Clinical Description
The phenotypic spectrum of untreated glutaric acidemia type 1 (GA-1) ranges from the more common form (infantile-onset disease) to the less common form (later-onset disease after age 6 years). Of note, the GA-1 phenotype can vary widely among untreated family members with the same genotype, primarily as a function of the age at which the first acute encephalopathic crisis occurred: three months to three years in infantile-onset GA-1 and after age six years in later-onset GA-1 [López-Laso et al 2007, Wang et al 2014]. Characteristically these crises result in acute bilateral striatal injury and subsequent complex movement disorders. Patients may also develop insidious-onset basal ganglia injury in the absence of an identified acute encephalopathic crisis.
In the era of newborn screening (NBS), the prompt initiation of treatment of asymptomatic infants detected by NBS means that most individuals who would have developed manifestations of either infantile-onset or later-onset GA-1 remain asymptomatic.
Infantile-onset GA-1. If untreated, 80%-90% of children with infantile-onset GA-1 will experience an acute encephalopathic crisis, 95% of which occur in the first 24 months of life. These crises can be precipitated by intercurrent febrile illness, febrile reaction to vaccinations, or fasting and catabolic stressors associated with anesthesia and surgical procedures [Kölker et al 2006, Boy et al 2017b]. Characteristically these crises result in acute bilateral striatal injury and are followed (typically between ages 3 months and 3 years; in rare cases, between ages 3 and 6 years) by progressive complex neurologic movement disorders. Disability and mortality are high after acute crises [Kyllerman et al 2004, Kölker et al 2006].
Dietary treatment and intense emergency treatment during intercurrent illness (see Management) have reduced the frequency of acute encephalopathic crises and movement disorders to 10%-20%.
Subdural hemorrhages, a rare manifestation of GA-1, may develop even in individuals diagnosed on NBS, managed appropriately, and without macrocephaly [Zielonka et al 2015, Ishige et al 2017]. Subdural hemorrhages may appear spontaneously or following mild head trauma in GA-1; they can also resolve spontaneously. Isolated subdural hemorrhage without other features of GA-1 on brain MRI is extremely uncommon [Vester et al 2015, Vester et al 2016].
Seizures are reported in 7% of individuals with GA-1 [Kölker et al 2015a]. While self-limited seizures may accompany the acute encephalopathic crisis, in other instances they may be the presenting manifestation [McClelland et al 2009]. Infantile spasms have been reported in some [Young-Lin et al 2013, Liu et al 2015].
When GA-1 is diagnosed after the onset of neurologic manifestations, outcome is poor and the therapeutic effect of the usual interventions is more limited [Hoffmann et al 1996, Bjugstad et al 2000, Busquets et al 2000a, Kyllerman et al 2004, Kölker et al 2006, Kamate et al 2012, Wang et al 2014]. Nonetheless, therapeutic intervention may prevent additional progressive neurologic deterioration in some [Hoffmann et al 1996, Bjugstad et al 2000, Kölker et al 2006, Badve et al 2015, Fraidakis et al 2015].
With early diagnosis and adherence to treatment, 80%-90% of individuals with GA-1 remain largely asymptomatic [Strauss et al 2011, Viau et al 2012, Couce et al 2013, Lee et al 2013, Boy et al 2018].
Insidious onset of manifestations was previously seen in an estimated 10%-20% of symptomatic individuals [Kölker et al 2006]; it now appears to be more common because early diagnosis and treatment of GA-1 have reduced the incidence of acute encephalopathic crises [Boy et al 2018].
Individuals who adhere to maintenance and emergency treatments rarely develop dystonia; those who do not are at high risk of developing a movement disorder [Kölker et al 2007, Heringer et al 2010, Strauss et al 2011, Kölker et al 2012, Boy et al 2018]. Those who have insidious onset generally have less severe movement disorders and less extensive lesions on brain MRI than those with acute encephalopathic crisis [Boy et al 2019]. The insidious phenotype may correlate with lack of adherence to chronic dietary treatment [Boy et al 2018].
Late-onset GA-1. Late-onset GA-1 is defined as onset of manifestations after age six years. Some individuals with late-onset GA-1 (e.g., mothers diagnosed due to the birth of a child with an abnormal NBS result) are entirely asymptomatic. Others have a variety of neurologic findings. Among eight symptomatic individuals ages eight to 71 years, the following were observed: chronic headaches (4), macrocephaly (4), epilepsy (2), tremor (2), and dementia (2). All had MRI evidence of frontotemporal hypoplasia and abnormal signal of the white matter; five had subependymal nodules. All showed the high excreting phenotype [Boy et al 2017a]. Others have reported clinical and neuroimaging findings [Külkens et al 2005, Pierson et al 2015, Zhang & Luo 2017].
Other reported manifestations of late-onset GA-1 include the following:
Non-neurologic disease manifestations observed in individuals in GA-1 regardless of age of onset. Chronic kidney disease may occur in those with GA-1, even with adherence to treatment, and may be an extracerebral manifestation in adults with GA-1 [Kölker et al 2015b].
Note: Infants with biochemical findings consistent with GA-1 on NBS, but normal blood levels of GA and 3-OH-GA and only one identifiable GCDH pathogenic variant, may warrant close clinical follow up. However, given the high sensitivity of GCDH molecular genetic testing, the chances that an infant with these findings is affected and at risk of developing acute striatal necrosis are low.