BIALLELIC, autosomal or pseudoautosomal Publications for gene: PMPCA were set to 25808372; 26657514; 27148589; 30617178 Phenotypes for gene: PMPCA were set to Spinocerebellar ataxia, autosomal recessive 2 (MIM 213200) Penetrance for gene: PMPCA were set to Complete Review for gene: PMPCA was set to GREEN gene: PMPCA was marked as current diagnostic Added comment: Biallelic pathogenic PMPCA variants cause Spinocerebellar ataxia, autosomal recessive 2 (SCAR2 - MIM 213200). More than 20 individuals from several unrelated families have been reported. At least 6 different pathogenic variants have been identified. Loss of PMPCA function is the suggested mechanism. ID is a feature of the disorder. PMPCA encodes the α-subunit of mitochondrial processing peptidase (αMPP), a heterodimeric enzyme responsible for the cleavage of nuclear-encoded mitochondrial precursor proteins after import in the mitochondria (summary by Jobling et al and OMIM). Arguments for involvement of the gene include the highly similar phenotype, segregation studies, expression of the gene in fetal and relevant adult tissues (in brain/cerebellum/cerebellar vermis), lower protein levels demonstrated for some variants, abnormal processing of frataxin (in line with the role of αMPP) demonstrated in most cases, rescue of the maturation defect upon transduction of wt PMPCA cDNA, disruption of REDOX balance in patient cells, etc. Relevant studies are summarized below. PMPCA is included in gene panels for ID offered by several diagnostic laboratories (incl. Radboud UMC, GeneDx, etc) and listed as a confirmed ID gene in SysID. It is not associated with any phenotype in G2P. As a result, this gene can be considered for inclusion in the current panel probably as green (or amber). ---- [1] - Jobling et al. (2015 - PMID: 25808372) described the phenotype of 17 individuals from 4 families, all presenting with non-progressive cerebellar ataxia and the majority with ID of variable severity (15/17 - relevant to the current panel). Individuals from 3 of the families - all of Lebanese origin - were homozygous for NM_015160.3:c.1129G>A (p.Ala377Thr). A further similarly affected subject was compound heterozygous for c.287C>T (p.Ser96Leu) and c.1543G>A (p.Gly515Arg). The homozygous variant in the first family was found within a 2.85 Mb linkage region on chr 9q34. An additional variant within this region (in CAMSAP1) was discarded following results in other families of the same origin. Semi-quantitative RT-PCR demonstrated fetal expression of the PMPCA as well as relatively higher expression in adult brain, cerebellum and cerebellar vermis. As for Ala377Thr, protein levels were shown to be lowest in affected individuals (LCLs, fibroblasts) and low - though somewhat higher - in carrier parents (LCL) compared to controls. RT-PCR on total RNA from LCLs did not show evidence of abnormal transcripts/additional splicing defect. Localization of mutant protein and morphology of mitochondrial reticulum was similar to controls. Maturation of frataxin - the protein depleted in Friedreich ataxia - was shown to be abnormal in patient lymphoblasts, compatible with the role of αMPP. In line with abnormal mitochondrial function, REDOX balance was increased in patient cells. [2] - Choquet et al. (2016 - PMID: 26657514) reported on 2 sibs - born to distantly related parents. The authors noted a phenotype corresponding to SCAR2 although the presentation was somewhat milder, intellectual disability was not a feature (despite some learning difficulties in one) and ataxia was progressive. WES demonstrated homozygosity for NM_015160:c.766G>A (p.Val256Met). Western blot in patient lymphoblasts showed αMPP levels similar to carriers and controls. Abnormal maturation (accumulation of specific isoforms) was shown for frataxin. [3] - Joshi et al. (2016 - PMID: 27148589) described the phenotype of 2 cousins belonging to a large Lebanese pedigree. Presentation in both was compatible with multisystem involvement incl. profound global DD, severe hypotonia, weakness, respiratory insufficiency, blindness suggestive of mitochondrial disorder. mtDNA, analyses of mitochondrial focused nuclear gene panel and aCGH were non-diagnostic. Both subjects were compound heterozygous for NM_015160.3:c.1066G>A (p.Gly356Ser) and c.1129G>A (p.Ala377Thr) following WES, with compatible segregation studies within the family. Western blot revealed PMPCA levels similar to control. Reduction of PMPCA staining and abnormally enlarged mitochondria were observed upon immunofluorescence in patient fibroblasts. Frataxin processing was abnormal. Lentiviral transduction of patient fibroblasts with wt PMPCA cDNA, led to increased PMPCA levels and correction of frataxin processing. [4] - Rubegni et al. (2019 - PMID: 30617178) report on a 7-y.o. boy with global DD, spastic-ataxic gait and 'low IQ'. MRI images were suggestive of cerebellar atrophy with hyperintensity in the striatum. The child was homozygous for c.553C>T / p.Arg185Trp (reference not specified, although the variant would be compatible with NM_015160.3). Sources: Literature, Radboud University Medical Center, Nijmegen |
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