Genetic Causes of Mental Retardation in Golestan Province

Objective: About 70 percent of mental retardation can be attributed to genetic causes. Whereas the recognization of genetic causes of mental retardation causes better programming and more precision council for prevention and control of mental retardation, so the aim of this study is to investigate the genetic causes of mental retardation in Golestan province. Materials & Methods: In this descriptive research which is a cross-sectional and applied study, fifty families with two or more affected children from different parts of Golestan province were collected with cooperation of Golestan state welfare organization and by simple sampling method. Mental retardation of affected people had been previously proved by physicians. Blood samples of patients and controls in the family were prepared. Patients were investigated for dysmorphism and microcephaly. Cytogenetic study, metabolic test, fragile X test, and linkage analysis for seven gene loci known for autosomal recessive primary microcephaly (MCPH) was carried out. Results: Chromosomal abnormalities were not observed in any family. One out of fifty families revealed fragile X syndrome and ten were affected to MCPH. Five out of ten microcephaly families were linked to MCPH (autosomal recessive primary microcephaly) loci. Conclusion: Autosomal recessive primary microcephaly (MCPH)make up about 20% 0f all mental retardation in Golestan province. This prevalence is very remarkable

Hum. Genet.

Mental retardation (MR) has a worldwide prevalence of around 2% and is a frequent cause of severe disability. Significant excess of MR in the progeny of consanguineous matings as well as functional considerations suggest that autosomal recessive forms of MR (ARMR) must be relatively common. To shed more light on the causes of autosomal recessive MR (ARMR), we have set out in 2003 to perform systematic clinical studies and autozygosity mapping in large consanguineous Iranian families with non-syndromic ARMR (NS-ARMR). As previously reported (Najmabadi et al. in Hum Genet 121:43–48, 2007), this led us to the identification of 12 novel ARMR loci, 8 of which had a significant LOD score (OMIM: MRT5–12). In the meantime, we and others have found causative gene defects in two of these intervals. Moreover, as reported here, tripling the size of our cohort has enabled us to identify 27 additional unrelated families with NS-ARMR and single-linkage intervals; 14 of these define novel loci for non-syndromic ARMR. Altogether, 13 out of 39 single linkage intervals observed in our cohort were found to cluster at 6 different loci on chromosomes, i.e., 1p34, 4q27, 5p15, 9q34, 11p11–q13 and 19q13, respectively. Five of these clusters consist of two significantly overlapping linkage intervals, and on chr 1p34, three single linkage intervals coincide, including the previously described MRT12 locus. The probability for this distribution to be due to chance is only 1.14 × 10−5, as shown by Monte Carlo simulation. Thus, in contrast to our previous conclusions, these novel data indicate that common molecular causes of NS-ARMR do exist, and in the Iranian population, the most frequent ones may well account for several percent of the patients. These findings will be instrumental in the identification of the underlying genes

Bi-allelic variants in CHKA cause a neurodevelopmental disorder with epilepsy and microcephaly

The Kennedy pathways catalyze the de novo synthesis of phosphatidylcholine and phosphatidylethanolamine, the most abundant components of eukaryotic cell membranes. In recent years, these pathways have moved into clinical focus since four out of ten genes involved have been associated with a range of autosomal recessive rare diseases such as a neurodevelopmental disorder with muscular dystrophy (CHKB), bone abnormalities and cone-rod dystrophy (PCYT1A), and spastic paraplegia (PCYT2, SELENOI). We identified six individuals from five families with bi-allelic variants in CHKA presenting with severe global developmental delay, epilepsy, movement disorders, and microcephaly. Using structural molecular modeling and functional testing of the variants in a in a cell-based S. cerevisiae model, we determined that these variants reduce the enzymatic activity of CHKA and confer a significant impairment of the first enzymatic step of the Kennedy pathway. In summary, we present CHKA as a novel autosomal recessive gene for a neurodevelopmental disorder with epilepsy and microcephaly

Bi-allelic HPDL Variants Cause a Neurodegenerative Disease Ranging from Neonatal Encephalopathy to Adolescent-Onset Spastic Paraplegia

International audienceWe report bi-allelic pathogenic HPDL variants as a cause of a progressive, pediatric-onset spastic movement disorder with variable clinical presentation. The single-exon gene HPDL encodes a protein of unknown function with sequence similarity to 4-hydroxyphenylpyruvate dioxygenase. Exome sequencing studies in 13 families revealed bi-allelic HPDL variants in each of the 17 individuals affected with this clinically heterogeneous autosomal-recessive neurological disorder. HPDL levels were significantly reduced in fibroblast cell lines derived from more severely affected individuals, indicating the identified HPDL variants resulted in the loss of HPDL protein. Clinical presentation ranged from severe, neonatal-onset neurodevelopmental delay with neuroimaging findings resembling mitochondrial encephalopathy to milder manifestation of adolescent-onset, isolated hereditary spastic paraplegia. All affected individuals developed spasticity predominantly of the lower limbs over the course of the disease. We demonstrated through bioinformatic and cellular studies that HPDL has a mitochondrial localization signal and consequently localizes to mitochondria suggesting a putative role in mitochondrial metabolism. Taken together, these genetic, bioinformatic, and functional studies demonstrate HPDL is a mitochondrial protein, the loss of which causes a clinically variable form of pediatric-onset spastic movement disorder