Golabi-Ito-Hall syndrome results from a missense mutation in the WW domain of the PQBP1 gene

BACKGROUND

Golabi, Ito, and Hall reported a family with X linked mental retardation (XLMR), microcephaly, postnatal growth deficiency, and other anomalies, including atrial septal defect, in 1984.

METHODS

This family was restudied as part of our ongoing study of XLMR, but significant linkage to X chromosome markers could not be found. Extreme short stature and microcephaly as well as other new clinical findings were observed. Mutations in the polyglutamine tract binding protein 1 gene (PQBP1) have recently been reported in four XLMR disorders (Renpenning, Hamel cerebro-palato-cardiac, Sutherland-Haan, and Porteous syndromes) as well as in several other families. The clinical similarity of our family to these patients with mutations in PQBP1, particularly the presence of microcephaly, short stature, and atrial septal defect, prompted examination of this gene.

RESULTS

A missense mutation in PQBP1 was identified which changed the conserved tyrosine residue in the WW domain at position 65 to a cysteine (p.Y65C).

CONCLUSIONS

This is the first missense mutation identified in PQBP1 and the first mutation in the WW domain of the gene. The WW domain has been shown to play an important role in the regulation of transcription by interacting with the PPxY motif found in transcription factors. The p.Y65C mutation may affect the proper functioning of the PQBP1 protein as a transcriptional co-activator.

XLMR syndrome characterized by multiple respiratory infections, hypertelorism, severe CNS deterioration and early death localizes to distal Xq28

We report on a family with severe X-linked mental retardation (XLMR) and progressive, severe central nervous system deterioration. Three of the five affected males died of secondary complications before the age of 10 years and none have survived past the age of 10. These complications included swallowing dysfunction and gastroesophageal reflux with secondary recurrent respiratory infections. In addition, hypotonia and a mild myopathy were also present. All had a characteristic facies, including downslanting palpebral fissures, hypertelorism, and a short nose with a low nasal bridge. The two older boys showed cerebral atrophy by CT. No metabolic abnormalities were identified. Three obligate carriers had an IQ less than 80. The causal gene has been localized distal to DXS8103 in Xq28, a region spanning 5cM. No other XLMR disorder with these manifestations have been localized to this region and this appears to be a new disorder.

XLMR genes: update 1998

Since the Seventh Fragile X and XLMR Mental Retardation (XLMR) Workshop in 1995, the genes for Coffin-Lowry, Mohr-Tranebjaerg, and Opitz G/BBB syndromes have been cloned. Jensen syndrome has been found to be allelic to Mohr-Tranebjaerg. Twenty new XLMR syndromes and metabolic or neuromuscular disorders have been reported. Twenty-four new localizations have been established, including five in previously reported conditions (FG, Carpenter, Arts, OPA2, and OFD1). The number of families with nonspecific XLMR that have been reported has continued to increase; 58 families or loci are now known. Eighteen new families with nonspecific mental retardation (MRX) have been reported. Two of them, however, were subsequently found to have mutations in the RABGDIA gene, which codes for a GDP-dissociation inhibitor for RAB proteins. In total, 41 more entries have been added to the X chromosome map of XLMR. The total number of known syndromes and MRX families has increased to 178. Of the 120 known XLMR disorders, 53 have been mapped, and 22 have been cloned. Assuming that at least 10 loci are necessary to account for the 58 families with MRX, the total number of XLMR loci counted so far would be 130. Although it is likely that many of the disorders will eventually prove to be allelic, it is not possible at present to determine the precise number of loci for nonspecific XLMR.

