New X-linked mental retardation syndrome with the gene mapped tentatively in Xp22.3.

X-linked mental retardation (XLMR) is genetically heterogeneous and clinically variable. We describe a new XLMR syndrome of severe mental retardation and multiple congenital anomalies. Two sisters have (with 3 different partners) 3 severely handicapped sons. In 2 cases, oligohydramnios and intrauterine growth retardation were noted. Common anomalies included a square-shaped face, high and broad forehead, frontal bossing, downward slant of palpebral fissures, hypertelorism, epicanthic folds, long philtrum, thin upper lip, and apparently low-set ears. One boy has bilateral microphthalmos and sclerocornea, and his cousin has atrophy of the optic nerve. All 3 patients are blind and have profound statomotor and mental retardation, seizures, and a grossly abnormal electroencephalographic pattern. Additional findings are short stature, delayed bone maturation, hydronephrosis, vesicorenal reflux, cryptorchidism, clinodactyly of the 5th fingers, and transverse palmar creases. The karyotype is normal (46,XY). Segregation analysis showed perfect coinheritance between the clinical phenotype and alleles at several loci in Xp22.3, whereas recombinants were identified with marker loci from Xp22.2-qter. Analysis of multiple informative meioses suggests that the disease locus maps in Xp22.3 distal to DXS16.

Eye tracking dysfunction is a putative phenotypic susceptibility marker of schizophrenia and maps to a locus on chromosome 6p in families with multiple occurrence of the disease.

The difficulties in defining the borders of the schizophrenia spectrum is one major source of variance in linkage studies of schizophrenia. The employment of biological markers may prove advantageous. Due to empirical evidence, eye tracking dysfunction (ETD) has been discussed to be the most promising marker for genetic liability to schizophrenia. With respect to the recent progress in genomic scans, which have pointed to the short arm of chromosome 6, we carried out a scan of the 6p21-23 region with 16 microsatellite markers to test for linkage between chromosomal markers and ETD as well as schizophrenia. We tested 5 models of inheritance of ETD and found maximum two-point lod scores of 3.51 for D6S271 and 3.44 for D6S282. By including these markers in a multipoint analysis, a lod score of 4.02 was obtained. In the case of schizophrenia, 7 models were tested; however, with non-significant results. Our findings, together with another recent linkage report, point to the possibility of a second susceptibility locus for schizophrenia which may be located centromeric to the HLA region. Also, the evidence of ETD being a susceptibility marker for schizophrenia receives further support.

Autosomal recessive retinitis pigmentosa locus maps on chromosome 1q in a large consanguineous family from Pakistan.

A large Pakistani family with several consanguineous marriages is described, in which autosomal recessive retinitis pigmentosa is segregating. Linkage studies revealed close linkage between the disease locus and six loci on chromosome 1q (D1S158, F13B, D1S422, D1S412, D1S413, and D1S53) with maximum lod scores ranging from 0.988-4.657 at theta = 0.065-0.235. However, the analysis of individual nuclear families showed very close linkage without recombination in three branches and several recombinants and negative lod scores throughout in the fourth branch. These results strongly suggest that mutations of two different genes are responsible for the disease in the 'linked' and 'unlinked' branches. Parallel to the linkage heterogeneity, clear phenotypic differences have been observed among the 'linked' and 'unlinked' parts. Our findings demonstrate that in case of recessive disorders the possibility of non-allelic genetic heterogeneity should always be considered, even within the same kindred and in genetic isolates if a largely extended pedigree is analysed.