Alexander Cooke

Genotype-phenotype correlations in XX males and their bearing on current theories of sex determination

SummaryClinical, chromosomal and molecular studies of a group of 15 XX males confirm the presence of two main groups. A Y+ve group of ten patients exhibit sex reversal as the result of transfer of the distal end of the short arm of the Y chromosome, including testis determining factors, to the short arm of one X-chromosome, presumably by accidental crossing-over in paternal meiosis. The ten patients have Klinefelters syndrome but differ from XXY cases in that they are short and shown no impairment of intelligence. The four Y-ve XX males have no demonstrable Y sequences and differ from Y+ve cases in abnormality of the external genitalia and invariable gynaecomastia; in this, they more closely resemble XX true hermaphrodites than XY males. These observations on Y-ve XX males and an additional exceptional Y+ patient suggest that the ZFY locus is not essential for male differentiation and is not the primary testis determining factor. Male sex determination in sporadic, and familial Y-ve XX males and true hermaphrodites is likely to be the result of mutation in an X-linked TDF gene and its consequent escape from the constraints of X-inactivation. It seems premature to abandon the dosage model of sex determination on the recent evidence that ZFX does not show dosage compensation.

Molecular Analysis of Pheochromocytoma after Maternal Transmission of SDHD Mutation Elucidates Mechanism of Parent-of-Origin Effect

CONTEXT Pheochromocytoma/paraganglioma occurs almost exclusively after paternal transmission of succinate dehydrogenase D (SDHD) mutations. This parent-of-origin effect has not been fully explained but is accompanied by obligate loss of the maternal copy of chromosome 11. Loss of wild-type SDHD and an additional imprinted gene (hypothesized to be H19) appears necessary for tumor formation. Two previous reports suggested tumor formation after maternal transmission of SDHD mutation, but histological and molecular characterization was unavailable. OBJECTIVE We report the first kindred in which histologically confirmed pheochromocytoma/paraganglioma occurred after maternal transmission of an SDHD mutation and investigate the molecular mechanism of tumor formation. DESIGN The design of the investigation was the study of a three-generation family with SDHD c.242C>T (p.Pro81Leu) mutation. RESULTS The index patient had a histologically confirmed pheochromocytoma and an identical SDHD germline mutation (p.Pro81Leu) to her mother (who had a glomus jugulare tumor) and paraganglioma tissue from her maternal grandfather. Tumor DNA from the index patient revealed loss of heterozygosity (LOH) at 11q23, causing loss of the wild-type paternal SDHD allele and LOH affecting maternal 11p15, including H19. These two regions of LOH were separated by a region exhibiting clearly retained heterozygosity, including SDHAF2, a recently reported paraganglioma susceptibility gene. CONCLUSIONS Tumor formation can occur after maternal transmission of SDHD, a finding with important clinical implications for SDHD families. Tumor formation in SDHD mutation requires the loss of both the wild-type SDHD allele and maternal 11p15, leading to the predominant but now not exclusive pattern of disease inheritance after paternal SDHD transmission.

Absence of learning difficulties in a hyperactive boy with a terminal Xp deletion encompassing the MRX49 locus

Editor—The genetic counselling of a pregnant woman who carries an Xp chromosomal deletion is far from straightforward. While the precise locations of the CDPX1 (arylsulphatase E), steroid sulphatase ( STS ), and Kallman ( KAL1 ) genes are known and FISH probes are available for these well characterised genes, the positions of putative mental retardation genes in this region have not yet been determined. Clinical and molecular studies undertaken over the past 10 years on patients with distal Xp deletions imply, however, that the putative X linked mental retardation (XLMR) gene, MRX49 , lies distal to GS1 and STS but proximal to DXS31 and CDPX1 (fig1).1-4 Figure 1 (a) Case 6, (b) case 8, (c) case 9, (d) case 4, (e) case 12, and (f) case 13 of Ballabio et al,1 (g)-(j) cases BA16, BA20, BA139, and BA75 of Schaefer et al,3 (k) boy with IQ of 46, short stature, generalised ichthyosis, hypogonadotrophic hypogonadism, nystagmus, and photophobia,2 (l) boy with aggressive and hyperactive behaviour, myoclonic epilepsy, developmental delay, and no speech aged 4 years 8 months,4 (m) monozygous male twins with X linked ichthyosis, learning difficulties (LD), and epilepsy,10 (n) our patient, with short stature, Binder syndrome, and ichthyosis (consistent with the loss of the SHOX, CDPX1, and STS genes, respectively) but no significant learning difficulties. The presence (+) or absence (-) of LD is indicated for each case. A broken line indicates the chromosomal region within …

Renin gene restriction fragment length polymorphisms do not show linkage with preeclampsia and eclampsia

Objective. To investigate linkage between the renin gene restriction fragment length polymorphisms in families with a history of preeclampsia/eclampsia.

X Chromosome deletions detectable by flow cytometry in some patients with steroid sulphatase deficiency (X-linked ichthyosis)

SummaryThe X chromosomes of individuals with isolated steroid sulphatase deficiency (X-linked ichthyosis) from ten families were studied by flow karyotype analysis. In four of the families, a small but significant reduction in the relative fluorescence of the X chromosome was detected consistent with a deletion ranging from 1.2%–3.4% of the X and amounting to a DNA loss of 1.9–5.2 million base pairs. In the remaining six families, three of which demonstrated a molecular deletion of the DNA sequence GMGX9 (DXS237), the relative fluorescence of the X chromosomes was indistinguishable from normal. The phenotypes of those with X deletions detectable by flow cytometry were similar to those of patients without such deletions.

