Phenotypic variation in a large family with autosomal dominant hypocalcaemia

BACKGROUND/AIMS

Autosomal dominant hypocalcaemia (ADH) is caused by activating mutations in the calcium- sensing receptor (CASR). We aimed to describe the phenotypic variation within a large family with ADH, especially kidney and cerebral basal ganglia calcifications.

METHODS

Fifteen related subjects carrying the CASR mutation T151M participated in a cross-sectional study of calcium homeostasis, renal ultrasonography, cerebral CT, bone mineral density, and health-related quality of life (HRQoL).

RESULTS

Eight subjects had received vitamin D treatment (mean duration 15.3 years; range 11-20 years). Urinary calcium excretion was elevated in 5/8 vitamin-D-treated and in 3/7 untreated subjects. Serum magnesium, calcium and parathyroid hormone remained at the lower reference limit or below. Renal calcifications were found in 12 of 14 (86%) and basal ganglia calcifications in 5 of 11 (46%) subjects, independently of vitamin D therapy. The glomerular filtration rate was moderately reduced in 3 subjects. Mean bone mineral density and bone markers were normal. HRQoL was impaired in the vitamin-D-treated group despite correction of the hypocalcaemia.

CONCLUSIONS

The impact of the CASR mutation on calcium homeostasis varied greatly. Kidney and basal ganglia calcifications are common in ADH independently of vitamin D treatment, which, however, increases urinary calcium excretion and may promote urolithiasis.

A novel Refsum-like disorder that maps to chromosome 20

OBJECTIVE

Clinical and genetic characterization of a neurologic disorder resembling Refsum disease in a Norwegian consanguineous family.

METHODS

The affected individuals comprise a brother and sister and their third cousin. The family comes from a small island community and genealogic studies showed that both sets of parents are descendants of a man born in 1585. Based on the hypothesis that this is an autosomal recessive disease and that the patients were homozygous for the same mutation (identical by descent), we used homozygosity mapping to define the genetic locus of this disorder.

RESULTS

This slowly progressive disorder starts in childhood with signs of peripheral neuropathy (pes cavus, tendoachilles contracture). Hearing loss and cataract become evident in the third decade. Subsequently, patients develop a disorder of gait due to the combination of ataxia and spasticity, and a pigment retinopathy. While the clinical picture is reminiscent of Refsum disease, affected individuals have normal phytanic and pristanic acid levels in plasma, as well as normal enzymatic activity for alpha-oxidation. We mapped the disease to a 15.96 Mb region on chromosome 20 (20p11.21-q12), containing approximately 200 genes (maximum lod score = 6.3). Sequencing of 23 candidate genes failed to demonstrate detrimental sequence variants.

CONCLUSIONS

Our findings show that the clinical syndromes that include Refsum disease are more heterogeneous than previously recognized. We have chosen to report the clinical features and mapping of this novel disorder in the hope that this will permit identification of other families and thus proper genetic characterization.

Familial angiolipomatosis

Large subcutaneous angiolipomata were observed bilaterally around the wrists, knees, and ankles in an adolescent boy. Growth had been slow since first noted at age 1 year. The tumors extended deeply between muscles, tendons and joint capsules, but without infiltration of these structures. The tumors recurred after subtotal excision. Muscular hypotrophy and deformation of bones near the affected joints were noted. An 8-year-old sister had similar tumors, suggesting a genetic etiology.

Cold-induced sweating syndrome A report of two cases and demonstration of genetic heterogeneity

OBJECTIVES

To characterize the specific autonomic disturbances underlying the cold-induced sweating syndrome (CISS), and to describe a novel genetic variant of this rare recessive disorder. The two not previously reported patients had similar dysmorphic features: abnormal facial appearance, high arched palate, low set rotated ears, flexion deformities of elbows and fingers and scoliosis. Most noticeable were their paradoxical sweat responses: cold ambient temperature induced a profuse sweating over the face, arms and trunk but not over the lower limbs; while in the heat very little sweating occurred primarily on the legs. Testing of autonomic functions demonstrated normal cardiovascular reflexes and postganglionic sympathetic efferent functions. Sural nerve morphology and number of unmyelinated fibers was normal and skin biopsies showed normal appearing eccrine sweat glands. MRI scans revealed no structural brain abnormalities. Oral clonidine, prescribed in one patient, completely suppressed cold-induced sweating. Observed clinical features matched those of two sisters reported from Israel and of two brothers reported from Norway. All six cases presented a similar phenotype. The Norwegian, Israeli and Canadian cases were homozygous or compound heterozygous, respectively, for mutations in the CRLF1 gene on chromosome 19p12 (CISS1). The Australian case, however, had no pathogenic sequence variants in the CRLF1 gene, but was compound heterozygous for mutations in the CLCF1 gene on chromosome 11q13.3 (CISS2).

