David Ravine

Renal cystic disease in tuberous sclerosis: role of the polycystic kidney disease 1 gene

Tuberous sclerosis is an autosomal dominant trait characterized by the development of hamartomatous growths in many organs. Renal cysts are also a frequent manifestation. Major genes for tuberous sclerosis and autosomal dominant polycystic kidney disease, TSC2 and PKD1, respectively, lie adjacent to each other at chromosome 16p13.3, suggesting a role for PKD1 in the etiology of renal cystic disease in tuberous sclerosis. We studied 27 unrelated patients with tuberous sclerosis and renal cystic disease. Clinical histories and radiographic features were reviewed, and renal function was assessed. We sought mutations at the TSC2 and PKD1 loci, using pulsed field- and conventional-gel electrophoresis and FISH. Twenty-two patients had contiguous deletions of TSC2 and PKD1. In 17 patients with constitutional deletions, cystic disease was severe, with early renal insufficiency. One patient with deletion of TSC2 and of only the 3 UTR of PKD1 had few cysts. Four patients were somatic mosaics; the severity of their cystic disease varied considerably. Mosaicism and mild cystic disease also were demonstrated in parents of 3 of the constitutionally deleted patients. Five patients without contiguous deletions had relatively mild cystic disease, 3 of whom had gross rearrangements of TSC2 and 2 in whom no mutation was identified. Significant renal cystic disease in tuberous sclerosis usually reflects mutational involvement of the PKD1 gene, and mosaicism for large deletions of TSC2 and PKD1 is a frequent phenomenon.

Gross rearrangements of the MECP2 gene are found in both classical and atypical Rett syndrome patients

MECP2 mutations are identifiable in ∼80% of classic Rett syndrome (RTT), but less frequently in atypical RTT. We recruited 110 patients who fulfilled the diagnostic criteria for Rett syndrome and were referred to Cardiff for molecular analysis, but in whom an MECP2 mutation was not identifiable. Dosage analysis of MECP2 was carried out using multiplex ligation dependent probe amplification or quantitative fluorescent PCR. Large deletions were identified in 37.8% (14/37) of classic and 7.5% (4/53) of atypical RTT patients. Most large deletions contained a breakpoint in the deletion prone region of exon 4. The clinical phenotype was ascertained in all 18 of the deleted cases and in four further cases with large deletions identified in Goettingen. Five patients with large deletions had additional congenital anomalies, which was significantly more than in RTT patients with other MECP2 mutations (2/193; p<0.0001). Quantitative analysis should be included in molecular diagnostic strategies in both classic and atypical RTT.

Mutation analysis in the MECP2 gene and genetic counselling for Rett syndrome

We looked for pathogenic MECP2 mutations in 11 families with an index case affected by Rett syndrome (RTT), together with a sib or other relative affected by RTT or a less specific developmental disturbance. In one family, we detected the same MECP2 mutation in two affected sisters and their unaffected mother, who was subsequently shown to have skewed X chromosome inactivation. In five families, one affected subject was found to have a MECP2 mutation, but the other relative in whom a diagnosis of RTT was suspected, did not carry this or any other detectable MECP2 mutation. In the remaining five families, no MECP2 mutation was detected in any subject. These results suggest that familial RTT is rare and may be overdiagnosed. Furthermore, and despite the small probability of recurrence, many relatives of females with the usual, sporadic RTT may seek genetic testing to clarify their situation.nnRett syndrome (RTT) is a neurodevelopmental disorder that mostly affects females and is usually sporadic. It has therefore often been considered to be an X linked dominant condition with male lethality, although it is now recognised that de novo mutations in RTT occur predominantly on the paternally derived X chromosome and this could lead to similar observations.1–4 It is an important cause of profound mental handicap in girls, accounting for up to 10% of all cases. The diagnosis is currently based upon the clinical criteria proposed by the Rett Syndrome Working Group in 1988.5 The major criteria are: (1) normal pre- and perinatal period and apparently normal development for the first 6 months of life, (2) a period of regression occurring at 6 months to 3 years of age, (3) deceleration in head growth, (4) acquisition of stereotypical hand movements, and (5) eventual profound developmental delay. In addition, there are a …

Prenatal diagnosis for facioscapulohumeral muscular dystrophy (FSHD)

This study outlines the molecular DNA findings derived from 12 separate prenatal diagnoses offered to families with a history of facioscapulohumeral muscular dystrophy. A high risk of the fetus being affected was identified in five pregnancies. Several practical problems are discussed, particularly those arising from the quality and quantity of DNA made available for molecular diagnosis. Evidence of the 4q35 and 10q26 telomeric exchanges is present in 20 per cent of the general population and the specificity of the test is 95 per cent. The eventual isolation and functional characterization of the FSHD gene should allow us to unravel many of the complexities currently associated with the molecular diagnosis of this disorder. Copyright

Reinforcing the association between distal 1q CNVs and structural brain disorder: A case of a complex 1q43-q44 CNV and a review of the literature

Copy Number Variations (CNVs) comprising the distal 1q region 1q43‐q44 are associated with neurological impairments, structural brain disorder, and intellectual disability. Here, we report an extremely rare, de novo case of a 1q43‐q44 deletion with an adjacent duplication, associated with severe seizures, microcephaly, agenesis of the corpus callosum, and pachygyria, a consequence of defective neuronal migration disorder. We conducted a literature survey to find that our patient is only the second case of such a 1q43‐q44 CNV ever to be described. Our data support an association between 1q43‐q44 deletions and microcephaly, as well as an association between 1q43‐q44 duplications and macrocephaly. We compare and contrast our findings with previous studies reporting on critical 1q43‐q44 regions and their constituent genes associated with seizures, microcephaly, and corpus callosum abnormalities [Ballif et al., 2012; Hum Genet 131:145–156; Nagamani et al., 2012; Eur J Hum Genet 20:176–179]. Taken together, our study reinforces the association between 1q43‐q44 CNVs and brain disorder.