A new locus for autosomal recessive non-syndromic mental retardation maps to 1p21.1-p13.3

Autosomal recessive inheritance of non-syndromic mental retardation (ARNSMR) may account for approximately 25% of all patients with non-specific mental retardation (NSMR). Although many X-linked genes have been identified as a cause of NSMR, only three autosomal genes are known to cause ARNSMR. We present here a large consanguineous Turkish family with four mentally retarded individuals from different branches of the family. Clinical tests showed cognitive impairment but no neurological, skeletal, and biochemical involvements. Genome-wide mapping using Human Mapping 10K Array showed a single positive locus with a parametric LOD score of 4.92 in a region on chromosome 1p21.1-p13.3. Further analyses using polymorphic microsatellite markers defined a 6.6-Mb critical region containing approximately 130 known genes. This locus is the fourth one linked to ARNSMR.

The R110C mutation in Notch3 causes variable clinical features in two Turkish families with CADASIL syndrome

Mutations in Notch3 gene are responsible for the cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). It is a late onset neurological disorder recognized by recurrent strokes and dementia. We describe here the clinical and molecular findings of three unrelated Turkish families with CADASIL syndrome. Two of the families were identified to have the same mutation, p.R110C (c.C328T), located in exon 3 of the Notch3 gene. Interestingly, the phenotypic expression of the disease in these two families was markedly different in severity and age of onset implicating additional genetic and/or non-genetic modulating factors involved in the pathogenesis. In addition, we identified the novel p.C201R (c.T601C) mutation in exon 4 of the Notch3 gene in a proband of the third family with two consecutive stroke-like episodes and typical MRI findings. Mutations described here cause an odd number of cysteines in the N-terminal of the EGF domain of Notch3 protein, which seems to have an important functional effect in the pathophysiology of CADASIL. The phenotypic variability in families carrying the same molecular defect as presented here makes the prediction of prognosis inconceivable. Although DNA analysis is effective and valuable in diagnosing approximately 90% of the CADASIL patients, lack of genotype-phenotype correlation and prognostic parameters makes the presymptomatic genetic counseling very difficult.

Cystic fibrosis mutations and associated haplotypes in Turkish cystic fibrosis patients

Identification of mutations causing cystic fibrosis (CF) in the Turkish population is essential for assessment of the molecular basis of CF in Turkey and the development of strategies for prenatal diagnosis and genetic counseling. Here, we present an updated report of mutations found in the Turkish CF population from an extensive screening study of the entire coding region, including exon-intron boundaries and the promoter region. Cases for which mutations could not be identified were also screened for previously defined large alterations and (TG)mTn-M470V loci. This study revealed a total of 27 different mutations accounting for almost 60% of disease genes in the Turkish population. In this study, we also identified the haplotypes associated with 17 mutations and those associated with unknown mutations. The mutation spectrum of CF in Turkey and its associated haplotypes indicated the presence of a major Mediterranean component in the contemporary Turkish population.

Evaluation of the fetal kidney maturation by assessment of amniotic fluid alpha-1 microglobulin levels

OBJECTIVE

To evaluate the fetal renal maturation by assessment of amniotic fluid microproteins and to show these proteins originate from fetal urine.

STUDY DESIGN

Amniotic fluid proteins (total protein, albumin, high molecular weight protein-HMWP, low molecular weight protein-LMWP, alpha(1)-microglobulin and beta(2)-microglobulin) were determined in 39 pregnant women at delivery and by amniocentesis in 30 pregnant women. These values were compared with first urine values of neonates with the same gestational age.

RESULTS

Albumin was the largest protein component in the amniotic fluid. LMWP showed an increase in the amniotic fluid until the end of the second trimester; and as pregnancy advanced a progressive decrease occurred in parallel to fetal renal maturation. After 26 weeks' gestation, a strong correlation was identified between LMWP levels and alpha(1)-microglobulin, and between LMWP and beta(2)-microglobulin. No significant difference was detected between LMWP levels in the first urine of the neonates and in amniotic fluids.

CONCLUSION

Microproteins in the fetal urine are of fetal origin. Fetal renal maturation can be evaluated by measuring microproteins in the amniotic fluid. Fetal renal maturation is best reflected by alpha(1)-microglobulin.

Glycine to tryptophan substitution in type I collagen in a patient with OI type III: a unique collagen mutation

We report a unique glycine substitution in type I collagen and highlight the clinical and biochemical consequences. The proband is a 9 year old Turkish boy with severely deforming osteogenesis imperfecta (OI). Biochemical analysis of (pro) collagen type I from a skin fibroblast culture showed both normal and overmodified alpha chains. Molecular analysis showed a G>T transversion in the COL1A2 gene, resulting in the substitution of glycine by tryptophan at position 277 of the alpha2(I) collagen chain. Glycine substitutions in type I collagen are the most frequent cause of the severe and lethal forms of OI. The phenotypic severity varies according to the nature and localisation of the mutation. Substitutions of glycine by tryptophan, which is the most voluminous amino acid, have not yet been identified in type I collagen or any other fibrillar collagen. The severe, though non-lethal OI phenotype associated with this mutation may appear surprising in view of the huge size of the tryptophan residue. The fact that the mutation resides within a so called "non-lethal" region of the alpha2(I) collagen chain supports a regional model in phenotypic severity for alpha2(I) collagen mutations, in which the phenotype is determined primarily by the nature of the collagen domain rather than the type of glycine substitution involved.