CONCLUSION

The rare cold-induced sweating syndrome is genetically heterogeneous and is probably caused by central and peripheral impairment of sudomotor functions. This is the first detailed report on the clinical consequences of mutations in the CLCF1 gene in humans. Directions for medical therapies are outlined to achieve long term symptom control.

Parathyroid adenoma in a subject with familial hypocalciuric hypercalcemia: coincidence or causality?

A middle-aged woman presented with a history of constipation, easy fatigue, depressive mood, lassitude, polydipsia, and polyuria. The patient posed a challenging diagnostic dilemma due to the presence of persistent severe hypercalcemia and relative lack of clinically manifested symptoms. Clinical, biochemical, and genetic examinations confirmed the diagnosis of familial hypocalciuric hypercalcemia as a result of C562Y calcium-sensing receptor mutation, and a coexisting parathyroid adenoma. After adenectomy, the patient's clinical situation improved markedly, and a modest equilibrium hypercalcemia persisted. This case presents an unusual combination of two relatively common endocrine disorders.

Fewer bacterial relapses after oral treatment with norfloxacin than with ceftibuten in acute pyelonephritis initially treated with intravenous cefuroxime

This double-blind, multicentre study was performed at nine centres on a total of 171 patients who presented with fever (> 38.5 degrees C) and signs of acute pyelonephritis. All were initially treated with intravenous cefuroxime. After 2-3 d, when the fever had subsided and urinary culture had revealed growth of Gram-negative bacteria ( > 10(7) colony-forming units per litre), treatment was changed to oral administration of ceftibuten 200 mg b.i.d. or norfloxacin 400 mg b.i.d. for 10 d. The patients were followed for signs of bacterial or clinical relapse 7-14 d after the end of treatment. The initial clinical and bacteriological cure was excellent in both groups, but there were significantly fewer bacterial relapses after oral treatment with norfloxacin than with ceftibuten in acute febrile pyelonephritis initially treated with intravenous cefuroxime. The causal strain was eradicated in 75% of patients (73% of males, 76% of females) in the ceftibuten group and in 89% of patients (94% of males, 85% of females) in the norfloxacin group. The relative frequency of eradication was 0.84 (p < 0.05; 95%, confidence interval 0.74-0.97). Adverse events were reported by 47% of the patients in the ceftibuten group and by 38% in the norfloxacin group. This difference was not significant, but diarrhoea or loose stools occurred more frequently in the ceftibuten group.

The results of routine evaluation of adult patients with haematuria analysed according to referral form information with 2-year follow-up

OBJECTIVE

With the principal aim of determining how often investigation of haematuria results in a malignancy diagnosis, the referrals (n = 581) during one year to a department of urology (catchment area 250,000 inhabitants) where haematuria was mentioned in the referral form have been registered and analysed. The case records were evaluated after two years.

RESULTS

The tumours detected were mainly bladder tumours (n = 43) and prostate cancers (n = 31). Only three upper urinary tract tumours were diagnosed. The incidence of malignancies was high in patients with macroscopic haematuria (24%), especially if it was asymptomatic (32%). The incidence was lower in microscopic haematuria (9%), especially if it was asymptomatic (5%). The incidence of malignancies was strongly age- and sex-related; in no female under 70 years and in no male under 45 years of age with microscopic haematuria was a malignant tumour detected.

CONCLUSION

Macroscopic haematuria, especially in older patients, is often associated with a malignancy and the investigation must be given high priority. The incidence of malignant tumours in patients with symptomatic microscopic haematuria also warrants an investigation. In the case of asymptomatic microhaematuria. the risk is so low, especially in women that the need for a work-up must be strongly questioned.

