Deletion of MAP2K2/MEK2: a novel mechanism for a RASopathy?

RASopathies are a class of genetic syndromes caused by germline mutations in genes encoding Ras/mitogen-activated protein kinase (Ras/MAPK) pathway components. Cardio-facio-cutaneous (CFC) syndrome is a RASopathy characterized by distinctive craniofacial features, skin and hair abnormalities, and congenital heart defects caused by activating mutations of BRAF, MEK1, MEK2, and KRAS. We define the phenotype of seven patients with de novo deletions of chromosome 19p13.3 including MEK2; they present with a distinct phenotype but have overlapping features with CFC syndrome. Phenotypic features of all seven patients include tall forehead, thick nasal tip, underdeveloped cheekbones, long midface, sinuous upper vermilion border, tall chin, angular jaw, and facial asymmetry. Patients also have developmental delay, hypotonia, heart abnormalities, failure to thrive, obstructive sleep apnea, gastroesophageal reflux and integument abnormalities. Analysis of epidermal growth factor-stimulated fibroblasts revealed that P-MEK1/2 was ∼50% less abundant in cells carrying the MEK2 deletion compared to the control. Significant differences in total MEK2 and Sprouty1 abundance were also observed. Our cohort of seven individuals with MEK2 deletions has overlapping features associated with RASopathies. This is the first report suggesting that, in addition to activating mutations, MEK2 haploinsufficiency can lead to dysregulation of the MAPK pathway.

Weight for age charts for children with achondroplasia.

To develop accurate weight for age charts for individuals with achondroplasia. These novel weight for age, gender-specific growth curves for achondroplasia patients from birth through 16 years were constructed from a longitudinal, retrospective, single observer cohort study of 334 individuals with achondroplasia. Weight for age data from 301 subjects in this achondroplasia cohort, constituting 1,964 total weight measurements, are presented in these weight for age curves. Percentiles (5, 25, 50, 75, 95th) were estimated across the age continuum by gender, using a 1 month window (+/-0.5 months) around each time point of interest. Percentiles were smoothed using a quadratic, penalized smoother by a semi-parametric model approach. Raw weight data from the achondroplasia cohort are compared to that of average stature children presented in the current CDC growth curves, divided into 0-36 months and 2-16 years. There was overlap of birth weight between achondroplasia and average stature infants. This statistical modeling method can be applied to other anthropometric parameters collected from this achondroplasia cohort (e.g., length, BMI), other skeletal dysplasia diagnoses, and to syndromic, non-skeletal dysplasia diagnoses which may benefit from standardization of weight for age.

Nail patella syndrome revisited: 50 years after linkage.

Nail Patella Syndrome (NPS; OMIM #161200) is a pleiotropic condition, with a classical clinical tetrad of involvement of the nails, knees, elbows and the presence of iliac horns. Kidney disease and glaucoma are now recognised as part of the syndrome. Fifty years ago, James Renwick chose NPS to develop methods of linkage analysis in humans and revealed the third linkage group identified in man--that between NPS and the ABO blood group loci. After a fallow period of some forty years, the gene mutated in NPS has been identified (LMX1B) and the condition serves as a model for understanding the complex relationships between disease loci, modifier genes and the resultant clinical phenotype.

Natural history of nonketotic hyperglycinemia in 65 patients.

BACKGROUND: Glycine encephalopathy, also known as nonketotic hyperglycinemia (NKH), is an autosomal recessive disorder caused by a defect in the glycine cleavage system. NKH is classically associated with neonatal apnea, lethargy, hypotonia, and seizures, followed by severe psychomotor retardation in those who survive. METHODS: To determine the natural history of NKH, the authors mailed a 44-question survey to 170 households in the International NKH Family Network. RESULTS: Data for 65 patients (36 boys, 29 girls) were collected from 58 families. One-third of the subjects died; 8 girls died during the neonatal period, and 14 patients died thereafter (2 girls, 12 boys). Median age of death for boys was 2.6 years vs <1 month for girls (p = 0.02). Mean birth weight and length, occipitofrontal circumference, and gestation duration were normal. Two-thirds of infants were ventilated during the neonatal period; of these, 40% died. Ninety percent had confirmed seizures, 75% during the first month of life. Interestingly, three NKH patients never developed seizures. An abnormal corpus callosum and/or hydrocephalus were associated with especially poor gross motor and speech development. Of 25 patients living > or =3 years, 10 were able to walk and say/sign words; all were boys. In six families with more than one affected child, disease course and mortality were similar within each family. CONCLUSIONS: This study reveals a striking and unexpected gender difference in mortality and developmental progress. Of the two-thirds of nonketotic hyperglycinemia patients surviving the newborn period, up to 20% (mostly boys) may learn to walk and communicate by saying or signing words.