MITOCHONDRIAL DISORDERS GUIDE 1

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IntroductionMitochondrial disorders are a group of related, clinically diverse, genetic diseases with a prevalence of 1/5,000 to 1/8,500 that result from dysfunction of the mitochondrial respiratory chain.1 They can be caused by defects in either the mitochondrial DNA (mtDNA) or in nuclear genes. The heterogeneous clinical features and genetic causes make diagnosing mitochondrial disorders challenging. An accurate diagnosis is important for patient management and genetic counseling.

Clinical PresentationMitochondrial disorders may affect a single organ, but many involve multiple organ systems, particularly those that are highly dependent on aerobic metabolism, such as the brain, skeletal muscle, heart, kidney, and endocrine system (Figure 1). Patients may present at any age; however, nuclear DNA mutations generally present in childhood and mtDNA mutations are more likely to present in late childhood or in adults. Some affected individuals exhibit clinical features that fall into discrete clinical syndromes, such as Leber’s Hereditary Optic Neuropathy (LHON) and Kearns-Sayre syndrome (KSS) (Table 1). However, often the clinical features are highly variable and non-specific and many affected persons do not fit into one particular category. Similar clinical features can be caused by different mutations in mtDNA or mutations in many different nuclear genes. Common features of mitochondrial disease may include:1-4

Common Symptoms of Mitochondrial Disorders

• Ataxia

• Cardiomyopathy

• Chorea

• Chronic diarrhea or constipation

• Delayed gastric emptying

• Dementia

• Developmental delay /Intellectual disability

• Diabetes mellitus

• Exercise intolerance

• Failure to thrive

• Gastrointestinal reflux

• Hypotonia

• Liver failure

• Migraines

• Muscle weakness

• Optic atrophy

• Pigmentary retinopathy

• Progressive external ophthalmoplegia

• Ptosis

• Recurrent vomiting

• Seizures

• Sensorineural deafness

• Spasticity

• Stroke-like episodes

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Disorder Primary symptoms

CPEO Eye muscle paralysis, droopy eyelids (both eyes)

NARPLate childhood- or adult-onset peripheral neuropathy, lack of muscular coordination, pigmentary retinopathy

MELASStroke-like episodes at younger than 40, seizures, dementia, lactic acidosis and/or ragged red fibers

MEMSA Myopathy, seizures, cerebellar ataxia

MERRFMuscle twitching, seizures, cerebellar ataxia, myopathy

LHON Subacute bilateral painless visual failure

Leigh Syndrome (LS)

Onset in first year, psychomotor regression, respiratory failure, failure to thrive, hypotonia

Table 1. Clinical syndromes of mitochondrial diseases (adapted from Chinnery, PF. 2010)

CPEO, chronic progressive external opthalmoplegia; NARP, neurologic weakness with ataxia and retinitis pigmentosa; MELAS, mitochondria encephalopathy with lactic acidosis and stroke-like episodes; MEMSA, myoclonic epilepsy myopathy sensory ataxia; MERRF, myoclonic epilepsy with ragged red fibers; LHON, Leber's Hereditary Optic Neuropathy

HeartConduction disorder

Wolff-Parkinson-Whitesyndrome

Cardiomyopathy

Skeletal muscleWeakness

FatigueMyopathy

Neuropathy

Inner earSensorineuralhearing loss

BloodPearson’s syndrome

PancreasDiabetes mellitus

KidneyFanconi’s syndrome

Glomerulopathy

LiverHepatopathy

BrainSeizures

MyoclonusAtaxiaStroke

DementiaMigraine

ColonPseudo-obstruction

Mitochondrial DNA

Nuclear DNA

EyeOptic neuropathyOphthalmoplegia

Retinopathy

Nuclear DNA

Subunits

Oxidativephospho-rylation

ATP

Figure 1. Symptoms of Mitochondrial Disorders

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MITOCHONDRIAL DISORDERS GUIDE 3

DiagnosisDiagnosing patients with mitochondrial disorders is challenging due to the varied clinical presentation, genetic heterogeneity, and frequent need for invasive testing procedures. The diagnosis is typically considered in patients with progressive disorders involving multiple organ systems and is sometimes obvious if the patient exhibits one of the “classic” syndromes with stereotypical features such as MELAS, MERRF, LHON, NARP, or KSS. If the diagnosis is not obvious, the following studies can be used to help guide the diagnostic process:

• Family history: especially if a maternal inheritance pattern is present.

• Neuroimaging studies: CT and MRI.

• Functional studies: brain stem dysfunction, abnormal BAERS/VERS/EEG, increased signal in the basal ganglia, delayed myelination, white matter abnormalities, cerebellar atrophy and lactate elevation on magnetic resonance spectroscopy (MRS).

