The M405V allele of the glutaryl-CoA dehydrogenase gene is an important marker for glutaric aciduria type I (GA-I) low excretors.

Glutaric aciduria type I (GA-I) is an autosomal recessive organic aciduria resulting from a functional deficiency of glutaryl-CoA dehydrogenase, encoded by GCDH. Two clinically indistinguishable diagnostic subgroups of GA-I are known; low and high excretors (LEs and HEs, respectively). Early medical and dietary interventions can result in significantly better outcomes and improved quality of life for patients with GA-I. We report on nine cases of GA-I LE patients all sharing the M405V allele with two cases missed by newborn screening (NBS) using tandem mass spectrometry (MS/MS). We describe a novel case with the known pathogenic M405V variant and a novel V133L variant, and present updated and previously unreported clinical, biochemical, functional and molecular data on eight other patients all sharing the M405V allele. Three of the nine patients are of African American ancestry, with two as siblings. GCDH activity was assayed in six of the nine patients and varied from 4 to 25% of the control mean. We support the use of urine glutarylcarnitine as a biochemical marker of GA-I by demonstrating that glutarylcarnitine is efficiently cleared by the kidney (50-90%) and that plasma and urine glutarylcarnitine follow a linear relationship. We report the allele frequencies for three known GA-I LE GCDH variants (M405V, V400M and R227P) and note that both the M405V and V400M variants are significantly more common in the population of African ancestry compared to the general population. This report highlights the M405V allele as another important molecular marker in patients with the GA-I LE phenotype. Therefore, the incorporation into newborn screening of molecular screening for the M405V and V400M variants in conjunction with MS/MS could help identify asymptomatic at-risk GA-I LE patients that could potentially be missed by current NBS programs.

Maternal uniparental disomy chromosome 14: case report and literature review.

Uniparental disomy is a genetic cause of disease implicated in a wide variety of neurologic disorders. A recently identified condition is maternal uniparental disomy for chromosome 14 (mUPD14) syndrome. A child with hypotonia and developmental delay was found to have mUPD14 after identification of a balanced karyotypic rearrangement involving both chromosomes 14. We explore the genetic mechanisms by which uniparental disomy can cause clinical abnormalities and karyotypic findings that should raise suspicion for uniparental disomy, review the literature on the mUPD14, and discuss clinical indications on which to suspect this diagnosis. Although it is more difficult to establish a diagnosis in the absence of visible karyotypic abnormalities involving chromosome 14, a distinct phenotype exists in mUPD14 syndrome: in utero growth restriction, congenital hypotonia, gross motor delay, arrested hydrocephalus, mild to moderate mental retardation, joint hyperextensibility, short stature, and precocious puberty. Testing for mUPD14 should be considered in infants with generalized hypotonia who have a history of in utero growth restriction.