Table 3. [Select Clinical Features of RRM2B Encephalomyopathic MDMD]. - GeneReviews®

Feature	# of Children ¹ w/Feature (%)	Comment
Neuromuscular	31 (100%)	Truncal hypotonia (almost universally present) gross motor delay, feeding difficulties, poor head control, generalized weakness, areflexia, ptosis, PEO, discoordinated swallow, exercise intolerance
Nervous system	Central	1-15 (3%-48%)	Encephalopathy: gross motor delay, seizures, focal &/or generalized UMN signs, microcephaly, neurologic regression, dystonia. MRI shows central hypomyelination, cerebral atrophy
Peripheral	2 (6%)	Demyelinating peripheral neuropathy
Respiratory	18 (58%)	Respiratory distress, respiratory failure. In some cases artificial ventilation may prolong life span.
Renal	17 (55%)	Tubulopathy (proximal), nephrocalcinosis, aminoaciduria, glycosuria, lactic acidemia, hypocalcemia
Faltering growth (previously known as failure to thrive)	16 (52%)	Likely due to multisystem involvement
Hearing loss	11 (35%)	Sensorineural hearing loss may only be identified on formal assessment.
Gastrointestinal	10 (32%)	Recurrent vomiting, feed intolerance, chronic diarrhea, cachexia
Eye	4 (13%)	Ophthalmoparesis, pigmentary retinopathy (rod-cone dystrophy), cataracts, megalocornea, blindness, nystagmus
Cardiovascular	4 (13%)	Left ventricular hypertrophy, cardiomyopathy, ventricular septal defect

Feature

# of Children ¹
w/Feature (%)

Comment

Neuromuscular

31 (100%)

Truncal hypotonia (almost universally present) gross motor delay, feeding difficulties, poor head control, generalized weakness, areflexia, ptosis, PEO, discoordinated swallow, exercise intolerance

Nervous system

Central

1-15 (3%-48%)

Encephalopathy: gross motor delay, seizures, focal &/or generalized UMN signs, microcephaly, neurologic regression, dystonia. MRI shows central hypomyelination, cerebral atrophy

Peripheral

2 (6%)

Demyelinating peripheral neuropathy

Respiratory

18 (58%)

Respiratory distress, respiratory failure. In some cases artificial ventilation may prolong life span.

Renal

17 (55%)

Tubulopathy (proximal), nephrocalcinosis, aminoaciduria, glycosuria, lactic acidemia, hypocalcemia

Faltering growth (previously known as failure to thrive)

16 (52%)

Likely due to multisystem involvement

Hearing loss

11 (35%)

Sensorineural hearing loss may only be identified on formal assessment.

Gastrointestinal

10 (32%)

Recurrent vomiting, feed intolerance, chronic diarrhea, cachexia

Eye

4 (13%)

Ophthalmoparesis, pigmentary retinopathy (rod-cone dystrophy), cataracts, megalocornea, blindness, nystagmus

Cardiovascular

4 (13%)

Left ventricular hypertrophy, cardiomyopathy, ventricular septal defect

From: RRM2B Mitochondrial DNA Maintenance Defects

GeneReviews^® [Internet].

Adam MP, Feldman J, Mirzaa GM, et al., editors.

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