[When is it meaningful to investigate hematuria? Macroscopic hematuria--investigate always. Microscopic hematuria--symptoms and age decide]

All patients (n = 578) referred during one year and for whom hematuria was mentioned in the referral form were monitored following urological evaluation including urography and cystoscopy. Evaluation of macroscopic hematuria was often associated with significant findings at both urography (stones) and cystoscopy (bladder tumors). The situation was the same even if not as pronounced for evaluation of microscopic hematuria with concomitant urinary tract symptoms. The evaluation of asymptomatic microscopic hematuria was, however, very rarely associated with significant findings, which were moreover totally lacking among women and younger males.

Urine tissue-polypeptide-specific antigen (TPS) as a marker for bladder cancer

OBJECTIVES

To determine the sensitivity and specificity of urine tissue-polypeptide-specific antigen (TPS) for bladder carcinomas and to evaluate whether urine TPS is influenced by tumour size, number, grade and stage.

PATIENTS AND METHODS

A total of 260 patients entered the study, one group (n = 151) with known bladder cancer disease (79 with recurrent tumour and 72 with no tumour at cystoscopy). The other group (n = 109) consisted of patients without previously known bladder tumour disease, 55 with newly detected bladder tumour(s) and 54 investigated for microhematuria found to be idiopathic. TPS in urine was measured using an ELISA-kit, a solid phase two-site immunosorbent assay with polyclonal antibodies against cytokeratin 18.

RESULTS

Urine TPS was significantly higher in patients with bladder tumours (p < 0.001). There was a significant correlation between TPS and tumour size (p = 0.004), grade (p = 0.001) and stage (p = 0.001). Tumour number was not significantly correlated to urine TPS (p = 0.75). With TPS 42 as a cut-off level, the sensitivity was 73% for newly detected tumours and 50% for recurrences; the specificity was 70% and 63% respectively. With a 95% specificity, the sensitivity for newly detected tumours was 33% and for recurrences 18%. The lower sensitivity and specificity for recurrences was mainly explained by differences in tumour size, grade and stage between the recurrences and the newly detected tumours.

CONCLUSIONS

Urine TPS is a marker for bladder carcinoma correlated to size, grade and stage. The sensitivity and specificity for newly detected tumours are quite comparable with other markers. Its clinical usefulness is however not established and it appears less useful in the follow-up of patients with known bladder tumour disease.

[Inline skating--high fracture risk. Two of three injured are boys and young men. Wrist fractures are most common]

In-line skating injuries have increased in recent years. Hospital based data from Umeå concerning 135 persons injured in in line skating collisions were analyzed. The highest yearly incidence of injury was found in males 10-19 years of age, at 1.7 per 1,000 inhabitants; the corresponding figure for females was 0.5. Two-thirds of incidents were caused by falls due to balance problems without the influence of any "external factor" such as rough road surfaces. No collisions with motor vehicles or other road users were registered. Nearly half of the injuries were fractures or dislocation injuries, most frequently of the upper extremities. Non-minor head injuries were rare. Protective gear for wrist and elbow may have the potential to reduce these injuries.

"Avoidable" deaths in two areas of Sweden - analysis of deaths in hospital after injury

OBJECTIVE

To describe causes of death and other characteristics of "avoidable" deaths in patients admitted to hospital after trauma, and estimate and analyse changes in the avoidable death rate during the years studied.

DESIGN

Retrospective analysis of medico legal autopsy material.

SETTING

One northern and one western area in Sweden 1988-1996.

SUBJECTS

335 cases who died in hospital after trauma.

MAIN OUTCOME MEASURES

Avoidable death, defined as an Injury Severity Score (ISS) of 35 or less and Abbreviated Injury Scale (AIS) head of 4 or less and cause of death.

RESULTS

We found 70 avoidable deaths (21%). Among these, 15 (21%) died of head injuries, 17 (24%) of thoracic, abdominal, or pelvic injuries, and 38 (54%) of medical complications. The number of deaths after trauma decreased considerably from 1988-90 to 1994-96, but the proportion who died in hospital remained almost constant. The proportion of avoidable deaths decreased from 22% to 17%, mainly because the proportion of deaths from medical complications was halved.

CONCLUSION

The standard of Swedish in-hospital trauma care has improved, particularly with a reduction in post-traumatic complications. However, there is still room for improvement in the treatment of complications among elderly people.

