Refining reproductive risk for FMR1 premutation carriers in the general obstetric population.

Female FMR1 premutation (FMR1 PM) carriers for fragile X syndrome (FXS) are at risk to have a child with FXS based on their CGG repeat size and AGG interruption number. Studies examining this risk in unselected populations of female PM carriers are lacking. This retrospective cohort study analyzed carrier status, CGG repeat length, AGG interruption result, and reproductive risk refinement in a population of female patients who underwent routine carrier screening for FXS. A total of 1536 PM carriers (0.43%) were identified, 95% of whom had between 55 and 90 CGG repeats. A number of 1334 carriers underwent AGG interruption testing. The majority had at least one AGG interruption and received a lower reproductive risk for FXS following AGG interruption testing (89% and 85%, respectively) as compared to their risk calculated based on CGG repeat size alone. The average change in risk across the population following AGG interruption testing was -3.4%, with a range from -50.8% to 48.9%. This article describes the range of CGG repeats and AGG interruptions in an unselected population of female PM carriers and suggests that most carriers would benefit from AGG interruption testing to refine their reproductive risk of having a child with FXS.

Expansion of B4GALT7 linkeropathy phenotype to include perinatal lethal skeletal dysplasia.

Proteoglycans have a core polypeptide connected to glycosaminoglycans (GAGs) via a common tetrasaccharide linker region. Defects in enzymes that synthesize the linker result in a group of autosomal recessive conditions called "linkeropathies". Disease manifests with skeletal and connective tissue features, including short stature, hyperextensible skin, and joint hypermobility. We report a family with three affected pregnancies showing short limbs, cystic hygroma, and perinatal death. Two spontaneously aborted; one survived 1 day after term delivery, and had short limbs, bell-shaped thorax, 11 ribs, absent thumbs, and cleft palate. Exome sequencing of the proband and one affected fetus identified compound heterozygous missense variants, NM_007255.3: c.808C>T (p.(Arg270Cys)) and NM_007255.3: c.398A>G (p.(Gln133Arg)), in B4GALT7, a gene required for GAG linker biosynthesis. Homozygosity for p.(Arg270Cys), associated with partial loss of B4GALT7 function, causes Larsen of Reunion Island syndrome (LRS), however no previous studies have linked p.(Gln133Arg) to disease. The p.(Gln133Arg) and p.(Arg270Cys) variants were transfected into CHO pgsB-618 cells. High protein expression of p.(Gln133Arg) was found, with mislocalization, compared to p.(Arg270Cys) that had a normal Golgi-like pattern. The p.(Gln133Arg) had almost no enzyme activity and little production of heparan sulfate GAGs, while p.(Arg270Cys) only had 17% of wild-type activity. These findings expand the phenotype of B4GALT7-related linkeropathies to include lethal skeletal dysplasia due to more severe loss of function.

Practice guidelines for communicating a prenatal or postnatal diagnosis of Down syndrome: recommendations of the national society of genetic counselors.

Down syndrome is one of the most common conditions encountered in the genetics clinic. Due to improvements in healthcare, educational opportunities, and community inclusion over the past 30 years, the life expectancy and quality of life for individuals with Down syndrome have significantly improved. As prenatal screening and diagnostic techniques have become more enhanced and widely available, genetic counselors can expect to frequently provide information and support following a new diagnosis of Down syndrome. This guideline was written for genetic counselors and other healthcare providers regarding the communication of a diagnosis of Down syndrome to ensure that families are consistently given up-to-date and balanced information about the condition, delivered in a supportive and respectful manner.