Inherited mutations in PTEN that are associated with breast cancer, cowden disease, and juvenile polyposis

PTEN, a protein tyrosine phosphatase with homology to tensin, is a tumor-suppressor gene on chromosome 10q23. Somatic mutations in PTEN occur in multiple tumors, most markedly glioblastomas. Germ-line mutations in PTEN are responsible for Cowden disease (CD), a rare autosomal dominant multiple-hamartoma syndrome. PTEN was sequenced from constitutional DNA from 25 families. Germ-line PTEN mutations were detected in all of five families with both breast cancer and CD, in one family with juvenile polyposis syndrome, and in one of four families with breast and thyroid tumors. In this last case, signs of CD were subtle and were diagnosed only in the context of mutation analysis. PTEN mutations were not detected in 13 families at high risk of breast and/or ovarian cancer. No PTEN-coding-sequence polymorphisms were detected in 70 independent chromosomes. Seven PTEN germ-line mutations occurred, five nonsense and two missense mutations, in six of nine PTEN exons. The wild-type PTEN allele was lost from renal, uterine, breast, and thyroid tumors from a single patient. Loss of PTEN expression was an early event, reflected in loss of the wild-type allele in DNA from normal tissue adjacent to the breast and thyroid tumors. In RNA from normal tissues from three families, mutant transcripts appeared unstable. Germ-line PTEN mutations predispose to breast cancer in association with CD, although the signs of CD may be subtle.

A novel X-linked gene, DDP, shows mutations in families with deafness (DFN-1), dystonia, mental deficiency and blindness

In 1960, progressive sensorineural deafness (McKusick 304,700, DFN-1) was shown to be X-linked based on a description of a large Norwegian pedigree. More recently, it was shown that this original DFN-1 family represented a new type of recessive neurodegenerative syndrome characterized by postlingual progressive sensorineural deafness as the first presenting symptom in early childhood, followed by progressive dystonia, spasticity, dysphagia, mental deterioration, paranoia and cortical blindness. This new disorder, termed Mohr-Tranebjaerg syndrome (referred to here as DFN-1/MTS) was mapped to the Xq21.3-Xq22 region2. Using positional information from a patient with a 21-kb deletion in chromosome Xq22 and sensorineural deafness along with dystonia, we characterized a novel transcript lying within the deletion as a candidate for this complex syndrome. We now report small deletions in this candidate gene in the original DFN-1/MTS family, and in a family with deafness, dystonia and mental deficiency but not blindness. This gene, named DDP (deafness/ dystonia peptide), shows high levels of expression in fetal and adult brain. The DDP protein demonstrates striking similarity to a predicted Schizosaccharomyces pombe protein of no known function. Thus, is it likely that the DDP gene encodes an evolutionarily conserved novel polypeptide necessary for normal human neurological development.

X-linked mental retardation with thin habitus, osteoporosis, and kyphoscoliosis: linkage to Xp21.3-p22.12

We reevaluated a family previously described as having nonspecific X-linked mental retardation (XLMR) by Snyder and Robinson [1969: Clin Pediatr 8:669-674] (MIM 309583). Clinical and DNA studies were conducted on 17 relatives, including 6 males with mild-to-moderate mental retardation, 3 carrier females, and 8 normal males. In contrast to the normal appearance and minimal clinical findings reported 22 years ago, affected males were found to have a characteristic set of clinical findings. These developed gradually over the first 2 decades, and included thin body build with diminished muscle mass, osteoporosis and kyphoscoliosis, slight facial asymmetry with a prominent lower lip, nasal speech, high narrow or cleft plate, and long great toes. Carrier females were clinically normal. Multipoint linkage analysis indicated linkage to markers distal to the 3' end of DMD (DXS41 and DXS989), with a maximal lod score of 4.7. On the basis of these findings, this entity is redefined as XLMR syndrome.

Temporal lobe surface area measurements on MRI in normal and dyslexic readers

In a neuroanatomical study of dyslexia, measurements were made of the superior surface of the temporal lobe (SSTL) on MRI scans in a sample of 17 dyslexics and 21 non-dyslexic subjects. Both anterior and posterior halves of the SSTL area showed significant leftward asymmetry in non-dyslexics, but showed symmetry in dyslexics. The total SSTL area showed greater leftward asymmetry in non-dyslexics than in dyslexics. The dyslexics also revealed a significant correlation (r = 0.69, P = 0.005) between Woodcock-Johnson Passage Comprehension scores and posterior SSTL asymmetry, such that those with higher scores had more leftward asymmetry. This suggests that among dyslexics the direction of SSTL asymmetry may serve as a risk factor and/or a marker for the severity of reading comprehension problems.