Accurate determination of the number of CAG repeats in the Huntington disease gene using a sequence-specific internal DNA standard

We have developed a sequence-specific internal DNA size standard for the accurate determination of the number of CAG repeats in the Huntington disease (HD) gene by cloning key fragments (between 15 and 64 CAG repeats) of the HD gene. These fragments, pooled to produce a sequence-specific DNA ladder, enabled us to observe the true number of CAG repeats directly, with no need for calculations. Comparison of the calculated numbers of CAG repeats in the HD gene using this sequence-specific DNA standard with a commercially available standard (GENESCAN-500 TAMRA) showed that the latter underestimated the number of CAG repeats by three when analyzed by capillary electrophoresis on the ABI 310 Genetic Analyzer (POP4 polymer). In contrast, the use of the same standard overestimated the number of CAG repeats by one when the samples were analyzed by denaturing polyacrylamide electrophoresis on ABI 377 DNA Sequencer (6% denaturing polyacrylamide gel). This suggests that our sequence-specific standard provides greater accuracy for the determination of the true number of CAG repeats in the HD gene than commercially available standards. The sequence-specific standard can be radioactively labeled and successfully replace conventional DNA size standards when analyzing polymerase chain reaction (PCR)-amplified HD alleles by denaturing polyacrylamide electrophoresis.

Progressive central and peripheral demyelinating disease of adult onset in a Norwegian family

OBJECTIVE

To describe the clinical features of a Norwegian family with a combined central and peripheral demyelinating disease.

DESIGN

Multiple case report.

SUBJECTS AND MATERIALS

Three generations of a Norwegian family. Medical records were available for all 9 members of the second generation and 5 affected members in the third generation.

RESULTS

At least 5 members had clinical features, neuroimaging findings, and electrophysiologic signs indicating a chronic progressive disorder affecting both the central and peripheral nervous systems. The clinical symptoms developed between the ages of 30 and 70 years in affected family members, who gradually developed sensory loss, muscle deterioration, and distal weakness in all extremities, unsteady gait, and dysarthria. Five of 9 persons in the second generation had strokes and experienced mental deterioration. The initial stroke episodes were recognized between the ages of 54 and 68 years, and death occurred between the ages of 62 and 75 years. In 7 subjects, cerebrospinal fluid protein levels were increased, and in 5 agar gel electrophoresis indicated blood-brain barrier dysfunction. Seven family members had neuroimaging signs of a widespread white matter disorder. In 4 subjects, neurophysiological investigations indicated a polyneuropathy, and in 3 subjects, results from a sural nerve biopsy showed a demyelinating neuropathy. There was no evidence of co-inheritance with genetic markers of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (19p), PMP22 (17q), APP (21q), CMTX1 (Xq), or PLP (Xq).

CONCLUSIONS

Progressive central and peripheral demyelinating disease seems to be a distinct type of hereditary adult-onset demyelinating disorder affecting both the peripheral and central nervous systems. Its exact nature remains unknown.

[Hereditary cancer]

A significant proportion of all cancers is inherited or develops in genetically susceptible individuals. An updated overview and tabulations are given on inherited cancer, including the monogenic cancer syndromes, cancer caused mainly by predisposition in heterozygous carriers for autosomal recessive syndromes, and the same of different types of cancers occurring in families exhibiting irregular autosomal dominant inheritance. Environmental factors act in concert with genetically susceptible genes to cause cancer. A mechanism for the initiation and progression of cancer on the cellular level is outlined. The identification of an ever-increasing number of cancer-susceptible genes enables the development of new genetic tests. Some advantages and problems associated with predictive genetic testing for cancer are discussed.

Mutation hot spots in 5q31-linked corneal dystrophies

Mutations in the BIGH3 gene on chromosome 5q31 cause four distinct autosomal dominant diseases of the human cornea: granular (Groenouw type I), Reis-Bücklers, lattice type I, and Avellino corneal dystrophies. All four diseases are characterized by both progressive accumulation of corneal deposits and eventual loss of vision. We have identified a specific recurrent missense mutation for each type of dystrophy, in 10 independently ascertained families. Genotype analysis with microsatellite markers surrounding the BIGH3 locus was performed in these 10 families and in 5 families reported previously. The affected haplotype could be determined in 10 of the 15 families and was different in each family. These data indicate that R555W, R124C, and R124H mutations occurred independently in several ethnic groups and that these mutations do not reflect a putative founder effect. Furthermore, this study confirms the specific importance of the R124 and R555 amino acids in the pathogenesis of autosomal dominant corneal dystrophies linked to 5q.