The potential of family flow karyotyping for the detection of chromosome abnormalities

SummaryChromosomes from the mother, father, and child of nine families were stained with ethidium bromide and analysed in flow. These flow karyotypes on average resolved separately the homologues of 4.8 of the offsprings chromosomes. A homologues relative DNA content (calculated from the flow karyotype) was found to be an accurate marker which could be used to trace that chromosome in a family. In this way the parental origin of 74.4% of the offsprings resolved homologues was determined. In the karyotypically normal families studied no chromosome was found in a child which was clearly different from a homologue present in one of the parents. Using parental flow karyotypes to identify familial heteromorphisms, a number of dysmorphic children were studied in an attempt to detect small “de novo” abnormalities. Although no chromosome abnormality was detected in these cases, the usefulness of family studies was illustrated. In one family a large chromosome 4 homologue was found in the child and this was shown to be similar to one found in the father, suggesting an inherited heteromorphism rather than a clinically significant duplication. Flow analysis of the parents of a patient diagnosed cytogenetically as having an interstitial deletion of the X chromosome revealed the abnormality to be a “de novo” 3;X translocation. It is suggested that flow karyotype analysis in families has potential for the detection of chromosome rearrangements at the limits of resolution of conventional cytogenetics.

Confirmation of a suspected 16q deletion in a dysmorphic child by flow karyotype analysis.

Cytogenetic examination of a dysmorphic infant with multiple congenital abnormalities revealed a possible de novo interstitial deletion in the long arm of chromosome 16. Conclusive proof of the deletion was obtained by flow karyotype analysis of the patient and both parents, which showed that the deleted segment was approximately 7000 kb in size.

Gastric carcinoid: germline and somatic mutation of the neurofibromatosis type 1 gene

Neurofibromatosis type 1 (NF1) is one of the most common autosomal dominantly inherited conditions. A range of complications has been described, including gastrointestinal manifestations. Gastric carcinoid tumours are associated with multiple endocrine neoplasia, atrophic gastritis and pernicious anaemia but have not been reported in NF1 in the absence of other predisposing factors. We report the occurrence and investigation of a gastric carcinoid tumour in a 23-year-old woman with previously uncomplicated NF1. Analysis of the tumour tissue revealed loss of heterozygosity at the NF1 gene locus but a normal karyotype and an absence of microsatellite instability. A germline NF1 gene nonsense mutation in exon 37 was detected by denaturing high-performance liquid chromatography and DNA sequence analysis. This is the first reported occurrence of a gastric carcinoid tumour in a patient with NF1 in the absence of other predisposing factors such as pernicious anaemia. The analyses indicate that the carcinoid arose through NF1 gene inactivation but in the absence of an inherited NF1 gene microdeletion. This case adds to the range of gastrointestinal tumours that may be encountered in patients with NF1, particularly in those who present with upper gastrointestinal haemorrhage.

Abstract 3673: Molecular analysis of pheochromocytoma after maternal transmission of SDHD mutation elucidates mechanism of parent-of-origin effect.

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL In SDHD mutation families, paragangliomas and pheochromocytomas usually occur only after paternal transmission of the mutation. This important but unexplained parent-of-origin effect is not due to imprinting of SDHD itself, as was initially suspected, since SDHD is biallelically expressed in several tissues. In clinically affected individuals who possess a paternally inherited SDHD mutation, there is loss of the entire maternal chromosome 11 in tumour DNA, implying that tumorigenesis requires loss of not only maternal (wild type) SDHD but also a further, imprinted, tumor suppressor gene (TSG). We report the second case of an SDHD-related tumor (a pheochromocytoma in a 33 year old woman possessing the common pathogenic mutation, p.Pro81Leu) occurring after maternal transmission. It is the first reported investigation of tumor DNA in this situation. Tumor DNA revealed loss of heterozygosity (LOH) at paternal 11q23 causing loss of the wild-type SDHD allele and also LOH affecting maternal 11p15, including H19. These two LOH regions were separated by a region exhibiting clearly retained heterozygosity, containing SDHAF2 (a recently reported paraganglioma TSG), which therefore appears uninvolved here. This case provides strong molecular evidence that the tumorigenic requirement for maternal 11p15 loss (in addition to inactivation of both SDHD alleles) drives the observed parent-of-origin effect. Thus, SDHD-related tumorigenesis most likely involves a “three-hit” mechanism that includes (as one of the hits) loss of an imprinted (paternally silenced and maternally active) TSG from chromosome 11, such as H19). Tumor formation more commonly results from paternal inheritance of SDHD mutations, as the necessary loss of both the wild type SDHD allele and maternal 11p15 can then occur by a single event (loss of maternal chromosome 11). These findings have important implications regarding the clinical management of carriers of maternally inherited SDHD mutations, who we confirm can develop pheochromocytomas, and the understanding of the parent-of-origin effect. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3673. doi:1538-7445.AM2012-3673