• Laboratory investigations: lactate, pyruvate, lactate/pyruvate ratio, alanine, acylcarnitine profile and urine organic acids.*

• Muscle, liver and/or heart biopsy: assay of electron transport chain activity, light microscopy, and electron microscopy.*

• Genetic testing

*Biochemical test results for mitochondrial disorders may not be reliable or reproducible, and rarely can the underlying etiology be determined without molecular studies. Molecular genetic testing is required to make a definitive diagnosis, provide guidance on management and prognosis, and permit accurate risk counseling. For mitochondrial disorders that result from mutations in nuclear genes, molecular genetic testing can also facilitate prenatal diagnosis.

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Genetic HeterogeneityThe inheritance pattern can be autosomal dominant, autosomal recessive, X-linked or maternal. Similar clinical features can be caused by mitochondrial (mtDNA) variants or nuclear gene variants (genetic heterogeneity), and conversely, a variant in a single nuclear or mitochondrial gene may be associated with different clinical features (clinical heterogeneity). Symptoms may present at any age; however, individuals with nuclear DNA variants generally present in childhood and those with mtDNA variants generally present in late childhood or in adults.

Approximately 1,500 nuclear genes and the mitochondrial genome are involved in maintaining proper mitochondrial respiratory chain function. Each mitochondrion has multiple copies of mtDNA and there are hundreds to thousands of mitochondria per cell, dependent on the cell type. The mtDNA encodes for ribosomal RNAs (two genes), transfer RNAs (22 genes), and 13 proteins that are part of the respiratory chain. The other genes required for mitochondrial function are encoded in the nuclear genome (Figure 2).

MtDNA variants can arise de novo (has arisen new in that individual and was not inherited from the mother) or are maternally inherited. In most cases, mtDNA point variants are inherited, whereas large deletions arise de novo.

Usually, mtDNA pathogenic variants affect only a fraction of the mitochondria; the coexistence of normal and pathogenic mtDNA is called heteroplasmy. When the percentage of pathogenic mtDNA reaches a certain threshold, which varies by tissue type, age, and specific variant, the function of that tissue may become impaired. The pathogenic load varies within and between tissues, and the manifestation of mitochondrial disease reflects tissue-specific pathogenic load. However, access to the relevant tissues for testing is not always possible.

MITOCHONDRIAL DISORDERS GUIDE 5

The mitochondrial genome and mitochondrial respiratory chain (RC), showing nDNA-encoded subunits (blue) and mtDNA-encoded subunits (colors corresponding to the genes in the mitochondrial genome above).

Complex IComplex IIIComplex IVComplex VTransfer RNARibosomal RNAControl region of DNA

125rRNA Cyt b

COXI

COXIICOXIII

ATPase6

165rRNA

ND1

ND2

ATPase8

ND6

ND5

ND4

ND4LND

3

ND1 ND2ND3ND4

ND6ND5 ND4L

COX ICOX IICyt b

COX III A6

A8

CoQ

Cyt c

Succinate

Complex I

mtDNA-encoded subunits 7 0 1 3 2

nDNA-encoded subunits ~39 4 10 10 ~16

Complex II Complex III Complex IV Complex V/ATPsynthase

Matrix

IMM

IMS

FumarateO2 H2O

ADP ATP

Figure 2. Mitochondrial genome and respiratory chain

Due to the bottle neck effect, the inheritance of mitochondrial DNA disorders within families is difficult to predict: A mother can pass on a small proportion of pathogenic mtDNA, or a very high proportion. In certain tissues, like blood, there may be selection against some of these variants, so that cells with normal mtDNA are selectively retained. Therefore, results of genetic testing from the blood may not accurately reflect the heteroplasmy in the relevant tissue(s).

Pathogenic variants in mtDNA may only be identified in specific tissues, particularly those with a lower rate of cell division, such as skeletal muscle, heart, and brain.

Disorders that arise from nuclear gene variants that affect mitochondrial function may be inherited in an autosomal dominant, autosomal recessive, or X-linked manner, and genetic testing from blood samples accurately reflects the genetic defect in all tissues.