The Ca(2+)-sensing receptor gene (PCAR1) mutation T151M in isolated autosomal dominant hypoparathyroidism

Isolated autosomal dominant hypoparathyroidism is a heterogeneous disorder characterized by parathyroid hormone (PTH) deficiency, hypocalcemia and hyperphosphatemia. The candidate gene approach was used to study a large Norwegian family. The loci for the PTH gene, PTH receptor gene and RET protooncogene were excluded using dinucleotide markers and restriction fragment length polymorphism analysis. Complete cosegregation of this trait was found with the chromosomal region 3q13, using the short tandem repeat markers D3S1267, D3S1269, D3S1303, D3S1518, and RHO. This region contains the candidate locus for the Ca(2+)-sensing receptor (PCAR1). By single-strand conformation polymorphism (SSCP) analysis of all PCAR1 exons followed by automated sequencing, we identified a C to T transition in exon 2 (cDNA position 452) on the mutant allele in the family. The mutation predicts a substitution of Thr to Met in amino acid position 151 (T151M). A StyI restriction site created by the nucleotide substitution was used to confirm the mutation on all alleles, as well as to exclude it among 100 normal alleles (blood donors). SSCP analysis also identified a novel polymorphism of PCAR1 intron 4 (1609-88t --> c) on normal alleles. The T151M mutation is located in the extracellular N-terminal domain of PCAR1, which belongs to the superfamily of G protein-coupled receptors. We suggest that this is a gain-of-function mutation that increases the sensitivity of the receptor to [Ca2+], thereby decreasing the calcium set point.

Phenylketonuria genotypes correlated to metabolic phenotype groups in Norway

In order to establish a genotype-phenotype relationship, we have identified both mutant phenylalanine hydroxylase (PAH) genes in 108 phenylketonuria (PKU) patients (27 different alleles, 54 different genotypes). One major group of patients with very high pretreatment phenylalanine values ("classical" PKU) exclusively comprised homozygotes of the PKU mutations I65T, G272X, F299C, Y356X, R408W, IVS12nt1, and compound heterozygotes of various combinations of these alleles with G46S, R261Q, R252W, A259T, R158Q, D143G, R243X, E280K, or Y204C. A second major group of patients with lower phenylalanine values ("mild" PKU) comprised mutations A300S, R408Q, Y414C in various compound heterozygous states, and R261Q, R408Q, Y414C in homozygotes. The phenylalanine values in these groups were non-overlapping. In addition, a smaller group of patients formed the transition between the two main groups. In sib pairs 4 of 15 had discordant pretreatment phenylalanine values.

CONCLUSION

Our results are consistent with the view that allelic heterogeneity at the PAH locus dominates the biochemical phenotype in PKU and that genotype information is able to predict the metabolic phenotype in PKU patients.

Mutations in the iduronate-2-sulfatase gene in five Norwegians with Hunter syndrome

We have identified the mutations in the iduronate-2-sulfatase (IDS) gene of five unrelated Norwegians with Hunter syndrome by reverse transcription-polymerase chain reaction (RT-PCR) analysis of IDS mRNA followed by single strand conformation polymorphism (SSCP) analysis and cDNA sequencing. One patient had a 5-bp deletion, located at the intron 5/exon 6 junction, that created a new alternative splice site. This expanded the deletion to 9 bp in mRNA, an in-frame deletion of the first 3 codons of exon 6 of the IDS gene. In two patients point mutations were identified, the S333L mutation, which has been reported previously, and A346D (a C-->A transversion at nucleotide 1161/exon 8), which is novel. Two patients had large 3' mRNA rearrangements. The A346D mutation was associated with the mild phenotype, all others with the severe form.

