Novel nonsense mutation in the hypoxanthine guanine phosphoribosyltransferase gene and nonrandom X-inactivation causing Lesch-Nyhan syndrome in a female patient

Lesch-Nyhan (LN) disease is a severe X-linked recessive neurological disorder associated with a loss of hypoxanthine guanine phosphoribosyltransferase activity (HPRT, EC 2.4.2.8). We have studied the second example of a female patient with LN disease. The molecular basis of HPRT deficiency in this patient was a previously undescribed nucleotide substitution in exon 6. In this gene, designated HPRT PARIS, a single nucleotide substitution from T to G at base position 558 changed a tyrosine (TAT) to a codon STOP (TAG) (Y153X). Analysis of the mother revealed a normal sequence of the HPRT cDNA and demonstrated that this mutation arose through a de novo gametic event. Allele-specific amplification of exon 6 from the patient's genomic DNA confirmed the single base substitution and showed that the patient was heterozygous for this mutation. Investigation of X-chromosomal inactivation by comparison of methylation patterns of patient's DNA isolated from fibroblasts, T lymphocytes, and polymorphonuclear cells digested with PstI and BstXI, with or without HpaII, and hybridized with M27 beta probe indicated a nonrandom pattern of X-chromosomal inactivation in which there was preferential inactivation of the maternal allele. The data indicate that nonrandom X-inactivation leading to selective inactivation of the maternal gene and a de novo point mutation in the paternal gene were responsible for the lack of HPRT activity in this patient.

Glutaric aciduria yype 1: First reported cases in three Saudi patients

The clinical and biochemical findings in three patients with glutaric aciduri Type 1 (GAT1) are presented. They had a normal postnatal period of three to 14 months. They developed sudden and severe encephalopathy following an infection or trauma (patient 3) that gradually progressed to severe dystonia, choreathetosis, spastic quadriplegia and mental retardation. Neuroradiologic studies of the brain revealed while matter disease and frontotemporal lobe hypoplasia. The urine findings by gas chromatography/mass spectrometry (GC)/(MS) were characteristic of GAT1. Since GAT1 is an organic acidemia without intermittent acidotic attacks, but primarily manifests with progressive encephalopathy, it is important to recognize the potential of its existence among handicapped children in chronic care facilities. The good clinical response in two of the patients urges early diagnosis in subsequent newborn siblings of the families with the disease. The diagnosis of three patients in less than two years indicate the need for neonatal screening for the recognition of this disease, among other treatable metabolic diseases, in Saudi Arabia.