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MITOCHONDRIAL DISORDERS GUIDE 7

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Clinical Indications

1. Diagnostic testing in an individual with a mitochondrial disorder

a. Confirm a clinical diagnosis of a specific genetic syndrome or type of mitochondrial disorder

b. Provide information about prognosis

2. Assistance with selection of optimal treatment options

3. Predictive testing for asymptomatic family members of a proband with a known pathogenic variant associated with a genetic form of mitochondrial disease

a. Enable clinical monitoring, follow-up, and optimal treatment when symptoms develop in an individual with a positive result

b. Reduce anxiety and forego clinical monitoring if result is negative

4. Prenatal diagnosis in at-risk pregnancies for known, pathogenic variants in nuclear genes

5. Genetic counseling, recurrence risk determination, and family planning

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Test Name Genes / Mutations Included TAT

MitoXpanded Panel (~1800 Genes)

~1800 genes please see website for a full gene list 6 weeks

Combined Mito Genome Plus Mito Nuclear Genes (319 Genes)

Full mitochondrial genome plus AARS, AARS2, ABCB11, ABCB4, ABCB7, ABCD4, ACAD9, ACADM, ACADVL, ACO2, ACSF3, ADCK3 (CABC1; COQ8), ADCK4, AFG3L2, AGK, AGL, AIFM1, ALAS2, ALDOA, ALDOB, ALG1, ALG11, ALG13, ALG2, ALG3, ALG6, ALG9, AMACR, APOPT1, APTX, ARG1, ASL, ASS1, ATP5A1, ATP5E, ATP7B, ATP8B1, ATPAF2 (ATP12), AUH, B4GALT1, BCKDHA, BCKDHB, BCS1L, BOLA3, C10ORF2, C12ORF65, C19ORF12, CA5A, CARS2, CHKB, CISD2, CLPB, COA5 (C2ORF64), COA6, COASY, COG4, COG5, COG6, COG7, COG8, COQ2, COQ4, COQ6, COQ9, COX10, COX14 (C12ORF62), COX15, COX20 (FAM36A), COX4I2, COX6A1, COX6B1, COX7B, CPS1, CPT1A, CPT2, CYC1, DARS, DARS2, DBT, DDHD1, DDHD2, DDOST, DGUOK, DLAT, DLD, DMGDH, DNA2, DNAJC19, DNM1L, DNM2 , DOLK, DPAGT1, DPM1, DPM3, EARS2, ECHS1, ELAC2, ENO3, ETFA, ETFB, ETFDH, ETHE1, FAH, FARS2, FASTKD2, FBP1, FBXL4, FDX1L, FH, FLAD1, FOXRED1, G6PC, GAA, GAMT, GARS, GATM, GBE1, GCDH, GFER, GFM1 (EFG1), GFM2, GLRX5, GMPPA, GSS, GTPBP3, GYG1, GYG2, GYS1, GYS2, HADHA, HADHB, HARS2, HCFC1, HIBCH, HLCS, HMGCL, HMGCS2, HSD17B10, HSPD1, IARS2, IBA57, ISCA2, ISCU, IVD, LAMP2, LARS, LARS2, LDHA, LIAS, LIPT1, LMBRD1, LRPPRC, LYRM4, LYRM7, MARS, MARS2, MCCC1, MCCC2, MCEE, MFF, MFN2, MGAT2, MGME1, MICU1, MLYCD, MMAA, MMAB, MMACHC, MMADHC (C2ORF25) , MOGS, MPC1 (BRP44L), MPDU1, MPI, MPV17, MRPL12, MRPL3, MRPL44, MRPS16, MRPS22, MRPS7, MTFMT, MTO1, MTPAP, MTR, MTRR, MUT, NADK2, NAGS, NARS2, NDUFA1, NDUFA10, NDUFA11, NDUFA12, NDUFA2, NDUFA4, NDUFA9, NDUFAF1, NDUFAF2, NDUFAF3 (C3ORF60), NDUFAF4 (C6ORF66), NDUFAF5, NDUFAF6, NDUFAF7 (C2ORF56), NDUFB3, NDUFB9, NDUFS1, NDUFS2, NDUFS3, NDUFS4, NDUFS6, NDUFS7, NDUFS8, NDUFV1, NDUFV2, NFS1, NFU1, NGLY1, NR2F1, NUBPL, OPA1, OPA3, OTC, PARS2, PC, PCCA, PCCB, PDHA1, PDHB, PDHX, PDP1, PDSS1, PDSS2, PET100, PFKM, PGAM2, PGM1, PHKA1, PHKA2, PHKB, PHKG2, PMM2, PNPT1, POLG, POLG2, PRKAG2, PRPS1, PTRH2, PUS1, PYGM, QARS, RANBP2, RARS, RARS2, REEP1 (C2ORF23), RFT1, RMND1, RRM2B, SARS2, SCO1, SCO2, SDHA, SDHAF1, SERAC1, SFXN4, SLC19A2, SLC19A3, SLC22A5, SLC25A1, SLC25A13, SLC25A15, SLC25A19, SLC25A20, SLC25A22, SLC25A3 (PHC), SLC25A38, SLC25A4, SLC2A2, SLC35A1, SLC35A2, SLC35C1, SLC37A4, SLC6A8, SLC7A7, SPAST, SPG7, SPTLC1, SRD5A3, SSR4, STT3A, STT3B, STXBP1, SUCLA2, SUCLG1, SURF1, TACO1, TARS2, TAZ, TIMM8A, TK2, TMEM126A, TMEM165, TMEM70, TPK1, TRIT1, TRMU, TRNT1, TSFM, TTC19, TUFM, TYMP, UQCC2 , UQCC3, UQCRB, UQCRC2, UQCRQ, VARS2, WDR45, WFS1, YARS