Relative frequency, heterogeneity and geographic clustering of PKU mutations in Norway

We have analysed 236 Norwegian phenylketonuria (PKU) alleles by a combination of mutation scanning methods, restriction enzyme-based assays and DNA sequencing. Thirty-three different mutations constituted 99.6% of all mutant alleles (only 1 allele remains unidentified), 23 of these have been identified also in other European countries. Twenty were predicted missense mutations, 6 splice mutations, 4 nonsense mutations and 2 deletion mutations and 1 mutation disrupted the start codon. The 8 most common mutations represented 83.5% of the PKU alleles, with single allele frequencies ranging from 5.9 to 15.7%. Four of these mutations (R261Q, R408W, Y414C, and 1VS12nt1) are commonly occurring also in PKU patients in other European countries, while the other 4 (G46S, G272X, F299C, and R408Q) have higher frequencies in Norway than in any other country studied. Six mutations (I65T, L249F, P281L, Y356X, R158Q, and R252W) have frequencies between 0.8% and 2.1%, and 19 mutations were encountered only once. The majority of PKU mutations were found on the same RFLP/VNTR haplotype backgrounds in Norway as in other European populations, suggesting that only a few of the mutations may represent recurrent mutations (< 3.4%). Among 10 mutations only reported for our population, we detected 2 de novo mutations (0.8%) arisen in Norway. From the birthplaces of the probands' grandparents, each mutation seemed to have an individual geographic distribution within Norway, with patterns of local mutation clustering. Our observations are compatible with multiple founder effects and genetic drift for the distribution of PKU mutations within Norway.

[Indirect genetic diagnosis of cystic fibrosis]

The diagnosis cystic fibrosis was made in a three years old girl. Her older brother and her mother's sister both had minor symptoms and signs suggestive of this disease. None of 17 mutations in the gene locus for cystic fibrosis was identified in the patient by DNA-analyses. By haplotype analyses her brother, but not her aunt, was shown to share the proband's haplotypes. This family is used as an example of the general diagnostic potential of indirect diagnosis of genetic disease by haplotype analysis. The prerequisite for haplotype analysis is the availability of DNA from both the patient and the patient's relatives, stressing the need for a DNA bank of material from persons with inherited disorders, for future use.

[Analysis of the Duchenne muscular dystrophy gene with PCR analysis in paraffin-embedded tissue. A new diagnostic possibility]

Analysis of DNA from archival, paraffin-embedded muscle tissue allowed tracing of the mutated dystrophin gene in two families with Duchenne muscular dystrophy. There were no living patients in these families. In one family this diagnosis contributed to the birth of a normal male, in the other family to the demonstration of carrier status. These analyses, based on the polymerase chain reaction, are relatively rapid and simple, and lend increased value to old tissue samples stored in pathology departments.

[DNA diagnosis of fragile X syndrome in a family. A new type of heredity--dynamic mutations]

In typical cases, the diagnosis of fragile X syndrome can be made clinically, but has so far been based on cytogenetic detection of a fragile site on the X chromosome at Xq27.3. Cytogenetic analyses are time-consuming, and false negative results have been a problem. Following the successful molecular cloning of the gene causing the fragile X syndrome, a novel genetic principle was discovered: the "dynamic" DNA mutation. DNA analyses have now the power to distinguish between normal copies of the gene, carrier mutations and fragile X mutations. We have performed both cytogenetic and DNA analyses in an extended fragile X family. DNA fragment length variations in the gene were identified by Southern blot analysis, and the results were used diagnostically in the family. Instability of the mutation (dynamic mutation) occurred between generations and within individuals. DNA analysis, as performed here, improves diagnostic accuracy and genetic counselling in fragile X families.

PKU mutations R408Q and F299C in Norway: haplotype associations, geographic distributions and phenotype characteristics

Details are given concerning the phenylketonuria (PKU) mutations R408Q and F299C. Both mutations were identified among 47 PKU patients, derived from the Norwegian PKU registry. A novel PKU mutation (R408Q) was identified, by single-strand conformation polymorphism analysis, on six out of eight mutant haplotype 12 chromosomes and on none of the other PKU chromosomes. The F299C mutation occurred exclusively on mutant haplotype 8, and was the only mutation associated with this haplotype (on six chromosomes). One patient homozygous for each mutation was found. The patient homozygous for F299C manifested severe PKU, whereas the R408Q homozygote exhibited a mild PKU variant. Pedigree analysis of these families has not, so far, revealed consanguinity. Information on the place of birth of the relevant grandparents of the PKU patients with these mutations suggests that each of these mutations in Norway has originated from a common gene source.