Identification of point mutations in Turkish DMD/BMD families using multiplex-single stranded conformation analysis (SSCA)

Small mutations are the cause of the disease in one third of cases of Duchenne and Becker muscular dystrophy (DMD/BMD). The identification of point mutations in the dystrophin gene is considered to be very important, because it may provide new insights into the function of dystrophin and direct information for genetic counselling. In this study, we have screened 18 deletion-prone exons (25.5% of the coding region) of the dystrophin gene by using a modified non-isotopic multiplex single-stranded conformation analysis (SSCA). Mutations responsible for the disease phenotype could be identified in five out of 56 unrelated DMD/BMD patients without detectable deletions. Two of these mutations, 980-981delCC and 719G > C, are novel mutations which have not been described previously. Four of the five mutations, including 980-981delCC detected in this study are found to be nonsense or frameshift mutations leading to the synthesis of a truncated dystrophin protein. The missense mutation, 719G > C, causing the substitution of highly conserved alanine residue at 171 with proline in the actin binding domain of the dystrophin, is associated with a BMD phenotype. This study also revealed the presence of six polymorphisms in Turkish DMD/BMD patients.

Genotype and phenotype in patients with dihydropyrimidine dehydrogenase deficiency

Dihydropyrimidine dehydrogenase (DPD) deficiency is an autosomal recessive disease characterised by thymine-uraciluria in homozygous deficient patients and has been associated with a variable clinical phenotype. In order to understand the genetic and phenotypic basis for DPD deficiency, we have reviewed 17 families presenting 22 patients with complete deficiency of DPD. In this group of patients, 7 different mutations have been identified, including 2 deletions [295-298delTCAT, 1897delC], 1 splice-site mutation [IVS14+1G>A)] and 4 missense mutations (85T>C, 703C>T, 2658G>A, 2983G>T). Analysis of the prevalence of the various mutations among DPD patients has shown that the G-->A point mutation in the invariant splice donor site is by far the most common (52%), whereas the other six mutations are less frequently observed. A large phenotypic variability has been observed, with convulsive disorders, motor retardation and mental retardation being the most abundant manifestations. A clear correlation between the genotype and phenotype has not been established. An altered beta-alanine, uracil and thymine homeostasis might underlie the various clinical abnormalities encountered in patients with DPD deficiency.

An insulin receptor mutant (Asp707 --> Ala), involved in leprechaunism, is processed and transported to the cell surface but unable to bind insulin

We have identified a homozygous mutation near the carboxyl terminus of the insulin receptor (IR) alpha subunit from a leprechaun patient, changing Asp707 into Ala. Fibroblasts from this patient had no high affinity insulin binding sites. To examine the effect of the mutation on IR properties, the mutant IR was stably expressed in Chinese hamster ovary cells. Western blot analysis and metabolic labeling showed a normal processing of the mutant receptor to alpha and beta subunits. No increase in high affinity insulin binding sites was observed on Chinese hamster ovary cells expressing the mutant receptor, and also, affinity cross-linking of 125I-labeled insulin by disuccinimidyl suberate to these cells failed to label the mutant alpha subunit. Biotinylation of cell surface proteins by biotin succinimidyl ester resulted in efficient biotinylation of the mutant IR alpha and beta subunits, showing its presence on the cell surface. On solubilization of the mutant insulin receptor in Triton X-100-containing buffers, 125I-insulin was efficiently cross-linked to the receptor alpha subunit by disuccinimidyl suberate. These studies demonstrate that Ala707 IR is normally processed and transported to the cell surface and that the mutation distorts the insulin binding site. Detergent restores this site. This is an example of a naturally occurring mutation in the insulin receptor that affects insulin binding without affecting receptor transport and processing. This mutation points to a major contribution of the alpha subunit carboxyl terminus to insulin binding.

Neu-Laxova syndrome: report of a case from Turkey

We describe a case of Neu-Laxova syndrome in a newborn female who was born at full-term to consanguineous Turkish parents. The pathological and radiological features are described.

Carrier detection by DNA analysis in Duchenne muscular dystrophy families

We applied DNA analysis techniques to Turkish families whose members were afflicted with Duchenne/Becker muscular dystrophy. The aim of this study was to establish a prenatal diagnosis of this anomaly and to determine the carrier state. All of the techniques used in established diagnosis centers are now applied routinely in our laboratory. Both Southern analysis and polymerase chain reaction (PCR) methods were used for deletion detection in patients and restriction enzyme fragment length polymorphism (RFLP) determination for linkage analysis in women at risk. CA repeated sequence length polymorphism, the most recent technique for linkage analysis, was also applied. About 250 individuals from seventy-nine families were investigated and thirty-six entire families were screened. Twenty-five women were found to be carriers while thirty seven were non-carriers. The carrier state could not be determined in three women.

Congenital insensitivity to pain with anyhydrosis: morphological studies of skin and peripheral nerves

Two male siblings born to consanguineous parents, with the diagnosis of congenital insensitivity to pain with anhydrosis are evaluated. The patients presented with unexplained bouts of fever, self-mutilation, repeated trauma and inability to sweat. Physical examination revealed both siblings to be insensitive to pain and temperature. The electron microscopic study of the skin was unremarkable whereas sural nerve biopsies yielded an essential lack of unmyelinated fibers.