6 weeks

XomeDxPlus Exome sequencing (ES) plus mitochondrial genome sequencing and deletion testing

8 weeks

Test Name Genes / Mutations Included TAT

Next-Generation Sequence Analysis and Deletion Testing of the Mitochondrial Genome

Full mitochondrial genome (including non-specific phenotypes, and MELAS, MERRF, NARP, LHON, MIDD, MICM, LS, KSS, CPEO, Pearson syndrome etc.)

4 weeks

65 Confirmed Disease-Causing mtDNA Point Mutations and Deletion Testing

65 confirmed disease-causing mtDNA point mutations (see list in Test Info Sheet) and large scale deletion analysis of the mitochondrial genome (including LHON [20 mutations], MELAS [16 mutations], LS/NARP [22 mutations], MIHL/MIDM [10 mutations)] MERRF [6 mutations], KSS, CPEO, Pearson syndrome, etc.)

3-4 weeks

Deletion/Duplication Testing of the Mitochondrial Genome

Large scale deletion/duplication analysis of the mitochondrial genome 3-4 weeks

Testing of the Mitochondrial Genome (mtDNA)

Testing of the Mitochondrial Genome and Nuclear Genes

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Testing Options

MITOCHONDRIAL DISORDERS GUIDE 9

Test Name Genes / Mutations Included TAT

Comprehensive Mitochondrial Nuclear Gene Panel(319 Genes)

AARS, AARS2, ABCB11, ABCB4, ABCB7, ABCD4, ACAD9, ACADM, ACADVL, ACO2, ACSF3, ADCK3 (CABC1; COQ8), ADCK4, AFG3L2, AGK, AGL, AIFM1, ALAS2, ALDOA, ALDOB, ALG1, ALG11, ALG13, ALG2, ALG3, ALG6, ALG9, AMACR, APOPT1, APTX, ARG1, ASL, ASS1, ATP5A1, ATP5E, ATP7B, ATP8B1, ATPAF2 (ATP12), AUH, B4GALT1, BCKDHA, BCKDHB, BCS1L, BOLA3, C10ORF2, C12ORF65, C19ORF12, CA5A, CARS2, CHKB, CISD2, CLPB, COA5 (C2ORF64), COA6, COASY, COG4, COG5, COG6, COG7, COG8, COQ2, COQ4, COQ6, COQ9, COX10, COX14 (C12ORF62), COX15, COX20 (FAM36A), COX4I2, COX6A1, COX6B1, COX7B, CPS1, CPT1A, CPT2, CYC1, DARS, DARS2, DBT, DDHD1, DDHD2, DDOST, DGUOK, DLAT, DLD, DMGDH, DNA2, DNAJC19, DNM1L, DNM2 , DOLK, DPAGT1, DPM1, DPM3, EARS2, ECHS1, ELAC2, ENO3, ETFA, ETFB, ETFDH, ETHE1, FAH, FARS2, FASTKD2, FBP1, FBXL4, FDX1L, FH, FLAD1, FOXRED1, G6PC, GAA, GAMT, GARS, GATM, GBE1, GCDH, GFER, GFM1 (EFG1), GFM2, GLRX5, GMPPA, GSS, GTPBP3, GYG1, GYG2, GYS1, GYS2, HADHA, HADHB, HARS2, HCFC1, HIBCH, HLCS, HMGCL, HMGCS2, HSD17B10, HSPD1, IARS2, IBA57, ISCA2, ISCU, IVD, LAMP2, LARS, LARS2, LDHA, LIAS, LIPT1, LMBRD1, LRP-PRC, LYRM4, LYRM7, MARS, MARS2, MCCC1, MCCC2, MCEE, MFF, MFN2, MGAT2, MGME1, MICU1, MLYCD, MMAA, MMAB, MMACHC, MMADHC (C2ORF25) , MOGS, MPC1 (BRP44L), MPDU1, MPI, MPV17, MRPL12, MRPL3, MRPL44, MRPS16, MRPS22, MRPS7, MTFMT, MTO1, MTPAP, MTR, MTRR, MUT, NADK2, NAGS, NARS2, NDUFA1, NDUFA10, NDUFA11, NDUFA12, NDUFA2, NDUFA4, NDUFA9, NDUFAF1, NDUFAF2, NDUFAF3 (C3ORF60), NDUFAF4 (C6ORF66), NDUFAF5, NDUFAF6, NDUFAF7 (C2ORF56), NDUFB3, NDUFB9, NDUFS1, NDUFS2, NDUFS3, NDUFS4, NDUFS6, NDUFS7, NDUFS8, NDUFV1, NDUFV2, NFS1, NFU1, NGLY1, NR2F1, NUBPL, OPA1, OPA3, OTC, PARS2, PC, PCCA, PCCB, PDHA1, PDHB, PDHX, PDP1, PDSS1, PDSS2, PET100, PFKM, PGAM2, PGM1, PHKA1, PHKA2, PHKB, PHKG2, PMM2, PNPT1, POLG, POLG2, PRKAG2, PRPS1, PTRH2, PUS1, PYGM, QARS, RANBP2, RARS, RARS2, REEP1 (C2ORF23), RFT1, RMND1, RRM2B, SARS2, SCO1, SCO2, SDHA, SDHAF1, SERAC1, SFXN4, SLC19A2, SLC19A3, SLC22A5, SLC25A1, SLC25A13, SLC25A15, SLC25A19, SLC25A20, SLC25A22, SLC25A3 (PHC), SLC25A38, SLC25A4, SLC2A2, SLC35A1, SLC35A2, SLC35C1, SLC37A4, SLC6A8, SLC7A7, SPAST, SPG7, SPTLC1, SRD5A3, SSR4, STT3A, STT3B, STXBP1, SUCLA2, SUCLG1, SURF1, TACO1, TARS2, TAZ, TIMM8A, TK2, TMEM126A, TMEM165, TMEM70, TPK1, TRIT1, TRMU, TRNT1, TSFM, TTC19, TUFM, TYMP, UQCC2 , UQCC3, UQCRB, UQCRC2, UQCRQ, VARS2, WDR45, WFS1, YARS2

