We describe a patient with 46,XY partial gonadal dysgenesis (PGD) who presented with polyneuropathy. Sural nerve pathology revealed peculiar findings characterized by extensive minifascicular formation within the endoneurium and with a decreased density of myelinated fibers. We found, in the patient, a homozygous missense mutation (ATG-->ACG) at the initiating codon in exon 1 of the desert hedgehog (DHH) gene, which predicts a failure of translation of the gene. The same heterozygous mutation was found in the patient's father. This is the first report of a human DHH gene mutation, and the findings demonstrate that mutation of the DHH gene may cause 46, XY PGD associated with minifascicular neuropathy.
Adult-onset type II citrullinemia (CTLN2) is characterized by a liver-specific deficiency of argininosuccinate synthetase (ASS) protein. We have recently identified the gene responsible for CTLN2, viz., SLC25A13, which encodes a calcium-binding mitochondrial carrier protein, designated citrin, and found five mutations of the SLC25A13 gene in CTLN2 patients. In the present study, we have identified two novel mutations, 1800ins1 and R605X, in SLC25A13 mRNA and the SLC25A13 gene. Diagnostic analysis for the seven mutations in 103 CTLN2 patients diagnosed by biochemical and enzymatic studies has revealed that 102 patients had one or two of the seven mutations and 93 patients were homozygotes or compound heterozygotes. These results indicate that CTLN2 is caused by an abnormality in the SLC25A13 gene, and that our criteria for CTLN2 before DNA diagnosis are correct. Five of 22 patients from consanguineous unions have been shown to be compound heterozygotes, suggesting a high frequency of the mutated genes. The frequency of homozygotes is calculated to be more than 1 in 20,000 from carrier detection (6 in 400 individuals tested) in the Japanese population. We have detected no cross-reactive immune materials in the liver of CTLN2 patients with any of the seven mutations by Western blot analysis with anti-human citrin antibody. From these findings, we hypothesize that CTLN2 is caused by a complete deletion of citrin, although the mechanism of ASS deficiency is still unknown.
We have recently identified SLC25A13 on chromosome 7q21.3 as the gene responsible for adult-onset type II citrullinemia (CTLN2) and found seven mutations in the SLC25A13 gene of CTLN2 patients. Most recently, the SLC25A13 mutations have been detected in neonatal/infantile patients with a type of neonatal hepatitis associated with cholestasis (NICCD). In the present study, we identified a novel mutation, E601X, in the SLC25A13 gene and established multiple DNA diagnosis methods for eight mutations by using a genetic analyzer with GeneScan and the single primer extension procedure (SNaPshot). An additional novel missense mutation (variation), E601K, was detected by SNaPshot analysis and was indistinguishable from the mutation E601X detected by the PCR/RFLP method. Multiple DNA diagnoses for the nine mutations revealed that 100 (male/female: 70/30) out of 115 CTLN2 and 38 (14/24) out of 45 NICCD patients tested were homozygotes or compound heterozygotes. The frequency of homozygotes carrying SLC25A13 mutations in both alleles is estimated to be minimally 1 in 21,000 from carrier detection (18 in 1,315 individuals tested) in the Japanese population. The differences in the gender ratio and in mutation types between CTLN2 and NICCD patients are significant. It is, however, unknown whether all homozygotes with mutated SLC25A13 in both alleles suffer from NICCD, CTLN2, both, or neither.
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