The Use of Expanded Carrier Screening in Reproductive Medicine: Scientific Impact Paper No. 74.

Expanded carrier screening (ECS) is a genetic screening test carried out by analysing a blood sample. This screen can be used to detect whether the individual unknowingly carries gene variants associated with common genetic conditions, such as cystic fibrosis, that may be passed on to their children. It is typically performed in reproductive medicine for those who are considering having a family either naturally or via fertility treatment. Many donor sperm and egg banks, particularly in the USA and Europe, also perform blanket ECS testing on all their prospective sperm and egg donors. ECS is not currently routine practice in the UK, but a growing number of patients are requesting it before treatment. All of us carry gene variants of some sort that may cause autosomal recessive disease in their children if their partner or donor also carry a variant in the same gene. An autosomal recessive disease means two copies of an abnormal gene must be present in order for the disease or trait (such as cystic fibrosis or sickle cell disease) to develop. One copy of the variant means the person is a carrier but does not have the condition. Two copies, i.e. from the mother and father, means the child has a 25% chance of having the genetic disease. Carrying a gene variant does not mean that the individual would necessarily have any symptoms of the disease or any features of the condition. Genetic tests for specific conditions are currently available either before or during pregnancy for prospective parents who have a family or personal history of a genetic condition, or for those from ethnic backgrounds where certain conditions - such as haemoglobinopathies (blood disorders) - are common, prompting referral to a clinical genetics department. Expanded carrier screens may test for more than 100 genetic conditions. The list of conditions screened for is called a panel. Common panels are 250 or 600 genes. Not all expanded carrier screens that are available analyse the same genes. Some may test for genes that do not cause serious disease, or cause diseases that occur in later life; others test for genes that cause severe conditions in childhood. There is no agreement as to which panel of genes should be tested for in an ECS. Understanding the screening that is being offered, and the meaning of any results, is complicated and requires support from appropriately trained professionals to best inform the prospective parent or parents.

A combined vascular surgical and clinical genetics approach to diffuse aneurysmal disease.

We report two patients who presented with extensive aneurysmal disease, in association with minimal external physical signs. Patient 1 remained genetically undiagnosed despite multiple structural, biochemical and genetic investigations. He made a good recovery following surgery for popliteal and left axillary artery aneurysms. Patient 2 was diagnosed with vascular type Ehlers-Danlos syndrome, associated with a high degree of tissue and blood vessel fragility, and is being managed conservatively. Early multidisciplinary assessment of such patients facilitates accurate diagnosis and management.

The role of the sonic hedgehog signalling pathway in patients with midline defects and congenital hypopituitarism.

INTRODUCTION: The Gli family of zinc finger (GLI) transcription factors mediates the sonic hedgehog signalling pathway (HH) essential for CNS, early pituitary and ventral forebrain development in mice. Human mutations in this pathway have been described in patients with holoprosencephaly (HPE), isolated congenital hypopituitarism (CH) and cranial/midline facial abnormalities. Mutations in Sonic hedgehog (SHH) have been associated with HPE but not CH, despite murine studies indicating involvement in pituitary development. OBJECTIVES/METHODS: We aimed to establish the role of the HH pathway in the aetiology of hypothalamo-pituitary disorders by screening our cohort of patients with midline defects and/or CH for mutations in SHH, GLI2, Shh brain enhancer 2 (SBE2) and growth-arrest specific 1 (GAS1). RESULTS: Two variants and a deletion of GLI2 were identified in three patients. A novel variant at a highly conserved residue in the zinc finger DNA-binding domain, c.1552G > A [pE518K], was identified in a patient with growth hormone deficiency and low normal free T4. A nonsynonymous variant, c.2159G > A [p.R720H], was identified in a patient with a short neck, cleft palate and hypogonadotrophic hypogonadism. A 26·6 Mb deletion, 2q12·3-q21·3, encompassing GLI2 and 77 other genes, was identified in a patient with short stature and impaired growth. Human embryonic expression studies and molecular characterisation of the GLI2 mutant p.E518K support the potential pathogenicity of GLI2 mutations. No mutations were identified in GAS1 or SBE2. A novel SHH variant, c.1295T>A [p.I432N], was identified in two siblings with variable midline defects but normal pituitary function. CONCLUSIONS: Our data suggest that mutations in SHH, GAS1 and SBE2 are not associated with hypopituitarism, although GLI2 is an important candidate for CH.

The mutational spectrum of human malignant autosomal recessive osteopetrosis.

Human malignant infantile osteopetrosis (arOP; MIM 259700) is a genetically heterogeneous autosomal recessive disorder of bone metabolism, which, if untreated, has a fatal outcome. Our group, as well as others, have recently identified mutations in the ATP6i (TCIRG1) gene, encoding the a3 subunit of the vacuolar proton pump, which mediates the acidification of the bone/osteoclast interface, are responsible for a subset of this condition. By sequencing the ATP6i gene in arOP patients from 44 unrelated families with a worldwide distribution we have now established that ATP6i mutations are responsible for approximately 50% of patients affected by this disease. The vast majority of these mutations (40 out of 42 alleles, including seven deletions, two insertions, 10 nonsense substitutions and 21 mutations in splice sites) are predicted to cause severe abnormalities in the protein product and are likely to represent null alleles. In addition, we have also analysed nine unrelated arOP patients from Costa Rica, where this disease is apparently much more frequent than elsewhere. All nine Costa Rican patients bore either or both of two missense mutations (G405R and R444L) in amino acid residues which are evolutionarily conserved from yeast to humans. The identification of ATP6i gene mutations in two families allowed us for the first time to perform prenatal diagnosis: both fetuses were predicted not to be affected and two healthy babies were born. This study contributes to the determination of genetic heterogeneity of arOP and allows further delineation of the other genetic defects causing this severe condition.