6 weeks

Mitochondrial Encephalopathy/Leigh Syndrome Nuclear Gene Panel (146 Genes)

AARS2, ACAD9, ACO2, ADCK3 (CABC1; COQ8), AFG3L2, AIFM1, APOPT1, APTX, ATP5A1, ATP5E, ATPAF2 (ATP12), AUH, BCS1L, BOLA3, C10ORF2, C12ORF65, CA5A, COG8, COQ2, COQ4, COQ6, COQ9, COX10, COX14 (C12ORF62), COX15, COX20 (FAM36A), COX6B1, CPT1A, CPT2, CYC1, DARS, DARS2, DGUOK, DLAT, DLD, DNM1L, EARS2, ECHS1, ETFDH, ETHE1, FARS2, FASTKD2, FBP1, FBXL4, FH, FOXRED1, GCDH, GFER, GFM1 (EFG1), GFM2, GTPBP3, GYG2, HIBCH, HLCS, HSPD1, IARS2, IBA57, ISCA2, LARS2, LIAS, LIPT1, LRPPRC, LYRM7, MARS2, MFF, MFN2, MPC1 (BRP44L), MPV17, MRPL44, MRPS22, MTFMT, MTPAP, NADK2, NARS2, NDUFA1, NDUFA10, NDUFA11, NDUFA12, NDUFA2, NDUFA4, NDUFA9, NDUFAF1, NDUFAF2, NDUFAF3 (C3ORF60), NDUFAF4 (C6ORF66), NDUFAF5, NDUFAF6, NDUFAF7 (C2ORF56), NDUFB3, NDUFS1, NDUFS2, NDUFS3, NDUFS4, NDUFS6, NDUFS7, NDUFS8, NDUFV1, NDUFV2, NFU1, NUBPL, PC, PCCA, PCCB, PDHA1, PDHB, PDHX, PDP1, PDSS1, PDSS2, PET100, PNPT1, POLG, RANBP2, RARS2, RMND1, RRM2B, SCO1, SCO2, SDHA, SDHAF1, SERAC1, SLC19A3, SLC22A5, SLC25A1, SLC25A15, SLC25A19, SLC25A22, SLC35A2, STXBP1, SUCLA2, SUCLG1, SURF1, TACO1, TARS2, TK2, TMEM70, TPK1, TRMU, TSFM, TTC19, TUFM, TYMP, UQCC2 , UQCC3, UQCRQ, VARS2

6 weeks

Testing of Nuclear Genes Important for Normal Mitochondrial Function

Testing Options

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Test Name Genes / Mutations Included TAT

Lactic Acidosis/Pyruvate Metabolism Nuclear Gene Panel (153 Genes)