Adult familial dyslexia: a retrospective developmental and psychosocial profile

This study investigated the developmental, demographic, educational, and psychosocial outcome of 36 adults with third-generation familial dyslexia. Control subjects were 44 unaffected age-matched family members. Compared with control subjects, those with familial dyslexia 1) had similar incidences of perinatal complications, left-handedness, and right-left confusion but reported more early speech/language problems; 2) performed worse in reading and spelling but had similar educational achievement; 3) were more likely to report depression/anxiety symptoms and to have attention-deficit disorder with hyperactivity; and 4) were similar in medical history, marital stability, and mean income. Data suggest that, despite continued isolated reading deficits, carefully selected subjects with adult familial dyslexia do not show the previously described downward course of the learning-disabled population.

Chorionic mosaicism: association with fetal loss but not with adverse perinatal outcome

Cytogenetic data from the United States NICHD collaborative study of chorionic villus sampling (CVS) were used to evaluate the clinical significance of chorionic mosaicism. The 10,754 patients with normal cytogenetic results were compared with 108 patients (1.0 per cent) with placental mosaicism and 181 patients (1.6 per cent) with pseudo-mosaicism. Of the pregnancies intended to continue, the pregnancy loss rate was significantly greater in patients with placental mosaicism than in the cytogenetically normal cohort (8.6 vs. 3.4 per cent, p less than 0.05). However, there was no difference in the frequencies of abruptio placenta, preterm labour or delivery, small-for-gestational-age newborns, pregnancy-induced hypertension, or neonates with Apgar scores less than 7.

Risk factors associated with transcervical CVS losses

Factors found to be associated with pregnancy loss after transcervical CVS were race (higher for non-white), history of spontaneous abortion, unplanned pregnancy, history of spotting or bleeding during the pregnancy prior to CVS, and placental position (higher for fundal or lateral locations). Whether the increase in loss risk is due to the factor, per se, or the factor plus the CVS cannot be determined due to the lack of appropriate control data.

Nomenclature guidelines for X-linked mental retardation

Nomenclature guidelines are proposed for non-specific and for syndromal forms of X-linked mental retardation. Non-specific mental retardations (MRX) are given unique symbols for each family (MRX1, MRX2, MRX3 ...). Syndromal mental retardations (MRXS) which do not as yet have specific symbols are given unique interim symbols for each syndrome (MRXS1, MRXS2, MRXS3 ...). The prerequisite for assignment of serial MRX and MRXS gene symbols is a minimum lod score (or multipoint lod score) of +2 between the MR locus and one or more X chromosome markers. Prior approval of availability for proposed gene symbols must be obtained from the Nomenclature Committee of the Human Gene Mapping Workshops.

[Distribution of cystinuria subtypes in the Democratic Republic of Germany]

The classic cystinuria is a hereditary disorder characterized by a defective transport of cystine and the dibasic amino acids arginine, lysine and ornithine in the epithelial cells of the renale tubule and the gastrointestinal tract. The excretion patterns of cystine and the dibasic amino acids in 24-hour urine samples from heterozygotes can be used to the differentiation between the genetic subtypes. 120 probands in the age range from 3 to 70 years from 22 families with cystinuria were investigated by thin-layer chromatography and by ion exchange chromatography. In patients with cystinuria the genotype I-I has a frequency of 50%. These results and the distribution of the other subtypes are in accordance with published data. From 98 persons investigated in 22 families with cystinuria 14 run the risk to form cystine stones. Therefore, the knowledge of the subtypes is relevant for practice.

