Sutherland-Haan syndrome

Definition

Sutherland-Haan syndrome is an inherited X-linked disorder characterized by mental retardation, small head circumference, small testes, and spastic diplegia. Grant Sutherland and co-workers first described the syndrome in 1988. At present, it has only been fully described in one single, large, Australian family. Thus, it is unknown if the disorder occurs worldwide or only in certain ethnic and racial groups. Since the responsible gene is located on the X chromosome , Sutherland-Haan syndrome is exclusively found in males. As the gene is unknown and only one family has been described (although there are families suspected of having Sutherland-Haan) the prevalence is unknown.

Description

Sutherland-Haan syndrome is among the group of genetic disorders known as X-linked mental retardation (XLMR) syndromes. Manifestations in males may be present prior to birth, as intrauterine growth appears to be mildly impaired since birth weight is below normal. Similarly, postnatal growth is slow with the head circumference being quite small (microcephaly) and height being rather short. Affected males exhibit poor feeding during infancy. Additionally, affected males have small testes after puberty.

The diagnosis is very difficult especially if there is no family history of mental retardation. If there is a family history of mental retardation and if the inheritance pattern is consistent with X-linkage, then the diagnosis is possible based on the presence of the above clinical findings and localization to Xp11.3 to Xq12.

Genetic profile

Sutherland-Haan syndrome is caused by an alteration in an unknown gene located in the pericentric region (area flanking the centromere) of the X chromosome. The altered gene in affected males is most likely inherited from a carrier mother. As males have only one X chromosome, a mutation in an X-linked gene is fully expressed in males. On the other hand, as carrier females have a normal, second X-chromosome, they do not exhibit any of the phenotype associated with Sutherland-Haan syndrome.

Female carriers have a 50/50 chance of transmitting the altered gene to a daughter or a son. A son with the altered gene will be affected but will likely not reproduce.

Demographics

Only males are affected with Sutherland-Haan syndrome. Carrier females exhibit none of the phenotypic features. Although Sutherland-Haan has only been reported in a single Australian family, there is no reason to assume it is not present in other racial/ethnic groups.

Signs and symptoms

Evidence of Sutherland-Haan syndrome is present at birth as affected males have below normal birth weight. This may reflect mildly impaired intrauterine growth. Postnatal growth is also slow. Head circumference is smaller than normal (microcephaly) and affected males tend to be short. Small testes are also present after puberty.

There are some somatic manifestations present in most of the males with Sutherland-Haan syndrome. These include mild to moderate spastic diplegia (increased muscular tone with exaggeration of tendon reflexes of the legs), upslanting of the eye openings, brachycephaly (disproportionate shortness of the head), and a thin body build. Additionally, a few of the affected males may have anal abnormalities.

Mental impairment is mild to moderate with IQ ranging from 43 to 60. One male was reported to have an IQ in the 63-83 range (borderline).

Diagnosis

The diagnosis of Sutherland-Haan can only be made on the basis of the clinical findings in the presence of a family history consistent with X-linked inheritance of mental retardation and segregation of X chromosome markers in Xp11.2-Xq12. Unfortunately, there are no laboratory or radiographic changes that are specific for Sutherland-Haan syndrome.

Renpenning syndrome , another X-linked mental retardation syndrome, also has microcephaly, short stature, small testes, and upslanting of the eye openings. Furthermore, this syndrome is localized to Xp11.2-p11.4, which overlaps with the localization of Sutherland-Haan. However, males with Renpenning syndrome lack spasticity of the legs, brachycephaly, and a thin appearance. It is possible these two syndromes have different mutations in the same gene.

Chudley-Lowry syndrome also has microcephaly, short stature, and small testes. However, males have distinct facial features, similar to those of XLMR-hypotonic facies, and obesity. As with Renpenning syndrome, this syndrome may result from a different mutation in the same gene responsible for Sutherland-Haan syndrome.

Two other X-linked mental retardation syndromes (XLMR-hypotonic facies and X-linked hereditary bullous dystrophy) have microcephaly, short stature, and small testes. However, these conditions have different somatic features and are not localized to Xp11.2-Xq12.

Treatment and management

There is neither treatment nor cure available for Sutherland-Haan syndrome as of early 2001. Early educational intervention is advised for affected males. Some affected males may require living in a more controlled environment outside the home.

Prognosis

Life threatening concerns usually have not been associated with Sutherland-Haan syndrome. However, two affected males were found to have anal abnormalities, which required some form of surgery.

Resources

PERIODICALS

Gedeon, A., J. Mulley, and E. Haan. "Gene Localization for Sutherland-Haan Syndrome (SHS:MIM309470)." American Journal of Medical Genetics 64 (1996): 78-79.

Sutherland, G.R., et al. "Linkage Studies with the Gene for an X-linked Syndrome of Mental Retardation, Microcephaly, and Spastic Diplegia (MRX2)." American Journal of Medical Genetics 30 (1988): 493-508.

Charles E. Schwartz, PhD