ACAD9, ADCK3 (CABC1; COQ8), AGK, AGL, AIFM1, ALDOB, ATP5E, ATPAF2 (ATP12), B4GALT1, BCKDHA, BCKDHB, BCS1L, BOLA3, C10ORF2, C12ORF65, CA5A, CARS2, COG4, COG8, COQ2, COQ4, COQ9, COX10, COX14 (C12ORF62), COX15, COX6B1, CYC1, DARS2, DBT, DGUOK, DLAT, DLD, DNM1L, EARS2, ECHS1, ELAC2, ETFA, ETFB, ETFDH, ETHE1, FARS2, FBP1, FBXL4, FDX1L, FH, FOXRED1, G6PC, GFER, GFM1 (EFG1), GTPBP3, GYG2, GYS2, HADHA, HADHB, HIBCH, HLCS, HMGCS2, HSD17B10, HSPD1, IBA57, ISCU, LARS, LARS2, LDHA, LIAS, LIPT1, LRPPRC, LYRM4, LYRM7, MARS, MFF, MLYCD, MPC1 (BRP44L), MPV17, MRPL12, MRPL44, MRPS16, MRPS22, MRPS7, MTFMT, MTO1, NADK2, NARS2, NDUFA1, NDUFA10, NDUFA11, NDUFA9, NDUFAF1, NDUFAF3 (C3ORF60), NDUFAF5, NDUFAF6, NDUFB3, NDUFB9, NDUFS1, NDUFS2, NDUFS3, NDUFS4, NDUFS6, NDUFS7, NDUFS8, NDUFV1, NFS1, NFU1, PARS2, PC, PCCA, PCCB, PDHA1, PDHB, PDHX, PDP1, PDSS1, PDSS2, PFKM, PHKG2, PNPT1, POLG, POLG2, PUS1, RARS2, RMND1, RRM2B, SARS2, SCO2, SDHAF1, SERAC1, SFXN4, SLC25A13, SLC25A19, SLC25A3 (PHC), SLC25A4, SLC2A2, SLC35A2, SLC37A4, SLC7A7, SUCLA2, SUCLG1, SURF1, TARS2, TAZ, TK2, TMEM70, TPK1, TRMU, TRNT1, TSFM, TTC19, TUFM, TYMP, UQCC2 , UQCC3, UQCRB, UQCRC2, UQCRQ, YARS2

6 weeks

Progressive External Ophthalmoplegia (PEO)/Optic Atrophy Nuclear Gene Panel(55 Genes)

ACO2, ALG13, ALG3, APTX, AUH, C10ORF2, C12ORF65, CISD2, CLPB, COX7B, DARS, DDHD2, DGUOK, DNA2, DNAJC19, DNM1L, DPM1, EARS2, FH, GYG2, ISCA2, MCEE, MFF, MFN2, MGME1, MOGS, MTFMT, MTO1, MTPAP, NARS2, NDUFAF3 (C3ORF60), NR2F1, OPA1, OPA3, PDHX, PDSS1, POLG, POLG2, PRPS1, RRM2B, SLC19A2, SLC19A3, SLC25A4, SPG7, SRD5A3, STT3B, SUCLA2, TACO1, TIMM8A, TK2, TMEM126A, TSFM, TYMP, VARS2, WFS1

4 weeks

Methylglutaconic Aciduria Nuclear Gene Panel (13 Genes)

AGK, ATP5E, ATPAF2 (ATP12), AUH, CLPB, DNAJC19, HMGCL, OPA3, POLG, SERAC1, SUCLA2, TAZ, TMEM70 4 weeks

POLG Sequence Analysis POLG 4-5

weeks

Mitochondrial Myopathy, Lactic Acidosis and Sidero-blastic Anemia (MLASA)

PUS1 4-5 weeks

Mitochondrial Complex II Deficiency (MT-C2D) SDHA 4 weeks

Testing of Nuclear Genes Important for Normal Mitochondrial Function Cont.

Additional testing options are available, including targeted variant testing for a previously identified pathogenic or likely pathogenic variant. Appropriate test selection depends on the specific clinical history of a patient, including family and personal health histories as well as familial test results. Testing for most genes includes sequencing and deletion/duplication analysis via next-generation sequencing and/or exon array testing.

Testing Options

MITOCHONDRIAL DISORDERS GUIDE 11

Sample SubmissionGenetic testing can be performed on blood, oral rinse or extracted DNA samples. GeneDx test kits are available to ordering providers, and include sample collection items (such as mouthwash for oral rinse and collection tubes), the necessary sample submission paperwork, and a self-addressed return shipping label.

