Topics in Genetic Counseling - Mitochondrial Disorders

Which of the following is a principle of mitochondrial inheritance?

• genes are all involved oxidative phosphorylation

• anticipation

• variable expressivity

• mostly recessive inheritance

• low mutation rate overall

Answer explanation

there's also...

Maternal inheritance

Heteroplasmy

Bottleneck effect

Which early indicator might suggest a mitochondrial disease is worth considering in diagnosis?

• High lactate levels

• Clear autosomal dominant inheritance

• Ketogenic acidosis

• Clear autosomal recessive inheritance

• Low B6 vitamin levels

All of the following are diagnostic tools when thinking about mitochondrial disorders EXCEPT...

• Phenotype

• Genetic Testing

• Biochemical Labs

• Family History

• Muscle Biopsy

Answer explanation

Family history, while sometimes helpful, is less useful in mitochondrial cases since symptoms can crop up at any time, age and tissue with different inheritance.

Which mitochondrial disorder is the most common?

• Kearns-Sayre Syndrome

• Myoclonic Epilepsy with Ragged-Red Fibers (MERRF)

• Leigh Syndrome

• POLG-related disorders

• Pearson Syndrome

Answer explanation

2% of the population are carriers.

This condition presents before the age of 20 years. The triad of symptoms are: external opthalmoplegia, pigmentary retinopathy, and cardiac conduction defects. These 3 conditions are sufficient to make a confident diagnosis of this rare entity.

• Kearns-Sayre Syndrom

• POLG related disorders

• Leigh Syndrome

• Myoclonic Epilepsy with Ragged-Red Fibers (MERRF)

• Pearson Syndrome

Which mitochondrial disorder is associated with autosomal dominant progressive external ophthalmoplegia?

• Kearns-Sayre Syndrome

• POLG related disorders

• Leigh Syndrome

• Myoclonic Epilepsy with Ragged-Red Fibers (MERRF)

• Pearson Syndrome

A 25-year-old male who presented with paroxysmal left upper limb tics and weakness for two years. Neurological examination revealed intact cranial nerves. A biopsy of the biceps muscle demonstrated a variation in fiber size.

• Kearns-Sayre Syndrome

• POLG related disorders

• Leigh Syndrome

• Myoclonic Epilepsy with Ragged-Red Fibers (MERRF)

• Pearson Syndrome

A 7 month old female child presented with status epilepticus, delayed developmental milestones and regression of the achieved milestones suspected to be a case of neurodegenerative disorder. MRI showed bilateral, symmetrical abnormal lesions in the basal ganglia. What is the diagnosis?

• Kearns-Sayre Syndrome

• POLG related disorders

• Leigh Syndrome

• Myoclonic Epilepsy with Ragged-Red Fibers (MERRF)

• Pearson Syndrome