The serum amino acid spectrum of insulin-dependent diabetics and controls from Ethiopia

The serum amino acid spectrum was examined in healthy men and insulin-dependent diabetics from Ethiopia. Comparison of serum amino acids of controls from Gondar with Ethiopians after adaptation to a free European diet revealed a marginal low protein nutrition, but not the characteristic changes of malnutrition or experimental starvation. There was no apparent nutritional deficiency of sulphur-containing amino acids in Ethiopians. Insulin-dependent diabetics showed significantly elevated serum levels of BCAA indicating an accelerated protein catabolism in recent-onset insulin-deficient patients and known diabetics respectively, most of them in poor metabolic condition. Serum glutamine levels were reduced, suggesting a considerable renal contribution to the hyperglycaemia/glucosuria of diabetics. The data may be best explained by the low residual insulin secretion at diabetes onset or by the poor degree of metabolic control of known Ethiopian diabetics.

Ketosis, serum carnitine and its precursor amino acids in normal and diabetic ethiopians

In a hospital-based study in northwestern Ethiopia some clinical and biochemical features of diabetes mellitus have been assessed to contribute to the problem of classification of diabetes in a tropical country. Diabetes requiring primary insulin treatment is presented by unequivocally elevated blood glucose levels and the classic symptoms of the disease. Newly discovered cases and readmitted rural diabetics show significantly lower body mass indices and 31% have been classified as underweight. The overall frequency of ketonuria at (re)admission was 45% together with moderately elevated or high 3-hydroxybutyrate serum concentrations. The hormonal status is characterized by a reduced beta-cell function. Serum concentrations of all carnitine fractions are lower in both normal and diabetic Ethiopians when compared with Caucasoids. Carnitine precursor amino acids are normal and the complete amino acid spectrum reveales no clear-cut pattern related to protein-energy malnutrition.

Serum free amino acids of healthy males and pregnant women from Ethiopia

Several clinical, anthropometric and biochemical parameters have been used for the evaluation of the nutritional status and diagnosis of protein-energy malnutrition [1]. Analysis of the complete serum amino-acid spectrum by ion-exchange chromatography provides valuable information on the adequacy of protein intake and on the metabolic response to protein depletion in undernourished subjects. However, the serum aminogram is quite differently affected by acute or chronic starvation or the great variety of starchy but low-protein foods and further toxic factors (e.g. mycotoxins) leading to kwashiorkor. Thus, very complex alterations of the serum amino-acid spectrum had to be expected [5, 9] and stimulated the present investigation for reference purposes. We report the results of amino acid determinations in apparently healthy adult males and pregnant women taking the traditional Ethiopian diet. For want of a better evaluation of the specific nutritional influence, we also collected data on serum amino acids of healthy Ethiopians consuming an average European diet.

A large kindred with X-linked mental retardation, marker X and macroorchidism

Thirty-eight members of a black kindred with mental retardation and the Marker X were studied. Ten of 14 affected males, 6 of 6 affected females, 18 carriers or possible carriers, and 7 normal males were examined. Eight of 9 affected males who could be measured had macroorchidism, but their ears and mandibles were not prominent. No distinct facies were evident, although minor anomalies, such as a slight pectus, were present in some. Clinical diagnosis in the absence of a strongly positive family history may be even more difficult among prepubertal black children than in whites. The risk of retardation among children of carriers was estimated at 20-40%.

Changes of the plasma tryptophan to neutral amino acids ratio in formula-fed infants: possible effects on brain development

The ratio of plasma concentrations of tryptophan to the sum of neutral amino acids (valine, isoleucine, leucine, phenylalanine and tyrosine) was found to be significantly lower in formula-fed infants as compared to breast-fed infants and to newborns at birth. This tryptophan to neutral amino acids ratio in the blood is thought to control the synthesis of serotonin in the brain. Serotonin deficiency in the developing brain based on a decreased plasma tryptophan to neutral amino acids ratio may contribute to developmental obesity and/or permanent changes of mental capacity and social adaptability as observed in human subjects who had been formula-fed as compared to those who had been breast-fed in neonatal life.

[Homocystinuria]

It is reported on a female patient with a classical homocystinuria who showed all typical symptoms of the cystathionine-synthesis-insufficiency, such as tall stature, phacetomy, arachnodactyly, kyphoscoliosis, generalized osteoporosis and thromboembolisms. While homocystin in the blood plasma and the urine could be proved only in the patient, the concentration of plasma methionine was much increased also in the clinically completely inconspicuous sister.