Additionally, all test requisition forms are available for download from the GeneDx website: www.genedx.com/forms

Please note that all testing must be performed under the guidance of a healthcare provider. For more information on the sample submission process, please visit our website: www.genedx.com/supplies or email us at: zebras@genedx.com

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MITOCHONDRIAL DISORDERS GUIDE 13

Genetic Test ResultsNearly all test results fall into one of four categories:

1. Positive (pathogenic variant(s) identified)

2. Likely pathogenic variant(s) identified

3. Variant(s) of uncertain significance (VUS) identified

4. Negative (no variants of clinical significance identified)

GeneDx test reports contain detailed information about a specific genetic result and, if available, medical management options. Genetic counseling is recommended prior to genetic testing to understand the benefits and limitations of testing and after genetic testing to discuss the implications of the genetic test results. Genetic counseling services across the country can be found at www.nsgc.org

Positive Result

A positive result indicates a pathogenic (disease-causing) genetic variant (change) was identified in a specific disease gene. This finding confirms an underlying genetic cause for the patient's symptoms and provides a diagnosis of a specific genetic disorder or indicates an increased risk for developing a genetic disorder. Knowledge of the specific pathogenic variant(s) provides valuable information to the patients, their healthcare providers and family members because it helps to determine the recurrence risk and to develop an appropriate medical management plan. A medical management plan may include lifestyle modifications, ongoing screening, preventative medications and measures, and/or surgical/medical device interventions. Furthermore, a positive genetic test result allows targeted testing of at-risk relatives to determine if any of them carry the pathogenic variant(s) as well as to address the recurrence risk of the disorder in future offspring.

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Likely Pathogenic Variant Result

A likely pathogenic result indicates the presence of genetic variant(s) in a specific disease gene for which there is significant, but not conclusive, evidence that the variant(s) are disease-causing. This finding strongly suggests an underlying genetic cause of the patient’s disorder or indicates an increased risk for developing a genetic disorder. With this type of result, medical management options and testing of family members are often similar as described above for a positive result.

Variant of Uncertain Significance (VUS)

A variant of uncertain significance (VUS) result indicates an inconclusive outcome of a genetic test. A VUS is a change in a gene for which the association with disease cannot be clearly established. The available information for the variant is either insufficient or conflicting, and it cannot be determined at this time whether the variant is associated with a specific genetic disorder or if the variant is a unrelated (benign) variant unrelated to the patient’s disorder.

In the case of a VUS test result, all medical management recommendations should be based on clinical symptoms, and past personal and family history. Predictive genetic testing of family members for a VUS is not indicated. Nevertheless, in some circumstances, it can be useful to test other family members through our Variant Testing Program to gain more evidence about the variant itself and its possible association with disease. Over time, additional clinical evidence may be collected about certain VUS, which could ultimately lead to the reclassification of the variant and test result.

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Negative Result

A negative result indicates that the genetic test did not identify reportable, medically relevant variant(s) in any of the genes tested. Therefore, the cause for the patient’s disorder or family history remains unknown. Although the patient’s disorder may be caused by non-genetic factors, a negative genetic test result does not completely rule out an underlying genetic cause. For example, the patient’s disorder may be due to unidentified genetic changes in gene regions or genes not included in the initial test. Depending on the patient’s personal and family health history, additional genetic testing may be indicated for the patient or another family member. A genetic specialist or other healthcare providers can determine if further genetic testing is appropriate.

In case of a negative genetic test result, all medical management recommendations should be based on clinical symptoms in addition to past personal and family history. Predictive genetic testing of family members is not available.

When an individual tests negative for a familial pathogenic variant that was previously identified in another affected family member, this is considered a ‘true’ negative test result. In most cases, this means that the individual has no greater risk for developing the specific genetic disorder that runs in the family than anyone in the general population.

Medical ManagementThe treatment of mitochondrial can vary. In most cases, physicians use a combination of vitamins, optimized nutrition, overall general health and prevention of symptom worsening during times of illness. Knowledge of the genetic etiology of a mitochondrial disorder may guide selection of the most appropriate treatment options in some cases.

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Implications for Family MembersRegardless of the result, patients should share their test report with their blood relatives, who can then discuss the results with their healthcare providers. Sharing a copy of the test result with family members and healthcare providers will help to determine if additional testing is necessary and will ensure that the proper test is ordered for relatives, if indicated.

For positive or likely pathogenic test results in autosomal dominant conditions, first-degree relatives (including parents, siblings, and children) have a 50% chance to have the same variant. The risk for other family members to carry the variant depends on how closely related they are to the person with a positive or likely pathogenic test result. It is important to remember that for most of these genes, not all people who inherit a pathogenic or likely pathogenic variant will mitochondrial impairment due to reduced penetrance.

