Mutational analysis of the adaptor protein 2 sigma subunit (AP2S1) gene: search for autosomal dominant hypocalcemia type 3 (ADH3)

CONTEXT

Autosomal dominant hypocalcemia (ADH) types 1 and 2 are due to calcium-sensing receptor (CASR) and G-protein subunit-α11 (GNA11) gain-of-function mutations, respectively, whereas CASR and GNA11 loss-of-function mutations result in familial hypocalciuric hypercalcemia (FHH) types 1 and 2, respectively. Loss-of-function mutations of adaptor protein-2 sigma subunit (AP2σ 2), encoded by AP2S1, cause FHH3, and we therefore sought for gain-of-function AP2S1 mutations that may cause an additional form of ADH, which we designated ADH3.

OBJECTIVE

The objective of the study was to investigate the hypothesis that gain-of-function AP2S1 mutations may cause ADH3.

DESIGN

The sample size required for the detection of at least one mutation with a greater than 95% likelihood was determined by binomial probability analysis. Nineteen patients (including six familial cases) with hypocalcemia in association with low or normal serum PTH concentrations, consistent with ADH, but who did not have CASR or GNA11 mutations, were ascertained. Leukocyte DNA was used for sequence and copy number variation analysis of AP2S1.

RESULTS

Binomial probability analysis, using the assumption that AP2S1 mutations would occur in hypocalcemic patients at a prevalence of 20%, which is observed in FHH patients without CASR or GNA11 mutations, indicated that the likelihood of detecting at least one AP2S1 mutation was greater than 95% and greater than 98% in sample sizes of 14 and 19 hypocalcemic patients, respectively. AP2S1 mutations and copy number variations were not detected in the 19 hypocalcemic patients.

CONCLUSION

The absence of AP2S1 abnormalities in hypocalcemic patients, suggests that ADH3 may not occur or otherwise represents a rare hypocalcemic disorder.

Transmission and prevalence of Burkholderia cepacia in Welsh cystic fibrosis patients

From 1987 to 1994, 16 of 162 cystic fibrosis (CF) patients attending CF clinics at three different hospitals in South Wales, U.K. were found to have respiratory secretions colonized with Burkholderia cepacia (B. cepacia). Bacteriological typing by polymerase chain reaction (PCR) ribotyping demonstrated seven strains of B. cepacia among these 16 CF patients. This typing confirmed that cross-infection was the mechanism of colonization in six of the nine patients who were colonized at the paediatric CF clinic at the University Hospital of Wales in Cardiff, and in three of the six patients who were colonized at the adult CF clinic at Llandough Hospital in Cardiff (cross-infection rate nine of 16 patients or 56%). A search was made for a nosocomial source, with screening of wards and clinics. Swabs from fomites produced four positive cultures for B. cepacia. Two isolates had the same PCR ribotype as that of the previous CF room occupant. To establish prevalence of B. cepacia among CF children living throughout Wales, respiratory secretions were cultured from 151 of 186 CF children (age < 16 years). This failed to demonstrate B. cepacia colonization other than in the CF patients already identified.

Peripheral long lines in cystic fibrosis

Improved cannula survival with peripheral long lines has been reported for patients requiring multiple courses of intravenous (i.v.) antibiotics, allowing a more normal and mobile pattern of life (1, 2). Since June 1992 we have used both the neonatal silastic long line (Epicutaneo-cava-catheter, Vygon, Aachen) and the Landmark catheter (Menlo Care, California) for administration of i.v. antibiotics to our cystic fibrosis (CF) patients. Information was collected prospectively on the performance of both types of cannulae over 18 months. Cannula survival time was the same and longer than with conventional short cannulae (1, 3). Patient preference for the neonatal line and a trend towards more phlebitis with the Landmark catheter resulted in the selection of the neonatal line for routine use.

Characterisation of Burkholderia cepacia from cystic fibrosis patients living in Wales by PCR ribotyping

Polymerase chain reaction (PCR) ribotyping detects differences in the intergenic spacer between the 16S and 23SrRNA genes. This method was applied to Burkholderia cepacia isolates from 16 Welsh cystic fibrosis (CF) patients attending three different clinics. Amplification of the intergenic spacer followed by an additional digestion step with TaqI restriction endonuclease identified seven distinct electrophoretic patterns among the patient isolates. Each of the seven patterns was distinct from that of the so called "epidemic strain" commonly isolated from patients attending clinics elsewhere in the UK. Two environmental isolates from the hospital clinics and four NCTC reference strains gave different patterns. The simplicity of the method lends itself to use in a general microbiological laboratory.

Assessment of in-line filters to prolong the life of intravenous cannulae in cystic fibrosis patients

Twelve patients with cystic fibrosis received 12 courses of intravenous antibiotics, each over 10-14 days, both with and without the use of an extended-life disposable filter. The design of the trial was to replace the Venflon cannulae as they became non-patent and inserting a filter on alternate occasions. Thus each patient acted as her/his own control. Comparison of times during which cannulae remained patent showed a 50% improvement with use of a filter for 4 patients and no change for 7 patients. There was no significant difference associated with the use of a filter for the group as a whole but our small sample size excludes modest improvements.

Cystic fibrosis, pancreatic sufficiency and distal intestinal obstruction syndrome: a report of four cases

Distal intestinal obstruction syndrome (DIOS), formerly termed meconium ileus equivalent, is usually considered to be unique to cystic fibrosis (CF) patients who have steatorrhoea. We report four CF patients without steatorrhoea ("pancreatic sufficient") who have had repeated episodes of faecal loading indistinguishable from DIOS.