J. Fernando Arena

Inherited mutations in PTEN that are associated with breast cancer, Cowden disease, and juvenile polyposis

PTEN, a protein tyrosine phosphatase with homology to tensin, is a tumor-suppressor gene on chromosome 10q23. Somatic mutations in PTEN occur in multiple tumors, most markedly glioblastomas. Germ-line mutations in PTEN are responsible for Cowden disease (CD), a rare autosomal dominant multiple-hamartoma syndrome. PTEN was sequenced from constitutional DNA from 25 families. Germ-line PTEN mutations were detected in all of five families with both breast cancer and CD, in one family with juvenile polyposis syndrome, and in one of four families with breast and thyroid tumors. In this last case, signs of CD were subtle and were diagnosed only in the context of mutation analysis. PTEN mutations were not detected in 13 families at high risk of breast and/or ovarian cancer. No PTEN-coding-sequence polymorphisms were detected in 70 independent chromosomes. Seven PTEN germ-line mutations occurred, five nonsense and two missense mutations, in six of nine PTEN exons. The wild-type PTEN allele was lost from renal, uterine, breast, and thyroid tumors from a single patient. Loss of PTEN expression was an early event, reflected in loss of the wild-type allele in DNA from normal tissue adjacent to the breast and thyroid tumors. In RNA from normal tissues from three families, mutant transcripts appeared unstable. Germ-line PTEN mutations predispose to breast cancer in association with CD, although the signs of CD may be subtle.

XLMRgenes: Update 1996

A current list of all known forms of X-linked mental retardation (XLMR) and a slightly revised classification are presented. The number of known disorders has not increased because 6 disorders have been combined based on new molecular data or on clinical grounds and only 6 newly described XLMR disorders have been reported. Of the current 105 XLMR disorders, 34 have been mapped, and 18 disorders and 1 non-specific XLMR (FRAXE) have been cloned. The number of families with nonspecific XLMR with a LOD score of {ge}2.0 has more than doubled, with 42 (including FRAXE) now being known. A summary of the localization of presumed nonspecific mental retardation (MR) genes from well-studied X-chromosomal translocations and deletions is also included. Only 10-12 nonoverlapping loci are required to explain all localizations of non-specific MR from both approaches. These new trends mark the beginning of a significantly improved understanding of the role of genes on the X chromosome in producing MR. Continued close collaboration between clinical and molecular investigators will be required to complete the process. 105 refs., 2 figs., 6 tabs.

Agenesis of the corpus callosum associated with MASA syndrome.

MASA syndrome include mental retardation, adducted thumbs, shuffling and aphasia or speech delay. MASA syndrome, X-linked hydrocephalus and X-linked spastic paraplegia have been linked to the same markers on Xq28 and perhaps represent variation in the clinical expression of the gene or manifestations of different mutant alleles. The present family includes five males in two generations with borderline to mild mental retardation (5/5), speech delay (5/5), adducted thumbs (2/5) and marked hydrocephalus (1/5). Of these males, four were evaluated by MRI or CT scan and all four were determined to have partial to complete agenesis of the corpus callosum (ACC). DNA studies confirm linkage to Xq28 probe St14 (DXS52) with a lod score of 2.86 and no recombination. It is not known if X-linked ACC is linked to the same Xq28 region.

X-linked mental retardation with variable stature, head circumference, and testicular volume linked to Xq12-q21

Clinical and molecular studies are reported on a family with X-linked mental retardation (XLMR) in which there are eight affected males in three generations. Although the males have somatic manifestations, these are variable and in most cases do not allow clear distinction of affected and unaffected males. Affected males are shorter and have a smaller head circumference. Several also have a sloping forehead (5/8), hearing loss (3/8), cupped ears (2/8), and small testes (4/6). An LOD score of 4.41 with zero recombination was obtained at locus DXS1166 in Xq13.2. This family highlights the difficulty in classifying XLMR conditions as either nonsyndromic or syndromic because of the variable somatic manifestations observed in the affected males.

X‐linked mental retardation syndrome with seizures, hypogammaglobulinemia, and progressive gait disturbance is regionally mapped between Xq21.33 and Xq23

We identified a family with three males in two generations with moderate mental retardation. The two oldest were first cousins whose mothers were sisters. The third affected was a grandson through a daughter of one of the sisters, strongly suggesting X- linked inheritance. The affected males had prominent glabella, synophrys, prognathism, generalized hirsutism, and bilateral single palmar creases. All developed seizures in childhood. The two oldest have had a slow deterioration in neurological status with poor gait and balance and progressive weakness. No deterioration in their mental status has been observed. The oldest had cerebellar atrophy confirmed on computed tomography and magnetic resonance imaging scans of the brain and prolonged nerve conduction velocity. Two of the males had hypogammaglobulinemia (IgA deficient). Two-point linkage analysis using 27 microsatellite markers on the X chromosome resulted in a maximum LOD score of 2.23 at straight theta = 0 for locus DSX101. Recombination was observed at locus DSX1170 in Xq21.33 and locus DXS8067 in Xq23. We conclude that this family represents an X-linked disorder associated with a recognizable phenotype, progressive neurological deterioration, and variable hypogammaglobulinemia. The gene appears to lie between Xq21.33 and Xq23.

Completed BRCA1/BRCA2 mutation analysis reveals a low rate of germline mutation in at-risk African American families

Completed BRCA1/BRCA2 mutation analysis reveals a low rate of germline mutation in at-risk African American families