In cases where the gene is associated with an autosomal recessive condition, an individual inherits two pathogenic variants, one from each parent. Siblings of the individual with a mitochondrial disorder have a 25% chance to inherit both pathogenic variants and develop a mitochondrial disorder

Genetic CounselingPrior to genetic testing, patients should speak with their healthcare provider and/or a genetics specialist about their personal and family health history. Healthcare providers should discuss the benefits and limitations of testing, as well as possible test results. These conversations help to determine if the patient is an appropriate candidate for testing, facilitate the ordering of appropriate test(s) and ensure that the patient has agreed to the proposed genetic testing (written informed consent).

If pathogenic variant(s) have already been identified in a family member, testing of the specific variant(s) is appropriate. If no pathogenic variant(s) are known in a family with a specific genetic disorder, an affected family member with the highest likelihood of a positive test outcome (an individual manifesting associated clinical symptoms) is ideally the best person for initial testing within a family. In instances when an affected family member is

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not available, testing of an unaffected family member may be considered, although a negative test result will not guarantee that the unaffected individual does not have an increased risk to develop the clinical symptoms that are present in the family.

Once a patient makes the decision to undergo genetic testing, post-test genetic counseling is recommended to understand the implications of the results, including a discussion of the appropriate medical management based on both the test results and the patient’s medical and family history. Genetic counseling services across the country can be found at www.nsgc.org

Insurance Coverage and Cost for Genetic TestingGeneDx accepts all commercial insurance plans and is a Medicare provider. Additionally, GeneDx is a registered provider with several Medicaid plans. If a patient does not have health insurance coverage or cannot afford to pay the cost of testing, GeneDx offers a financial assistance program to help ensure that all patients have access to medically necessary genetic testing.

For more information on the paperwork that is required by some insurance carriers, as well as additional details on patient billing and our financial assistance program, please visit our website: www.genedx.com/billing

Genetic Information Nondiscrimation ActThe Genetic Information Nondiscrimination Act of 2008, also referred to as GINA, is a federal law that protects Americans from discrimination by health insurance companies and employers based on their genetic information. However, this law does not cover life insurance, disability insurance, or long-term care insurance. GINA’s employment protections do not extend to individuals in the U.S. military, federal employees, Veterans Health Administration and Indian Health Service. Some of these organizations may have internal policies to address genetic discrimination. For more information, please visit: http://genome.gov/10002328

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Resources for Patients1. United Mitochondrial Disease Foundation, a patient

organization that promotes research and education for the diagnosis, treatment, and cure of mitochondrial disorders: www.umdf.org

2. American Epilepsy Society: www.aesnet.org

3. Epilepsy Foundation: www.epilepsyfoundation.org

4. GeneDx neurology page: www.genedx.com/neurology

5. GeneReviews, a database of genetic diseases: www.geneclinics.org

6. National Society of Genetic Counselors, to help you find a counselor near you: www.nsgc.org

References1. Chinnery, P.F. Mitochondrial disorders overview. NCBI

Bookshelf–GeneReviews. NIH National Library of Medicine. 2000–2010. [www.ncbi.nlm.nih.gov/books/NBK1224].

2. Longo, N. Mitochondrial encephalopathy. Neurol Clin N Am 21: 817-831. 2003.

3. van Adel B.A. and Tarnopolsky, M.A. Metabolic myopathies: Update 2009. J Clin Neuromuscular Disease. 10(3): 97-121.

4. Tarnopolsky, MA and Sandeep, R. Mitochondrial myopathies: Diagnosis, exercise intolerance and treatment options. (2005). Medicine and Science in Sports and Exercise. 37(12): 2086-2093.

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Notes

207 Perry ParkwayGaithersburg, MD 20877T 1 888 729 1206 (Toll-free), 1 301 519 2100 • F 1 201 421 2010E wecare@genedx.com • www.genedx.com

© 2017 GeneDx, Inc. All rights reserved. 40236 V2 08/17 Information current as of 08/17

About GeneDx

GeneDx was founded in 2000 by two scientists from the National Institutes of Health (NIH) to address the needs of patients diagnosed with rare disorders and the clinicians treating these conditions. Today, GeneDx has grown into a global industry leader in genomics, having provided testing to patients and their families in over 55 countries. Led by its world-renowned clinical genomics program, and an unparalleled comprehensive genetic testing menu, GeneDx has a continued expertise in rare and ultra-rare disorders. Additionally, GeneDx also offers a number of other genetic testing services, including: diagnostic testing for hereditary cancers, cardiac, mitochondrial, and neurological disorders, prenatal diagnostics, and targeted variant testing. At GeneDx, our technical services are backed by our unmatched scientific expertise and our superior customer support. Our growing staff includes more than 35 geneticists and 140 genetic counselors specializing in clinical genetics, molecular genetics, metabolic genetics, and cytogenetics who are just a phone call or email away to assist you with your questions and testing needs. We invite you to visit our website: www.genedx.com to learn more about us..