Lack of transmission of deleted mtDNA from a woman with Kearns-Sayre syndrome to her child

We have investigated the daughter of a woman with Kearns-Sayre syndrome. The woman had a high percentage of deleted mtDNA in muscle, but no deleted mtDNA was detected in fibroblasts, bone marrow, and peripheral blood cells by Southern blot analysis. With PCR, analytical sensitivity was significantly increased, and deleted mtDNA was detected in all examined tissues from this patient. The patient had healthy parents and nine healthy siblings. No deleted mtDNA was detected in blood from the mother of the patient. The patient had an uneventful pregnancy and delivered at term. Deleted mtDNA could not be detected in placenta by Southern blot analysis. With PCR, deleted mtDNA was detected in the majority of placental specimens. This finding may, however, be due to contamination with maternal DNA. The patient's daughter was healthy at age 5 mo, and morphologic examination of muscle was normal. No transmission of deleted mtDNA to the daughter could be detected by Southern blot and PCR analysis of peripheral blood cells, bone marrow, fibroblasts, and muscle. The presence of deleted mtDNA was excluded at a fractional level of less than 1:100,000 in all examined tissues from the daughter.

Mechanisms of ring chromosome formation in 11 cases of human ring chromosome 21

We studied the mechanism of ring chromosome 21 (r(21)) formation in 13 patients (11 unique r(21)s), consisting of 7 from five families with familial r(21) and 6 with de novo r(21). The copy number of chromosome 21 sequences in the rings of these patients was determined by quantitative dosage analyses for 13 loci on 21q. Nine of 11 r(21)s, including the 5 familial r(21)s, showed no evidence for duplication of 21q sequences but did show molecular evidence of partial deletion of 21q. These data were consistent with the breakage and reunion of short- and long-arm regions to form the r(21), resulting in deletion of varying amounts of 21q22.1 to 21qter. The data from one individual who had a Down syndrome phenotype were consistent with asymmetric breakage and reunion of 21q sequences from an intermediate isochromosome or Robertsonian translocation chromosome as reported by Wong et al. Another patient, who also exhibited Down syndrome, showed evidence of a third mechanism of ring formation. The likely initial event was breakage and reunion of the short and long arms, resulting in a small r(21), followed by a sister-chromatid exchange resulting in a double-sized and symmetrically dicentric r(21). The phenotype of patients correlated well with the extent of deletion or duplication of chromosome 21 sequences. These data demonstrate three mechanisms of r(21) formation and show that the phenotype of r(21) patients varies with the extent of chromosome 21 monosomy or trisomy.

A de novo phenylketonuria mutation: ATG (Met) to ATA (Ile) in the start codon of the phenylalanine hydroxylase gene

We here describe the detection of a de novo mutation in the phenylalanine hydroxylase gene in a Norwegian phenylketonuria (PKU) patient. This novel mutation, M1I, disrupts the start codon of the gene by a G to A transition. The compound heterozygote genotype (IVS-12/M1I) of this patient predicts that no phenylalanine hydroxylase enzyme is formed, thus leading to a severe classical PKU. Determination of haplotypes and DNA fingerprint patterns indicates a paternal origin of the de novo mutation.

Application of natural and amplification created restriction sites for the diagnosis of PKU mutations

PCR amplification, either conventional, or as site directed mutagenesis using primers with mismatched 3'-ends, followed by restriction endonuclease digestion, provides rapid, non-isotope assays of known mutations in the human phenylalanine hydroxylase gene. Such assays were shown to have the potential to detect all of the 18 presently reported phenylketonuria mutations. The practical applicability of this approach was demonstrated for eight mutations in Norwegian phenylketonuria patients, among them the most common ones.

A termination mutant prevalent in Norwegian haplotype 7 phenylketonuria genes

RFLPs in the phenylalanine hydroxylase (PAH) gene locus were determined in 47 Norwegian nuclear families that had at least one child with phenylketonuria (PKU). The PKU haplotype distribution differed somewhat from that of other European populations. Mutant haplotype 7 is relatively rare in other populations but constituted 20% of all mutant haplotypes in Norway. In 14 of the 17 mutant haplotypes 7, a previously unreported deletion of the BamHI restriction site in exon 7 of the PAH gene was observed. The abrogation of the BamHI site was shown to be due to a G-to-T transversion, changing Gly 272 to Ter 272 in exon 7 of the gene, thus directly identifying the PKU mutation. Unlike the families of the other PKU patients, the families with this mutation clustered along the southeastern coast of Norway, suggesting a founder effect for this mutation.