Isolated 3-methylcrotonyl coenzyme A carboxylase (MCC) deficiency was documented in four adult women from the Amish/Mennonite population of Lancaster County, Pennsylvania. Metabolic and enzymatic investigations in these individuals were instituted after the detection of abnormal acylcarnitine profiles in blood spots obtained from their newborn children, in whom MCC activity was normal.

Genetic studies of complex hereditary disorders require for their mapping the determination of genotypes at several hundred polymorphic loci in several hundred families. Because only a minority of markers are expected to show linkage and association in family data, a simple screen of genetic markers to identify those showing linkage in pooled DNA samples can greatly facilitate gene identification. All studies involving pooled DNA samples require the comparison of allele frequencies in appropriate family samples and subsamples. We have tested the accuracy of allele frequency estimates, in various DNA samples, by pooling DNA from multiple individuals prior to PCR amplification. We have used the ABI 377 automated DNA sequencer and GENESCAN software for quantifying total amplification using a 58 fluorescently labeled forward PCR primer and relative peak heights to estimate allele frequencies in pooled DNA samples. In these studies, we have genotyped 11 microsatellite markers in two separate DNA pools, and an additional four markers in a third DNA pool, and compared the estimated allele frequencies with those determined by direct genotyping. In addition, we have evaluated whether pooled DNA samples can be used to accurately assess allele frequencies on transmitted and untransmitted chromosomes, in a collection of families for fine-structure gene mapping using allelic association. Our studies show that accurate, quantitative data on allele frequencies, suitable for identifying markers for complex disorders, can be identified from pooled DNA samples. This approach, being independent of the number of samples comprising a pool, promises to drastically reduce the labor and cost of genotyping in the initial identification of disease loci. Additional applications of DNA pooling are discussed. These developments suggest that new statistical methods for analyzing pooled DNA data are required.

We report an autosomal recessive form of ataxia that is not allelic to Friedreich’s disease in six individuals from a large kindred with family origins traced to a common founder of German-Swiss descent. The disorder begins during early childhood with a concentric contraction of the visual fields and proprioceptive loss. Eventually blindness, a severe sensory ataxia, achalasia, scoliosis, and inanition develop by third decade. Inversion recovery MRIs of the spinal cord in affected individuals demonstrate a hyperintense signal in the posterior columns. Finding the gene responsible for this disorder may aid in our understanding of the mechanisms that cause sensory neuronal degeneration.

Experienced clinicians recognize that some children who appear to have static cerebral palsy (CP) actually have underlying genetic-metabolic disorders. We report a series of patients with motor disorders seen in children with extrapyramidal CP in whom brain magnetic resonance imaging abnormalities provided important diagnostic clues in distinguishing genetic-metabolic disorders from other causes. One cause of static extrapyramidal CP, hypoxic-ischemic encephalopathy at the end of a term gestation, produces a characteristic pattern of hyperintense signal and atrophy in the putamen and thalamus. Other signal abnormalities and atrophy in the putamen, globus pallidus, or caudate can point to genetic-metabolic diseases, including disorders of mitochondrial and organic acid metabolism. Progress in understanding and treating genetic diseases of the developing brain makes it essential to diagnose disorders that masquerade as static CP. Brain magnetic resonance imaging is a useful diagnostic tool in the initial evaluation of children who appear to have CP.

We have diagnosed type I glutaric aciduria (GA-I) in 14 children from 7 Old Order Amish families in Lancaster County, Pennsylvania. An otherwise rare disorder, GA-I appears to be a common cause of acute encephalopathy and cerebral palsy among the Amish. The natural history of the disease, which was previously unrecognized in this population, is remarkably variable and ranges from acute infantile encephalopathy and sudden death to static extrapyramidal cerebral palsy to normal adult. Ten patients first manifested the disease between 3 and 18 months at the time of an acute infectious illness. Four of these children died in early childhood, also during acute illnesses. However, there has been little progression of the neurological disease after age 5 years in the surviving children and intellect usually has been preserved, even in children with severe spastic paralysis. When well, patients have plasma glutaric acid concentrations ranging from 4.8 to 14.2 mumol/liter (nl 0-5.6 mumol/liter) and urinary glutaric acid concentrations from 12.5 to 196 mg/g creatinine (nl 0.5-8.4 mg/g creatinine). We have found that GA-I can be diagnosed in the Amish by measurement of urinary glutaric acid concentrations using isotope-dilution gas chromatography/mass spectrometry, whereas the diagnosis can easily be missed by routine urine organic acid gas chromatography.